Campbell | IRGASON | Product manual | Campbell IRGASON Product manual

IRGASON Integrated CO2/H2O
Open-Path Gas Analyzer and
3D Sonic Anemometer
2/12
C o p y r i g h t © 2 0 1 0 - 2 0 1 2
C a m p b e l l S c i e n t i f i c , I n c .
Warranty
“PRODUCTS MANUFACTURED BY CAMPBELL SCIENTIFIC, INC. are
warranted by Campbell Scientific, Inc. (“Campbell”) to be free from defects in
materials and workmanship under normal use and service for twelve (12)
months from date of shipment unless otherwise specified in the corresponding
Campbell pricelist or product manual. Products not manufactured, but that are
re-sold by Campbell, are warranted only to the limits extended by the original
manufacturer. Batteries, fine-wire thermocouples, desiccant, and other
consumables have no warranty. Campbell's obligation under this warranty is
limited to repairing or replacing (at Campbell's option) defective products,
which shall be the sole and exclusive remedy under this warranty. The
customer shall assume all costs of removing, reinstalling, and shipping
defective products to Campbell. Campbell will return such products by surface
carrier prepaid within the continental United States of America. To all other
locations, Campbell will return such products best way CIP (Port of Entry)
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accidents of nature, or shipping damage. This warranty is in lieu of all other
warranties, expressed or implied. The warranty for installation services
performed by Campbell such as programming to customer specifications,
electrical connections to products manufactured by Campbell, and product
specific training, is part of Campbell’s product warranty. CAMPBELL
EXPRESSLY DISCLAIMS AND EXCLUDES ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A
PARTICULAR PURPOSE. Campbell is not liable for any special, indirect,
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IRGASON Table of Contents
PDF viewers: These page numbers refer to the printed version of this document. Use the
PDF reader bookmarks tab for links to specific sections.
1. Introduction..................................................................1
2. Cautionary Statements................................................1
3. Initial Inspection ..........................................................2
4. Overview.......................................................................2
5. Specifications ..............................................................2
5.1
5.2
5.3
5.4
Measurements ...........................................................................................2
Output Signals ..........................................................................................5
Physical Description .................................................................................5
Power Requirements During Power-up and Operation ............................7
6. Installation....................................................................7
6.1 Orientation ................................................................................................7
6.2 Mounting ..................................................................................................7
6.3 Wiring and Connections .........................................................................11
7. Settings.......................................................................15
7.1 Factory Defaults .....................................................................................16
7.2 Bandwidth...............................................................................................16
7.3 SDM Address .........................................................................................16
7.4 Unprompted Output................................................................................17
7.5 Unprompted Output Rate........................................................................17
7.6 RS-485 Baud Rate ..................................................................................17
7.7 Analog Output ........................................................................................17
7.8 ECMon Update Rate...............................................................................17
7.9 Temperature Sensor ................................................................................17
7.10 Fixed Temperature Value .....................................................................17
7.11 Pressure Sensor.....................................................................................18
7.11.1 Pressure Gain ..............................................................................18
7.11.2 Pressure Offset............................................................................18
7.11.3 Fixed Pressure Value ..................................................................18
7.12 Pressure Differential Enable .................................................................18
7.13 Heater Control ......................................................................................18
7.14 ECMon..................................................................................................19
7.15 Device Configuration Utility ................................................................21
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IRGASON Table of Contents
8. EC100 Outputs ...........................................................22
8.1 SDM Output........................................................................................... 22
8.2 USB or RS-485 Output .......................................................................... 22
8.3 Analog Outputs ...................................................................................... 24
9. Maintenance ...............................................................25
9.1 Routine Maintenance ............................................................................. 25
9.2 Wick Maintenance ................................................................................. 25
9.2.1 Sonic Wicks ................................................................................. 25
9.2.2 Gas Analyzer Wicks..................................................................... 26
9.3 Gas-Analyzer Window Cleaning ........................................................... 28
9.4 Zero and Span ........................................................................................ 28
9.5 Replacing Desiccant and Scrubber Bottles ............................................ 32
9.6 Factory Recalibration............................................................................. 33
10. Datalogger Programming ........................................34
10.1 EC100() Instruction ............................................................................. 34
10.2 EC100Configure() Instruction ............................................................. 37
10.2.1 ConfigCmd 11 Zero-and-span Control ...................................... 39
10.2.2 ConfigCmd 18 Heater Voltage................................................... 39
10.3 Example CRBasic Program.................................................................. 40
11. Theory of Operation.................................................41
11.1 IRGASON Sonic Anemometer ............................................................ 41
11.1.1 Wind Speed ................................................................................ 41
11.1.2 Temperature ............................................................................... 42
11.2 IRGASON Gas Analyzer ..................................................................... 43
11.3 Theory References ............................................................................... 44
Appendices
A. Filter Bandwidth and Time Delay ........................... A-1
B. Equations ................................................................. B-1
C. Material Safety Data Sheets (MSDS)......................C-1
C.1 Magnesium Perchlorate MSDS ........................................................... C-1
C.2 Decarbite MSDS ................................................................................. C-2
Figures
5-1(a). IRGASON dimensions, side view...................................................... 6
5-1(b). IRGASON dimensions, front view .................................................... 6
6-1. Exploded view of mounting the IRGASON........................................... 9
6-2. EC100-enclosure mounting bracket mounted on a vertical mast (left)
and a tripod leg (right)....................................................................... 10
6-3. Exploded view of mounting the EC100 enclosure ............................... 10
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IRGASON Table of Contents
6-4. Mounting the IRGASON Temperature Probe.......................................11
6-5. EC100 electronics front panel with enhanced barometer. At left,
as received from Campbell Scientific. At right, all wiring and
connections complete. ........................................................................12
6-6. Base of EC100 enclosure ......................................................................13
6-7. Sensor connections to EC100................................................................13
7-1. Main window of ECMon software........................................................20
7-2. Setup window in ECMon ......................................................................21
8-1. An example of USB data output in terminal mode ...............................23
9-1. Proper location of the sonic top wick (left)
and bottom wick (right)......................................................................26
9-2. Proper location of the gas analyzer top wick (left) and bottom
wick (right).........................................................................................27
9-3. The zero-and-span shroud mounted on the zero-and-span stand.
The top tube is the gas intake, the black cable is the temperature
thermistor, and the short bottom tube is the gas exhaust....................29
9-4. ECMon zero-and-span window.............................................................30
9-5. Replacing the desiccant and CO2 scrubber bottles ...............................33
A-1. Frequency and amplitude response of EC100 filter at various
bandwidths ...................................................................................... A-2
A-2. Frequency response comparison of the EC100 10 Hz bandwidth
and a 50 ms moving average........................................................... A-3
Tables
6-1. EC100 SDM Output to a Campbell Scientific CR1000, CR3000,
or CR5000 Datalogger .......................................................................14
7-1. Factory Default Settings........................................................................16
8-1. USB and RS-485 Output Elements .......................................................23
8-2. Multipliers and Offsets for Analog Outputs..........................................25
9-1. Rain Wick Replacement Parts ...............................................................27
10-1. Output Modes for EC100 Instruction..................................................35
10-2. Bits in the Sonic Diagnostic Flag ........................................................35
10-3. Bits in the Gas Diagnostic Flag ...........................................................36
10-4. ConfigCmd Values for Setting and Retrieving Settings ......................38
A-1. Filter Time Delays for Various Bandwidths...................................... A-3
B-1. Table of Equation Variables and Constants........................................B-1
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IRGASON Table of Contents
iv
IRGASON Integrated CO2/H2O OpenPath Gas Analyzer and 3D Sonic
Anemometer
1. Introduction
The IRGASON is an in-situ, open-path, mid-infrared absorption gas analyzer
integrated with a three-dimensional sonic anemometer. The gas analyzer
provides measurements of absolute densities of carbon dioxide and water
vapor, while the sonic anemometer measures orthogonal wind components.
Before using the IRGASON, please study
• Section 2, Cautionary Statements
• Section 3, Initial Inspection
• Section 6, Installation
More details are available in the remaining sections.
2. Cautionary Statements
•
•
•
DANGER:
o The scrubber bottles (see Section 9.5, Replacing Desiccant and
Scrubber Bottles) contain the strong oxidizing agents sodium
hydroxide (caustic soda, NaOH) and anhydrous magnesium
perchlorate (Mg(ClO4)2.
ƒ Avoid direct contact with the chemicals.
ƒ Ensure your work area is well ventilated and free of
reactive compounds, including liquid water.
ƒ Store used chemical bottles in a sealed container until
disposal.
ƒ Dispose of chemicals and bottles properly.
ƒ Materials Safety Data Sheets (MSDS) are provided in
Appendix C. MSDS are updated periodically by
chemical manufacturers. Obtain current MSDS at
www.campbellsci.com.
WARNING:
o Do not carry the IRGASON by the arms or the strut between the
arms. Always hold it by the block, where the upper and lower
arms connect.
o Handle the IRGASON carefully. The optical source may be
damaged by rough handling, especially while the analyzer is
powered.
o Over-tightening bolts will damage or deform the mounting
hardware.
CAUTION:
o Grounding the EC100 measurement electronics is critical. Proper
grounding to earth (chassis) will ensure maximum ESD
(electrostatic discharge) protection and improve measurement
accuracy.
o Do not connect or disconnect the gas analyzer or sonic connectors
while the EC100 is powered.
1
IRGASON Integrated CO2/H2O Open-Path Gas Analyzer and 3D Sonic Anemometer
o
o
o
The SDM, USB, and RS-485 output options include IRGASON
diagnostic data. Be aware that the absence of diagnostic data in
the analog output option could make troubleshooting difficult and
may lead to the user not being aware of potential problems with
the instrumentation (see Section 8, EC100 Outputs).
Resting the analyzer on its side during the zero-and-span
procedure may result in measurement inaccuracy.
When cleaning the gas-analyzer window, make sure the alcohol
and any residual water completely evaporate before proceeding
with the zero-and-span procedure (see Section 9.3, Gas-Analyzer
Window Cleaning).
3. Initial Inspection
Upon receipt of the IRGASON, inspect the packaging and contents for
damage. File damage claims with the shipping company.
4. Overview
The IRGASON is an in-situ, open-path, mid-infrared absorption analyzer
integrated with a three-dimensional sonic anemometer. The gas analyzer
provides measurements of absolute densities of carbon dioxide and water
vapor, while the sonic anemometer measures orthogonal wind components.
The IRGASON is measured and controlled by the EC100 electronics, which
synchronizes gas and wind data, essential for valid flux calculations using the
eddy-covariance method. The EC100 electronics also uses inputs from an
included temperature thermistor probe and a barometer. “IRGASON” and
“EC100” are often used interchangeably in this manual.
The IRGASON has been optimized for remote eddy-covariance- flux
applications, addressing issues of aerodynamics, power consumption, spatial
displacement, and temporal synchronicity. Specifically, its unique design
contains no obstructions surrounding the sample volume; it operates with only
5 Watts of power at room temperature; it has no spatial displacement between
the sample volumes of the gas analyzer and the sonic anemometer; and the
EC100 synchronously samples data from the gas analyzer and sonic
anemometer.
