user manual sr05

Hukseflux
Thermal Sensors
USER MANUAL SR05
Digital second class pyranometer
Copyright by Hukseflux | manual v1610 | www.hukseflux.com | info@hukseflux.com
Warning statements
Putting more than 30 Volt across the sensor wiring
of the main power supply can lead to permanent
damage to the sensor.
For proper instrument grounding: use SR05 with its
original factory-made SR05 cable. See chapter on
grounding and use of the shield.
Using the same Modbus address for more than one
device will lead to irregular behaviour of the entire
network.
Your data request may need an offset of +1 for each
SR05 register number, depending on processing by
the network master. Consult the manual of the
device acting as the local master.
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Contents
Warning statements
Contents
List of symbols
Introduction
1
Ordering and checking at delivery
1.1
Ordering SR05
1.2
Included items
1.3
Quick instrument check
2
Instrument principle and theory
3
Specifications of SR05
3.1
Specifications of SR05-DA1 and SR05-DA2
3.2
Dimensions of SR05
4
Standards and recommended practices for use
4.1
Classification standard
4.2
General use for solar radiation measurement
4.3
General use for sunshine duration measurement
4.4
Specific use for outdoor PV system performance testing
4.5
Specific use in meteorology and climatology
5
Installation of SR05
5.1
Site selection and installation
5.2
Mounting and levelling SR05
5.3
Installing SR05
5.4
Installing SR05 with its ball levelling and tube mount
5.5
Placing and removing SR05’s ball levelling shim
5.6
Electrical connection of SR05: wiring diagram
5.7
Grounding and use of the shield
5.8
Using SR05-DA1’s analogue 0 to 1 V output
5.9
Using SR05-DA2’s analogue 4 to 20 mA output
5.10 Using SR05-DA1’s and SR05-DA2’s digital output
5.11 Connecting SR05-DA1 to an RS-485 network
5.12 Connecting SR05-DA2 to a TTL device
5.13 Connecting SR05 to a PC
6
Communication with SR05
6.1
PC communication: Sensor Manager software
6.2
Network communication: function codes, registers, coils
6.3
Network communication: getting started
6.4
Network communication: example master request to SR05
7
Making a dependable measurement
7.1
The concept of dependability
7.2
Reliability of the measurement
7.3
Speed of repair and maintenance
7.4
Uncertainty evaluation
8
Maintenance and trouble shooting
8.1
Recommended maintenance and quality assurance
8.2
Trouble shooting
8.3
Calibration and checks in the field
8.4
Data quality assurance
9
Appendices
9.1
Appendix on cable extension / replacement
SR05 manual v1610
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9.2
9.3
9.4
9.5
9.6
9.7
9.8
9.9
9.10
9.11
9.12
Appendix on tools for SR05
Appendix on spare parts for SR05
Appendix on standards for classification and calibration
Appendix on calibration hierarchy
Appendix on meteorological radiation quantities
Appendix on ISO and WMO classification tables
Appendix on definition of pyranometer specifications
Appendix on terminology / glossary
Appendix on floating point format conversion
Appendix on function codes, register and coil overview
EU declaration of conformity
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List of symbols
Quantities
Symbol
Unit
Voltage output
Sensitivity
Solar irradiance
U
S
E
V
V/(W/m2)
W/m2
Output of 0-1 V
Transmitted range of 0-1 V
U
r
V
W/m2
Output of 4-20 mA current loop
Resistance
Transmitted range of 4-20 mA
I
R
r
A
Ω
W/m2
(see also appendix 9.6 on meteorological quantities)
Subscripts
Not applicable
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Introduction
SR05 is a digital pyranometer meeting ISO 9060 second class requirements. It is ideal
for general solar radiation measurements in (agro-)meteorological networks and PV
monitoring. SR05 is easy to mount and install. Various outputs are available, both digital
and analogue, for ease of integration.
SR05 measures solar radiation received by a plane surface, in W/m2, from a 180 o field of
view angle. Different configurations are available, depending on its mounting and the
output needed.
SR05 benefits:
•
•
•
Industry standard digital outputs: easy implementation and servicing
Easy mounting and levelling
Pricing: second class pyranometers finally affordable for large networks
SR05 pyranometer employs a thermopile sensor with black coated surface, one dome
and an anodised aluminium body with visible bubble level. SR05 has a variety of industry
standard outputs, both digital and analogue:
•
•
Version SR05-DA1: digital sensor with Modbus over RS-485 and analogue 0-1 V output
Version SR05-DA2: digital sensor with Modbus over TTL and analogue 4–20 mA output
Optionally the sensor has a unique ball levelling mechanism and / or tube mount, for
easy installation.
Figure 0.1 On the left SR05 digital second class pyranometer with bubble level and M12-A
cable connector in its standard configuration (3 metre cable standard included); on the
right SR05 with optional ball levelling, for easy mounting and levelling on (non-)horizontal
surfaces (included mounting screws not displayed)
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Figure 0.2 SR05 digital second class pyranometer with optional ball levelling and tube
mount for easy mounting and levelling on a tube (tube not included)
For communication between a PC and SR05, the Hukseflux Sensor Manager software is
included (downloadable). It allows the user to plot and export data, and change the SR05
Modbus address and its communication settings.
Figure 0.3 User interface of the Sensor Manager
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Suggested use for SR05:
•
•
•
general solar radiation measurements
(agro-)meteorological networks
PV power plant monitoring
SR05-DA1 is suited for use in SCADA (Supervisory Control And Data Acquisition)
systems, supporting Modbus RTU (Remote Terminal Unit) protocol over RS-485. In these
networks the sensor operates as a slave. Using SR05-DA1 in a network is easy. Once it
has the correct Modbus address and communication settings and is connected to a power
supply, the instrument can be used in RS-485 networks. A typical network will request
the irradiance (registers 2 + 3) and temperature data (register 6) every 1 second, and
eventually store the averages every 60 seconds. How to issue a request, process the
register content and convert it to useful data is described in the paragraphs about
network communication. The user should have sound knowledge of the Modbus
communication protocol when installing sensors in a network. When using the analogue
0 to 1 V output provided by SR05-DA1, the instrument can be connected directly to
commonly used datalogging systems capable of handling a 0 to 1 V signal.
When using SR05-DA2’s digital output, it can be connected to TTL devices via Modbus
over TTL, or when using SR05-DA2’s analogue 4 to 20 mA output, to commonly used
datalogging systems capable of handling a 4 to 20 mA current loop signal.
Both SR05 versions should be used in accordance with the recommended practices of
ISO, WMO and ASTM.
The recommended calibration interval of pyranometers is 2 years. The registers
containing the applied sensitivity and the calibration history of SR05 are accessible for
users with a password. This allows the user to choose his own local calibration service.
The same register access may also be used for remotely controlled re-calibration of
pyranometers in the field. Ask Hukseflux for information on this feature and on ISO and
ASTM standardised procedures for field calibration.
The ASTM E2848 “Standard Test Method for Reporting Photovoltaic Non-Concentrator
System Performance” (issued end 2011) confirms that a pyranometer is the preferred
instrument for PV system performance monitoring. SR05 pyranometer complies with the
requirements of this standard. For more information, see our pyranometer selection
guide.
WMO has approved the “pyranometric method” to calculate sunshine duration from
pyranometer measurements in WMO-No. 8, Guide to Meteorological Instruments and
Methods of Observation. This implies that SR05 may be used, in combination with
appropriate software, to estimate sunshine duration. This is much more cost-effective
than using a dedicated sunshine duration sensor. Ask for our application note.
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1
Ordering and checking at delivery
1.1
Ordering SR05
There are two standard configurations for SR05, each with several options:
•
SR05-DA1: with Modbus over RS-485 and 0-1 V output
standard cable length: 3 metres
•
SR05-DA2: with Modbus over TTL and 4-20 mA current loop output
standard cable length: 3 metres
Common options are:
• longer cable (10, 20 metres). Specify total cable length
• extension cable with connector pair (10, 20 metres). Specify total cable length
• ball levelling
• tube mount with ball levelling (for tube diameters 25 to 40 mm)
Ball levelling and tube mount are suited for retrofitting.
Table 1.1.1 Ordering codes for SR05
VERSIONS OF SR05 (part numbers), without cable
SR05-DA1
digital second class pyranometer, with Modbus over RS-485
and 0-1 V output
SR05-DA1-BL
digital second class pyranometer, with Modbus over RS-485
and 0-1 V output, with ball levelling
SR05-DA1-TMBL
digital second class pyranometer, with Modbus over RS-485
and 0-1 V output, with tube mount on ball levelling
SR05-DA2
digital second class pyranometer, with Modbus over TTL and
4-20 mA output
SR05-DA2-BL
digital second class pyranometer, with Modbus over TTL and
4-20 mA output, with ball levelling
SR05-DA2-TMBL
digital second class pyranometer, with Modbus over TTL and
4-20 mA output, with tube mount on ball levelling
CABLE FOR SR05, with female M12-A connector at sensor end, non-stripped on other end
‘-03’ after SR05 part number
‘-10’ after SR05 part number
‘-20’ after SR05 part number
standard cable length: 3 m
cable length: 10 m
cable length: 20 m
CABLE EXTENSION FOR SR05, with male and female M12-A connectors
C06E-10
C06E-20
cable length: 10 m
cable length: 20 m
An extension cable (with connector pair) can be used in combination with a regular cable
(with one connector at sensor end) to make alternative SR05 cable lengths possible.
Example: Cable length needed: 15 m. In this case, it is easiest to buy SR05 with a 20 m
cable and to cut it to desired length.
Example: Cable length needed: 30 m. In this case, it is easiest to buy SR05 with 10 m
cable and a cable extension of 20 m.
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1.2
Included items
Arriving at the customer, the delivery should include:
•
•
•
pyranometer SR05
cable of the length as ordered
product certificate matching the instrument serial number
For SR05-DAx-BL, also
• ball levelling
• 4 mm hex key
• 1 x shim
• 2 x M5x20 screws
• 2 x M5 nuts
For SR05-DAx-TMBL, also
• ball levelling
• 4 mm hex key
• 1 x shim
• 2 x M5x20 screws
• 2 x M5 nuts
• tube mount
• 2 x M5x30 screws
• 2 x M5x40 screws
Please store the certificate in a safe place.
The Hukseflux Sensor Manager can be downloaded via www.hukseflux.com/page/downloads
1.3
Quick instrument check
A quick test of the instrument can be done by connecting it to a PC and installing the
Sensor Manager software. See the chapters on installation and PC communication for
directions.
1. At power–up the signal may have a temporary output level different from zero; an
offset. Let this offset settle down.
2. Check if the sensor reacts to light: expose the sensor to a strong light source, for
instance a 100 W light bulb at 0.1 m distance. The signal should read > 100 W/m2 now.
Darken the sensor either by putting something over it or switching off the light. The
instrument irradiance output should go down and within one minute approach 0 W/m2.
3. Inspect the bubble level.
4. Inspect the instrument for any damage.
6. Check the instrument serial number as indicated by the software against the label on
the instrument and against the certificates provided with the instrument.
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2
Instrument principle and theory
4
3
5
6
2
1
7
12
11
10
9
8
Figure 2.1 Overview of SR05:
shaded areas in exploded view show ball levelling mount and shim
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
(9)
(10)
(11)
cable (standard length 3 metres, optional longer cable)
connector
bubble level
thermal sensor with black coating
glass dome
sensor body
tube mount (optional)
mounting screw (included with ball levelling and tube mount; requires 4 mm hex key)
shim (included with and needed for ball levelling mount)
ball levelling mount (optional)
countersunk set screw for levelling adjustment (included with ball levelling mount;
requires 4 mm hex key)
(12) opening for Ø 25 to Ø 40 mm tube when using ball levelling and tube mount
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SR05’s scientific name is pyranometer. A pyranometer measures the solar radiation
received by a plane surface from a 180 ° field of view angle. This quantity, expressed in
W/m2, is called “hemispherical” solar radiation. The solar radiation spectrum extends
roughly from 285 to 3000 x 10-9 m. By definition a pyranometer should cover that
spectral range with a spectral selectivity that is as “flat” as possible.
In an irradiance measurement by definition the response to “beam” radiation varies with
the cosine of the angle of incidence; i.e. it should have full response when the solar
radiation hits the sensor perpendicularly (normal to the surface, sun at zenith, 0 ° angle
of incidence), zero response when the sun is at the horizon (90 ° angle of incidence, 90 °
zenith angle), and 50 % of full response at 60 ° angle of incidence.
A pyranometer should have a so-called “directional response” (older documents mention
“cosine response”) that is as close as possible to the ideal cosine characteristic.
In order to attain the proper directional and spectral characteristics, a pyranometer’s
main components are:
•
a thermal sensor with black coating. It has a flat spectrum covering the 200 to 50000
x 10-9 m range, and has a near-perfect directional response. The coating absorbs all
solar radiation and, at the moment of absorption, converts it to heat. The heat flows
through the sensor to the sensor body. The thermopile sensor generates a voltage
output signal that is proportional to the solar irradiance.
•
a glass dome. This dome limits the spectral range from 285 to 3000 x 10-9 m (cutting
off the part above 3000 x 10-9 m), while preserving the 180 ° field of view angle.
Another function of the dome is that it shields the thermopile sensor from the
environment (convection, rain).
SR05 has a high-end 24-bit A/D converter, which is used by SR05 to convert the
analogue thermopile voltage to a digital signal.
Pyranometers can be manufactured to different specifications and with different levels of
verification and characterisation during production. The ISO 9060 - 1990 standard, “Solar
energy - specification and classification of instruments for measuring hemispherical solar
and direct solar radiation”, distinguishes between 3 classes; secondary standard (highest
accuracy), first class (second highest accuracy) and second class (third highest
accuracy).
From second class to first class and from first class to secondary standard, the achievable
accuracy improves by a factor 2.
