Manual optris CTratio
optris® CTratio
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Fiber Optics Ratio Thermometer
Operators manual
CE-Conformity
The product complies with the following standards:
EMC:
Safety:
Laser Safety:
EN 61326-1:2013 (Basic requirements)
EN 61326-2-3:2013
EN 61010-1:2010
EN 60825-1:2015
The product accomplishes the requirements of the EMC Directive 2014/30/EU and
of the Low Voltage Directive 2014/35/EU.
This product is in conformity with Directive 2011/65/EU (RoHS) of the European
Parliament and of the Council of 8 June 2011 on the restriction of the use of
certain hazardous substances in electrical and electronic equipment.
Optris GmbH
Ferdinand-Buisson-Str. 14
D – 13127 Berlin
GERMANY
Tel.: +49-30-500 197-0
Fax: +49-30-500 197-10
E-mail: info@optris.de
Internet: www.optris.com
References to other chapters are marked as: ►.
Warranty
Each single product passes through a quality process. Nevertheless, if failures occur please contact the customer
service at once. The warranty period covers 24 months starting on the delivery date. After the warranty is expired the
manufacturer guarantees additional 6 months warranty for all repaired or substituted product components. Warranty
does not apply to damages, which result from misuse or neglect. The warranty also expires if you open the product. The
manufacturer is not liable for consequential damage or in case of a non-intended use of the product. If a failure occurs
during the warranty period the product will be replaced, calibrated or repaired without further charges. The freight costs
will be paid by the sender. The manufacturer reserves the right to exchange components of the product instead of
repairing it. If the failure results from misuse or neglect the user has to pay for the repair. In that case you may ask for a
cost estimate beforehand.
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Content
Page
Description
Scope of Supply
Maintenance
Safety Note
Cautions
Factory Default Settings
Technical Data
General Specifications
Electrical Specifications
Measurement Specifications
Optics
Mechanical Installation
Accessories
Laser Sighting
Electrical Installation
Cable Connections
Ground Connection
Outputs and Inputs
Analog Output
Digital I/O pins
Programming Interface
Relay Outputs
Alarms
3
4
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5
5
6
7
7
8
9
10
13
15
17
18
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21
21
22
23
24
25
Page
Operating
Sensor Setup
Software CompactConnect
Installation
Communication Settings
Basics of Infrared Thermometry
The Ratio Principle
Emissivity
Definition
Determination of unknown Emissivities
Characteristic Emissivities
Characteristic Slope Values
Determination of unknown Slope values
Attenuation
Appendix A – Emissivity Table Metals
Appendix B – Emissivity Table Non Metals
Appendix C – Smart Averaging
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Description
The sensors of the optris CTratio series are noncontact infrared temperature sensors.
They calculate the surface temperature based on the emitted infrared energy of objects. The CTratio can
work in the 1-color-mode as well as in the ratio- or 2-color-mode [► Basics of Infrared Thermometry]. The
optical sensing head of the CTratio is made of stainless steel (IP65/ NEMA-4 rating) and is connected via a
rugged fiber optics, which is protected by a stainless steel armour, with the sensor electronics (die casting
zinc box).
1-color-mode [1C]
The 1-color-mode is best for measuring the temperature of objects in areas where no sighting obstructions
(solid, gases or dust) exist. The measurement object must fill completely the measurement spot, if the 1color-mode is used.
2-color-mode [2C]
In this mode the object temperature will be determined from the ratio of the signal of two separate and
overlapping infrared bands. The 2-color-mode is best for measuring the temperature of objects which are
partially obscured by other objects, openings or viewing windows that reduce energy and by dirt, smoke or
steam in the atmosphere. Another benefit of the 2-color-mode is that the measurement object can be smaller
than the measurement spot, provided the background is cooler than the target [► The Ratio Principle].
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The CTratio sensing head is a sensitive optical system. Please use only the thread for mechanical
installation.
Avoid mechanical violence on the head – this may destroy the system (expiry of warranty).