5. Specifications
5.1 Measurements
Features
•
2
To compute carbon dioxide and water vapor fluxes using the eddycovariance method, the IRGASON measures:
o absolute carbon dioxide
o water vapor densities
o three-dimensional wind speed
o sonic air temperature
o air temperature
o barometric pressure. These measurements are required to
compute carbon dioxide and water vapor fluxes using the
IRGASON Integrated CO2/H2O Open-Path Gas Analyzer and 3D Sonic Anemometer
•
Standard outputs:
o ux, uy, and uz orthogonal wind components
o sonic temperature (based on the measurement of c, the speed of
sound)
o sonic diagnostic flags
o CO2 density, H2O density
o gas analyzer diagnostic flags
o air temperature, air pressure
o CO2 signal strength, H2O signal strength
o Air temperature and air pressure are auxiliary sensor inputs.
Compatibility:
CR1000
CR3000
CR5000
Measurement
Rate:
Output bandwidth2:
Output rate2:
100 Hz
5, 10, 12.5, 20, or 25 Hz
5 to 50 Hz
Operating temperature:
-30o to 50oC
Gas analyzer
Measurement precision1
CO2 density:
H2O density:
Factory calibrated range
CO2:
H2O:
Analyzer temp:
Baro pressure:
0.2 mg·m-3 (0.15 µmol·mol-1)
0.00350 g·m-3 (0.006 mmol·mol-1)
0 to 1830 mg·m-3 (0 to 1000 ppm)
0 to 42 g·m-3 (-60o to 37oC dew point)
-30o to 50oC
70 to 106 kPa
CO2 performance
Zero max drift3:
Gain Drift:
Sensitivity to H2O:
±0.55 mg·m-3·°C-1 (±0.3 μmol·mol·°C-1)
±0.1% of reading·°C-1 (maximum)
±1.1 x 10-4 µmol CO2·mol-1 H2O (max)
H2O performance
Zero max drift3:
Gain Drift:
Sensitivity to CO2:
±0.037 g·m-3·°C-1 (±0.05 mmol·mol-1·°C-1)
±0.3% of reading·°C-1 (maximum)
±0.1 mol H2O·mol-1 CO2 (maximum)
Sonic measurement precision4
ux:
1 mm·s-1
1 mm·s-1
uy:
0.5 mm·s-1
u z:
Sonic temperature:
0.025oC
3
IRGASON Integrated CO2/H2O Open-Path Gas Analyzer and 3D Sonic Anemometer
Sonic accuracy5
Offset error
ux, uy:
< ±8 cm·s-1
< 4 cm·s-1
u z:
Gain error
Wind vector ±5° horizontal: < ±2% of reading
Wind vector ±10° horizontal: < ±3% of reading
Wind vector ±20° horizontal: < ±6% of reading
Sonic reporting range
Full scale wind:
Sonic temperature:
±65.553 m/s
-50° to +60°C
Auxiliary sensors6
Barometer
Internal basic barometer
Manufacturer: Freescale
Model:
MPXAZ6115A
Accuracy:
±2.2 kPa (0o to 85oC)
Linear rise:
±2.2 kPa at 0oC to ±5.5 kPa at -30oC
Optional enhanced barometer:
Manufacturer: Campbell Scientific
Model:
CS106 (Vaisala PTB110)
Accuracy:
±0.85 kPa (0o to 60oC)
Linear rise:
0.85 kPa at 0°C to 1.90 kPa at -30°C
IRGASON temperature sensor:
Manufacturer: BetaTherm
Model:
100K6A1A Thermistor
Accuracy:
±0.15oC (0o to 50oC)
4
1
noise rms, assumes:
o
25°C
o
85 kPa
o
14 g·m-3 H2O
o
597 mg·m-3 CO2
o
25 Hz bandwidth.
2
user selectable
3
-30° to 50°C
4
noise rms
5
assumes:
o
-30° to +50°C
o
wind speed <30 m·s-1
o
azimuth angles between ±170°
6
refer to manufacturer’s product brochure or manual for details
IRGASON Integrated CO2/H2O Open-Path Gas Analyzer and 3D Sonic Anemometer
5.2 Output Signals
Features
• EC100 electronics outputs data using:
o CS SDM
o RS-485
o USB
o Analog out
Digital
SDM (Synchronous Device for Measurement)1
Data type:
FLOAT
RS-485
Data type:
Output Rate:
Baud rate:
USB
Data type:
Output rate:
ASCII
5 to 50 Hz (user selectable)
1200 to 230400 bps (user selectable)
ASCII
5 to 50 Hz (user selectable)
Analog (two outputs for CO2 and H2O densities)
Voltage range:
0 mV to 5000 mV
Resolution:
76 µV (16 bit)
Update rate:
100 Hz
±3 mV
Accuracy (at 25oC):
CO2 density equation:
Full scale range:
mg·m-3 = 0.38632· (mVout) - 102.59
-103 to 1829 mg·m-3
H2O density equation:
Full scale range:
g·m-3 = 0.00865· (mVout) - 2.26
-2 to 41 g·m-3
1
Synchronous Device for Measurement. A Campbell Scientific, Inc. proprietary serial interface
for datalogger to peripheral and sensor communication. See Section 8.1, SDM Output for details.
5.3 Physical Description
Optical path length:
15.37 cm (6.05 in)
Sonic path length:
10.0 cm
Sonic path angle from vertical: 30°
Spatial separation between gas analyzer and sonic volumes: 0 cm
Dimensions
IRGASON
Length:
Height:
Cable Length:
EC100 Enclosure:
51.5 cm (20.3 in)
31.1 cm (12.2 in)
3 m (9.8 ft)
24.1 x 35.6 x 14 cm (9.5 x 14.0 x 5.5 in)
Weight
IRGASON with Cable:
EC100 with Enclosure:
2.8 kg (6.1 lbs)
3.2 kg (7 lbs)
5
IRGASON Integrated CO2/H2O Open-Path Gas Analyzer and 3D Sonic Anemometer
FIGURE 5-1(a). IRGASON dimensions, side view
FIGURE 5-1(b). IRGASON dimensions, front view
6
IRGASON Integrated CO2/H2O Open-Path Gas Analyzer and 3D Sonic Anemometer
5.4 Power Requirements During Power-up and Operation
Power requirement
Source:
10 to 16 Vdc
Load
at 25oC:
420 mA
at 25oC in power-down mode1: 250 mA
1
sonic anemometer fully powered and gas analyzer in stand-by
6. Installation
6.1 Orientation
During operation, the IRGASON should be leveled and pointed into the
prevailing wind to minimize flow distortions from the instrument arms and
other supporting structures. Leveling can be done using the leveling bubble on
top of the instrument block. In the proper orientation, the product label will
read right-side-up, with the upper arm (source) of the gas analyzer directly
above the lower arm (detector).
6.2 Mounting
The IRGASON is supplied with mounting hardware to attach it to the end of a
horizontal pipe with a diameter of 1.31 in., such as the Campbell Scientific
CM202, CM204, or CM206 crossarm. The following steps describe the
normal mounting procedure. Refer to Figure 6-1.
WARNING
1.
Secure the chosen crossarm to a tripod or other vertical structure using a
CM210 Crossarm-to-Pole Mounting Kit (p/n 17767).
2.
Point the horizontal arm into the direction of the prevailing wind and
tighten the nuts and bolts.
Do not carry the IRGASON by the arms or the strut
between the arms. Always hold it by the block, where
the upper and lower arms connect.
3.
Bolt the IRGASON mounting bracket (p/n 27496) to the CM250 Leveling
Mount (p/n 26559) (see Figure 6-1).
4.
Install the IRGASON to the mounting bracket by inserting the mounting
bolt and pin into the corresponding holes. Tighten the bolt. Make sure the
analyzer is vertically oriented so the label is right-side-up and the upper
arm (source) is directly above the lower arm (detector).
5.
Mount the IRGASON assembly by fitting the boom adapter over the end
of the crossarm. Tighten the set screws on the boom adapter with a 3/16
inch hex socket head wrench.
7
IRGASON Integrated CO2/H2O Open-Path Gas Analyzer and 3D Sonic Anemometer
WARNING
8
Handle the IRGASON carefully. The optical source
may be damaged by rough handling, especially while
the analyzer is powered.
6.
If the assembly is not level, slightly loosen the bolt that holds the
mounting bracket on the boom adapter and adjust the assembly until the
leveling bubble on top of the IRGASON block is within the bullseye.
Retighten the bolt.
7.
Attach the EC100 enclosure to the mast, tripod leg, or other part of the
mounting structure. To do this, attach the EC100-enclosure mounting
bracket (p/n 26604) to the pipe by loosely tightening the u-bolts around the
pipe. The u-bolts are found in the mesh pocket inside the EC100
enclosure. If the pipe does not run vertically (for example, if the enclosure
is being attached to a leg of a tripod), rotate the bracket to the side of the
pipe. The enclosure must hang upright. Make angle adjustments as
needed by loosening the four nuts and rotating the bracket plates relative
to one another. If the necessary angle cannot be achieved in the given
orientation, the four nuts may be removed and the top plate indexed by 90°
to allow the bracket to travel in the other direction (see Figure 6-2). Once
adjusted, tighten all the nuts. Finally, attach the EC100 enclosure to the
bracket by loosening the bolts on the back of the enclosure, hanging the
enclosure on the mounting bracket (it should slide into place and be able to
securely hang from the bracket), and tightening the bolts (see Figure 6-3).
IRGASON Integrated CO2/H2O Open-Path Gas Analyzer and 3D Sonic Anemometer
IRGASON
IRGASON
Mounting Bracket
(p/n 27496)
CM250 Leveling Mount
(p/n 26559)
CM20X (p/n 1790X)
or equivalent crossarm
FIGURE 6-1. Exploded view of mounting the IRGASON
WARNING
Over-tightening bolts will damage or deform the
mounting hardware.
9
IRGASON Integrated CO2/H2O Open-Path Gas Analyzer and 3D Sonic Anemometer
FIGURE 6-2. EC100-enclosure mounting bracket mounted on a vertical
mast (left) and a tripod leg (right)
FIGURE 6-3. Exploded view of mounting the EC100 enclosure
10
IRGASON Integrated CO2/H2O Open-Path Gas Analyzer and 3D Sonic Anemometer
8.
Mount the IRGASON temperature probe so that it measures temperature at
the same height as the sample volume of the IRGASON. To do this, first
attach the R.M. Young 41303-5A 6-Plate Solar Radiation Shield (p/n
4020) to the mast with the included u-bolt. Next, insert the end of the
probe into the hole on the bottom of the shield. Tighten the screws to hold
the probe in place. See Figure 6-4. For more detailed information about
the temperature probe installation and specifications, refer to the Model
107 Temperature Probe manual, which is available at
www.campbellsci.com.
9.
Remove the EC100- enclosure desiccant from the plastic bag and place it
in the mesh pocket of the enclosure. Attach the humidity indicator card to
the inside of the enclosure.
FIGURE 6-4. Mounting the IRGASON Temperature Probe
6.3 Wiring and Connections
Figures 6-5, 6-6, and 6-7 show the EC100 electronics panel, the bottom of the
EC100 enclosure, and sensor connections to the EC100, respectively. Refer to
these figures during wiring and connecting.