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relative spectral content /
response [arbitrary units]
1,2
1
solar radiation
0,8
pyranometer
response
0,6
0,4
0,2
0
100
1000
10000
wavelength [x 10-9 m]
Figure 2.2 Spectral response of the pyranometer compared to the solar spectrum. The
pyranometer only cuts off a negligible part of the total solar spectrum.
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3
Specifications of SR05
3.1
Specifications of SR05-DA1 and SR05-DA2
SR05 measures the solar radiation received by a plane surface from a 180 o field of view
angle. This quantity, expressed in W/m2, is called “hemispherical” solar radiation.
SR05-DA1 offers irradiance in W/m2 as a digital output and as a 0-1 V output. It must be
used in combination with suitable power supply and a data acquisition system which uses
the Modbus communication protocol over RS-485 or one that is capable of handling a 0-1
V signal.
SR05-DA2 offers irradiance in W/m2 as a digital output and as a 4-20 mA output. It must
be used in combination with suitable power supply and a data acquisition system which
uses the Modbus communication protocol over TTL or one that is capable of handling a 420 mA current loop signal.
The instrument is classified according to ISO 9060 and should be used in accordance with
the recommended practices of ISO, IEC, WMO and ASTM.
Table 3.1.1 Specifications of SR05 (continued on next pages)
SR05 MEASUREMENT SPECIFICATIONS:
LIST OF CLASSIFICATION CRITERIA OF ISO 9060*
ISO classification (ISO 9060: 1990)
WMO performance level (WMO-No. 8,
seventh edition 2008)
Response time (95 %)
Zero offset a (response to 200 W/m2
net thermal radiation)
Zero offset b (response to 5 K/h
change in ambient temperature)
Non-stability
Non-linearity
Directional response
Spectral selectivity
Temperature response
Tilt response
second class pyranometer
moderate quality pyranometer
18 s
< 15 W/m2 unventilated
< ± 4 W/m2
<
<
<
<
<
<
±
±
±
±
±
±
1 % change per year
1 % (100 to 1000 W/m2)
25 W/m2
5 % (0.35 to 1.5 x 10-6 m)
3 % (-10 to +40 °C)
2 % (0 to 90 ° at 1000 W/m2)
*For the exact definition of pyranometer ISO 9060 specifications see the appendix.
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Table 3.1.1 Specifications of SR05 (continued)
SR05 ADDITIONAL SPECIFICATIONS
Measurand
Measurand in SI radiometry units
Optional measurand
Field of view angle
Output definition
Recommended data request interval
Measurement range
Measurement function / optional
programming for sunshine duration
Internal temperature sensor
Rated operating temperature range
Spectral range
(20 % transmission points)
Standard governing use of the
instrument
Standard cable length (see options)
Cable diameter
Chassis connector
Chassis connector type
Cable connector
Cable connector type
Connector protection class
Cable replacement
Mounting (see options)
Levelling (see options)
Levelling accuracy
Desiccant
IP protection class
Gross weight including 3 m cable
Net weight including 3 m cable
Packaging
CALIBRATION
Calibration traceability
Calibration hierarchy
Calibration method
Calibration uncertainty
Recommended recalibration interval
Reference conditions
Validity of calibration
Adjustment after re-calibration
.
SR05 manual v1610
hemispherical solar radiation
irradiance in W/m2
sunshine duration
180 °
running average over 4 last measurements,
measurement interval 0.1 s, refreshed every 0.1 s
1 s, storing 60 s averages
0 to 2000 W/m2
programming according to WMO guide paragraph
8.2.2
MAX31725 Digital temperature sensor
-40 to +80 °C
285 to 3000 x 10-9 m
ISO/TR 9901:1990 Solar energy -- Field pyranometers
-- Recommended practice for use
ASTM G183 - 05 Standard Practice for Field Use of
Pyranometers, Pyrheliometers and UV Radiometers
3m
4.8 x 10-3 m
M12-A straight male connector, male thread, 5-pole
M12-A
M12-A straight female connector, female thread, 5pole
M12-A
IP67
replacement and extension cables with connector(s)
can be ordered separately from Hukseflux
2 x M5 bolt at 46 mm centre-to-centre distance on
north-south axis, requires 4 mm hex key
bubble level is included
< 0.6 ° bubble entirely in ring
silica gel, 1.0 g, in a HDPE bag, (25 x 45) mm
IP67
0.45 kg
0.35 kg
box of (170 x 100 x 80) mm
to WRR
from WRR through ISO 9846 and ISO 9847, applying
a correction to reference conditions
indoor calibration according to ISO 9847, Type IIc
< 1.8 % (k = 2)
2 years
20 °C, normal incidence solar radiation, horizontal
mounting, irradiance level 1000 W/m2
based on experience the instrument sensitivity will not
change during storage. During use under exposure to
solar radiation the instrument “non-stability”
specification is applicable.
via a PC, as power user with the Sensor Manager
software. Request “power user” status at the factory
for sensitivity adjustment and for writing the
calibration history data.
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Table 3.1.1 Specifications of SR05 (started on previous pages)
HEATING
Heater
no heating
MEASUREMENT ACCURACY AND RESOLUTION
Uncertainty of the measurement
WMO estimate on achievable accuracy
for daily sums (see appendix for a
definition of the measurement conditions)
WMO estimate on achievable accuracy
for hourly sums (see appendix for a
definition of the measurement conditions)
Irradiance resolution
Instrument body temperature resolution
Instrument body temperature accuracy
SR05-DA1: DIGITAL
Digital output
Rated operating voltage range
Power consumption
Communication protocol
Transmission mode
System requirements for use with PC
Software requirements for use with PC
User interface on PC
SR05-DA1: ANALOGUE 0 TO 1 V
0 to 1 V output
Transmitted range
Output signal
Standard setting (see options)
Rated operating voltage range
Power consumption
SR05-DA2: DIGITAL
Digital output
Rated operating voltage range
Power consumption
Communication protocol
Transmission mode
System requirements for use with PC
Software requirements for use with PC
SR05 manual v1610
statements about the overall measurement
uncertainty can only be made on an individual basis.
see the chapter on uncertainty evaluation
10 %
20 %
0.2 W/m2
3.9 x 10-3 °C
± 0.5 °C
irradiance in W/m2
instrument body temperature in °C
5 to 30 VDC
< 75 x 10-3 W at 12 VDC
Modbus over 2-wire RS-485
half duplex
Modbus RTU
Windows Vista and later, USB or RS-232 (COM) port
and connector, RS-485 / USB converter or RS-485 /
RS-232 converter
Java Runtime Environment – software
available free of charge at http://www.java.com
Hukseflux Sensor Manager software
downloadable: to download and for available software
updates, please check
http://www.hukseflux.com/page/downloads
irradiance in W/m2
0 to 1600 W/m2
0 to 1 V
0 V at 0 W/m2 and
1 V at 1600 W/m2
5 to 30 VDC
< 75 x 10-3 W at 12 VDC
irradiance in W/m2
instrument body temperature in °C
5 to 30 VDC
< 240 x 10-3 W at 12 VDC
Modbus over TTL
Modbus RTU
Windows Vista and later, USB or RS-232 (COM) port
and connector, TTL / USB converter or TTL / RS-232
converter
Java Runtime Environment – software
available free of charge at http://www.java.com
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Table 3.1.1 Specifications of SR05 (started on previous pages)
User interface on PC
SR05-DA2: ANALOGUE 4 TO 20 mA
4 to 20 mA output
Transmitted range
Output signal
Standard setting (see options)
Principle of 4 to 20 mA output
Rated operating voltage range
Power consumption
OPTIONS
Longer cable: 10,20 m
Cable with M12-A female connector on
sensor end, non-stripped on other end
Extension cable with connector pair:
10, 20 m. Cable with male and female
M12-A connectors
Ball levelling
Tube mount with ball levelling
Adapted transmitted range 0 to 1 V
Adapted transmitted range 4 to 20 mA
SR05 manual v1610
Hukseflux Sensor Manager software
downloadable: to download and for available software
updates, please check
http://www.hukseflux.com/page/downloads
irradiance in W/m2
0 to 1600 W/m2
4 to 20 x 10-3 A
4 x 10-3 A at 0 W/m2 and
20 x 10-3 A at 1600 W/m2
2-wire current loop
5 to 30 VDC
< 240 x 10-3 W at 12 VDC
option code = total cable length
option code = C06E-10 for 10 metres, C06E-20 for
20 metres
mountable on (non-)horizontal surfaces
with angle compensation up to 10 °; retrofittable; one
shim, two M5x20 mounting screws and two M5 nuts
included; requires 4 mm hex key for levelling and 4
mm hex key and 8 mm wrench for mounting
option code = BL
mountable on tubes Ø 25 to Ø 40 mm
with angle compensation up to 10 °; retrofittable;
one shim, two M5x30 and two M5x40 mounting
screws included;
requires 4 m hex key for levelling and mounting
option code = TMBL
can be adjusted at the factory upon request
can be adjusted at the factory upon request
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3.2
Dimensions of SR05
Figure 3.2.1 Dimensions of SR05 in x 10-3 m. The bottom drawing shows the height of
SR05 combined with its optional ball levelling mount and the tube diameter required for
use with SR05’s optional tube mount. M5 mounting screws and the countersunk set
screw require a 4 mm hex key for mounting and levelling.
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4
Standards and recommended practices
for use
Pyranometers are classified according to the ISO 9060 standard and the WMO-No. 8
Guide. In any application the instrument should be used in accordance with the
recommended practices of ISO, IEC, WMO and / or ASTM.
4.1
Classification standard
Table 4.1.1 Standards for pyranometer classification. See the appendix for definitions of
pyranometer specifications, and a table listing the specification limits.
STANDARDS FOR INSTRUMENT CLASSIFICATION
ISO STANDARD
EQUIVALENT
ASTM STANDARD
WMO
ISO 9060:1990
Solar energy -- specification and
classification of instruments for
measuring hemispherical solar and
direct solar radiation
Not available
WMO-No. 8; Guide to
Meteorological Instruments
and Methods of Observation,
chapter 7, measurement of
radiation, 7.3 measurement
of global and diffuse solar
radiation
4.2
General use for solar radiation measurement
Table 4.2.1 Standards with recommendations for instrument use in solar radiation
measurement
STANDARDS FOR INSTRUMENT USE FOR HEMISPHERICAL SOLAR RADIATION
ISO STANDARD
EQUIVALENT
ASTM STANDARD
WMO
ISO/TR 9901:1990
Solar energy -- Field
pyranometers -- Recommended
practice for use
ASTM G183 - 05
Standard Practice for Field
Use of Pyranometers,
Pyrheliometers and UV
Radiometers
WMO-No. 8; Guide to
Meteorological Instruments
and Methods of Observation,
chapter 7, measurement of
radiation, 7.3 measurement
of global and diffuse solar
radiation
4.3
General use for sunshine duration measurement
According to the World Meteorological Organization (WMO, 2003), sunshine duration
during a given period is defined as the sum of that sub-period for which the direct solar
irradiance exceeds 120 W/m2.
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WMO has approved the “pyranometric method” to estimate sunshine duration from
pyranometer measurements (Chapter 8 of the WMO Guide to Instruments and
Observation, 2008). This implies that a pyranometer may be used, in combination with
appropriate software, to estimate sunshine duration. Ask for our application note.
Table 4.3.1 Standards with recommendations for instrument use in sunshine duration
measurement
STANDARDS FOR INSTRUMENT USE FOR SUNSHINE DURATION
WMO
WMO-No. 8; Guide to Meteorological Instruments and Methods of Observation, chapter 8,
measurement of sunshine duration, 8.2.2 Pyranometric Method
4.4
Specific use for outdoor PV system performance testing
SR05 is applicable in outdoor PV system performance testing. See also Hukseflux model
SR12 “first class pyranometer for solar energy test applications”.
Table 4.4.1 Standards with recommendations for instrument use in PV system
performance testing
STANDARDS ON PV SYSTEM PERFORMANCE TESTING
IEC / ISO STANDARD
EQUIVALENT ASTM STANDARD
IEC 61724; Photovoltaic system performance
monitoring – guidelines for measurement, data
exchange and analysis
ASTM 2848-11; Standard Test Method for
Reporting Photovoltaic Non-Concentrator
System Performance
COMMENT: Allows pyranometers or reference
cells according to IEC 60904-2 and -6.
Pyranometer reading required accuracy better
than 5% of reading (Par 4.1)
COMMENT: confirms that a pyranometer is the
preferred instrument for outdoor PV testing.
Specifically recommends a “first class”
pyranometer (paragraph A 1.2.1.)
COMMENT: equals JISC 8906 (Japanese
Industrial Standards Committee)
4.5
Specific use in meteorology and climatology
The World Meteorological Organization (WMO) is a specialised agency of the United
Nations. It is the UN system's authoritative voice on the state and behaviour of the
earth's atmosphere and climate. WMO publishes WMO-No. 8; Guide to Meteorological
Instruments and Methods of Observation, in which a table is included on “level of
performance” of pyranometers. Nowadays WMO conforms itself to the ISO classification
system.
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5
Installation of SR05
5.1
Site selection and installation
Table 5.1.1 Recommendations for installation of pyranometers
Location
the situation that shadows are cast on the instruments
is usually not desirable. The horizon should be as free
from obstacles as possible. Ideally there should be no
objects between the course of the sun and the
instrument.
Mechanical mounting / thermal insulation
preferably use the ball levelling mount to mount SR05
to a (non-)horizontal surface. A pyranometer is
sensitive to thermal shocks. Do not mount the
instrument on objects that become very hot (black
coated metal plates).
Instrument mounting with 2 screws
2 x M5 screw at 46 mm centre-to-centre distance on
north-south axis, connection through the sensor
bottom in SR05’s standard configuration.
with ball levelling option: 2 x M5 screw at 46 mm
centre-to-centre distance, connection through ball
levelling mount, M5x20 screws and M5 nuts included.
with ball levelling on tube mount option: 2 x M5 screw
at 46 mm centre-to-centre distance, connection
through tube and ball levelling mount, M5x30 and
M5x40 screws included.