Scope of Supply




CTratio sensing head with fibre connection cable and electronic box
2 mounting nuts
Mounting bracket, adjustable in one axis
Operators manual
Maintenance
Lens cleaning: Blow off loose particles using clean
compressed air. The lens surface can be cleaned with a
soft, humid tissue moistened with water or a water based
glass cleaner.
PLEASE NOTE: Never use cleaning
compounds which contain solvents (neither
for the lens nor for the housing).
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Safety Note
WARNING!
This sensor contains an internal HIGH POWER LASER which is used for spot size illumination via
the fiber optics cable.
Before you open the electronics, remove the fiber optical cable from the
electronics or disassemble the optical head the sensor must be switched off
and disconnected from the power supply and USB interface!
The laser power at properly usage of the sensor (fiber optical cable incl.
sensing head connected) is < 1mW and fulfils laser class 2 according
IEC 60825-1:2015.
Cautions
Avoid static electricity. The fiber optical cable has a minimum bending radius of 40 mm.
In case of problems or questions which may arise when you use the CTratio, please contact our service
department.
Read the manual carefully before the initial start-up. The producer reserves the right to change the herein
described specifications in case of technical advance of the product.
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Factory Default Settings
The unit has the following presetting at time of delivery:
Signal output object temperature
Emissivity
Slope
Averaging (AVG)
Smart Averaging
Peak hold
Valley hold
Output channel 1
Lower limit temperature range [°C]
Upper limit temperature range [°C]
Lower limit signal output
Upper limit signal output
Max. attenuation
Temperature unit
Baud rate [kBaud]
0-5 V
1,000
1,000
inactive
inactive
inactive
inactive
T 2C (2C temperature)
700
1800
0V
5V
95 %
°C
115
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Smart Averaging means a
dynamic average adaptation at
high signal edges [activation via
software only].
► Appendix C
Technical Data
General Specifications
Sensing head
Electronic box
Environmental rating
Ambient Temperature
Storage temperature
Relative humidity
IP65 (NEMA-4)
-20...250 °C
-40...250 °C
10...95%, non condensing
IP65 (NEMA-4)
0...85 °C (70 °C with Laser ON)
-40...85 °C
10...95%, non condensing
Material
Dimensions
die casting zinc
89 mm x 70 mm x 30 mm
Weight
stainless steel
length: 78,1 mm (SF head)
82,6 mm (CF head)
thread: M18x1
375 g (incl. fiber optics 3 m)
Fiber optics
Fiber optics length
multimode fiber, stainless steel armour
3 m (standard), 6 m, 10 m, 15 m, 22 m
Vibration
Shock
IEC 68-2-6: 3G, 11 – 200Hz, any axis
IEC 68-2-27: 50G, 11ms, any axis
Software
CompactConnect (optional; for programming only)
420 g
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Electrical Specifications
Power Supply
Current draw
Aiming laser
8–36 VDC
max. 200 mA
650 nm, 1mW, On/ Off via programming keys or software
Outputs/ analog
selectable: 0/ 4–20 mA, 0–5/ 10 V
Digital I/O pins
2 programmable in-/ outputs, usable as:
 Alarm output (open collector output [24 V/ 1 A])
 Digital input for triggered signal output and peak hold function
Output impedances
mA
mV
max. loop resistance 500 Ω (at 8-36 VDC)
min. 100 KΩ load impedance
Digital interface
USB (optional; for programming only)
Relay outputs
2 x 60 VDC/ 42 VACRMS, 0,4 A; optically isolated (optional plug-in module)
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Measurement Specifications
Temperature range (scalable)
Spectral range
Optical resolution
1)
700...1800 °C
0,7...1,1 µm
40:1 (SF optics)
40:1 (CF2 optics)
2)
System accuracy
1)
Repeatability
Temperature resolution (>900 °C)
Response time (95 % signal)
±(1 % of reading +1 °C)
2)
±(0,5 % of reading +1 °C)
0,1 K
3)
5 ms...10 s
Emissivity
Slope
Signal processing
0,050...1,000 (adjustable via programming keys or analog input)
0,800...1,200 (adjustable via programming keys or analog input)
One-color-, Two-color-mode, Attenuation monitoring, Alarm, Average,
Peak hold, Valley hold, Advanced peak hold with threshold and
hysteresis
(adjustable via programming keys or software)
1)
at ambient temperature 235 °C
 = 1/ Response time 1s
3)
with dynamic adaptation at low signal levels
2)
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Optics
The CTratio is available in two focus versions:
SF optics:
CF2 optics:
41 mm@ 1524 mm (D:S = 40:1)
7,7 mm@ 305 mm (D:S = 40:1)
The following optical charts show the diameter of the measuring spot in dependence on the distance
between measuring object and sensing head. The spot size refers to 95 % of the radiation energy.