1.
Find the thicker black cable coming from the block of the IRGASON.
This is the IRGASON gas-analyzer cable. Connect this cable to the
EC100 electronics by removing the black-rubber cable entry plug (p/n
26224) on the bottom right of the EC100 enclosure. (This plug can be
stored in the mesh pocket of the enclosure). Next, insert the cable entry
plug that is attached to the cable into the vacant slot. Push the connector at
the end of the cable onto its mating connector (labeled Gas Analyzer) and
11
IRGASON Integrated CO2/H2O Open-Path Gas Analyzer and 3D Sonic Anemometer
tighten the thumbscrews (see Figure 6-5). The gas analyzer cable is
approximately 3 meters in length.
2.
Connect the IRGASON sonic cable. Similar to (a), begin by removing the
black- rubber cable-entry plug found on the bottom left of the EC100
enclosure. Insert the cable entry plug on the cable into the slot and
connect the male end to the female connector labeled Sonic Anemometer
on the EC100 electronics (see Figure 6-5). The sonic cable is
approximately 3 meters in length.
FIGURE 6-5. EC100 electronics front panel with enhanced barometer.
At left, as received from Campbell Scientific. At right, all wiring and
connections complete.
12
IRGASON Integrated CO2/H2O Open-Path Gas Analyzer and 3D Sonic Anemometer
FIGURE 6-6. Base of EC100 enclosure
NOTE
Unique calibration information is stored in the gas and sonic
connectors of the IRGASON rather than in the EC100. This
means that any IRGASON may be used with any EC100.
FIGURE 6-7. Sensor connections to EC100
13
IRGASON Integrated CO2/H2O Open-Path Gas Analyzer and 3D Sonic Anemometer
3.
Connect the IRGASON temperature probe. Unscrew the temperature
connector cover, which is found on the base of the EC100 enclosure (see
Figure 6-6). Insert the 3-prong probe connector into the female connector
on the enclosure and screw it firmly in place. The IRGASON temperature
probe cable is approximately 3 meters in length.
4.
Ground the EC100 by attaching a thick wire (e.g., 12 AWG) to the
grounding lug found on the base of the EC100 enclosure. The other end of
the wire should be connected to earth (chassis) ground using a grounding
rod. For more details on grounding, see the CR3000 datalogger manual,
grounding section.
CAUTION
Grounding electronics such as the EC100 is critical in a
measurement system. Proper grounding to earth (chassis)
will ensure maximum ESD (electrostatic discharge)
protection and improve measurement accuracy.
CAUTION
Do not connect or disconnect the gas analyzer or sonic
connectors while the EC100 is powered.
5.
Connect a communications signal cable to the EC100. Loosen the nut on
one of the cable entry seals (Cable 1 or Cable 2) on the base of the EC100
enclosure, remove the plastic plug (plug may be stored in mesh pocket of
enclosure), insert the cable, and retighten the nut by hand. Refer to the
sections below on SDM, USB, RS-485, and Analog communications for
information on required signal cable types and connections to the EC100
panel.
o
SDM communications: Use cable CABLE4CBL-L (p/n 21972).
“L” denotes the length of the cable, which is customer-specified
at time of order. Table 6-1 details which color of wire in the
cable should be connected to each terminal found on the SDM
connector of the EC100 panel.
TABLE 6-1. EC100 SDM Output to a Campbell Scientific CR1000,
CR3000, or CR5000 Datalogger
EC100 Channel
Description
Color
SDM-C1
SDM Data
Green
SDM-C2
SDM Clock
White
SDM-C3
SDM Enable
Red (or Brown)
G
Digital Ground
Black
G
Shield
Clear
o
o
14
USB communications: Use the EC100 USB cable (p/n 26561) to
connect a PC to the base of the EC100 enclosure.
RS-485 communications: use cable CABLE3TP-L (p/n 26987)
for lengths less than 500 ft. The connector on the EC100 panel
labeled RS-485 displays which terminals are for receiving and
transmitting.
IRGASON Integrated CO2/H2O Open-Path Gas Analyzer and 3D Sonic Anemometer
o
Analog output: use cable CABLE4CBL-L (p/n 21972) or
CABLE2TP-L (p/n 26986-L). Once again, the customer
specifies the length of this cable at time of order. The connector
labeled Analog Outputs on the EC100 panel indicates where each
wire should be connected (CO2 voltage signal, H2O voltage
signal, and two ground connections).
6.
Wire power and ground (i.e., power reference) cable CABLEPCBL-L (p/n
21969-L) to the EC100. Feed the cable through one of the cable port
openings in the base of the EC100 enclosure and attach the ends into the
green EC100 power connector (p/n 3768). Plug the connector into the
female power connector on the EC100 panel. Ensure that the power and
ground ends are going to the appropriate terminals labeled 12V and
ground, respectively.
7.
Connect the power cable to a power source. The power and ground ends
may be wired to the 12V and G ports, respectively, of a Campbell
Scientific datalogger or to another 12 Vdc source.
8.
Once power is applied to the EC100, three status LEDs on the EC100
panel will illuminate. The power LED is green and the sonic and gas
LEDs are orange until the unit has warmed up and is ready to make
measurements at which time the LEDs become green. If , after several
minutes, the LEDs turn red, a diagnostic flag has been detected. Check the
individual diagnostic bits to determine the specific fault. Diagnostics may
be monitored using the Status Window of ECMon, the user interface
software included with the IRGASON (see Section 7, Settings), or with a
datalogger (see Section 10, Datalogger Programming). The diagnostics
may reveal that the unit needs service such as cleaning the optical
windows on the gas analyzer, clear the sonic transducers of ice or debris,
etc. (see Section 9, Maintenance).
7. Settings
Operation of the IRGASON can be customized by changing settings. Factory
defaults work well for most applications, but the user may adjust the settings
with a PC using either the Campbell Scientific ECMon software (see Section
7.14, ECMon) or DevConfig (see Section 7.15, Device Configuration Utility),
or with a datalogger using the EC100Configure() instruction (see Section
10.2, EC100Configure() Instruction).
15
IRGASON Integrated CO2/H2O Open-Path Gas Analyzer and 3D Sonic Anemometer
7.1 Factory Defaults
Table 7-1 shows the default value for each setting described in the following
sections.
TABLE 7-1. Factory Default Settings
Bandwidth
20 Hz
SDM Address
1
Unprompted Output
disabled
RS-485 baud rate
115200 bps
Unprompted Output Rate
10 Hz
Analog Output
disabled
ECMon Update Rate
10 Hz
Temperature Sensor
Auto-Select (IRGASON Temp Sensor)
Pressure Sensor
EC100 Basic or EC100 Enhanced (depending on
order)
Pressure Differential
Enable
Auto-Select (Disabled for IRGASON)
Heater Control
Disabled
7.2 Bandwidth
The EC100 has a user-selectable low-pass filter to select the bandwidth (5, 10,
12.5, 20, or 25 Hz). Setting the bandwidth to a lower value will reduce noise.
However, it must be set high enough to retain the high-frequency fluctuations
in CO2 and H2O, or else the high frequency contributions to the flux will be
lost. The factory default bandwidth of the EC100 is 20 Hz, which is sufficient
for most flux applications. Lower bandwidth settings may be used for higher
measurement heights, which inherently have lower-frequency content. Refer to
Appendix A, Filter Bandwidth and Time Delay for more information on the
digital filter options.
If a spectral analysis is being done to evaluate the experimental setup, the
bandwidth should be set to the Nyquist frequency, which is half the datalogger
sample rate (for SDM output) or half the unprompted output rate (for USB and
RS-485 output). This ensures that the data will not be under-sampled and that
higher-frequency variations will not be aliased to lower frequencies. Note that
if too small a bandwidth is selected, high-frequency fluxes may be undermeasured.
7.3 SDM Address
This parameter must be set to use SDM output from the EC100. See Section
8.1, SDM Output for details on using SDM output.
Each SDM device on the SDM bus must have a unique address. The
IRGASON has a factory default SDM address of 1, but it may be changed to
16
IRGASON Integrated CO2/H2O Open-Path Gas Analyzer and 3D Sonic Anemometer
any integer value between 0 and 14. The value 15 is reserved as an SDM-group
trigger.
7.4 Unprompted Output
If the EC100 is to output data as USB or RS-485 (see Section 8.2, USB or
RS-485 Output), this setting must be set to USB Port or RS485, respectively.
The factory default is to disable the unprompted output and assume data are to
be logged via SDM (see Section 8.1, SDM Output).
Only one unprompted-output type (i.e., USB or RS-485) may be selected at a
given time. The rate at which the EC100 outputs these data is determined by
the Unprompted Output Rate setting.
7.5 Unprompted Output Rate
This setting determines the output rate for unprompted output (USB or RS-485;
see Section 8.2, USB or RS-485 Output). If the unprompted output is disabled,
this parameter is not used. The factory-default output rate is 10 Hz, but it may
be set to 10, 25, or 50 Hz.
7.6 RS-485 Baud Rate
If the unprompted output mode is set to RS-485, this parameter determines the
baud rate. Otherwise, this setting is not used. The RS-485 baud rate defaults
to 115200 bps, although the user may enter another value.
7.7 Analog Output
The EC100 has two analog outputs for CO2 and H2O densities (see Section 8.3,
Analog Outputs for more information). These outputs may be enabled or
disabled with this setting. The default is for analog output to be disabled. Note
that the analog output does not include sonic data.
7.8 ECMon Update Rate
This setting determines the rate at which data are sent over the USB connection
to the PC while running ECMon. The default setting of 10 Hz should be
adequate in most situations.
7.9 Temperature Sensor
This setting configures the EC100 electronics to integrate with the IRGASON.
The IRGASON measures ambient air temperature using a thermistor
temperature sensor. With Auto-Select selected, the EC100 will detect that the
IRGASON is connected and will report ambient air temperature measurements
from the thermistor.
To diagnose problems with the temperature measurement, a fixed temperature
value may be used, or the temperature sensor may be selected manually.
7.10 Fixed Temperature Value
If the Temperature Sensor setting is None, the IRGASON will use the value
of this setting for the sample temperature. This mode is intended for
17
IRGASON Integrated CO2/H2O Open-Path Gas Analyzer and 3D Sonic Anemometer
troubleshooting only. In normal operation, Temperature Sensor is set to
Auto-Select, and this setting is not used.
7.11 Pressure Sensor
This setting identifies which barometric pressure sensor is used. The EC100
always includes the basic barometer, but it may be ordered with the optional
enhanced barometer (model CS106). This setting defaults to EC100
Enhanced if the CS106 is ordered and to EC100 Basic otherwise.
There are two other possible settings for Pressure Sensor. First, the user may
supply a different pressure sensor. In this case, the setting should be changed
to User Supplied, with the appropriate values for gain and offset entered (see
below).
The final option is to select None for Pressure Sensor. The EC100 will use a
fixed (see below) value for pressure. This mode is intended for
troubleshooting only.
7.11.1 Pressure Gain
If Pressure Sensor is set to User Supplied, this setting gives the gain factor
(kPa/V) used to convert measured voltage to pressure. Normally, Pressure
Sensor is set to EC100 Basic or EC100 Enhanced, and this setting is not
used.