Performing a representative
measurement
the pyranometer measures the solar radiation in the
plane of the sensor. This may require installation in a
tilted or inverted position. The black sensor surface
(sensor bottom plate) should be mounted parallel to
the plane of interest.
In case a pyranometer is not mounted horizontally or
in case the horizon is obstructed, the
representativeness of the location becomes an
important element of the measurement. See the
chapter on uncertainty evaluation.
Levelling
in case of horizontal mounting use the bubble level
and optionally the ball levelling mount. The bubble
level is visible and can be inspected at all times.
Instrument orientation
by convention with the cable exit pointing to the
nearest pole (so the cable exit should point north in
the northern hemisphere, south in the southern
hemisphere).
Installation height
in case of inverted installation, WMO recommends a
distance of 1.5 m between soil surface and sensor
(reducing the effect of shadows and in order to obtain
good spatial averaging).
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5.2
Mounting and levelling SR05
SR05 in its standard configuration is equipped with a visible bubble level and two
mounting holes. For easy mounting and levelling on a (non-)horizontal surface, SR05’s
optional ball levelling is recommended. Ball levelling offers:
•
easy levelling
•
easy cable orientation
•
easy instrument exchange
•
easy mounting (mounting screws and nuts included)
When installing SR05, ball levelling allows SR05 to rotate 360 ° and to tilt up to 10 °.
This allows compensation for up to a ten degree angle when installing on a nonhorizontal surface. A 4 mm hex key (un)locks the ball levelling mechanism. When using a
tube or rod for installing SR05, the optional tube mount is recommended. Combined with
ball levelling it allows mounting to a 25 to 40 mm diameter tube with the same ease of
levelling and instrument exchange.
SR05
SR05-BL
SR05-TMBL
Figure 5.2.1 From left to right: SR05 in its standard configuration with 3 metre cable;
with optional ball levelling for easy mounting and levelling on a (non-)horizontal surface;
with optional ball levelling and tube mount for easy installation on a 25 to 40 mm
diameter tube. Mounting screws are included with the ball levelling and / or tube mount.
5.3
Installing SR05
SR05 without ball levelling and tube mounting options can be mounted using two M5
screws (not included). For the required screw lengths, 5 to 7 mm should be added to the
thickness of the user’s mounting platform. See the chapter on required tooling.
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5.4
Installing SR05 with its ball levelling and tube mount
Two M5x20 screws and two M5 nuts are included with SR05’s ball levelling option. These
are to be used to mount SR05 with its ball levelling to a (non-)horizontal surface.
Two M5x30 screws and two M5x40 screws are included with SR05’s tube mount with ball
levelling. These screws are to be used to clamp both ball levelling and tube mount to a
25 to 40 mm diameter tube. For tube diameters larger than or equal to 33 mm, use the
M5x40 screws instead of the M5x30 screws for a secure fit.
The unique ball head mechanism of SR05’s ball levelling mount is used to level SR05.
When ordering ball levelling with SR05, it is delivered attached to SR05. In that case
follow steps 1 to 7 below to mount and level SR05. Make sure the glass dome is
protected at all times.
In case SR05 is not attached to its ball levelling mount yet, the user has to ensure a shim
is placed properly in the centre of the bottom plate of SR05 before mounting and
levelling. The shim allows smooth levelling and is shown top left in Figure 5.4.1. See
chapter 5.5 for placing SR05’s ball levelling shim. When ordering SR05 combined with
ball levelling, the shim is already positioned in its place in the factory.
Figure 5.4.1 On the left SR05’s ball levelling including shim (mounting screws not
displayed) and on the right SR05 placed on the ball levelling mount. Loosen the
countersunk set screw on SR05’s side to unlock, allowing placement of the ball head and
SR05 levelling, and tighten it to lock the ball head mechanism. A 4 mm hex key is the
only tool needed to place and remove the ball levelling and to allow and disallow levelling
adjustment. The shim, included when ordering ball levelling, allows for smooth levelling
and should be positioned properly in the centre of the bottom plate of SR05.
1)
Loosen SR05’s countersunk set screw with a 4 mm hex key by turning the hex key
counter clockwise until the screw is slightly protruding (sticking out).
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2)
Hold SR05 in one hand, the ball levelling mount in the other.
3)
Separate SR05 from the ball levelling mount by gently pulling out the ball levelling
mount.
4)
Mount the ball levelling to a surface or platform with its M5 screws and nuts. See
chapter on tooling required.
5)
Place SR05 on the ball levelling mount by gently pushing the sensor onto the ball
head until it clicks.
6)
SR05 can now be rotated 360 ° on its ball head by hand. This rotation allows easy
cable orientation adjustment. It can be tilted up to 10 °. This allows angle
compensation on non-horizontal surfaces up to 10 °.
7)
When SR05 is mounted and levelled, judging by its bubble level, lock the ball head
mechanism by turning the set screw clockwise with the 4 mm hex key until it is
tightened. SR05 is now locked in its position.
A similar approach is followed when levelling SR05 on its tube mount in the field:
1) judge bubble level and cable orientation 2) loosen set screw to tilt and rotate SR05
3) tighten set screw to lock ball levelling
4) SR05 is mounted and levelled
Figure 5.4.2 Levelling steps for SR05 when mounted on tube mount with ball levelling
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When retrofitting SR05 or when ordering SR05 pyranometer and its optional ball levelling
in separate orders, the user has to ensure a shim is placed properly in the centre of the
bottom plate of SR05. The shim allows smooth levelling. Read the following chapter on
placing and removing the shim. When ordering SR05 combined with ball levelling, the
shim is already positioned in its place in the factory.
5.5
Placing and removing SR05’s ball levelling shim
Only when ordering SR05 pyranometer and its optional ball levelling separately or when
exchanging a SR05 sensor on a ball levelling mount (retrofitting), the user has to ensure
a dedicated shim is placed properly in the centre of the bottom plate of SR05. When
ordering SR05 combined with ball levelling the shim is already positioned in its place in
the factory. The aluminium shim ensures a secure fit between SR05 and ball levelling and
allows the ball head to rotate smoothly for easy levelling. The shim, a loose set screw, a
4 mm hex key, two M5x20 mounting screws and two M5 nuts are included when ordering
the ball levelling mount separately.
Figure 5.5.1 Line drawing indicating placement of the aluminium shim and photo
showing the shim properly positioned in the centre of SR05’s bottom plate. Note the
position of the protruding ledge when placing the shim.
The shim can be placed into SR05’s bottom plate following these steps:
1)
If your SR05 has a small black plastic cover cap on the countersunk set screw
opening on SR05’s side, remove it. A small flathead screwdriver may be used. Then
insert the loose set screw with a 4 mm hex key by turning the hex key clockwise
until the screw is only slightly protruding (sticking out).
2)
Hold SR05 in one hand, the shim in the other.
3)
Ensure the orientation of the shim fits with that of SR05’s bottom plate. Note the
position of the protruding ledge (see Figure 9.4.1).
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4)
Pinch the shim slightly in order to reduce its diameter and to make it fit easily into
SR05’s bottom plate.
5)
While pinching, push the shim into its position on SR05’s bottom plate.
The shim is placed. For mounting and levelling, continue with the following steps:
6)
Mount the ball levelling with its mounting screws.
7)
SR05, with its shim positioned, can now be placed on the ball levelling mount.
Gently push the sensor onto the ball head until it clicks.
8)
The ball head can be rotated 360 ° and allows angle compensation on nonhorizontal surfaces up to 10 °.
9)
When SR05 is mounted and levelled, judging by its bubble level, lock the ball head
mechanism by turning the set screw clockwise with a 4 mm hex key until it is
tightened. The set screw should be countersunk and not protruding (not sticking
out).
When the ball head is not inserted in SR05, the shim makes a minor rattling noise when
moving SR05. This is normal, caused by mechanical freedom between the two parts.
The shim can be removed from SR05’s bottom plate by hand with the assistance of a
small flathead screwdriver. See the chapter on tooling required. Let the screwdriver
gently tip the shim out. When removing or placing the shim, make sure the glass dome is
protected at all times.
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5.6
Electrical connection of SR05: wiring diagram
The instrument must be powered by an external power supply, providing an operating
voltage in the range from 5 to 30 VDC. SR05-DA1 offers irradiance in W/m2 as a digital
output (Modbus over RS-485) and as an analogue 0 to 1 V output. SR05-DA2 offers
irradiance in W/m2 as a digital output (Modbus over TTL) and as an analogue 4 to 20 mA
output.
Table 5.6.1 Wiring diagram of SR05-DA1
PIN
WIRE
SR05-DA1
Modbus over RS-485
SR05-DA1
0 to 1 v output
1
Brown
VDC [+]
VDC [+]
4
Black
VDC [−]
VDC [−]
3
Blue
not connected
0 to 1 V output
2
White
RS-485 B / B’ [+]
not connected
5
Grey
RS-485 A / A’ [−]
not connected
Yellow
shield
shield
Note 1: at the connector-end of the cable, the shield is connected to the connector housing
Note 2: it is not possible to use SR05-DA1’s digital and analogue outputs at the same time
Table 5.6.2 Wiring diagram of SR05-DA2
PIN
WIRE
SR05-DA2
Modbus over TTL
SR05-DA2
4 to 20 mA output
1
Brown
VDC [+]
VDC [+]
4
Black
common / not connected *
not connected
3
Blue
VDC [−]
4 to 20 mA output
2
White
TTL [Tx]
not connected
5
Grey
TTL [Rx]
not connected
Yellow
shield
shield
* In standard configurations, using an external power supply, the black wire is attached
to the common of the read-out device. If SR05-DA2 is powered from the read-out
device itself, do not connect the black wire.
Note 1: at the connector-end of the cable, the shield is connected to the connector housing
Note 2: it is not possible to use SR05-DA2’s digital and analogue outputs at the same time
5.7
Grounding and use of the shield
Grounding and shield use are the responsibility of the user. The cable shield (called shield
in the wiring diagram) is connected to the aluminium instrument body via the connector.
In most situations, the instrument will be screwed on a mounting platform that is locally
grounded. In these cases the shield at the cable end should not be connected at all.
When a ground connection is not obtained through the instrument body, for instance in
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laboratory experiments, the shield should be connected to the local ground at the cable
end. This is typically the ground or low voltage of the power supply or the common of the
network. In exceptional cases, for instance when both the instrument and a datalogger
are connected to a small size mast, the local ground at the mounting platform is the
same as the network ground. In such cases ground connection may be made both to the
instrument body and to the shield at the cable end.
5.8
Using SR05-DA1’s analogue 0 to 1 V output
SR05-DA1 gives users the option to use 0 to 1 V output instead of its digital output.
When using 0 to 1 V output, please read this chapter first. When opting solely for SR05DA1’s digital output, please continue with the next chapter on SR05-DA1: chapter 5.9.
Using the 0 to 1 V output provided by SR05-DA1 is easy. The instrument can be
connected directly to commonly used datalogging systems. The irradiance, E, in W/m2 is
calculated by measuring the SR05-DA1 output, a voltage U, in V, and then multiplying by
the transmitted range r. The transmitted range is provided with SR05-DA1 on its product
certificate. By convention 0 W/m2 irradiance corresponds with 0 V transmitter output
voltage. The transmitted range, which is the irradiance at output voltage of 1 V, and is
typically 1600 W/m2. The transmitted range can be adjusted at the factory upon request.
The central equation governing SR05-DA1 is:
E = r·U
(Formula 5.7.1)
The standard setting is: E = 1600·U. See chapter 5.5 and the diagram below for
electrical connections to voltmeters, when using SR05-DA1’s 0 to 1 V output.
SR05-DA1
brown [+]
yellow
black
ground
blue 0 to 1 V output
V
voltmeter
U = 0 - 1 VDC
power supply 5 to 30 VDC
Figure 5.8.1 Electrical diagram of the connection of SR05-DA1 to a typical voltmeter or
datalogger with the capacity to measure voltage signals. SR05-DA1 operates on a supply
voltage of 5 to 30 VDC.
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5.9
Using SR05-DA2’s analogue 4 to 20 mA output
SR05-DA2 gives users the option to use 4 to 20 mA output instead of its digital output.
When using 4 to 20 mA output, please read this chapter first. When opting solely for
SR05-DA2’s digital output, please continue with the next chapter on SR05-DA2: chapter
5.10.
Using the 4 to 20 mA output provided by SR05-DA2 is easy. The instrument can be
connected directly to commonly used datalogging systems. The irradiance, E, in W/m2 is
calculated by measuring the SR05-DA2’s output, a small current I, subtracting 4 x 10-3 A
from it, and then multiplying by the transmitted range r. The transmitted range is
provided with SR05-DA2 on its product certificate. By convention 0 W/m2 irradiance
corresponds with 4 x 10-3 A transmitter output current I. The transmitted range, which is
the irradiance at output current of 20 x 10-3 A, and is typically 1600 W/m2. The
transmitted range can be adjusted at the factory upon request.
The central equation governing SR05-DA2 is:
E = r·(I - 4 x 10-3)/(16 x 10-3)
(Formula 5.9.1)
The standard setting is: E = 1600·(I - 4 x 10-3)/(16 x 10-3)
Table 5.9.1 Requirements for data acquisition and amplification equipment
Capability to
- measure 4-20 mA or
- measure currents or
- measure voltages
SR05 manual v1610
SR05-DA2 has a 4-20 mA output. There are several
possibilities to handle this signal. It is important to realise
that the signal wires not only act to transmit the signal but
also act as power supply for the 4-20 mA current loop circuit.
SR05-DA2 operates on a supply voltage of 5 to 30 VDC.
Some dataloggers have a 4-20 mA input. In that case SR05DA2 can be connected directly to the datalogger.
Some dataloggers have the capability to measure currents.
In some cases the datalogger accepts a voltage input.