The distance is always measured from the front edge of the sensing head.
SF optics
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CF2 optics
distance = distance from front edge of the sensing head to the measurement object
The D:S ratio is valid for the focus point.
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Sensor placement [1C mode]
The size of the measuring object and the optical resolution of the infrared thermometer determine the
maximum distance between sensing head and measuring object. In order to prevent measuring errors the
object should fill out the field of view of the optics completely. Consequently, the spot should at all times have
at least the same size like the object or should be smaller than that.
Sensor placement [2C mode]
In the 2-color-mode the sensing head can be placed under various conditions, like:




Measurement through holes smaller than the spot size
Measurement through dust, smoke or steam in the atmosphere
Measurement of objects smaller than the measurement spot
Measurement through a dirty lens or dirty sighting window
[► The Ratio Principle]
Please note that the sensor accuracy is not guaranteed for signal reductions of more than 95%.
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Mechanical Installation
The CTratio sensing heads are equipped with a metrical M18x1-thread and can be installed either directly via
the sensor thread or with help of the hex nuts (2 pieces included in scope of supply) to the mounting bracket
available. Various mounting brackets, which make the adjustment of the sensing head easier, can be
additionally ordered as accessories.
Sensing head
Please make sure that the minimum bending radius of the
fiber optics of 40 mm will be considered during installation.
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Electronic box
The electronic box is also available with closed cover (display and programming keys
with no access from outside) [ACCTCOV].
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Accessories
Mounting bracket, adjustable in
one axis [ACCTFBMH]
Air purge collar [ACCTAPMH]
The lens must be kept clean at all times from dust, smoke, fumes and other contaminants in order to avoid
reading errors (in the 1-color-mode). These effects can be reduced by using an air purge collar. Make sure to
use oil-free, technically clean air, only.
The needed amount of air (approx. 2...10 l/ min.) depends on the application
and the installation conditions on-site.
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Rail Mount Adapter for Electronic box
With the rail mount adapter the CTratio electronics can be mounted easily on a DIN rail (TS35) according
EN50022.
ACCTRAIL
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Laser Sighting
The integrated laser sighting supports the alignment and focusing of the optics. The size
of the laser dot is equal to the real measurement spot size at any distance.
If the laser is activated the temperature measurement is not possible!
The laser can be activated/ deactivated via the programming keys on the unit or via the
software. If the laser is activated a yellow LED will shine (beside temperature display).
[► Electrical Installation/ Operating]
At ambient temperatures >70 °C on the electronic box the laser will switch off
automatically.
WARNING: Do not point the laser directly at the eyes of persons or animals! Do not stare into the laser
beam. Avoid indirect exposure via reflective surfaces!
WARNING: Inside the electronic box a HIGH POWER LASER is located. The laser light is coupled into
the fiber optics. On the outlet at the optical head the laser power is < 1mW and fulfils laser class 2
according IEC 60825-1:2015.
Before you open the box, remove the fiber optical cable from the electronics or disassemble the
optical head the sensor must be switched off and disconnected from the power supply and USB
interface!
SAFETY SWITCH: If the fiber optical cable will be removed from the electronics the laser will be
switched off automatically. Any manipulation at this safety switch is prohibited.
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Electrical Installation
Cable Connections
For the electrical installation of the CTratio please open at first the cover of the electronic box (4 screws).
Below the display are the screw terminals for the cable connection.