7.11.2 Pressure Offset
If Pressure Sensor is set to User Supplied, this setting gives the offset (kPa)
used to convert measured voltage to pressure. Normally, Pressure Sensor is
set to EC100 Basic or EC100 Enhanced, and this setting is not used.
7.11.3 Fixed Pressure Value
If Pressure Sensor is None, the EC100 will use the value of this setting for the
barometric pressure. This mode is intended for troubleshooting only. In
normal operation, this setting is not used.
7.12 Pressure Differential Enable
This setting should remain disabled. It is used only for closed-path analyzers.
7.13 Heater Control
When enabled, this setting applies a voltage between 0 and 4500 mV to heaters
near the optical windows of the analyzer. Heated windows inhibit the
formation of condensation, such as dew and frost, and help the analyzer
recover more quickly when precipitation has blocked the optical path. Use this
setting with caution. Excessive heating may lead to density fluctuations and
subsequent flux measurement errors. More information about heater control,
and specifically using a datalogger for control, may be found at the end of
Section 10.2, EC100Configure() Instruction.
18
IRGASON Integrated CO2/H2O Open-Path Gas Analyzer and 3D Sonic Anemometer
7.14 ECMon
Settings for the IRGASON are easily verified or changed using the Windows
PC support software ECMon (Eddy Covariance Monitor), which is found on
the IRGASON, EC150 & EC155 Support CD (p/n 27007) or at
www.campbellsci.com.
Before installing ECMon, read the file titled _Read_me.txt found on the
IRGASON, EC150 & EC155 Support CD. This file directs the user to install
USB drivers (also found on the support CD), which are required for
communications between the PC and the EC100 via the EC100 USB cable (p/n
26561). Some newer PC operating systems will automatically find and
download the USB drivers from the internet when the USB cable is connected
to the PC. Once the drivers are installed, download and run the ECMon.exe
install file. Launch ECMon, and connect the EC100 electronics to the PC with
the included EC100 USB cable (p/n 26561). The USB connection for the
EC100 electronics is found on the base of the enclosure (see Figure 6-7). Once
connected, select the appropriate communications port in the ECMon main
page and click Connect (see Figure 7-1). Next, click on the Setup button. All
of the preceding settings are now available for editing (see Figure 7-2).
Besides changing settings, ECMon is a useful tool for common tasks such as:
•
•
•
Monitoring real-time data from the IRGASON from the main window
Performing manual zero and span of the instrument (see Section 9.4, Zero
and Span)
Troubleshooting and monitoring diagnostics using the Status window.
19
IRGASON Integrated CO2/H2O Open-Path Gas Analyzer and 3D Sonic Anemometer
FIGURE 7-1. Main window of ECMon software
20
IRGASON Integrated CO2/H2O Open-Path Gas Analyzer and 3D Sonic Anemometer
FIGURE 7-2. Setup window in ECMon
7.15 Device Configuration Utility
DevConfig software (Device Configuration Utility) may also be used to
change settings, although ECMon is generally preferred because of its more
user-friendly interface. DevConfig may be downloaded from the IRGASON,
EC150 & EC155 Support CD (p/n 27007), or may be downloaded free of
charge from the Campbell Scientific website www.campbellsci.com).
DevConfig requires a USB driver to communicate with the EC100, similar to
ECMon. See Section 7.14, ECMon for notes on installing a USB driver.
After launching DevConfig, select “EC100” from the list of device types. The
EC100 electronics should be connected to the PC with the EC100 USB cable
(p/n 26561) and the appropriate USB port selected before connecting. Once
connected, the settings tab displays all the current settings. The Apply button
must be clicked to save any changes.
DevConfig is also used to send an updated operating system to the EC100
electronics. The Send OS tab gives directions on this procedure.
21
IRGASON Integrated CO2/H2O Open-Path Gas Analyzer and 3D Sonic Anemometer
8. EC100 Outputs
The EC100 is the IRGASON electronics module that measures the sensors and
controls the system. It outputs data in one of four types: SDM, USB, RS-485,
or analog. In general, Campbell Scientific recommends that SDM be used if a
Campbell Scientific datalogger is responsible for data collection. However,
RS-485 output is recommended if cable lengths exceed 100 meters. If a PC is
being used as the collection vehicle, USB and RS-485 are suitable outputs.
Analog output may also be used; however, only CO2 density and H2O density
will be output. Information regarding each output type is provided in the
following sections.
8.1 SDM Output
SDM (Synchronous Device for Measurement) is a proprietary Campbell
Scientific communication protocol that allows synchronized measurement and
rapid communication between a Campbell Scientific datalogger and multiple
devices, including the IRGASON. Although nearly all Campbell Scientific
dataloggers support SDM, only the CR1000, CR3000, and CR5000 dataloggers
support the IRGASON.
To use SDM data output, connect an SDM-communications cable from the
EC100 (see Section 6.3, Wiring and Connections) to a CR1000, CR3000, or
CR5000 datalogger. On CR1000 dataloggers, the SDM protocol uses ports C1,
C2, and C3. These are multipurpose ports that are SDM-activated when an
SDM instruction is used in the datalogger’s program. On CR3000 and CR5000
dataloggers, the SDM protocol uses SDM-dedicated ports SDM-C1, SDM-C2,
and SDM-C3.
Each SDM device on the SDM bus must have a unique address. The
IRGASON has a factory default SDM address of 1, but it may be changed to
any integer value between 0 and 14 (see Section 7.2, Bandwidth).
The sample rate for SDM output is determined by the inverse of the datalogger
scan interval, as set by the user in the datalogger program. Data are output
from the EC100 when a request is received from the logger, that is, a prompted
output mode. The number of data values sent from the EC100 to the
datalogger is also set by the user in the datalogger program. CRBasic, the
programming language used by Campbell Scientific dataloggers, uses the
EC100() instruction to get data from an IRGASON. This instruction is
explained in detail under Section 10.1, EC100() Instruction.
8.2 USB or RS-485 Output
In contrast to the SDM output mode, which is prompted by a datalogger, data
can also be output from the EC100 via USB or RS-485 in an unprompted
mode. In this case, the EC100 sends out data without initiation from the
receiving device at a rate determined by the EC100. Only one unprompted
output type, USB or RS-485, may be selected at a given time. RS-485 output
is recommended if cable lengths exceed 100 meters. If a Campbell Scientific
datalogger is not being used to collect the data from the IRGASON, either
unprompted mode is recommended.
22
IRGASON Integrated CO2/H2O Open-Path Gas Analyzer and 3D Sonic Anemometer
To use USB or RS-485 output, connect a USB or RS-485 cable from the
EC100 to the receiving device (see Section 6.3, Wiring and Connections), and
configure the settings (see Section 7, Settings).
The Unprompted Output setting must be set to USB or RS-485.
If RS-485 is selected, the RS485 Baud Rate must be set.
The Unprompted Output Rate must be set to the desired output
rate.
All output data are formatted as comma delimited ASCII. Each record
terminates with a carriage return and line feed. Table 8-1 lists the elements in
each output array, and Figure 8-1 shows an example USB data feed in terminal
mode.
TABLE 8-1. USB and RS-485 Output Elements
Data Element
Description
Units/comments
1
Ux
m/s
2
Uy
m/s
3
Uz
m/s
4
Sonic temperature
°C
5
Sonic diagnostic flag
6
CO2 density
mg/m3
7
H2O density
g/m3
8
Gas diagnostic flag
9
Air temperature
°C
10
Air pressure
kPa
11
CO2 signal strength
Nominally 0.0 to 1.0
12
H2O signal strength
Nominally 0.0 to 1.0
13
Not used
14
Counter
Arbitrary
15
Signature
Arbitrary in hexadecimal
FIGURE 8-1. An example of USB data output in terminal mode
23
IRGASON Integrated CO2/H2O Open-Path Gas Analyzer and 3D Sonic Anemometer
The final data element in each row or output array is the signature. The
signature is a four character hexadecimal value that is a function of the
sequence and number of bytes in the output array. The recording device (i.e.,
PC or datalogger) calculates its own signature using each transmitted byte until
encountering the transmitted signature. The computed signature and the
transmitted signature are compared. If they match, the data were received
correctly. This is very similar to a cyclic redundancy check (CRC).
In most situations, a PC begins by reading the ASCII data and extracting the
last four ASCII characters and casting them as Long data type. The signature
is then calculated on the science data sent from the IRGASON, starting with
CO2 and ending on the counter. All the characters after the counter are not part
of the signature. Once the signature is computed using the following
algorithm, it is compared to the transmitted signature. If signatures do not
match, the data should be disregarded.
Following is an example implementation of Campbell Scientific’s signature
algorithm in the programming language C. To generate the signature of an
output array of bytes, the “seed” needs to be initialized to 0xaaaa and a pointer
passed to the first byte of the output array. The number of bytes in the output
array should be entered in as the “swath”. The returned value is the computed
signature.
//signature(), signature algorithm.
// Standard signature is initialized with a seed of 0xaaaa.
// Returns signature.
unsigned short signature( unsigned char* buf, int swath,
unsigned short seed ) {
unsigned char msb, lsb;
unsigned char b;
int i;
msb = seed >> 8;
lsb = seed;
for( i = 0; i < swath; i++ ) {
b = (lsb << 1) + msb + *buf++;
if( lsb & 0x80 ) b++;
msb = lsb;
lsb = b;
}
return (unsigned short)((msb << 8) + lsb);
}
8.3 Analog Outputs
If analog output is enabled, the EC100 will output two analog signals that
correspond to CO2 density and H2O density. These signals range from 0 to
5000 mV. Table 8-2 gives the multipliers and offsets for the analog outputs.
Note that the analog outputs contain no sonic data.
CAUTION
24
Be aware that the absence of diagnostic data in analog
output could make troubleshooting difficult and may lead to
the user not being aware of potential problems with the
instrumentation.
IRGASON Integrated CO2/H2O Open-Path Gas Analyzer and 3D Sonic Anemometer
TABLE 8-2. Multipliers and Offsets for Analog Outputs
Density
(mg m-3)
Voltage Output Multiplier
(mg m-3 V-1)
Offset
(mg m-3)
CO2
386.32
-102.59
H2O
8.65
-2.26
9. Maintenance
IRGASON operation requires six maintenance tasks:
•
•
•
•
•
•
routine maintenance
wick maintenance
analyzer window cleaning
zero and span
replacing the analyzer desiccant / scrubber bottles
factory recalibration
9.1 Routine Maintenance
Periodically do the following:
•
Check the humidity indicator card in the EC100 enclosure. If the highest
dot has turned pink, replace or recharge the desiccant bags. Replacement
desiccant may be purchased (p/n 6714) or old desiccant packs may be
recharged by heating in an oven. See the manual ENC10/12, ENC12/14,
ENC14/16, ENC16/18, available at www.campbellsci.com, for more
details on recharging desiccant bags.
•
Make sure the LED Status Lights on the EC100 panel are green. If not,
verify that all connections are secure and that the instruments are powered.