Usually a 100 Ω precision resistor is used to convert the
current to a voltage (this will then be in the 0.4 – to 2 VDC
range). This resistor must be put in series with the blue wire
of the sensor.
See next page and chapter 5.5 for electrical connections.
29/77
See chapter 5.5 and the diagrams below for electrical connections to am- and
voltmeters, when using SR05-DA2’s 4 to 20 mA output.
SR05-DA2
blue 4 to 20 mA output
brown [+]
yellow
A
ground
ammeter
I = 4 to 20 mA
power supply 5 to 30 VDC
Figure 5.9.1 Electrical diagram of the connection of SR05-DA2 to a typical ammeter or
datalogger with capacity to measure current signals. SR05-DA2 operates on a supply
voltage of 5 to 30 VDC.
SR05-DA2
blue 4 to 20 mA output
brown [+]
yellow
voltmeter
ground
R
V
I = U/R
I = 4 to 20 mA
power supply 5 to 30 VDC
Figure 5.9.2 Electrical diagram of the connection of SR05-DA2 to a typical voltmeter or
datalogger with the capacity to measure voltage signals. Usually a 100 Ω shunt resistor
(R) is used to convert the current to a voltage. SR05-DA2 operates on a supply voltage
of 5 to 30 VDC.
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5.10 Using SR05-DA1’s and SR05-DA2’s digital output
When using SR05’s digital output, SR05-DA1 can be connected to an RS-485 network,
whereas SR05-DA2 can be connected to TTL devices. Both models can be connected to a
PC for communication with the Sensor Manager software.
5.11 Connecting SR05-DA1 to an RS-485 network
SR05-DA1 is suited for a two-wire (half-duplex) RS-485 network. In such a network
SR05-DA1 acts as a slave, receiving data requests from the master. An example of the
topology of an RS-485 two-wire network is shown in the figure below. SR05-DA1 is
powered from 5 to 30 VDC. The power supply is not shown in the figure. The VDC [-]
power supply ground must be connected to the common line of the network.
Master
D
R
5V
Pull up
RS-485 B / B’ [+]
Balanced pair
LT
LT
RS-485 A / A’ [-]
Pull down
Common ( VDC [ - ] )
D
R
SR05-DA1
/ Slave 1
D
R
Slave n
Figure 5.11.1 Typical topology of a two-wire RS-485 network, figure adapted from:
Modbus over serial line specification and implementation guide V1.02 (www.modbus.org).
The power supply is not shown in this figure.
After the last nodes in the network, on both sides, line termination resistors (LT) are
required to eliminate reflections in the network. According to the EIA/TIA-485 standard,
these LT have a typical value of 120 to 150 Ω. Never place more than two LT on the
network and never place the LT on a derivation cable. To minimise noise on the network
when no transmission is occurring, a pull up and pull down resistor are required. Typical
values for both resistors are in the range from 650 to 850 Ω.
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not connected
blue
shield
yellow
brown
black
[+] 5 to 30 VDC
[ - ] 5 to 30 VDC
common
SR05-DA1
white
[+] data, RS-485 B / B’
grey
[ - ] data, RS-485 A / A’
wire
RS-485 network
Figure 5.11.2 Connection of SR05-DA1 to an RS-485 network. SR05-DA1 is powered by
an external power supply of 5 to 30 VDC.
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5.12 Connecting SR05-DA2 to a TTL device
yellow
brown
blue
black
SR05-DA2
shield
[+] 5 to 30 VDC
[ - ] 5 to 30 VDC
common
white
data, TTL [ Tx ]
grey
data, TTL [ Rx ]
wire
TTL device
Figure 5.12.1 Connection of SR05-DA2 to a TTL device, in case SR05-DA2 is powered
by an external power supply of 5 to 30 VDC.
not connected
black
shield
yellow
brown
SR05-DA2
[+] 5 to 30 VDC
blue
[ - ] 5 to 30 VDC
white
data, TTL [ Tx ]
grey
data, TTL [ Rx ]
wire
TTL device
Figure 5.12.2 Connection of SR05-DA2 to a TTL device, in case SR05-DA2 is powered
by the read-out device itself.
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5.13 Connecting SR05 to a PC
Both SR05-DA1 and SR05-DA2 can be accessed via a PC. In that case communication
with the sensor is done via the user interface offered by the Sensor Manager software
(see the next chapters) or by another Modbus testing tool.
5.13.1
Connecting SR05-DA1 to a PC
Depending on the available ports on the PC, either an RS-485 to USB converter or an RS485 to RS-232 converter is used. The figure below shows how connections are made. The
converter must have galvanic isolation between signal input and output to prevent static
electricity or other high-voltage surges to enter the data lines. An external power supply
is required to power the SR05-DA1 (5 to 30 VDC). An RS-485 to USB converter is usually
powered via the USB interface: in this case no external power is needed to feed the
converter. If an RS-485 to RS-232 converter is used, this converter should be powered
by an external source. This may be the same supply used for the SR05-DA1.
not connected
blue
shield
yellow
brown
black
[+] 5 to 30 VDC
[ - ] 5 to 30 VDC
common
white
SR05-DA1
[+] data
grey
[ - ] data
wire
RS-485 / USB converter
USB to PC
Figure 5.13.1.1 Connecting SR05-DA1 to an RS-485 to USB converter and a PC
5.13.2
Connecting SR05-DA2 to a PC
Depending on the available ports on the PC, either a TTL to USB converter or a TTL to
RS-232 converter is used. The figure on the next page shows how connections are made.
The converter must have galvanic isolation between signal input and output to prevent
static electricity or other high-voltage surges to enter the data lines. An external power
supply is required to power the SR05-DA2 (5 to 30 VDC). A TTL to USB converter is
usually powered via the USB interface: in this case no external power is needed to feed
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the converter. If a TTL to RS-232 converter is used, this converter should be powered by
an external source. This may be the same supply used for the SR05-DA2.
shield
yellow
brown
blue
SR05-DA2
[+] 5 to 30 VDC
[ - ] 5 to 30 VDC
black
common
grey
[+] data
white
[ - ] data
wire
TTL / USB converter
USB to PC
Figure 5.13.2.1 Connecting SR05-DA2 to a TTL to USB converter and a PC
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6
Communication with SR05
6.1
PC communication: Sensor Manager software
SR05 can be accessed via a PC. In that case the communication with the sensor is done
via the user interface offered by the Hukseflux Sensor Manager software or by another
Modbus testing tool. The Sensor Manager can be downloaded by the user via
www.hukseflux.com/page/downloads. Alternatively, there are links to testing tools, paid
or freeware, available at www.modbus.org.
This chapter describes the functionality of the Sensor Manager only.
The Hukseflux Sensor Manager software provides a user interface for communication
between a PC and SR05. It allows the user to locate, configure and test one or more
SR05’s and to perform simple laboratory measurements using a PC. The Sensor
Manager’s most common use is for initial functionality testing and modification of the
SR05 Modbus address and communication settings. It is not intended for long-term
continuous measurement purposes. For available software updates of the Sensor
Manager, please check www.hukseflux.com/page/downloads.
6.1.1 Installing the Sensor Manager
Running the Sensor Manager requires installation of the latest version of Java Runtime
Environment software. Java Runtime Environment may be obtained free of charge from
www.java.com. The SR05 specifications overview (Table 3.1.1) shows the system and
software requirements for using a PC to communicate with SR05.
1) Download the Hukseflux Sensor Manager via www.hukseflux.com/page/downloads.
2) Unzip the downloaded files and copy the folder “Hukseflux Sensor Manager” to a
folder on a PC. For proper installation the user should have administrator rights for
the PC.
3)
Double-click “Hukseflux_Sensor_Manager.jar” in the folder “Hukseflux Sensor
Manager”. This will start up the Sensor Manager.
6.1.2 Trouble shooting during Sensor Manager installation
•
When Java Runtime Environment software is not installed, a Windows message
comes up, displaying “the file “Hukseflux_Sensor_Manager.jar” could not be opened”.
The solution is to install Java Runtime Environment on the PC and try again.
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6.1.3 Sensor Manager: main window
Figure 6.1.3.1 Main window of the Sensor Manager
When the Sensor Manager is started and a SR05 is connected to the PC, the user can
communicate with the instrument.
If the instrument address and communication settings are known, the serial connection
settings and the Modbus address can be entered directly. Clicking “Connect” will establish
contact.
If the instrument address and communication settings are not known, the instrument is
found by using the “Find” or “Find All” function. The Sensor Manager scans the specified
range of Modbus addresses, however only using the “Serial connection settings” as
indicated on screen. When only one sensor is connected, using “Find” is suggested
because the operation stops when a sensor is found. “Find all” will continue a scan of the
complete range of Modbus addresses and may take extra time.
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If the “Find” or “Find all” operation does not find instruments, a dialog box opens, asking
to confirm a scan of the address range using all possible communication settings. The
time this operation takes, depends on the address range to be scanned. To complete a
scan of 247 addresses will take over 15 minutes. When an instrument is found, a dialog
box opens providing its serial number, Modbus address and communication settings.
Communicating with the instrument is possible after changing the communication
settings and Modbus address in the main window to the values of the instrument, and
then clicking “Connect”.
Figure 6.1.3.2 Sensor Manager main window with three connected SR05’s
When an instrument is found, temperature and irradiance data are displayed. Updates
are done manually or automatically. Automatic updates can be made every second, every
5 seconds or every minute.
6.1.4 Sensor Manager: plotting data
When the “Plot on Live Chart” button in the lower right corner is clicked the “Plot
window” opens. A live graph is shown of the measurement with the selected instrument.
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The x-axis, time, is scaled automatically to display data of the complete measurement
period. After checking the box “Show tail only”, only the last minutes of measured data
are displayed. When the “update interval” is 1 second, the “Show tail only” function is
available after around 10 minutes of data collection. The y-axis displays the measured
irradiance in W/m2. The Y-axis automatically scales to display the full measured range.
Figure 6.1.4.1 Example of a SR05 irradiance plot in the Sensor Manager
6.1.5 Sensor Manager: information about the instrument
The main window shows the “Show details” button, giving access to the “Sensor details”
window. This window displays calibration results and calibration history, temperature
coefficients and other properties of the selected instrument, as shown on the next page.
The sensor serial number and all calibration information should match the information on
the instrument label and on the product certificate.
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Figure 6.1.5.1 Sensor details window in the Sensor Manager
6.1.6 Sensor Manager: changing Modbus address and communication settings
In the “Sensor details” window the “Change settings” function opens the “Change serial
communication settings” window, as shown in the figure below.
Figure 6.1.6.1 Change serial communication settings window in the Sensor Manager
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When new communication settings or a new Modbus address are entered, these need to
be confirmed by clicking “Change settings”. The instrument will then automatically
restart. In case the “Change settings” function is not activated, the original settings
remain valid. If the Modbus address is changed, the Sensor Manager will automatically
reconnect with the instrument using the new address after restart.
6.1.7 Sensor Manager: adjustment of the sensitivity by power users
The Sensor Manager does not allow a “standard user” to change any settings that have a
direct impact on the instrument output, i.e. the irradiance in W/m2. However, in case the
instrument is recalibrated it is common practice that the sensitivity is adjusted, and that
the latest result is added to the calibration history records. This can be done after
obtaining a password and becoming a “power user”. Please contact the factory to obtain
the password and to get directions to become a “power user”.
Example: During a calibration experiment, the result might be that SR05 has an
irradiance output in W/m2 that is 990, whereas the standard indicates it should be 970.
The SR05 output is in this example 2.06 % too high. The original sensitivity of
16.15 x 10-6 V/(W/m2) ought to be changed to 16.48, using registers 41 + 42. The old
calibration result is recorded in the calibration history file. In case there are still older
results these are moved over to higher register numbers 63 to 81.
6.2
Network communication: function codes, registers, coils
Warning: Using the same Modbus address for more than one device will lead to irregular
behaviour of the entire network. This chapter describes function codes, data model and
registers used in the SR05 firmware. Communication is organised according to the
specifications provided by the Modbus Organization. These specifications are explained in
the documents “Modbus application protocol v1.1b” and “Modbus over serial line v1.02”.
These documents can be acquired free of charge at www.modbus.org.
Table 6.2.1 Supported Modbus function codes
SUPPORTED MODBUS FUNCTION CODES
FUNCTION CODE (HEX)
DESCRIPTION
0x01
Read Coils
0x02
Read Discrete Inputs
0x03
Read Holding Registers
0x04
Read Input Register
0x05
Write Single Coil
0x06
Write Single Holding Register
0x0F
Write Multiple Coils
0x10
Write Multiple Registers
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Table 6.2.2 Modbus data model
MODBUS DATA MODEL
PRIMARY TABLES
OBJECT TYPE
TYPE OF
Discrete input
Single bit
R
Coil
Single bit
R/W
Input register
16 bit word
R
Holding register
16 bit word
R/W
R = read only, W = write only, R/W = read / write
The instrument does not distinguish between discrete input and coil; neither between
input register and holding register.
Table 6.2.3 Format of data
FORMAT OF DATA
DESCRIPTION
U16
Unsigned 16 bit integer
S16
Signed 16 bit integer
U32
Unsigned 32 bit integer
S32
Signed 32 bit integer
Float
IEEE 754 32 bit floating point format
String
A string of ASCII characters
The data format includes signed and unsigned integers. The difference between these
types is that a signed integer passes on negative values, which reduces the range of the
integer by half. Up to five 16 bit registers can be requested in one request; if requesting
six or more registers, multiple requests should be used.
If the format of data is a signed or an unsigned 32 bit integer, the first register received
is the most significant word (MSW) and the second register is the least significant word
(LSW). This way two 16 bit registers are reserved for a 32 bit integer. If the format of
data is float, it is a 32 bit floating point operator and two 16 bit registers are reserved as
well. Most network managing programs have standard menus performing this type of
conversion. In case manual conversion is required, see the appendix on conversion of a
floating point number to a decimal number. MSW and LSW should be read together in
one request. This is necessary to make sure both registers contain the data of one
internal voltage measurement. Reading out the registers with two different instructions
may lead to the combination of LSW and MSW of two measurements at different points in
time.