Designation
+8..36VDC
GND
GND
I/O 2
I/O 1
OUT-mV/mA
Power supply
Ground (0V) of power supply
Ground (0V) of in- and outputs
I/O pin 2 (digital In- /Output or
analog input)
I/O pin 1 (digital In-/ Output or
analog input)
Analog output object temperature
(mV or mA)
CAUTION: Please do never connect a supply
voltage to the analog outputs as this will destroy
the output!
The CTratio is not a 2-wire sensor!
Opened electronic box with terminal connections
Power supply
Please use a power supply unit with an output voltage of 8–36 VDC which can supply 200 mA. The ripple
should be max. 200 mV. Please use shielded cables only for all power and data lines.
The sensor shield has to be grounded.
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Cable Assembling
The cable gland M12x1,5 allows the use of cables with a diameter of 3 to 5 mm.
Remove the isolation from the cable (40 mm power supply, 50 mm signal outputs, 60 mm functional inputs).
Cut the shield down to approximately 5 mm and spread the strands out. Extract about 4 mm of the wire
isolation and tin the wire ends.
Place the pressing screw, the rubber washer and the metal washers of the cable gland one after the other
onto the prepared cable end. Spread the strands and fix the shield between two of the metal washers. Insert
the cable into the cable gland until the limit stop. Screw the cap tight.
Every single wire may be connected to the according screw clamps according to their colors.
Use shielded cables only. The sensor
shield has to be grounded.
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Ground Connection
On the mainboard PCB you will find a black wire which is connecting factory-default the ground connections
(GND power supply/ outputs) with the ground of the electronics housing.
To avoid ground loops and related signal interferences in industrial environments it might be necessary to
interrupt this connection.
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Outputs and Inputs
The CTratio has an analog output and two digital I/O pins (programmable as in- or output).
Analog Output
The selection of the signal on output channel 1 can be done via the programming keys [► Operating].
The following output signals can be selected:
0-5 V
0-10 V
0-20 mA
4-20 mA
CAUTION: Please do never connect a supply voltage to the
analog outputs as this will destroy the output.
The CTratio is not a 2-wire sensor!
The following signal sources can be selected for output channel 1:
T 2C
T 1C
Attenuation
2C temperature
1C temperature
Signal attenuation in %
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I/O pins
The CTratio has two digital pins which can be programmed as outputs (digital) or as inputs (digital or analog)
using the CompactConnect software. The following functions are available:
Function
Digital Alarm
I/O pin acts as
output digital
Valid LO
input digital
Valid HI
input digital
Hold ‗/¯
input digital
Hold ¯\‗
input digital
Slope external
input analog
Emiss. external
input analog
High level:
Low level:
Description
Open collector output/ definition as HIGH- or LOW alarm via
norm. open/ norm. close options in software dialog.
The output follows the object temperature as long as there is
a Low level at the I/O pin. After discontinuation of the Low
level the last value will be held.
The output follows the object temperature as long as there is
a High level at the I/O pin. After discontinuation of the High
level the last value will be held.
The last value will be held if there is a signal with a rising
edge on the I/O pin.
The last value will be held if there is a signal with a falling
edge on the I/O pin.
The slope value can be adjusted via a 0-10 V signal on the
I/O pin (scaling possible via software).
The emissivity value can be adjusted via a 0-10 V signal on
the I/O pin (scaling possible via software).
 0,8 V
 0,8 V
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Programming Interface
CTratio sensors can be optionally equipped with an USB-interface for
programming of the sensor.
If you want to install the interface, plug the interface board into the place
provided, which is located beside the display. In the correct position the
holes of the interface match with the thread holes of the electronic box.
Now press the board down to connect it and use both M3x5 screws for
fixing it. Plug the preassembled interface cable with the terminal block into
the male connector of the interface board.
If the USB interface is used the sensor is powered by the computer. If you use the laser and/ or display backlight we
recommend an additional power supply.
The usage of the USB interface is only recommended for programming purposes of the sensor.
A continuous operation with interface is not permitted!
Please pay attention to the notes in the according interface manuals.