Also check the individual diagnostic bits for the specific fault. See Table
10-2, Bits in the Sonic Diagnostic Flag and Table 10-3, Bits in the Gas
Diagnostic Flag.
9.2 Wick Maintenance
9.2.1 Sonic Wicks
The IRGASON cannot measure wind when water droplets completely obscure
the face of the sonic transducers. If the site experiences frequent rainfall, using
wicks on the sonic transducers may be desirable. The wicks help remove
water. Under some conditions, however, droplets may build up and remain on
the transducer faces. As soon as the water droplets evaporate or are removed,
the IRGASON will again measure wind. Remove the water droplets by
dabbing a cotton swab or tissue on the faces of the transducers.
The user must use discretion to determine if wicks are necessary. If wicks are
not used, gently remove the wicks from the sonic transducers, taking care not
to damage or peal the matching layer (rubber tips) from the brass housing of
the transducers.
25
IRGASON Integrated CO2/H2O Open-Path Gas Analyzer and 3D Sonic Anemometer
Remove the wicks during the winter. The wicks will accumulate snow or
freezing rain, resulting in blockage of the sonic signals.
When installing wicks, be sure they are located in the proper position. The top
wick must be flush with the transducer face, with the wick tail located at the
lowest point of the transducer (see Figure 9-1). The end of the bottom
transducer wick must extend above the transducer face by one-half to one mesh
line (see Figure 9-1). Secure the wicks to the transducer with a drop of
adhesive (e.g., super glue). Take care that super glue is not deposited on the
transducer face.
Replacement top wicks (p/n 17388) and bottom wicks (p/n 17389) can be
purchased from Campbell Scientific. A complete set of wicks consists of three
top wicks and three bottom wicks.
FIGURE 9-1. Proper location of the sonic top wick (left)
and bottom wick (right)
9.2.2 Gas Analyzer Wicks
IRGASON gas analyzer windows are polished and slanted at an angle to
prevent water from collecting on their surfaces. However, due to increased
surface tension at the interface with the snout, water can pool at the edges and
partially block the optical path and attenuate the signal. To minimize the
occurrence of such events and the resulting data loss, consider using wicks.
The weave of the wick fabric promotes capillary action that wicks the water
away from the edge of the windows. The seam and the straight edge of the
wicks are permeated with a rubberized compound to prevent them from
shifting during operation.
Proper installation of the wicks is critical. They should not block or encroach
on the optical path. Before installation, record signal strengths for both H2O
and CO2. Following installation, these values should be unchanged.
26
IRGASON Integrated CO2/H2O Open-Path Gas Analyzer and 3D Sonic Anemometer
Wicks are available as listed in Table 9-1.
TABLE 9-1. Rain Wick Replacement Parts
Wick
Campbell Scientific, Inc
Part Number
Campbell Scientific Description
Bottom
Wick
28652
FAB EC150/IRGASON RAIN
WICK BOTTOM
Top Wick
28653
FAB EC150/IRGASON RAIN
WICK TOP
The top wick has a short seam which has to be aligned with the short side of
the top snout. The angled edge of the wick must closely follow the edge of the
window without encroaching on the optical path (see Figure 9-2, Proper
location of the sonic top wick and bottom wick). The bottom wick is installed
in a similar manner, except the long seam should be aligned with the long side
of the bottom snout. Once in place, the wicks should fit snuggly over the
cylindrical part of the snout without any creases or wrinkles.
The wicks are constructed with a UV-resistant fabric and should function over
long time periods. Nevertheless, they should be inspected periodically. Check
for contamination from dust, pollen, pitch or other debris. If needed, wash
them in warm water with mild detergent or replace them. When performing
the zero-and-span procedure, the wicks should be removed before installing the
zero-and-span shroud.
Remove the wicks during the winter. The wicks will accumulate snow or
freezing rain, resulting in blockage of the optical path. Besides the wicks,
controlling the heaters in the snouts is another method the user may consider in
preventing data loss during precipitation and condensation events. The heaters
can be controlled statically using the Setup window in ECMon or dynamically
using a datalogger (see Section 10.2, EC100Configure() Instruction for more
details).
FIGURE 9-2. Proper location of the gas analyzer top wick (left) and
bottom wick (right)
27
IRGASON Integrated CO2/H2O Open-Path Gas Analyzer and 3D Sonic Anemometer
9.3 Gas-Analyzer Window Cleaning
The windows of the analyzer should be cleaned if the signal strength for CO2
or H2O drops below 0.7 or 70% of the original value. These values may be
monitored in the output data, or they can be viewed with ECMon. To clean the
windows, use isopropyl alcohol (2-propanol / isopropanol) and a cotton swab
or a non-scratching tissue or cloth. Verify that following cleaning the signal
strengths are restored to values close to 1.0.
9.4 Zero and Span
As is the case with optical instrumentation, the IRGASON gas analyzer may
drift slightly with exposure to natural elements, so a zero-and-span procedure
should be performed occasionally—on the order of weeks or months. As a
starting point, after cleaning the analyzer windows (Section 9.3, Gas Analyzer
Window Cleaning), perform the zero-and-span procedure. After the first
several zero-and-span procedures, the rate of drift in gain and offset (explained
later in this section) should be analyzed to better determine how frequently the
analyzer should be zeroed and spanned. If the IRGASON is employed at a site
with large seasonal changes in ambient conditions, the zero-and-span
procedure should be done at least seasonally.
The first part of the following procedure simply measures the CO2 and H2O
zero and span, without making adjustments. This allows the CO2 and H2O gain
factors to be calculated. These gain factors quantify the state of the analyzer
before the zero-and- span procedure, and in theory could be used to correct
recent measurements for drift. The last part of the zero-and-span procedure
adjusts internal processing parameters to correct subsequent measurements.
If the zero-and-span procedure is being performed off-site (e.g., in a lab), be
sure to mount the IRGASON on the lab stand (p/n 27278). This will ensure the
analyzer is in the correct upright orientation and has the correct optical
alignment.
It is imperative that the zero-and-span procedure be done correctly and not
rushed; allocate plenty of time for the procedure (at least an hour).
CAUTION
Resting the analyzer on its side during the zero-and-span
procedure may result in measurement inaccuracy.
To check and then set the IRGASON zero and span, follow the steps below:
CAUTION
1.
Remove power from the EC100.
2.
If not already done, clean the windows and snouts with alcohol and a nonscratching tissue or cloth.
Make sure the alcohol and any residual water completely
evaporate from the analyzer before proceeding with the
zero-and-span procedure.
3.
28
As shown in Figure 9-3, position the IRGASON zero-and-span shroud (p/n
26390) over the upper and lower snouts. To do this, twist the two ends of
the shroud together to minimize the length of the shroud. Make sure the
IRGASON Integrated CO2/H2O Open-Path Gas Analyzer and 3D Sonic Anemometer
rubber seals on the ends of the shroud are clean and in good condition.
Position one end of the shroud over the lower snout and twist the top part
of the shroud, allowing it to extend and cover the upper snout; while doing
so, avoid making contact with the sonic transducers. Continue twisting the
shroud until it is fully extended and covering both snouts. Twist the
shroud so that the gas tubes and temperature thermistor cable are directed
towards the back of the sensor. Hang the tubes and cable over the trunk of
the sensor to alleviate any strain on the optical arms. See Figure 9-3, The
zero-and-span shroud mounted on the zero-and-span stand.
Intake
Thermistor Cable
Exhaust
FIGURE 9-3. The zero-and-span shroud mounted on the zero-andspan stand. The top tube is the gas intake, the black cable is the
temperature thermistor, and the short bottom tube is the gas
exhaust.
4.
Disconnect the IRGASON temperature sensor from the EC100 and
connect the shroud temperature sensor in its place.
5.
Connect the EC100 to a PC with the EC100 USB cable (p/n 26561).
6.
Resume power to the EC100. Wait for all the Gas and Power LED status
lights on the EC100 panel to turn green.
7.
Launch ECMon, select the appropriate USB port, and click Connect. The
main screen should now be reporting real-time CO2 and H2O
concentrations. Click Zero/Span. A graph will appear in the lower half
of the zero-and-span window showing measured CO2 and H2O
concentrations (see Figure 9-4).
29
IRGASON Integrated CO2/H2O Open-Path Gas Analyzer and 3D Sonic Anemometer
8.
NOTE
Connect a gas tank of known CO2 concentration to a pressure regulator,
then to a flow controller, and finally to the intake of the shroud.
Optimally, the concentration of span CO2 should be near the concentration
of CO2 being measured in the field. Begin with both the pressure regulator
and flow controller turned off. Then use the pressure regulator to slowly
increase pressure to the recommended setting for the flow controller. Next
set the flow between 0.4 and 0.6 l/min. Watch the ECMon zero-and-span
graph for the CO2 measurement readings to stabilize (5 to 10 minutes).
Once stable, write down the reported CO2 concentration.
Use mixtures of CO2 and ambient air for the CO2 span gas. The
use of reference CO2 gas mixtures in pure nitrogen will lead to
errors due to a carrier gas effect on pressure-broadening of the
CO2 absorption lines since oxygen gas has a smaller linebroadening coefficient than nitrogen.
FIGURE 9-4. ECMon zero-and-span window
9.
30
Remove the CO2 span gas from the inlet of the shroud, and replace it with
H2O span gas from a dew-point generator or another standard reference.
Because water molecules can adsorb to inside of the tubing and the shroud,
it may take many minutes for the H2O concentration to stabilize. If
desired, increase the flow rate for the first several minutes to more quickly
stabilize the system before returning it to between 0.4 and 0.6 l/min to
make the H2O measurement. Write down the reported H2O concentration.
IRGASON Integrated CO2/H2O Open-Path Gas Analyzer and 3D Sonic Anemometer
10. Remove the H2O span gas, and connect a zero air source (no CO2 or H2O)
to the inlet tube of the shroud. As described in step 8, use a pressure
regulator and flow controller so that zero air flows through the shroud
between 0.4 and 0.6 l/min. Wait for the measurement readings to stabilize
(this may require several minutes) and write down the reported values for
CO2 and H2O concentrations. If the readings remain erratic, ensure that
flow of the zero air is sufficient and the shroud is correctly seated on the
snouts.
11. Examine the measurements that were written down for span CO2, span
H2O, and zero air. Compute the drift in instrument gain using the
following equation:
gain =
spanactual
spanmeas − zeromeas
where,
•
•
•
spanactual = known concentration of the span gas
spanmeas = measured concentration of the span gas
zeromeas = measured concentration in zero gas.
Note that in the zero-and- span window of ECMon, spanactual is reported to
the right of the box where the user enters the span dew-point temperature.
The software calculates spanactual by taking into account the dew-point
temperature and current ambient temperature and pressure. The equations
used for this calculation may be found in Appendix B. If drift (offset or
gain) for CO2 or H2O is excessive, it may be time to replace the desiccant
and CO2 scrubber bottles (see Section 9.5, Replacing Desiccant and
Scrubber Bottles).
12. With zero air still flowing and measurements stabilized, click on the Zero
CO2 and H2O button in the ECMon zero-and-span window.
NOTE
Air flow into the shroud should be close to the recommended
rate. If the flow is too low, the shroud will not be properly
flushed; if it is too high, the air pressure within the shroud will be
too high, and the analyzer will not be zeroed and spanned
properly.