An Unsigned 32 bit integer can be calculated by the formula: (MSW x 216)+LSW = U32.
An example of such a calculation is available in the paragraph “Network communication:
example master request to SR05”.
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Your data request may need an offset of +1 for each SR05 register number,
depending on processing by the network master. Example: SR05 register
number 7 + master offset = 7 + 1 = master register number 8. Consult the
manual of the device acting as the local master.
Table 6.2.4 Modbus registers 0 to 11, measurements. For basic operation, Hukseflux
recommends to read out registers 2 + 3 for solar radiation, register 6 for instrument
body temperature and register 40 for the sensor serial number.
MODBUS REGISTERS 0-11
REGISTER
NUMBER
PARAMETER
0
Modbus address
1
2+3
Serial communication
settings
Irradiance
4+5
Factory use only
6
Sensor body
temperature
Sensor electrical
resistance
Scaling factor irradiance
7
8
9
10 + 11
Scaling factor
temperature
Sensor voltage output
12 to 31
Factory use only
DESCRIPTION OF CONTENT
TYPE
OF
FORMAT
OF DATA
Sensor address in Modbus
network, default = 1
Sets the serial
communication, default = 5
signal in x 0.01 W/m²
R/W
U16
R/W
U16
R
S32
In x 0.01 °C
R
S16
In x 0.1 Ω
R
U16
Default = 100
R
U16
Default = 100
R
U16
In x 10-9 V
R
S32
Register 0, Modbus address, contains the Modbus address of the sensor. This allows the
Modbus master to detect the slave, SR05-DA1, in its network. The address can be
changed; the value of the address must be between 1 and 247. The default Modbus
address is 1.
Note: The sensor needs to be restarted before changes become effective.
Register 1, Serial communication settings, is used to enter the settings for baud rate and
the framing of the serial data transfer. Default setting is setting number 5: 19200 baud,
8 data bits, even parity and 1 stop bit. Setting options are shown in the table below.
Note: The sensor needs to be restarted before changes become effective.
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Table 6.2.5 Setting options of register 1
SETTING OPTIONS
SETTING
NUMBER
BAUD RATE
1
9600
2
3
DATABITS
STOPBITS
PARITY
8
1
none
9600
8
1
even
9600
8
1
odd
4
19200
8
1
none
5 ( = default)
19200
8
1
even
6
19200
8
1
odd
10
38400
8
1
none
11
38400
8
1
even
12
38400
8
1
odd
16
115200
8
1
none
17
115200
8
1
even
18
115200
8
1
odd
Register 2 + 3, Irradiance, provides the solar radiation output in 0.01 W/m². The value
given must be divided by 100 to get the value in W/m². MSW and LSW should be read
together in one request.
Register 6, Instrument body temperature, provides the temperature of the instrument
body in 0.01 °C. The data must be divided by 100 to achieve the value in °C.
Register 7, Sensor electrical resistance, sensor resistance in 0.1 Ω. The data needs to be
divided by 10 to get the value in Ω. This register returns a 0 by default. To read the
resistance, first a measurement has to be performed. This can be done by writing 0xFF00
to coil 2. Hukseflux recommends to use this function only when necessary for diagnostics
in case of sensor failure.
Register 8, Scaling factor irradiance, default scaling factor is 100
Register 9, Scaling factor temperature, default scaling factor is 100.
Register 10 + 11, Sensor voltage output, sensor voltage output signal of the thermopile
in x 10-9 V.
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Table 6.2.6 Modbus registers 32 to 62, sensor and calibration information
MODBUS REGISTERS 32-62
REGISTER
NUMBER
PARAMETER
DESCRIPTION OF CONTENT
TYPE
OF
FORMAT
OF DATA
32 to 35
Sensor model
Part one of sensor description
R
String
36 to 39
Sensor model
Part two of sensor description
R
String
40
Sensor serial number
41 + 42
Sensor sensitivity
In x 10-6 V/(W/m2)
R
U16
R
Float
43
Response time
In x 0.1 s
R
U16
44
Sensor resistance
In x 0.1 Ω
R
U16
45
Reserved
Always 0
R
U16
46 + 47
Sensor calibration date
Calibration date of the sensor
in YYYYMMDD
R
U32
48 to 60
Factory use
61
Firmware version
R
U16
62
Hardware version
R
U16
Register 32 to 39, Sensor model, String of 8 registers. This register will return 8
numbers, which correspond with ASCII characters.
Register 40, Sensor serial number
Register 41 + 42, Sensor sensitivity, the sensitivity of the sensor in x 10-6 V/(W/m²).
Format of data is float,
Register 43, Response time, the response time of the sensor as measured in the factory
in x 0.1 s. The value must be divided by 10 to get the value in s.
Register 44, Sensor electrical resistance, returns the electrical resistance measured
during the sensor calibration. The resistance is in x 0.1 Ω and must be divided by 10 to
get the value in Ω.
Register 46 + 47, Sensor calibration date, last sensor calibration date, from which the
sensitivity in register 41 and 42 was found, in YYYYMMDD.
Register 61, Firmware version.
Register 62, Hardware version.
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Table 6.2.7 Modbus registers 63 to 82, calibration history
MODBUS REGISTERS 63-82
REGISTER
NUMBER
PARAMETER
DESCRIPTION OF
CONTENT
TYPE
OF
FORMAT
OF DATA
63 + 64
Sensor sensitivity history 1
R
Float
65 + 66
Calibration date history 1
R
U32
67 + 68
Sensor sensitivity history 2
In x 10-6 V/(W/m2)
Default value is 0
Former calibration date of
the sensor in YYYYMMDD
Default value is 0
See register 63 + 64
R
Float
69 + 70
Calibration date history 2
See register 65 + 66
R
U32
71 + 72
Sensor sensitivity history 3
See register 63 + 64
R
Float
73 + 74
Calibration date history 3
See register 65 + 66
R
U32
75 + 76
Sensor sensitivity history 4
See register 63 + 64
R
Float
77 + 78
Calibration date history 4
See register 65 + 66
R
U32
79 + 80
Sensor sensitivity history 5
See register 63 + 64
R
Float
81 + 82
Calibration date history 5
See register 65 + 66
R
U32
Register 63 to 82: Only accessible for writing by Sensor Manager power users: power
users can write calibration history to registers 63 to 82. If default values are returned, no
re-calibration has been written. Last calibration sensitivity and calibration date are
available in register 41 + 42 and 46 + 47 respectively.
Please note that if your data request needs an offset of +1 for each SR05
register number, depending on processing by the network master, this offset
applies to coils as well. Consult the manual of the device acting as the local
master.
Table 6.2.8 Coils
COILS
COIL
PARAMETER
DESCRIPTION
TYPE OF
OBJECT TYPE
0
Restart
Restart the sensor
W
Single bit
1
Reserved
2
Check
Measure sensor
electrical resistance
W
Single bit
Coil 0, Restart, when 0xFF00 is written to this coil the sensor will restart. If applied, a
new Modbus address or new serial settings will become effective.
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Coil 2, Check, when 0xFF00 is written to this coil the internal electronics will measure the
electrical resistance of the thermopile. After the measurement, a new value will be
written into register 7. Requesting to write this coil with a high repetition rate will result
in irregular behaviour of the sensor; the check must be executed as an exceptional
diagnostics routine only.
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6.3
Network communication: getting started
Once it has the correct Modbus address and communication settings, SR05-DA1 can be
connected directly to an RS-485 network and a power supply. How to physically connect
a sensor as a slave in a Modbus network is shown in chapter 5.11: Connecting a SR05DA1 to an RS-485 network. In such a connection the sensor is powered via an external
power supply of 5 to 30 VDC. When the sensor is screwed onto a grounded mounting
plate, which is usually the case, the shield is not connected to ground at the cable end.
Installing a SR05-DA1 in the network also requires configuring the communication for
this new Modbus device. This usually consists of defining a request that can be broadcast
by the master. If the SR05-DA1 is not already defined as a standard sensor type on the
network, contact the supplier of the network equipment to see if a library file for the
SR05-DA1 is available.
Typical operation requires the master to make a request of irradiance data in registers 2
+ 3, sensor temperature in register 6, and the sensor serial number in register 40 every
1 second, and store the 60 second averages. The data format of register 2 + 3 is a
signed 32 bit integer and the temperature in register 6 is a signed 16 bit integer.
Up to five 16 bit registers can be requested in one request. In case six or more registers
are requested in just one request, SR05-DA1 will not respond. If requesting six or more
registers, multiple requests should be used: SR05-DA1 will respond as expected.
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6.3.1 Adapting Modbus address and communication settings
Setting the instrument address and baud rate can be done in different ways:
• by connecting the sensor to the PC and using the Sensor Manager;
• by connecting the sensor to the PC and using another Modbus testing tool. There are
links to different solutions available at www.modbus.org;
• by using the available network user interface software.
The Modbus address is stored in register 0 and has a default value of 1. A user may
change the address to a value in the range of 1 to 247. The address value must be
unique in the network. The communication settings are stored in register 1. The default
setting is setting number 5 representing a communication with 19200 baud, even parity
bit, 8 data bits and 1 stop bit. After a new address or communication setting is written
the sensor must be restarted. This can be done by writing 0XFF00 to coil 0.
6.4
Network communication: example master request to SR05
Normal sensor operation consists of requesting the output of registers 2 + 3; the
temperature compensated solar radiation. For quality assurance also the sensor serial
number, register 40 and the temperature in register 6, are useful.
In this example a SR05 has address 64. The example requests the solar radiation
(temperature compensated) register 2 + 3, sensor serial number, register 40, and the
temperature of the instrument register 6. The values are represented in hexadecimals.
Note: 32 bit data are represented in 2 registers. MSW and LSW should be read together
in one request.
Request for solar radiation, register 2 + 3:
Master Request:
[40] [03] [00][00] [00][04] [4B][18]
[40] = Modbus slave address, decimal equivalent = 64
[03] = Modbus function; 03 Read holding registers
[00][00] = Starting register, the master requests data starting from register 0.
[00][04] = Length, the number of registers the master wants to read. 4 registers
[4B][18] = CRC, the checksum of the transmitted data
Sensor response:
[40] [03] [08] [00][40] [00][05] [00][01] [7C][4F] [79][DA]
[40] = Modbus slave address, decimal equivalent = 64
[03] = Modbus function
[08] = Number of bytes returned by the sensor. 8 bytes transmitted by the sensor
[00][40] = Register 0; Modbus address
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[00][05] = Register 1; Serial settings, 19200 baud, 8 data bits, even parity bit, 1
stop bit
[00][01] = Register 2; Temperature compensated signal, Most Significant Word
(MSW). Decimal equivalent = 1
[7C][4F] = Register 3; Temperature compensated signal, Least Significant Word
(LSW) = Decimal equivalent = 31823
[79][DA] = CRC, the checksum of the transmitted data
Together, register 2 and 3 are representing the temperature compensated solar
radiation output measured by the SR05-DA1. The MSW is in register 2 and the
LSW in 3. The output has to be calculated by the formula: ((MSW x 216) +
LSW)/100. In this example the result is: ((216 x 1) + 31823)/100 = 973.59 W/m²
Request for body temperature, register 6:
Master Request:
[40][03][00][06][00][01][6B][1A]
[40] = Modbus Slave address
[03] = Modbus function
[00][06] = Start register
[00][01] = Number of registers
[6B][1A] = CRC
Sensor response:
[40][03][02][08][B1][43][FF]
[40] = Modbus Slave address
[03] = Modbus function
[02] = Number of bytes
[08][B1] = Content of register 7, decimal equivalent = 2225
[43][FF] = CRC
Temperature = Register 7 x 0.01 = 2225 x 0.01 = 22.25 °C
Register 6 represents the sensors body temperature. The received data needs to
be divided by 100 to represent the correct outcome. In this example the result is:
2225 x 0.01 = 22.25 °C
Request for serial number, register 40:
Master Request:
[40][03][00][28][00][01][0B][13]
[40] = Modbus slave address
[03] = Modbus function
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[00][28] = Start register
[00][01] = Number of registers
[0B][13] = CRC
Sensor response:
[40][03][02][0A][29][43][35]
[40] = Modbus Slave address
[03] = Modbus function
[02] = Number of bytes
[0A][29] = Content of register 40, decimal equivalent = 2601
[43][35] = CRC
Register 40 represents the sensors serial number. In this example the serial
number is 2601.
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7
Making a dependable measurement
7.1
The concept of dependability
A measurement with a pyranometer is called “dependable” if it is reliable, i.e. measuring
within required uncertainty limits, for most of the time and if problems, once they occur,
can be solved quickly.
The requirements for a measurement with a pyranometer may be expressed by the user
as:
•
•
•
required uncertainty of the measurement (see following paragraphs)
requirements for maintenance and repairs (possibilities for maintenance and repair
including effort to be made and processing time)
a requirement to the expected instrument lifetime (until it is no longer feasible to
repair)
It is important to realise that the uncertainty of the measurement is not only determined
by the instrument but also by the way it is used.
See also ISO 9060 note 5. In case of pyranometers, the measurement uncertainty as
obtained during outdoor measurements is a function of:
•
•
•
•
•
•
the instrument class
the calibration procedure / uncertainty
the duration of instrument employment under natural sunlight (involving the
instrument stability specification)
the measurement conditions (such as tilting, ventilation, shading, instrument
temperature)
maintenance (mainly fouling)
the environmental conditions*
Therefore, ISO 9060 says, “statements about the overall measurement uncertainty under
outdoor conditions can only be made on an individual basis, taking all these factors into
account”.
* defined at Hukseflux as all factors outside the instrument that are relevant to the
measurement such as the cloud cover (presence or absence of direct radiation), sun
position, the local horizon (which may be obstructed) or condition of the ground (when
tilted). The environmental conditions also involve the question whether or not the
measurement at the location of measurement is representative of the quantity that
should be measured.