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Relay Outputs
The CTratio can be optionally equipped with a relay output. The relay board will be installed the same way as
the programming interface.
A simultaneous installation of the programming interface and the relay outputs is not possible.
The relay board provides two fully isolated switches, which have the capability to switch
max. 60 VDC/ 42 VACRMS, 0,4 A DC/AC. A red LED shows the closed switch.
The switching thresholds are in accordance with the values for the visual alarms (LCD backlight).
To set the alarm values the digital programming interface (USB) and the software is needed.
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Alarms
The CTratio has the following Alarm features:
All alarms have a fixed hysteresis of 2 K.
Visual Alarms
These alarms will cause a change of the color of the LCD display and will also change the status of the
optional relays interface.
Digital Alarm 1 and 2
Both of the I/O pins can be programmed as alarm output. In this case the pin acts as an open collector
output (24 V/ 1A).
The following signal sources can be selected:
T 2C/ T 1C/ Attenuation/ TBox/ TProcess (Temperature signal which has been selected for the analog
output)
For a setup of the alarm values, selection of the signal sources and definition as high or low alarm (via change of
normally open/ closed) the programming interface (USB) including the software is needed.
Different wirings of the open collector output
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Operating
After power up the unit the sensor starts an initializing routine for some seconds. During this time the display
will show INIT. After this procedure the object temperature is shown in the display. The display backlight
color changes according to the alarm settings [► Alarms/ Visual Alarms].
Sensor Setup
The programming keys Mode, Up and Down enable the user to set the sensor on-site. The current
measuring value or the chosen feature is displayed. With Mode the operator obtains the chosen feature, with
Up and Down the functional parameters can be selected – a change of parameters will have immediate
effect. If no key is pressed for more than 10 seconds the display automatically shows the calculated object
temperature (according to the signal processing).
Pressing the Mode button again recalls the last called
function on the display. The signal processing features Peak
hold and Valley hold cannot be selected simultaneously.
Factory Default Setting
To set the CTratio back to the factory default settings, please
press at first the Down-key and then the Mode-key and keep
both pressed for approx. 3 seconds.
The display will show RESET for confirmation.
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Display
Mode [Sample]
Adjustment Range
S ON
700.0 ||
600.0 |
65.0 %
23.3 CB
 MV5
Laser Sighting [On]
Current 2C temperature [700,0 °C]
Current 1C temperature [600,0 °C]
Current attenuation [65,0 %]
Box temperature [23,3 °C]
Signal output channel 1 [0-5 V]
R 1.000
E 0.970
D 95.0
MD 2C
Slope [1,000]
Emissivity [0,970]
Max. attenuation [95,0 %]
Main display (on electronic box) [2C temperature value]
A 0.2
P---V---u 700.0
n 1500
[ 0.00
] 5.00
U °C
M 01
B 115
Signal output Average [0,2 s]
Signal output Peak hold [inactive]
Signal output Valley hold [inactive]
Lower limit temperature range [700 °C]
Upper limit temperature range [1500 °C]
Lower limit signal output [0 V]
Upper limit signal output [5 V]
Temperature unit [°C]
Multidrop adress [1] (only with RS485 interface)
Baud rate in kBaud [115]
ON/ OFF
fixed
fixed
fixed
fixed
0-20 = 0–20 mA/  4-20 = 4–20 mA/  MV5 = 0–5 V/
 MV10 = 0-10 V
0,800 ... 1,200
0,050 ... 1,000
-50,0 ... 99,0
2C = 2C temperature/ 1C = 1C temperature/
AT = attenuation
A---- = inactive/ 0,1 … 999,9 s
P---- = inactive/ 0,1 … 999,9 s/ P oo oo oo oo = infinite
V---- = inactive/ 0,1 … 999,9 s/ V oo oo oo oo = infinite
depending on model
depending on model
according to the range of the selected output signal
according to the range of the selected output signal
°C/ °F
01 … 32
9,6/ 19,2/ 38,4/ 57,6/ 115,2 kBaud
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S ON
Activating (ON) and Deactivating (OFF) of the integrated Sighting Laser
By pressing Up or Down the laser will be switched on or off. If the laser is activated a
measurement cannot be done.