13. Remove the zero air source and replace it with the CO2 span gas. Allow
the gas to flow through the shroud, maintaining a flow between 0.4 and 0.6
l/min. Wait for readings to stabilize.
14. In the zero-and-span window, enter the known concentration of CO2 (in
ppm) in the box labeled Span Concentration (dry) and press Span.
15. Replace the CO2 span gas with an H2O span gas of known dew point.
Allow the gas to flow through the shroud; higher flows may be desired for
a couple of minutes to more quickly establish equilibrium before resuming
a flow between 0.4 and 0.6 l/min. Wait for the readings to stabilize.
31
IRGASON Integrated CO2/H2O Open-Path Gas Analyzer and 3D Sonic Anemometer
16. Enter the known dew point (in C°) in the box labeled Span Dew Point and
press Span.
17. The zero-and-span procedure is now complete. Remove the shroud,
reconnect the IRGASON temperature probe, and prepare the site for
normal operation.
9.5 Replacing Desiccant and Scrubber Bottles
If more than two years have passed since replacing the desiccant / scrubber
bottles within the IRGASON, or if the zero-and-span readings have drifted
excessively (see Section 9.4, Zero and Span), the bottles should be replaced.
To do this, twist the scrubber-bottle covers of the upper and lower arms
counter-clockwise until they detach (they should loosen by hand). Remove the
IRGASON chemical bottles (p/n 26510) from inside the covers, and replace
them with new bottles lid-first (see Figure 9-5). Once this is done, firmly
screw the covers back on the arms. Allow the sensor to equilibrate for at least
24 hours (longer if in high humidity), and then perform a zero-and-span
procedure. If readings continue to be suspect, the sensor may need factory
recalibration (see Section 9.6, Factory Recalibration).
DANGER
The scrubber bottles contain strong oxidizing agents.
Avoid direct contact with the chemicals inside the bottles.
Also, ensure your work area is well ventilated and free of
any reactive compounds, including liquid water. Store
used chemical bottles in a sealed container until disposal.
The chemical bottles should be disposed of according to local and federal
regulations. For more information, MSDS (Material Safety Data Sheets) for
the chemicals are available in Appendix C and at www.campbellsci.com.
32
IRGASON Integrated CO2/H2O Open-Path Gas Analyzer and 3D Sonic Anemometer
Scrubber bottle cover
Scrubber bottle cover
FIGURE 9-5. Replacing the desiccant and CO2 scrubber bottles
9.6 Factory Recalibration
When the IRGASON is manufactured, the gas analyzer calibrated over a wide
range of temperatures, pressures, and gas concentrations. All CO2 calibration
gases used in this process are mixtures of CO2 in ambient air and are traceable
to the WMO Mole Fraction Scale maintained by the Central Carbon Dioxide
Laboratory and the Carbon Cycle Greenhouse Gases Group of the Global
Monitoring Division / National Oceanographic and Atmospheric
Administration in Boulder, CO, USA.
After an extended period of time in the field, the IRGASON gas analyzer may
need to undergo this factory calibration again to ensure valid measurements.
When recalibration is deemed necessary, contact Campbell Scientific.
The IRGASON sonic anemometer also undergoes an initial factory calibration.
Usually this calibration remains valid unless a transducer fails or damage to the
instrument leads to a change in geometry. The sonic anemometer requires
calibration when
•
•
it develops a wind offset greater than the specification.
it sets diagnostic flags under dry conditions with little to no wind and
with no obstruction in the ultra sonic paths.
The wind offset is tested by creating a zero wind environment by encircling the
sensor with a large plastic bag (unused refuse bag), using caution not to block
the sonic paths. See the manual CSAT3 Three Dimensional Sonic Anemometer,
Section 11.2.2, Test for Wind Offset, available at www.campbellsci.com.
When recalibration is deemed necessary, contact Campbell Scientific.
33
IRGASON Integrated CO2/H2O Open-Path Gas Analyzer and 3D Sonic Anemometer
10. Datalogger Programming
The datalogger is programmed in the CRBasic language, which features two
instructions for communication with the EC100 via SDM. The first instruction
is EC100(), which reads measurement data from the EC100. The second is the
EC100Configure(), which receives and sends configuration settings.
10.1 EC100() Instruction
The EC100() instruction is used to retrieve data from the IRGASON via SDM.
The instruction syntax is:
EC100 (Dest, SDMAddress, EC100Cmd)
Dest is the input variable name in which to store data from the IRGASON.
The length (i.e., number of data elements) of the input variable array will
depend on the selected value for EC100Cmd. A value of -99999 will be loaded
into Dest(1) if a signature error on SDM data occurs.
EC100Cmd
0
1
2
Dest Variable Length
8
12
13
SDMAddress defines the address of the IRGASON with which to
communicate. Valid SDM addresses are 0 through 14. Address 15 is reserved
for the SDMTrigger() instruction.
EC100Cmd is a parameter that requests data from the analyzer. The results for
the command are returned in the array specified by the Dest parameter. A
numeric code is entered to request the data, as shown in Table 10-1.
34
IRGASON Integrated CO2/H2O Open-Path Gas Analyzer and 3D Sonic Anemometer
TABLE 10-1. Output Modes for EC100 Instruction
Output
Mode
0, 1, 2,
1, 2
Data
Field
Description
Units
1
Ux
m/s
2
Uy
m/s
3
Uz
m/s
4
Sonic Temperature
ºC
5
Sonic Diagnostic Flag
6
CO2 Density
mg/m3
7
H2O Density
g/m3
8
Gas Diagnostic Flag
9
Air Temperature
ºC
10
Air Pressure
kPa
CO2 Signal Strength
nominally 0.0 ≤ strength
≤1.0
H2O Signal Strength
nominally 0.0 ≤ strength
≤1.0
Sample Cell Pressure
Differential
kPa
11
12
2
13
As shown in Table 10-1, all output modes give two diagnostic values: Sonic
Diagnostic Flag and Gas Diagnostic Flag. The values contain a bit field with
each bit representing a monitored condition. When a certain condition is
detected, the corresponding bit is set. The value remains set until the event that
caused the condition is no longer present. Tables 10-2 and 10-3 describe the
bits in the sonic diagnostic flag and the gas diagnostic flag, respectively.
TABLE 10-2. Bits in the Sonic Diagnostic Flag
bit
hex
value
decimal
Name
Function
0
0x1
1
Low Amp
Acoustic signal has
dropped below threshold
1
0x2
2
High Amp
High-amplitude threshold
exceeded
2
0x4
4
Tracking
Tracking error
3
0x8
8
Hi 3 Axis DC
Measured speed of sound
exceeds threshold
4
0x10
16
Acquiring
Sonic is re-acquiring
signals
5
0x20
32
Cal Mem Err
Head calibration memory
signature error
35
IRGASON Integrated CO2/H2O Open-Path Gas Analyzer and 3D Sonic Anemometer
TABLE 10-3. Bits in the Gas Diagnostic Flag
36
bit
hex value
decimal
Name
Function
0
0x1
1
Bad Data
Data are suspect (there is
an active diagnostic flag)
1
0x2
2
Sys Fault
General system fault
2
0x4
4
Sys Startup
System is starting up
3
0x8
8
Motor Speed
Motor speed out of bounds
4
0x10
16
TEC Temp
Detector temperature out of
bounds
5
0x20
32
Light Power
Light source power out of
bounds
6
0x40
64
Light Temp
Light source temperature
out of bounds
7
0x80
128
Light I
Light source current out of
bounds
8
0x100
256
Power Off
Gas head is not powered
9
0x200
512
Chan Err
Measurement channel
synchronization error
10
0x400
1024
Amb Temp
Ambient temperature out
of bounds
11
0x800
2048
Amb Press
Ambient pressure out of
bounds
12
0x1000
4096
CO2 I
CO2 I out of bounds
13
0x2000
8192
CO2 Io
CO2 Io out of bounds
14
0x4000
16384
H2O I
H2O I out of bounds
15
0x8000
32768
H2O Io
H2O Io out of bounds
16
0x10000
65536
CO2 Io Var
CO2 Io noise out of bounds
17
0x20000
131072
H2O Io Var
H2O Io noise out of bounds
18
0x40000
262144
CO2 Io Ratio
CO2 Io ratio out of bounds
19
0x80000
524288
H2O Io Ratio
H2O Io ratio out of bounds
20
0x100000
1048576
Cal Mem Err
Gas head calibration
memory signature error
IRGASON Integrated CO2/H2O Open-Path Gas Analyzer and 3D Sonic Anemometer
10.2 EC100Configure() Instruction
EC100Configure() provides a third option, beside the ECMon software and
DevConfig utility, for retrieving and modifying settings. ECmon and Device
Configuration are user-interactive, whereas the EC100Configure() instruction
allows automated control under CRBasic datalogger programming.
EC100Configure() is a processing instruction. Whether running in pipeline
mode or sequential mode, the datalogger will execute the instruction from the
processing task. This functionality allows EC100Configure() to be placed in
conditional statements. Running from the processing task has ramifications
when attempting to execute EC100Configure() while other SDM instructions
are executing in pipeline mode. EC100Configure() locks the SDM port
during the duration of its execution. If the pipelined SDM task sequencer
needs to run while the SDM is locked, it will be held off until the instruction
completes. This locking will likely result in skipped scans when reconfiguring
an IRGASON.
For the IRGASON to save settings, it must go through a lengthy write-readverify process. To avoid saving the settings after each set command, the result
code can be used to determine if any settings were modified from their original
value. When a change is detected, the save settings command (command code
99) can then be sent to the IRGASON. The DestSource parameter variable
should be set to 2718 to save the settings. The reception of this command is
acknowledged, but since it takes up to a second to complete, a successful return
code does not mean that all data were successfully written to the appropriate
non-volatile memory.
The instruction syntax is:
EC100Configure (Result, SDMAddress, ConfigCmd, DestSource)
Result is a variable that contains a value indicating the success or failure of the
command. A result code of 0 means the command was successful. If reading a
setting, 0 in the result code means that the value in the DestSource variable is
the value the desired setting has in the IRGASON. When writing a setting, if
the result code is 0, the value and setting were compatible, but the value was
not changed because it contained the same value that was sent. A result code
of 1 from the set operation means that the value was valid, different, set and
acknowledged. This allows CRBasic code to control whether or not to save the
settings. A result code of NAN (i.e., not a number) indicates the setting was not
changed or acknowledged, or a signature failure occurred.
SDMAddress defines the address of the IRGASON to configure. Valid SDM
addresses are 0 through 14 (address 15 is reserved for SDMTrigger()).
ConfigCmd is a variable that indicates whether to get or set a setting. The
options are listed in Table 10-4.