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7.2
Reliability of the measurement
A measurement is reliable if it measures within required uncertainty limits for most of the
time. We distinguish between two causes of unreliability of the measurement:
•
•
related to the reliability of the pyranometer and its design, manufacturing, calibration
(hardware reliability).
related to the reliability of the measurement uncertainty (measurement reliability),
which involves hardware reliability as well as condition of use.
Most of the hardware reliability is the responsibility of the instrument manufacturer.
The reliability of the measurement however is a joint responsibility of instrument
manufacturer and user. As a function of user requirements, taking into account
measurement conditions and environmental conditions, the user will select an instrument
of a certain class, and define maintenance support procedures.
In many situations there is a limit to a realistically attainable accuracy level. This is due
to conditions that are beyond control once the measurement system is in place. Typical
limiting conditions are:
•
•
•
the measurement conditions, for instance when working at extreme temperatures
when the instrument temperature is at the extreme limits of the rated temperature
range.
the environmental conditions, for instance when installed at a sub-optimal
measurement location with obstacles in the path of the sun.
other environmental conditions, for instance when assessing PV system performance
and the system contains panels at different tilt angles, the pyranometer
measurement may not be representative of irradiance received by the entire PV
system.
The measurement reliability can be improved by maintenance support. Important aspects
are:
•
•
•
dome fouling by deposition of dust, dew, rain or snow. Fouling results in undefined
measurement uncertainty (sensitivity and directional error are no longer defined).
This should be solved by regular inspection and cleaning.
sensor instability. Maximum expected sensor aging is specified per instrument as its
non-stability in [% change / year]. In case the sensor is not recalibrated, the
uncertainty of the sensitivity gradually will increase. This is solved by regular
recalibration.
moisture condensing under pyranometer domes resulting in a slow change of
sensitivity (within specifications). This is solved by regular replacement of desiccant
or by maintenance (drying the entire sensor) in case the sensor allows this. For nonserviceable sensors like most second class pyranometers, this may slowly develop
into a defect. For first class and secondary standard models (for instance model SR11
first class pyranometer and SR20-D2 digital secondary standard pyranometer) extra
desiccant (in a set of 5 bags in an air tight bag) is available.
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Another way to improve measurement reliability is to introduce redundant sensors.
•
•
the use of redundant instruments allows remote checks of one instrument using the
other as a reference, which leads to a higher measurement reliability.
in PV system performance monitoring, in addition to instruments measuring in the
plane of array, horizontally placed instruments are used for the measurement of
global radiation. Global irradiance data enable the user to compare the local climate
and system efficiency between different sites. These data can also be compared to
measurements by local meteorological stations.
7.3
Speed of repair and maintenance
Dependability is not only a matter of reliability but also involves the reaction to
problems; if the processing time of service and repairs is short, this contributes to the
dependability.
Hukseflux pyranometers are designed to allow easy maintenance and repair. The main
maintenance actions are:
•
•
replacement of desiccant
replacement of cabling
For optimisation of dependability a user should:
•
•
•
estimate the expected lifetime of the instrument
design a schedule of regular maintenance
design a schedule of repair or replacement in case of defects
When operating multiple instruments in a network Hukseflux recommends keeping
procedures simple and having a few spare instruments to act as replacements during
service, recalibrations and repair.
7.4
Uncertainty evaluation
The uncertainty of a measurement under outdoor or indoor conditions depends on many
factors, see paragraph 1 of this chapter. It is not possible to give one figure for
pyranometer measurement uncertainty. The work on uncertainty evaluation is “in
progress”. There are several groups around the world participating in standardisation of
the method of calculation. The effort aims to work according to the guidelines for
uncertainty evaluation (according to the “Guide to Expression of Uncertainty in
Measurement” or GUM).
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7.4.1 Evaluation of measurement uncertainty under outdoor conditions
Hukseflux actively participates in the discussions about pyranometer measurement
uncertainty; we also provide spreadsheets, reflecting the latest state of the art, to assist
our users in making their own evaluation. The input to the assessment is summarised:
1) The formal evaluation of uncertainty should be performed in accordance with ISO 98-3
Guide to the Expression of Uncertainty in Measurement, GUM.
2) The specifications of the instrument according to the list of ISO 9060 classification of
pyranometers and pyrheliometers are entered as limiting values of possible errors, to be
analysed as type B evaluation of standard uncertainty per paragraph 4.3.7. of GUM. A
priori distributions are chosen as rectangular.
3) A separate estimate has to be entered to allow for estimated uncertainty due to the
instrument maintenance level.
4) The calibration uncertainty has to be entered. Please note that Hukseflux calibration
uncertainties are lower than those of alternative equipment. These uncertainties are
entered in measurement equation (equation is usually Formula 0.1: E = U/S), either as
an uncertainty in E (zero offsets, directional response) in U (voltage readout errors) or
in S (tilt error, temperature dependence, calibration uncertainty).
5) In uncertainty analysis for pyranometers, the location and date of interest is entered.
The course of the sun is then calculated, and the direct and diffuse components are
estimated, based on a model; the angle of incidence of direct radiation is a major factor
in the uncertainty.
6) In uncertainty analysis for modern pyrheliometers: tilt dependence often is so low that
one single typical observation may be sufficient.
7) In case of special measurement conditions, typical specification values are chosen.
These should for instance account for the measurement conditions (shaded / unshaded,
ventilated/ unventilated, horizontal / tilted) and environmental conditions (clear sky /
cloudy, working temperature range).
8) Among the various sources of uncertainty, some are “correlated”; i.e. present during
the entire measurement process, and not cancelling or converging to zero when
averaged over time; the off-diagonal elements of the covariance matrix are not zero.
Paragraph 5.2 of GUM.
9) Among the various sources of uncertainty, some are “uncorrelated”; cancelling or
converging to zero when averaged over time; the off-diagonal elements of the covariance
matrix are zero. Paragraph 5.1 of GUM.
10) Among the various sources of uncertainty, some are “not included in analysis”; this
applies for instance to non-linearity for pyranometers, because it is already included in
the directional error, and the spectral response for pyranometers and pyrheliometers
because it is already taken into account in the calibration process.
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Table 7.4.1.1 Preliminary estimates of achievable uncertainties of measurements with
Hukseflux pyranometers. The estimates are based on typical pyranometer properties and
calibration uncertainty, for sunny, clear sky days and well maintained stations, without
uncertainty loss due to lack of maintenance and due to instrument fouling. The table
specifies expanded uncertainties with a coverage factor of 2 and confidence level of
95 %. Estimates are based on 1 s sampling. IMPORTANT NOTE: there is no international
consensus on uncertainty evaluation of pyranometer measurements, so this table should
not be used as a formal reference.
Pyranometer
class
(ISO 9060)
season
latitude
uncertainty
minute totals
at solar noon
uncertainty
hourly totals
at solar noon
uncertainty
daily totals
secondary
standard
summer
mid-latitude
2.7 %
2.0 %
1.9 %
equator
pole
2.6 %
7.9 %
1.9 %
5.6 %
1.7 %
4.5 %
winter
mid-latitude
3.4 %
2.5 %
2.7 %
summer
mid-latitude
4.7 %
3.3 %
3.4 %
equator
4.4 %
3.1 %
2.9 %
pole
16.1%
11.4 %
9.2 %
winter
mid-latitude
6.5 %
4.5 %
5.2 %
summer
mid-latitude
8.4 %
5.9 %
6.2 %
equator
7.8 %
5.5 %
5.3 %
pole
29.5 %
21.6 %
18.0 %
mid-latitude
11.4 %
8.1 %
9.9 %
first class
second class
(SR05)
winter
7.4.2 Calibration uncertainty
New calibration procedures were developed in close cooperation with PMOD World
Radiation Center in Davos, Switzerland. The latest calibration method results in an
uncertainty of the sensitivity of less than 1.8 %, compared to typical uncertainties of
higher than 3.5 % for this pyranometer class. See the appendix for detailed information
on calibration hierarchy.
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8
Maintenance and trouble shooting
8.1
Recommended maintenance and quality assurance
SR05 can measure reliably at a low level of maintenance in most locations. Usually
unreliable measurements will be detected as unreasonably large or small measured
values. As a general rule this means that regular visual inspection combined with a
critical review of the measured data, preferably checking against other measurements, is
the preferred way to obtain a reliable measurement.
Table 8.1.1 Recommended maintenance of SR05. If possible the data analysis and
cleaning (1 and 2) should be done on a daily basis. (continued on next page)
MINIMUM RECOMMENDED PYRANOMETER MAINTENANCE
INTERVAL
SUBJECT
ACTION
1
1 week
data analysis
compare measured data to maximum possible / maximum
expected irradiance and to other measurements nearby
(redundant instruments). Also historical seasonal records can
be used as a source for expected values. Analyse night time
signals. These signals may be negative (down to - 5 W/m2 on
clear windless nights), due to zero offset a. In case of use with
PV systems, compare daytime measurements to PV system
output. Look for any patterns and events that deviate from
what is normal or expected
2
2 weeks
cleaning
use a soft cloth to clean the dome of the instrument,
persistent stains can be treated with soapy water or alcohol
3
6 months
inspection
inspect cable quality, inspect connectors, inspect mounting
position, inspect cable, clean instrument, clean cable, inspect
levelling, change instrument tilt in case this is out of
specification, inspect mounting connection, inspect interior of
dome for condensation
4
2 years
desiccant
replacement
desiccant is specified to last for minimum 2 years. In case the
user wants to replace desiccant himself, this is at own risk and
should only be executed in an ESD-safe work environment.
The bottom plate of SR05 should be removed by unscrewing 3
x T10 screws with a Torx 10 screwdriver. The desiccant bag is
taped on the bottom plate of SR05. Care should be taken
when mounting the bottom plate on SR05
5
2 years
recalibration
recalibration by side-by-side comparison to a higher standard
instrument in the field according to ISO 9847
request “power user” status and a password at the factory
permitting to write to registers holding the sensitivity and the
calibration history data via the Sensor Manager
lifetime
assessment
judge if the instrument should be reliable for another 2 years,
or if it should be replaced
6
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MINIMUM RECOMMENDED PYRANOMETER MAINTENANCE (continued)
7
parts
replacement
if applicable / necessary replace the parts that are most
exposed to weathering; cable, connector. NOTE: use Hukseflux
approved parts only
8
internal
inspection
if applicable: open instrument and inspect / replace O-rings;
dry internal cavity around the circuit board
9
recalibration
high-accuracy recalibration indoors according to ISO 9847 or
outdoors according to ISO 9846
8.2
6 years
Trouble shooting
Table 8.2.1 Trouble shooting for SR05 (continued on next page)
General
Inspect the instrument for any damage.
Inspect if the connector is properly attached.
Check the condition of the connectors (on chassis as well as the cable).
Inspect if the sensor receives DC voltage power in the range of 5 to 30 VDC.
Inspect the connection of the shield (typically not connected at the network side).
Inspect the connection of the sensor power supply, typically the negative is
connected to the network common.
Prepare for
indoor testing
Install the Sensor Manager software on a PC. Equip the PC with RS-485 or TTL
communication for respectively SR05-DA1 and SR05-DA2. Put DC voltage power
to the sensor and establish communication with the sensor. At power–up the
signal may have a temporary output level different from zero; an offset. Let this
offset settle down.
The sensor
does not give
any signal
Check if the sensor reacts to light: expose the sensor to a strong light source, for
instance a 100 W light bulb at 0.1 m distance. The signal should read > 100 W/m2
now. Darken the sensor either by putting something over it or switching off the
light. The instrument voltage output should go down and within one minute
approach 0 W/m2. Check the data acquisition by replacing the sensor with a spare
sensor with the same address.
Not able to
communicate
with the
sensor
Check all physical connections to the sensor and try connecting to the sensor
again. If communicating is not possible, try to figure out if the address and
communication settings are correct. Analyse the cable performance by measuring
resistance from pins to cable ends. The electrical resistance should be < 10 Ω. In
case of doubt, try a new cable.
Connect sensor to a PC and perform the “Find” and “Find all” operation with the
Sensor Manager to locate the sensor and verify the communication settings. If all
physical connections are correct, and the sensor still cannot be found, please
contact the factory to send the sensor to the manufacturer for diagnosis and
service.
SR05 does not
respond to a
request for 6
or more
registers
It is not possible to request more than five 16 bit registers in one request. In case
of requesting six or more registers in just one request, the sensor will not
respond. If requesting six or more registers, use multiple requests: the sensor will
respond as expected.
The sensor
Note that night-time signals may be negative (down to -5 W/m2 on clear windless
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signal is
unrealistically
high or low
nights), due to zero offset a.
Check if the pyranometer has a clean dome.
Check the location of the pyranometer; are there any obstructions that could
explain the measurement result.
Check the orientation / levelling of the pyranometer.
Check the cable condition looking for cable breaks. Check the condition of the
connectors (on chassis as well as the cable).
The sensor
signal shows
unexpected
variations
Check
Check
Check
Check
Check
the presence of strong sources of electromagnetic radiation (radar, radio).
the condition and connection of the shield.
the condition of the sensor cable.
if the cable is not moving during the measurement.
the condition of the connectors (on chassis as well as the cable)
The dome
Arrange to send the sensor back to Hukseflux for diagnosis.
shows internal
condensation
8.3
Calibration and checks in the field
Recalibration of field pyranometers is typically done by comparison in the field to a
reference pyranometer. The applicable standard is ISO 9847 “International StandardSolar Energy- calibration of field pyranometers by comparison to a reference
pyranometer”. At Hukseflux an indoor calibration according to the same standard is used.
Hukseflux recommendation for re-calibration:
if possible, perform calibration indoor by comparison to an identical reference instrument,
under normal incidence conditions.