 MV5
Selection of the Output signal. By pressing Up or Down the different output signals can be
selected [► Outputs and Inputs].
R 1.000
Setup of Slope. Pressing Up increases the value, Down decreases the value (also valid
for all further functions). The slope is the quotient of the emissivities of both of the
overlapping wavelengths and therewith the deciding parameter for measurements in 2-color
mode. [► Characteristic Slope Values]
E 0.970
Setup of Emissivity. The emissivity is a material constant factor to describe the ability of the
body to emit infrared energy. The emissivity only affects measurements in the 1-color mode.
[► Emissivity]
D 95.0
Setup of the allowed Attenuation. The temperature measurement will stop if the attenuation
exceeds this limit [► Attenuation].
MD 2C
Setup of the Main display on the electronic box. By pressing Up or Down you can select if
the 2C temperature, 1C temperature or attenuation should be displayed (independent from
the selected output signal).
A 0.2
Setup of Average time. If the value is set to 0.0 the display will show --- (function
deactivated). In this mode an arithmetic algorithm will be performed to smoothen the signal.
The set time is the time constant. This function can be combined with all other post
processing functions.
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P----
Setup of Peak hold. If the value is set to 0.0 the display will show --- (function deactivated).
In this mode the sensor is waiting for descending signals. If the signal descends the
algorithm maintains the previous signal peak for the specified time.
After the hold time the signal will drop down to the second highest value or will descend by
1/8 of the difference between the previous peak and the minimum value during the hold time.
This value will be held again for the specified time. After this the signal will drop down with
slow time constant and will follow the current object temperature.
V----
Setup of Valley hold. If the value is set to 0.0 the display will show --- (function deactivated).
In this mode the sensor waits for ascending signals. The definition of the algorithm is
according to the peak hold algorithm (inverted).
u 700.0
Setup of the Lower limit of temperature range. The minimum difference between lower
and upper limit is 20 K. If you set the lower limit to a value ≥ upper limit the upper limit will be
adjusted to [lower limit + 20 K] automatically.
n 1800
Setup of the Upper limit of the temperature range. The minimum difference between
upper and lower limit is 20 K. The upper limit can only be set to a value = lower limit + 20 K.
[ 0.00
Setup of the Lower limit of the signal output. This setting allows an assignment of a
certain signal output level to the lower limit of the temperature range. The adjustment range
corresponds to the selected output mode (e.g. 0-5 V).
] 5.00
Setup of the Upper limit of the signal output. This setting allows an assignment of a
certain signal output level to the upper limit of the temperature range. The adjustment range
corresponds to the selected output mode (e.g. 0-5 V).
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Signal graph with P----
▬ TProcess with Peak Hold (Hold time = 1s)
▬ TActual without post processing
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U °C
Setup of the Temperature unit [°C or °F].
M 01
Setup of the Multidrop address. In a RS485 network each sensor will need a specific
address. This menu item will only be shown if a RS485 interface board is plugged in.
B 115k
Setup of the Baud rate for digital data transfer.
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Software CompactConnect
Installation
Insert the installation CD into the according drive on
your computer. If the autorun option is activated the
installation wizard will start automatically.
Otherwise please start CDsetup.exe from the CDROM. Follow the instructions of the wizard until the
installation is finished.
Min. system requirements:
 Windows XP, Vista, 7
 USB interface
 Hard disc with at least 30 MByte free space
 At least 128 MByte RAM
 CD-ROM drive
The installation wizard will place a launch icon on the desktop and in the start menu:
[Start]\Programs\CompactConnect.
If you want to uninstall the software from your system please use the uninstall icon in the start menu.
You will find a detailed software manual on the CD.
Main Features:
 Complete sensor setup
 Adjustment of signal processing functions
 Programming of outputs and functional inputs
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Communication Settings
Serial Interface
Baud rate:
Data bits:
Parity:
Stop bits:
Flow control:
9,6...115,2 kBaud (adjustable on the unit or via software)
8
none
1
off
Protocol
All sensors of the CTratio series are using a binary protocol.