37
IRGASON Integrated CO2/H2O Open-Path Gas Analyzer and 3D Sonic Anemometer
TABLE 10-4. ConfigCmd Values for Setting and Retrieving Settings
ConfigCmd
Variable
Set
Retrieve
Setting Description
(some settings list possible values for the DestSource
variable)
0
100
Bandwidth: 5 = 5 Hz, 10 = 10 Hz, 12 = 12.5 Hz, 20 = 20
Hz, 25 = 25 Hz
1
101
Unprompted output: 10 = 10 Hz, 25 = 25 Hz, 50 = 50 Hz
2
102
Pressure sensor: 0 = EC100 basic, 1 = user-supplied, 2 =
EC100 enhanced, 3 = none (use fixed value)
3
103
Differential pressure: 0 = disable, 1 = enable
4
104
Fixed pressure value
5
105
Pressure offset
6
106
Pressure gain
7
107
Temperature sensor:
0 = IRGASON/EC150 temperature probe
1 = EC155 sample cell thermistor
2 = EC155 sample cell thermocouple
3 = None (use fixed value)
4 = Auto-select
8
108
Fixed temperature value
9
109
Unprompted output mode: 0 = Disable, 1 =USB, 2 = RS485
10
110
RS-485 baud rate
11
111
Zero-and-span control: 0 = inactive, 1 = zero, 2 = span
CO2, 3 = span H2O (See Section 10.2.1, ConfigCmd 11
Zero-and-span Control)
12
112
CO2 span concentration
13
113
H2O span dew point temperature
14
114
CO2 zero
15
115
CO2 span
16
116
H2O zero
17
117
H2O span
18 or
218
118
Heater voltage (0 to 4.5375V, −1 = Off) (See Section
10.2.2, ConfigCmd 18 Heater Voltage)
19
119
Reserved
20
120
Analog output enable: 0 = disable, 1 = enable
21
121
Power down: 0 = Gas head on, 1 = Gas head off
99
N/A
Save settings to EEPROM memory
DestSource is a variable that will contain the value to read when getting a
setting, or that will contain the value to send when writing a setting to the
IRGASON.
38
IRGASON Integrated CO2/H2O Open-Path Gas Analyzer and 3D Sonic Anemometer
10.2.1 ConfigCmd 11 Zero-and-span Control
To perform zeroing of CO2 and H2O , ConfigCmd 11 is set to 1. After the
IRGASON completes the zero, it will write the value to -1. The datalogger
program can poll this value or simply wait for a period of time to allow the
zeroing to complete. To perform CO2 span, the CO2 Span Concentration
setting (ConfigCmd 12) must be written to the proper value in ppm CO2 prior
to setting the zero-and-span control setting (ConfigCmd 11) to 2. After the
CO2 span is completed, the value of the zero-and-span control setting will
change to -2. H2O span is similar to CO2. First the H2O Span Dew Point
Temperature value (ConfigCmd 13) must be written to the desired value. Then
the zero-and-span control setting is set to 3. After the IRGASON completes
the span, the span control setting is written as -3. ConfigCmd 14 through 17
automatically store the results of the zero-and-span procedure. Each result is a
coefficient used in the gas analyzer’s algorithms for calculating gas
concentrations.
10.2.2 ConfigCmd 18 Heater Voltage
Normally, the EC100Configure() instruction is run in the processing task.
Skipped scans can occur when the EC100Configure() instruction executes.
When changing operational parameters, these skipped scans are acceptable.
However, they may not be acceptable when changing the heater voltage.
ConfigCmd 218 allows EC100Configure() to operate in the SDM task, thus
avoiding skipped scans. When using ConfigCmd 218, the command must be a
constant and the instruction cannot be placed in a conditional statement.
The IRGASON includes heaters near the optical windows. This setting gives
the voltage applied to the heater. It can be set to -1 to disable the heater, or set
it to any voltage between 0 and 4.5375 V.
The heater resistance is 5 ohms, so the heater power (PH) expressed as Watts
(W) is given by:
PH =
V2
5
The maximum power at 4.5375 V is 4.12 W.
Operating the heaters following a precipitation event encourages water droplets
on the windows to evaporate more quickly, thus restoring signal strength.
Heater usage may also be desired to prevent formation of dew and frost on the
windows, which leads to invalid measurements due to differences in absorption
spectra of liquid water and water vapor.
The heaters, however, should be disabled when they are not needed. Heating
near the sample volume may cause air density fluctuations that can affect flux
measurements. Disabling the heaters will also conserve power. Care should be
taken to avoid operating the heaters if the system voltage is too low or if the
ambient temperature is > 45°C. Operation at temperatures > 45°C will
overload the thermoelectric coolers of the detector, as indicated by the TEC
Temp diagnostic flag (see Table 10-3, Bits in the Gas Diagnostic Flag).
A datalogger may be used to dynamically control the heaters by using input
from another moisture sensor such as a leaf-wetness sensor. When the sensor
39
IRGASON Integrated CO2/H2O Open-Path Gas Analyzer and 3D Sonic Anemometer
output indicates moisture is present, the datalogger can send the
EC100Configure() instruction to the IRGASON and enable the heaters.
10.3 Example CRBasic Program
'CR3000 Series Datalogger
Public sonic_irga(12)
Alias sonic_irga(1) = Ux
Alias sonic_irga(2) = Uy
Alias sonic_irga(3) = Uz
Alias sonic_irga(4) = Ts
Alias sonic_irga(5) = diag_sonic
Alias sonic_irga(6) = CO2
Alias sonic_irga(7) = H2O
Alias sonic_irga(8) = diag_irga
Alias sonic_irga(9) = cell_tmpr
Alias sonic_irga(10) = cell_press
Alias sonic_irga(11) = CO2_sig_strgth
Alias sonic_irga(12) = H2O_sig_strgth
Units Ux = m/s
Units Uy = m/s
Units Uz = m/s
Units Ts = C
Units diag_sonic = arb
Units CO2 = mg/m^3
Units H2O = g/m^3
Units diag_irga = arb
Units cell_tmpr = C
Units cell_press = kPa
Units CO2_sig_strgth = arb
Units H2O_sig_strgth = arb
DataTable (ts_data,TRUE,-1)
DataInterval (0,0,mSec,10)
Sample (12,Ux,IEEE4)
EndTable
BeginProg
Scan (100,mSec,0,0)
EC100 (Ux,1,1)
CallTable ts_data
NextScan
EndProg
40
IRGASON Integrated CO2/H2O Open-Path Gas Analyzer and 3D Sonic Anemometer
11. Theory of Operation
11.1 IRGASON Sonic Anemometer
The CSAT3 measures wind speeds and the speed of sound by determining the
time of flight of sound between pairs of transducers. However, unlike many
other commercial anemometers, it does not use simple threshold detection to
determine the ultrasonic times of flight. Instead, it uses advanced digital signal
processing techniques to determine the arrival of the transmitted ultrasonic
signal. In comparison to other systems, the digital signal processing techniques
result in more accurate, lower noise measurements.
11.1.1 Wind Speed
Each axis of the sonic anemometer pulses two ultrasonic signals in opposite
directions. The time of flight of the first signal (out) is given by:
to =
d
c + ua
(1)
and the time of flight of the second signal (back) is given by:
tb =
d
c - ua
(2)
where to is the time of flight out along the transducer axis, tb is the time of
flight back, in the opposite direction, ua is the wind speed along the transducer
axis, d is the distance between the transducers, and c is the speed of sound.
The wind speed, ua, along any axis can be found by inverting the above
relationships, subtracting Eq. (2) from (1), and solving for ua.
ua =
1⎤
d⎡ 1
⎢ − ⎥
2 ⎢⎣ t o t b ⎥⎦
(3)
The wind speed is measured on all three non-orthogonal axes to give ua, ub, and
uc, where the subscripts a, b, and c refer to the non-orthogonal sonic axes.
The non-orthogonal wind speed components are then transformed into
orthogonal wind speed components, ux, uy, and uz, with the following:
⎡u ⎤
⎡u ⎤
⎢ x⎥
⎢ a⎥
⎢u y ⎥ = A⎢ ub ⎥
⎢ ⎥
⎢ ⎥
⎣u z ⎦
⎣uc ⎦
(4)
where A is a 3 x 3 coordinate transformation matrix, that is unique for each
CSAT3 and is stored in ROM memory.
41
IRGASON Integrated CO2/H2O Open-Path Gas Analyzer and 3D Sonic Anemometer
11.1.2 Temperature
The sonically determined speed of sound can be found from the sum of the
inverses of Eq. (1) and (2). The CSAT3 corrects online for the effect of wind
blowing perpendicular to the sonic path. No additional off-line corrections are
required as suggested by Liu et al., 2001.
c=
1⎤
d⎡ 1
⎢ + ⎥
2 ⎢⎣ t o t b ⎥⎦
(5)
The speed of sound in moist air is a function of temperature and humidity and
is given by:
c = γP ρ = γRd Tv = γRd T( 1 + 0.61q)
2
(6)
where γ is the ratio of specific heat of moist air at constant pressure to that at
constant volume, P is pressure, ρ is air density, Rd is the gas constant for dry
air, Tv is virtual temperature, T is the air temperature, and q is the specific
humidity defined as the ratio of the mass of water vapor to the total mass of air
(Kaimal and Gaynor, 1991; Wallace and Hobbs, 1977).
Note that γ is a function of specific humidity. It would be convenient if the
effects of humidity could be consolidated into one term.
The specific heats for moist air at constant pressure and volume are given by:
C p = qC pw + (1 − q)C pd
= C pd (1 + 0.84q)
(7a)
C v = qC vw + (1 − q)C vd
= C vd (1 + 0.93q)
(7b)
where Cp and Cv are the specific heats of moist air at constant volume and
pressure, Cpw and Cvw is the specific heat of water vapor, and Cpd and Cvd is the
specific heat of dry air, respectively (Fleagle and Businger, 1980).
Substitute Eq. (7a) and (7b) into (6) and ignore the higher order terms. This
yields
2
c = γ dRdTs = γ dRd T(1 + 0.51q)
(8)
where Ts is sonic virtual temperature and γd is the ratio of specific heat of dry
air at constant pressure to that at constant volume (Fleagle and Businger, 1980;
Kaimal and Gaynor, 1991; Kaimal and Businger, 1963; Schotanus et al., 1983).
With Eq. (8), the effect of humidity, on the speed of sound, is included in the
sonic virtual temperature.
42
IRGASON Integrated CO2/H2O Open-Path Gas Analyzer and 3D Sonic Anemometer
The sonic virtual temperature, in degrees Celsius, is given by Eq. (9), where γd
= 1.4 and Rd = 287.04 J·K-1·kg-1.
Ts =
c
2
γ dRd
− 273.15
(9)
11.2 IRGASON Gas Analyzer
The IRGASON gas analyzer is a non-dispersive mid-infrared absorption
analyzer. Infrared radiation is generated in the upper arm of the analyzer head
before propagating along a 15 cm optical path. Chemical species located
within the optical beam will absorb radiation at characteristic frequencies. A
mercury cadmium telluride (MCT) detector in the lower arm of the gas
analyzer measures the decrease in radiation intensity due to absorption, which
can then be related to analyte concentration using the Beer-Lambert Law:
P = Po e −εcl
(10)
where P is irradiance after passing through the optical path, Po is initial
irradiance, ε is molar absorptivity, c is analyte concentration, and l is
pathlength.