The recommended calibration interval of pyranometers is 2 years. The registers
containing the applied sensitivity and the calibration history of SR05 are accessible for
users. This allows the user to choose his own local calibration service. The same feature
may be used for remotely controlled re-calibration of pyranometers in the field. Ask
Hukseflux for information on ISO and ASTM standardised procedures for field calibration.
Request “power user” status and a password at the factory permitting to write to
registers holding the sensitivity and the calibration history data via the Sensor Manager.
In case of field comparison; ISO recommends field calibration to a higher class
pyranometer. Hukseflux suggests also allowing use of sensors of the same model and
class, because intercomparisons of similar instruments have the advantage that they
suffer from the same offsets. It is therefore just as good to compare to pyranometers of
the same brand and type as to compare to an instrument of a higher class. ISO
recommends to perform field calibration during several days; 2 to 3 days under cloudless
conditions, 10 days under cloudy conditions. In general this is not achievable. In order to
shorten the calibration process Hukseflux suggests to allow calibration at normal
incidence, using hourly totals near solar noon.
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Hukseflux main recommendations for field intercomparisons are:
1) to take normal incidence as a reference and not the entire day.
2) to take a reference of the same brand and type as the field pyranometer or a
pyranometer of a higher class, and
3) to connect both to the same electronics, so that electronics errors (also offsets) are
eliminated.
4) to mount all instruments on the same platform, so that they have the same body
temperature.
5) assuming that the electronics are independently calibrated, to analyse radiation values
at normal incidence radiation (possibly tilting the radiometers to approximately normal
incidence), if this is not possible to compare 1 hour totals around solar noon for
horizontally mounted instruments.
6) for second class radiometers, to correct deviations of more than ± 10 %. Lower
deviations should be interpreted as acceptable and should not lead to a revised
sensitivity.
7) for first class pyranometers, to correct deviations of more than ± 5 %. Lower
deviations should be interpreted as acceptable and should not lead to a revised
sensitivity.
8) for secondary standard instruments, to correct deviations of more than ± 3 %. Lower
deviations should be interpreted as acceptable and should not lead to a revised
sensitivity.
8.4
Data quality assurance
Quality assurance can be done by:
•
•
•
•
analysing trends in solar irradiance signal
plotting the measured irradiance against mathematically generated expected values
comparing irradiance measurements between sites
analysis of night time signals
The main idea is that one should look out for any unrealistic values. There are programs
on the market that can semi-automatically perform data screening. See for more
information on such a program: www.dqms.com.
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9
Appendices
9.1
Appendix on cable extension / replacement
The sensor cable of SR05 is equipped with a M12-A straight connector. In case of cable
replacement, it is recommended to purchase a new cable with connector at Hukseflux.
In case of cable extension, it is recommended to purchase an extension cable with
connector pairs at Hukseflux. Please note that Hukseflux does not provide support for
Do-It-Yourself connector- and cable assembly.
SR05 is equipped with one cable. Maximum length of the sensor cable depends on the
RS-485 network topology applied in the field. In practice, daisy chain topologies or point
to point (PtP) topologies are used. The length of the sensor cable should be as short as
possible to avoid signal reflections on the line, in particular in daisy chain configurations.
In point to point configurations cable lengths can in theory be much longer; RS-485 is
specified for cable lengths up to 1200 metres.
Connector and cable specifications are summarised on the next page.
Figure 9.1.1 On the left the SR05 cable with M12-A female connector on sensor end.
The cable is non-stripped on the other end. Its length is 3 metres standard and available
in 10 and 20 metres too. On the right Hukseflux extension cable with connector pairs,
with male and female M12-A connectors, available in 10 and 20 metres.
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Table 9.1.1 Specifications for SR05 cable replacement and extension
General replacement
please order a new cable with connector at Hukseflux
General cable extension
please order an extension cable with connector pairs at Hukseflux
Connectors used
chassis: M12-A straight male connector, male thread, 5-pole
manufacturer: Binder
cable: M12-A straight female connector, female thread, 5-pole
manufacturer: Binder
The shield is electrically connected to the connector
Cable
5-wire, shielded
manufacturer: Binder
Length
Cables should be kept as short as possible, in particular in daisy chain
topologies. In point to point topologies cable length should not exceed RS485 specifications of maximum 1200 metres.
Outer sheath
with specifications for outdoor use
(for good stability in outdoor applications)
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9.2
Appendix on tools for SR05
Table 9.2.1 Specifications of tools for SR05
CONFIGURATION
TOOLS
INCLUDED
tooling required for mounting SR05
without ball levelling
two M5 screws
applicable screwdriver
no
no
tooling required for mounting SR05
with ball levelling
hex key 4 mm
wrench size 8 mm for M5 nuts
yes
no
tooling required for mounting SR05
with tube mount
hex key 4 mm
yes
tooling required for levelling SR05
with ball levelling and tube mount
hex key 4 mm
yes
tooling required for tipping the aluminium
shim out of SR05’s bottom panel position
screwdriver blade width 2 to 4
mm
no
9.3
•
•
•
•
•
•
•
•
•
•
•
Appendix on spare parts for SR05
SR05 cable with female M12-A connector on sensor end, non-stripped on other end
(3, 10, 20 m). Specify cable length
SR05 extension cable with connector pair, with male and female M12-A connectors,
(10, 20 m). Specify extension cable length
Ball levelling (order number BL01)
Tube mount (order number TM01)
Tube mount with ball levelling (order number TMBL01)
Shim for ball levelling mount
Countersunk set screw
2 x M5x40 mounting screw
2 x M5x30 mounting screw
2 x M5x20 mounting screw with 2 x M5 nuts
Desiccant (silica gel, 1.0 g, in a HDPE bag)
NOTE: Dome, level and sensor of SR05 cannot be supplied as spare parts
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9.4
Appendix on standards for classification and calibration
Both ISO and ASTM have standards on instrument classification and methods of
calibration. The World Meteorological Organisation (WMO) has largely adopted the ISO
classification system.
Table 9.4.1 Pyranometer standardisation in ISO and ASTM.
STANDARDS ON INSTRUMENT CLASSIFICATION AND CALIBRATION
ISO STANDARD
EQUIVALENT ASTM STANDARD
ISO 9060:1990 Solar energy -- Specification
and classification of instruments for measuring
hemispherical solar and direct solar radiation
not available
Comment: work is in progress on a new ASTM
equivalent standard
Comment: a standard “Solar energy --Methods
for testing pyranometer and pyrheliometer
characteristics” has been announced in ISO
9060 but is not yet implemented.
not available
ISO 9846:1993 Solar energy -- Calibration of
a pyranometer using a pyrheliometer
ASTM G167 - 05 Standard Test Method for
Calibration of a Pyranometer Using a
Pyrheliometer
ISO 9847:1992 Solar energy -- Calibration of
field pyranometers by comparison to a
reference pyranometer
ASTM E 824 -10 Standard Test Method for
Transfer of Calibration from Reference to Field
Radiometers
ASTM G207 - 11 Standard Test Method for
Indoor Transfer of Calibration from Reference to
Field Pyranometers
ISO 9059:1990 Solar energy -- Calibration of
field pyrheliometers by comparison to a
reference pyrheliometer
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ASTM E 816 Standard Test Method for
Calibration of Pyrheliometers by Comparison to
Reference Pyrheliometers
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9.5
Appendix on calibration hierarchy
The World Radiometric Reference (WRR) is the measurement standard representing the
Sl unit of irradiance. Use of WRR is mandatory when working according to the standards
of both WMO and ISO. ISO9874 states under paragraph 1.3: the methods of calibration
specified are traceable to the WRR. The WMO manual states under paragraph 7.1.2.2:
the WRR is accepted as representing the physical units of total irradiance.
The worldwide homogeneity of the meteorological radiation measurements is guaranteed
by the World Radiation Center in Davos Switzerland, by maintaining the World Standard
Group (WSG) which materialises the World Radiometric Reference.
See www.pmodwrc.ch
The Hukseflux standard is traceable to an outdoor WRR calibration. Some small
corrections are made to transfer this calibration to the Hukseflux standard conditions:
sun at zenith and 1000 W/m2 irradiance level. During the outdoor calibration the sun is
typically at 20 to 40° zenith angle, and the total irradiance at a 700 W/m2 level.
Table 9.5.1 Calibration hierarchy for pyranometers
WORKING STANDARD CALIBRATION AT PMOD / WRC DAVOS
Calibration of working standard pyranometers:
Method: ISO 9846, type 1 outdoor. This working standard has an uncertainty “uncertainty of
standard”. The working standard has been calibrated under certain “test conditions of the
standard”. The working standard has traceability to WRR world radiometric reference.
CORRECTION OF (WORKING) STANDARD CALIBRATION TO STANDARDISED
REFERENCE CONDITIONS
Correction from “test conditions of the standard” to “reference conditions” i.e. to normal
incidence and 20 °C:
Using known (working) standard pyranometer properties: directional, non linearity, offsets,
temperature dependence). This correction has an uncertainty; “uncertainty of correction”.
At Hukseflux we also call the working standard pyranometer “standard”.
INDOOR PRODUCT CALIBRATION
Calibration of products, i.e. pyranometers:
Method: according to ISO 9847, Type IIc, which is an indoor calibration.
This calibration has an uncertainty associated with the method.
(In some cases like the BSRN network the product calibration is with a different method; for
example again type 1 outdoor)
CALIBRATION UNCERTAINTY CALCULATION
ISO 98-3 Guide to the Expression of Uncertainty in Measurement, GUM Determination of
combined expanded uncertainty of calibration of the product, including uncertainty of the
working standard, uncertainty of correction, uncertainty of the method (transfer error). The
coverage factor must be determined; at Hukseflux we work with a coverage factor k = 2.
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9.6
Appendix on meteorological radiation quantities
A pyranometer measures irradiance. The time integrated total is called radiant exposure.
In solar energy radiant exposure is often given in W∙h/m 2.
Table 9.6.1 Meteorological radiation quantities as recommended by WMO (additional
symbols by Hukseflux Thermal Sensor). POA stands for Plane of Array irradiance. The
term originates from ASTM and IEC standards.
SYMBOL
DESCRIPTION
CALCULATION
UNITS
E↓
downward irradiance
E↓ = Eg ↓ + El↓
W/m2
H↓
downward radiant exposure
for a specified time interval
H↓ = Hg↓ + Hl ↓
J/m2
E↑
upward irradiance
E↑ = Eg ↑ + El ↑
W/m2
H↑
upward radiant exposure
for a specified time interval
H↑ = Hg↑ + Hl ↑
J/m2
W∙h/m2
Change of
units
E
direct solar irradiance
normal to the apparent
solar zenith angle
solar constant
W/m2
DNI
Direct
Normal
Irradiance
E0
Eg ↓
h
Eg ↓
t
Ed ↓
global irradiance;
hemispherical irradiance on
a specified, in this case
horizontal surface.*
global irradiance;
hemispherical irradiance on
a specified, in this case
tilted surface.*
downward diffuse solar
radiation
W/m2
Eg↓ = E cos θh + Ed↓
W/m2
GHI
Global
Horizontal
Irradiance
Eg ↓ = E∙cos θt +
Ed ↓ t + Er↑ t ***
W/m2
POA
Plane of
Array
W/m2
DHI
Diffuse
Horizontal
Irradiance
El ↑, El ↓
upward / downward longwave irradiance
W/m2
Er↑
reflected solar irradiance
W/m2
E*
net irradiance
T↓
apparent surface
temperature**
apparent sky
temperature**
sunshine duration
T↑
SD
ALTERNATIVE
EXPRESSION
E* = E↓ – E↑
W/m2
ºC or K
ºC or K
h
θ is the apparent solar zenith angle θh relative to horizontal, θt relative to a tilted surface
g = global, l = long wave, t = tilted *, h = horizontal*
*
distinction horizontal and tilted from Hukseflux,
**
T symbols introduced by Hukseflux,
*** contributions of Ed ↓ t and Er↑ t are Ed ↓ and Er↑ both corrected for the tilt angle of the
surface
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9.7
Appendix on ISO and WMO classification tables
Table 9.7.1 Classification table for pyranometers per ISO 9060 and WMO.
NOTE: WMO specification of spectral selectivity is different from that of ISO. Hukseflux
conforms to the ISO limits. WMO also specifies expected accuracies. ISO finds this not to
be a part of the classification system because it also involves calibration. Please note that
WMO achievable accuracies are for clear days at mid latitudes and that the uncertainty
estimate does not include uncertainty due to calibration*.
ISO CLASSIFICATION** TABLE
ISO CLASS
SECONDARY
STANDARD
FIRST CLASS
SECOND
CLASS
15 s
+ 7 W/m2
30 s
+ 15 W/m2
60 s
+ 30 W/m2
± 2 W/m2
± 4 W/m2
± 8 W/m2
± 0.8 %
± 0.5 %
± 10 W/m2
± 1.5 %
±1%
± 20 W/m2
±3%
±3%
± 30 W/m2
Spectral selectivity (350 to 1 500 x 10-9 m)
(WMO 300 to 3 000 x 10-9 m)
±3%
±5%
± 10 %
Temperature response (interval of 50 K)**
2%
4%
8%
Tilt response
(0 to 90 ° at 1000 W/m2)
± 0.5 %
±2%
±5%
HIGH QUALITY
GOOD QUALITY
WMO: achievable accuracy for daily sums*
2%
5%
MODERATE
QUALITY
10 %
WMO: achievable accuracy for hourly sums*
3%
8%
20 %
WMO: achievable accuracy for minute sums*
not specified
not specified
not specified
WMO: resolution
(smallest detectable change)
1 W/m2
5 W/m2
10 W/m2
individual
instrument only:
all specs must
comply
group
compliance
group
compliance
Specification limit
Response time (95 %)
Zero offset a (response to 200 W/m2 net
thermal radiation)
Zero offset b (response to 5 K/h in ambient
temperature)
Non-stability (change per year)
Non-linearity (100 to 1000 W/m2)
Directional response
ADDITIONAL WMO SPECIFICATIONS
WMO CLASS
CONFORMITY TESTING***
ISO 9060
* WMO 7.2.1: The estimated uncertainties are based on the following assumptions: (a)
instruments are well-maintained, correctly aligned and clean; (b) 1 min and 1 h figures
are for clear-sky irradiances at solar noon; (c) daily exposure values are for clear days at
mid-latitudes. WMO 7.3.2.5: Table 7.5 lists the expected maximum deviation from the
true value, excluding calibration errors.
** At Hukseflux the expression ± 1 % is used instead of a range of 2 %.
*** an instrument is subject to conformity testing of its specifications. Depending on the
classification, conformity compliance can be proven either by group- or individual
compliance. A specification is fulfilled if the mean value of the respective test result does
not exceed the corresponding limiting value of the specification for the specific category
of instrument.
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9.8
Appendix on definition of pyranometer specifications
Table 9.8.1 Definition of pyranometer specifications
SPECIFICATION
DEFINITION
SOURCE
Response time
(95 %)
time for 95 % response. The time interval between the instant
when a stimulus is subjected to a specified abrupt change and the
instant when the response reaches and remains within specified
limits around its final steady value.The response time is a measure
of the thermal inertia inherent in the stabilization period for a final
reading.
response to 200 W/m2 net thermal radiation (ventilated).
Hukseflux assumes that unventilated instruments have to specify
the zero-offset in unventilated – worst case – conditions.
Zero offsets are a measure of the stability of the zero-point.
Zero offset a is visible at night as a negative offset, the instrument
dome irradiates in the far infra red to the relatively cold sky. This
causes the dome to cool down. The pyranometer sensor irradiates
to the relatively cool dome, causing a negative offset. Zero offset
a is also assumed to be present during daytime.
response to 5 K/h change in ambient temperature.
Zero offsets are a measure of the stability of the zero-point.
ISO
90601990
WMO
1.6.3
Zero offset a:
(200 W/m2 net
thermal
radiation )
Zero offset b:
(5 K/h in ambient
temperature)
Non-stability
(change per
year)
Non-linearity
(100 to 1000
W/m2)
Directional
response
Spectral
selectivity (350
to 1500 x 10-9 m)
(WMO 300 to
3000 x 10-9 m)
Temperature
response
(interval of 50 K)
Tilt response
(0° to 90° at
1000 W/m2)
Sensitivity
Spectral range
percentage change in sensitivity per year. The dependence of
sensitivity resulting from ageing effects which is a measure of the
long-term stability.
percentage deviation from the sensitivity at 500 W/m2 due to the
change in irradiance within the range of 100 W/m2 to 1000 W/m2.
Non-linearity has an overlap with directional response, and
therefore should be handled with care in uncertainty evaluation.
the range of errors caused by assuming that the normal incidence
sensitivity is valid for all directions when measuring from any
direction a beam radiation whose normal incidence irradiance is
1000 W/m2 . Directional response is a measure of the deviations
from the ideal “cosine behaviour” and its azimuthal variation.
percentage deviation of the product of spectral absorptance and
spectral transmittance from the corresponding mean within 350 x
10-9 m to 1500 x 10-9 m and the spectral distribution of irradiance.
Spectral selectivity is a measure of the spectral selectivity of the
sensitivity.
percentage deviation of the sensitivity due to change in ambient
temperature within an interval of 50 K the temperature of the
pyranometer body.
percentage deviation from the sensitivity at 0° tilt (horizontal) due
to change in tilt from 0° to 90° at 1000 W/m2 irradiance. Tilt
response describes changes of the sensitivity due to changes of
the tilt angle of the receiving surface.
the change in the response of a measuring instrument divided by
the corresponding change in the stimulus.
the spectral range of radiation to which the instrument is
sensitive. For a normal pyranometer this should be in the 0.3 to 3
x 10-6 m range. Some pyranometers with coloured glass domes
have a limited spectral range.
SR05 manual v1610
ISO
90601990
ISO
90601990
ISO
90601990
ISO
90601990
ISO
90601990
ISO
90601990
ISO
90601990
ISO
90601990
WMO
1.6.3
Hukseflux
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9.9
Appendix on terminology / glossary
Table 9.9.1 Definitions and references of used terms
TERM
DEFINITION (REFERENCE)
Solar energy
or solar
radiation
solar energy is the electromagnetic energy emitted by the sun. Solar energy is
also called solar radiation and shortwave radiation. The solar radiation incident
on the top of the terrestrial atmosphere is called extra-terrestrial solar radiation;
97 % of which is confined to the spectral range of 290 to 3 000 x 10-9 m. Part of
the extra-terrestrial solar radiation penetrates the atmosphere and directly
reaches the earth’s surface, while part of it is scattered and / or absorbed by the
gas molecules, aerosol particles, cloud droplets and cloud crystals in the
atmosphere. The former is the direct component, the latter is the diffuse
component of the solar radiation. (ref: WMO, Hukseflux)
solar radiation received by a plane surface from a 180° field of view angle (solid
angle of 2 π sr).(ref: ISO 9060)
the solar radiation received from a 180° field of view angle on a horizontal
surface is referred to as global radiation. Also called GHI. This includes radiation
received directly from the solid angle of the sun’s disc, as well as diffuse sky
radiation that has been scattered in traversing the atmosphere. (ref: WMO)
Hemispherical solar radiation received by a horizontal plane surface.
(ref: ISO 9060)
also POA: hemispherical solar irradiance in the plane of a PV array.
(ref: ASTM E2848-11 / IEC 61724)
radiation received from a small solid angle centred on the sun’s disc, on a given
plane. (ref: ISO 9060)
radiation not of solar origin but of terrestrial and atmospheric origin and having
longer wavelengths (3 000 to 100 000 x 10-9 m). In case of downwelling El ↓ also
the background radiation from the universe is involved, passing through the
”atmospheric window”. In case of upwelling El ↑, composed of long-wave
electromagnetic energy emitted by the earth’s surface and by the gases, aerosols
and clouds of the atmosphere; it is also partly absorbed within the atmosphere.
For a temperature of 300 K, 99.99 % of the power of the terrestrial radiation has
a wavelength longer than 3 000 x 10-9 m and about 99 per cent longer than
5 000 x 10-9 m. For lower temperatures, the spectrum shifts to longer
wavelengths. (ref: WMO)
measurement standard representing the Sl unit of irradiance with an uncertainty
of less than ± 0.3 % (see the WMO Guide to Meteorological Instruments and
Methods of Observation, 1983, subclause 9.1.3). The reference was adopted by
the World Meteorological Organization (WMO) and has been in effect since 1 July
1980. (ref: ISO 9060)
ratio of reflected and incoming solar radiation. Dimensionless number that varies
between 0 and 1. Typical albedo values are: < 0.1 for water, from 0.1 for wet
soils to 0.5 for dry sand, from 0.1 to 0.4 for vegetation, up to 0.9 for fresh snow.
angle of radiation relative to the sensor measured from normal incidence (varies
from 0° to 90°).
Hemispherical
solar radiation
Global solar
radiation
Plane-of-array
irradiance
Direct solar
radiation
Terrestrial or
Longwave
radiation
World
Radiometric
Reference
(WRR)
Albedo
Angle of
incidence
Zenith angle
Azimuth angle
Sunshine
duration
angle of incidence of radiation, relative to zenith. Equals angle of incidence for
horizontally mounted instruments
angle of incidence of radiation, projected in the plane of the sensor surface.
Varies from 0 ° to 360 °. 0 is by definition the cable exit direction, also called
north, east is + 90 °. (ASTM G113-09)
sunshine duration during a given period is defined as the sum of that sub-period
for which the direct solar irradiance exceeds 120 W/m2. (ref: WMO)
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9.10 Appendix on floating point format conversion
For efficient use of microcontroller capacity some registers in the SR05 contain data in a
float or floating point format. In fact, a floating point is an approximation of a real
number represented by a number of significant digits (mantissa) and an exponent. For
implementation of the floating point numbers, Hukseflux follows the IEEE 754 standard.
In this example the floating point of register 41 and 42 is converted to the decimal value
it represents. In the Sensor Manager software and other Modbus tools, floating point
data will be converted to decimal data automatically.
Example of the calculation of register 41 + 42 representing a floating point for the
sensitivity of the sensor, which is 15.14:
Data in register 41, 16754 (MSW)
Data in register 42, 15729 (LSW)
Double word:
(MSW x 216) + LSW
so: (16754 x 216) + 15729 = 1098005873
According to IEEE 754:
Sign bit:
1098005873 < 2147483647
so: sign bit = 1;
The number 2147483647 is defined by IEEE 754
Exponent:
1098005873 / 223 = 130 (digits after the decimal point are ignored)
130 – 127 = 3
so: exponent = 3;
The number 127 is a constant defined by IEEE 754
Mantissa:
130 x 223 = 1090519040
1098005873 – 1090519040 = 7486833
7486833 / 223 = 0.8925
According to IEEE 754, 1 has to be added to get mantissa
0.8925 + 1 = 1.8925
so: mantissa = 1.8925
Calculation of floating point:
float = sign bit x mantissa x (2exponent) = 1 x 1.8925 x 23 = 15.14
so: floating point = 15.14
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9.11 Appendix on function codes, register and coil overview
Table 9.11.1 Supported Modbus function codes
SUPPORTED MODBUS FUNCTION CODES
FUNCTION CODE (HEX)
DESCRIPTION
0x01
Read Coils
0x02
Read Discrete Inputs
0x03
Read Holding Registers
0x04
Read Input Register
0x05
Write Single Coil
0x06
Write Single Holding Register
0x0F
Write Multiple Coils
0x10
Write Multiple Registers
Your data request may need an offset of +1 for each SR05 register number,
depending on processing by the network master. Example: SR05 register
number 7 + master offset = 7 + 1 = master register number 8. Consult the
manual of the device acting as the local master.
Table 9.11.2 Modbus registers 0 to 82
MODBUS REGISTERS 0 - 82
REGISTER
NUMBER
PARAMETER
0
Modbus address
1
2+3
Serial communication
settings
Irradiance
4+5
Factory use only
6
Sensor body
temperature
Sensor electrical
resistance
Scaling factor irradiance
7
8
9
DESCRIPTION OF CONTENT
TYPE
OF
FORMAT
OF DATA
Sensor address in Modbus
network, default = 1
Sets the serial
communication, default = 5
signal in x 0.01 W/m²
R/W
U16
R/W
U16
R
S32
In x 0.01 °C
R
S16
In x 0.1 Ω
R
U16
Default = 100
R
U16
Default = 100
R
U16
In x 10-9 V
R
S32
10 + 11
Scaling factor
temperature
Sensor voltage output
12 to 31
Factory use only
32 to 35
Sensor model
Part one of sensor description
R
String
36 to 39
Sensor model
Part two of sensor description
R
String
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MODBUS REGISTERS 0 – 82, continued
REGISTER
NUMBER
PARAMETER
DESCRIPTION OF CONTENT
32 to 35
Sensor model
Part one of sensor description
36 to 39
Sensor model
Part two of sensor description
40
Sensor serial number
41 + 42
Sensor sensitivity
43
TYPE
OF
FORMAT
OF DATA
R
String
R
String
R
U16
In x 10-6 V/(W/m2)
R
Float
Response time
In x 0.1 s
R
U16
44
Sensor resistance
In x 0.1 Ω
R
U16
45
Reserved
Always 0
R
U16
46 + 47
Sensor calibration date
Calibration date of the sensor
in YYYYMMDD
R
U32
48 to 60
Factory use
61
Firmware version
R
U16
62
Hardware version
R
U16
In x 10 V/(W/m )
Default value is 0
Former calibration date of the
sensor in YYYYMMDD
Default value is 0
See register 63 +64
R
Float
R
U32
R
Float
See register 65 + 66
R
U32
Sensor sensitivity
history 3
Calibration date history 3
See register 63 + 64
R
Float
See register 65 + 66
R
U32
Sensor sensitivity
history 4
Calibration date history 4
See register 63 + 64
R
Float
See register 65 + 66
R
U32
Sensor sensitivity
history 5
Calibration date history 5
See register 63 + 64
R
Float
See register 65 + 66
R
U32
63 + 64
65 + 66
67 + 68
69 + 70
71 + 72
73 + 74
75 + 76
77 + 78
79 + 80
81 + 82
Note 1:
Sensor sensitivity
history 1
Calibration date history 1
Sensor sensitivity
history 2
Calibration date history 2
-6
2
Up to five 16 bit registers can be requested in one request. If requesting six
or more registers, use multiple requests.
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Please note that if your data request needs an offset of +1 for each SR05 register
number, depending on processing by the network master, this offset applies to
coils as well. Consult the manual of the device acting as the local master.
Table 9.11.3 Coils
COILS
COIL
PARAMETER
DESCRIPTION
TYPE OF
OBJECT TYPE
0
Restart
Restart the sensor
W
Single bit
1
Reserved
2
Check
Measure sensor
electrical resistance
W
Single bit
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9.12 EU declaration of conformity
We,
Hukseflux Thermal Sensors B.V.
Delftechpark 31
2628 XJ Delft
The Netherlands
in accordance with the requirements of the following directive:
2014/30/EU
The Electromagnetic Compatibility Directive
hereby declare under our sole responsibility that:
Product model:
Product type:
SR05
Pyranometer
has been designed to comply and is in conformity with the relevant sections and
applicable requirements of the following standards:
Emission:
Immunity:
IEC/EN 61000-6-1, Class B, RF emission requirements, IEC CISPR11
and EN 55011 Class B requirements
IEC/EN 61000-6-2 and IEC 61326 requirements
Report:
SR05-DA1, SR05-DA2, 30 November 2015
Eric HOEKSEMA
Director
Delft
07 December, 2015
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© 2016, Hukseflux Thermal Sensors B.V.
www.hukseflux.com
Hukseflux Thermal Sensors B.V. reserves the right to change specifications without notice.
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