In the IRGASON, radiation is generated by applying constant power to a
tungsten lamp, which acts as a 2200 K broadband radiation source. Specific
wavelengths are then selected using interference filters located on a spinning
chopper wheel. For CO2, light with a wavelength of 4.3 µm is selected, as it
corresponds to the molecule’s asymmetric stretching vibrational band. For
H2O, radiation at 2.7 µm, corresponding to water’s symmetric stretching
vibrational band, is used.
The IRGASON gas analyzer is a dual wavelength single-beam analyzer; thus,
rather than using a separate reference cell and detector, the initial intensity of
the radiation is calculated by measuring the intensity of nearby, non-absorbing
wavelengths (4 µm for CO2 and 2.3 µm for H2O). These measurements
account for any source and detector aging and window contamination.
The chopper wheel spins at a rate of 100 revolutions per second, and the
detector is measured 512 times per revolution, resulting in a detector sampling
rate of 76.8 kHz. The detector is maintained at -40oC using a 3-stage
thermoelectric cooler and is coupled to a low-noise pre-amp module.
The EC100 electronics digitize and process the detector data (along with
ancillary data such as sample temperature and pressure) to give the CO2 and
H2O molar mixing ratio for each chopper wheel revolution (100 Hz), filtered to
the user-specified bandwidth. The EC100 also synchronously measures and
processes data from the IRGASON sonic anemometer.
43
IRGASON Integrated CO2/H2O Open-Path Gas Analyzer and 3D Sonic Anemometer
11.3 Theory References
Kaimal, J. C. and Businger, J. A.: 1963, “A Continuous Wave Sonic
Anemometer-Thermometer”, J. Applied Meteorol., 2, 156-164.
Kaimal, J. C. and Gaynor, J. E.: 1991, “Another Look at Sonic Thermometry”,
Boundary-Layer Meteorol., 56, 401-410.
Fleagle, R. G. and Businger, J. A.: 1980, An Introduction to Atmospheric
Physics, Academic Press, Inc., New York.
Liu, H., Peters, G., and Foken, T.: 2001, “New Equations for Sonic
Temperature Variance and Buoyancy Heat Flux with an Omnidirectional
Sonic Anemometer”, Boundary-Layer Meteorol., 100, 459-468.
Schotanus, P., Nieuwstadt, F. T. M., and de Bruin, H. A. R.: 1983,
“Temperature Measurement with a Sonic Anemometer and its Application
to Heat and Moisture Fluxes”, Boundary-Layer Meteorol., 26, 81-93.
Wallace, J. M. and Hobbs, P. V.: 1977, Atmospheric Science an Introductory
Survey, Academic Press, Inc., New York.
44
Appendix A. Filter Bandwidth and Time
Delay
The EC100 measures CO2, H2O, 3-D wind components, and sonic temperature
from the IRGASON at 100 Hz and then applies a user-selectable low-pass
filter. The available filter bandwidths are 5, 10, 12.5, 20, and 25 Hz. Figure
A-1 shows the amplitude response of these filters. The EC100 filters provide a
flat pass band, a steep transition from pass band to stop band, and a wellattenuated stop band. Figure A-2 compares the EC100 10 Hz filter to a 50 ms
moving average filter with approximately the same bandwidth.
The ideal eddy-covariance filter is one that is wide enough to preserve the lowfrequency signal variations that transport flux and narrow enough to attenuate
high-frequency noise. In addition, to minimize aliasing (the misinterpretation
of high-frequency variation as lower-frequency variation), the measurement
bandwidth must be less than half of the sample rate (datalogger scan rate).
Two factors complicate choosing the ideal eddy-covariance bandwidth. First,
the flux signal bandwidth varies from one installation to another, and the flux
signal bandwidth varies with mean wind speed at a given installation. Second,
the fast sample rate required to anti-alias a desired signal bandwidth may result
in large, unwieldy data sets.
Fortunately, the covariance calculation itself relaxes the need for the ideal
bandwidth. First, the time-averaged (typically thirty-minute) covariance
calculations inherently reduce noise, and second, aliasing does not degrade the
accuracy of covariance calculations. Therefore, the factory default for the
EC100 bandwidth (20 Hz) is rather wide to preserve the signal variations that
transport flux, and that bandwidth is suitable for most flux applications.
Additional bandwidths are available for experimenters desiring to match the
EC100 filter bandwidth to their data acquisition sample rate to avoid aliasing.
In this case, the selected bandwidth should be one-half of the sample rate
(datalogger scan rate), and experimenters should be careful to avoid attenuation
of flux-carrying signals.
The EC100 electronics synchronously sample the gas analyzer and sonic
anemometer of the IRGASON. However, experimenters wishing to
synchronize their EC100 data with other measurements (e.g., energy balance
sensors) in the data acquisition system must account for the time delay of the
EC100 filter. Table A-1 shows the delay for each of the filter bandwidths. The
EC100 provides a constant time delay for all spectral components within each
filter’s pass band.
The following examples show how to use Table A-1. To synchronize EC100
data to other datalogger measurements when the datalogger scan rate is 25 Hz
and the EC100 bandwidth is set to 20 Hz (a 200 ms delay from Table A-1),
delay the non-EC100 data by five datalogger scans. Similarly, for a 10 Hz
datalogger scan rate and the same 20 Hz EC100 bandwidth, delay the nonEC100 data by two datalogger scans to match the EC100 data. For the best
synchronicity, choose a datalogger scan interval that is an integer multiple of
the EC100 filter delay.
A-1
Appendix A. Filter Bandwidth and Time Delay
The EC100 measures gas and wind data at 100 Hz, and 100 Hz data are downsampled to the datalogger scan rate through SDM communications (see Section
8, EC100 Outputs). This process synchronizes EC100 gas and wind data with
other signals measured by the datalogger to within ±5 ms (plus or minus onehalf of the inverse of 100 Hz). Alternatively, when sending data to a nonCampbell data acquisition system, the EC100 down-samples its USB and RS485 outputs to a user-selectable rate of 10, 25, or 50 Hz. Although the gas and
wind data from the EC100 remain synchronized, the user must consider the
down-sampled output interval when synchronizing the EC100 data with other
measurements in their system. These slower output intervals increase the
asynchronicity of EC100 data with other system measurements.
EC100 Bandwidths (Amplitude Responses)
10
1
5 Hz
10 Hz
0.1
No Units
12.5 Hz
20 Hz
25 Hz
0.01
0.001
0.0001
1
10
70
Hertz
FIGURE A-1. Frequency and amplitude response of EC100 filter at
various bandwidths
A-2
Appendix A. Filter Bandwidth and Time Delay
EC100 10-Hz Filter Compared to 20-msec Moving Average (Amplitude Responses)
10
1
No Units
0.1
EC100 10-Hz Bandwidth Filter
10-Hz Bandwidth from a 50-msec Moving Average
0.01
0.001
0.0001
1
10
70
Hertz
FIGURE A-2. Frequency response comparison of the EC100 10 Hz
bandwidth and a 50 ms moving average
TABLE A-1. Filter Time Delays for Various Bandwidths
Bandwidth (Hz)
Time Delay (ms)
5
800
10
400
12.5
320
20
200
25
160
A-3
Appendix A. Filter Bandwidth and Time Delay
A-4
Appendix B. Equations
Table B-1 lists variables and constants used in the following equations.
TABLE B-1. Table of Equation Variables and Constants
Variable or Constant
Description
Units
ρc
CO2 Mass Density
mg·m-3
ρv
H2O Mass Density
g·m-3
ρd
Mass Density of Dry Air
g·m-3
Xc
µmol·mol-1
Xv
CO2 Molar Mixing Ratio
(concentration relative to dry air)
H2O Molar Mixing Ratio
(concentration relative to dry air)
Mc
Molecular Weight of CO2
44 mg·mmol-1
Md
Molecular weight of dry air
0.029 g·mmol-1
Mv
Molecular weight of H2O
0.018 g·mmol-1
P
R
T
e
f
Ambient Pressure
kPa
mmol·mol-1
Universal Gas Constant
8.3143 x 10-6 kPa·m3·K-1·mmol-1
Ambient Temperature
Vapor Pressure
o
Enhancement Factor
Arbitrary
Td
Dew Point Temperature
o
Td _ tmp
Temporary variable for dew point
calculation
C
kPa
C
Arbitrary
Mass Density from Molar Mixing Ratios
⎛
ρ ⎞
P
⎜⎜
− v ⎟⎟
⎝ R(T + 273.15) M v ⎠
ρc =
X cM c
10 6
ρv =
X v PM v
R(T + 273.15)(1000 + X v )
ρd =
(P − e )M d
R(T + 273.15)
⎛
XvP ⎞
⎜⎜ P −
⎟M d
1000 + X v ⎟⎠
⎝
ρd =
R(T + 273.15)
(B-11)
(B-21)
(B-3)
(B-4)
B-1
Appendix B. Equations
⎛
PM
⎞⎛
⎞
X
d
v
⎟
⎟⎟⎜⎜1 −
ρ d = ⎜⎜
(
)
R
T
273
.
15
1000
X v ⎟⎠
+
+
⎠⎝
⎝
(B-5)
Dew Point from Molar Mixing Ratio
Td =
240.97 Td _ tmp
(B-62)
17.502 − Td _ tmp
⎛
⎞
XvP
⎟⎟
Td _ tmp = ln⎜⎜
(
)
⋅
+
0
.
61121
f
1000
X
v ⎠
⎝
(B-72)
f = 1.00072 + (3.2 ×10 −5 )P + (5.9 ×10 −9 )PT 2
(B-82)
Water Vapor Molar Mixing Ratio from Dew Point
Xv =
e
1000
P−e
(B-9)
⎛ 17.502Td
e = 0.61121 ⋅ f ⋅ EXP⎜⎜
⎝ 240.97 + Td
⎞
⎟⎟
⎠
(B-102)
Water Vapor Mass Density from Dew Point
ρv =
(0.018)(0.61121) f
R(T + 273.15)
⎛ 17.502Td
EXP⎜⎜
⎝ 240.97 + Td
⎞
⎟⎟
⎠
(B-112)
Vapor Pressure from Molar Mixing Ratio and Water Vapor Density
e=
e=
XvP
1000 + X v
ρ v R(T + 273.15)
Mv
(B-12)
(B-13)
1
Leuning, R (2004) Measurements of Trace Gas Fluxes in the Atmosphere
Using Eddy Covariance: WPL Revisited. The Handbook of Micrometeorology,
29, 119-132. New York: Kluwer Academic Publishers. Eq. 6.23
2
Buck, A L (1981) New Equations for Computing Vapor Pressure and
Enhancement Factor. Journal of Applied Meteorology 20, 1527-1532. Eqs.
2a, 3a, and 6
B-2
Appendix C. Material Safety Data
Sheets (MSDS)
MSDS are available for chemicals used in IRGASON filters. The MSDS
samples below are made available for convenience. However, chemical
manufacturers may change MSDS at any time. Up-to-date MSDS are available
at www.campbellsci.com.
C.1 Magnesium Perchlorate MSDS
C-1
Appendix C. Material Safety Data Sheets (MSDS)
C.2 Decarbite MSDS
C-2
Appendix C. Material Safety Data Sheets (MSDS)
C-3
Appendix C. Material Safety Data Sheets (MSDS)
C-4
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