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Basics of Infrared Thermometry
Depending on the temperature each object emits a certain amount of infrared radiation. A change in the
temperature of the object is accompanied by a change in the intensity of the radiation. For the measurement
of “thermal radiation” infrared thermometry uses a wave-length ranging between 1 µ and 20 µm.
The intensity of the emitted radiation depends on the material. This material contingent constant is described
with the help of the emissivity which is a known value for most materials (see enclosed table emissivity).
Infrared thermometers are optoelectronic sensors. They calculate the surface temperature on the basis of
the emitted infrared radiation from an object. The most important feature of infrared thermometers is that
they enable the user to measure objects contactless. Consequently, these products help to measure the
temperature of inaccessible or moving objects without difficulties. Infrared thermometers basically consist of
the following components:
 lens
 spectral filter
 detector
 electronics (amplifier/ linearization/ signal processing)
The specifications of the lens decisively determine the optical path of the infrared thermometer, which is
characterized by the ratio Distance to Spot size.
The spectral filter selects the wavelength range, which is relevant for the temperature measurement. The
detector in cooperation with the processing electronics transforms the emitted infrared radiation into electrical
signals.
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The Ratio Principle
The 2-color ratio technology makes possible accurate and repeatable temperature measurements that are
free from dependence on absolute radiated energy values. In use, a 2-color sensor determines temperature
from the ratio of the radiated energies in two separate wavelength bands (colors). The benefits of 2-color
sensors are that accurate measurements can be made under the following conditions:
►
►
►
When the field of view to the target is partially blocked or obscured.
When the target is smaller than the sensor’s field of view.
When target emissivities are low or changing by the same factor in both wavelength bands.
Another benefit is that 2-color sensors measure closer to the highest temperature within the measured spot
(spatial peak picking) instead of an average temperature. A 2-color sensor can be mounted farther away,
even if the target does not fill the resulting spot size. The convenience is that you are not forced to install the
sensor at some specific distance based upon target size and the sensor’s optical resolution.
Partially Obscured Targets
The radiated energy from a target is, in most cases, equally reduced when objects or atmospheric materials
block some portion of the optical field of view. It follows that the ratio of the energies is unaffected, and thus
the measured temperatures remain accurate.
A 2-color sensor is better than a 1-color sensor in the following conditions:
►
►
►
Sighting paths are partially blocked (either intermittently or permanently).
Dirt, smoke, or steam is in the atmosphere between the sensor and target.
Measurements are made through items or areas that reduce emitted energy, such as grills,
screens, channels or small openings
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►
►
Measurements are made through a viewing window that has unpredictable and changing
infrared transmission due to accumulating dirt and/or moisture on the window surface.
The sensor itself is subject to dirt and/or moisture accumulating on the lens surface.
1-color sensors see polluted atmosphere and dirty windows and lenses as a reduction in
energy and give much lower than actual temperature readings.
Targets Smaller Than Field of View
When a target is not large enough to fill the field of view, or if the target is moving within the field of view,
radiated energies are equally reduced, but the ratio of the energies is unaffected and measured
temperatures remain accurate. This remains true as long as the background temperature is much lower than
the target temperature.
Example:
►
Measuring of wire or rod — often too narrow for field of view or moving or vibrating unpredictably. It
is much easier to obtain accurate results because sighting is less critical with 2-color sensors.
Low or Changing Emissivities
If the emissivities in both wavelengths (colors) were the same, as they would be for any blackbody
(emissivity = 1.0) or greybody (emissivity < 1.0 but constant), then their ratio would be 1, and target
emissivity would not be an influence. However, in nature there is no such thing as a greybody. The emissivity
of all real objects changes with wavelength and temperature, at varying degrees, depending on the material.
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When emissivity is uncertain or changing, a 2-color sensor can be more accurate than a 1-color instrument
as long as the emissivity changes by the same factor in both wavelength bands. Note, however, that
accurate measurement results are dependent on the application and the type of material being measured.
To determine how to use 2-color sensors with your application when uncertain or changing emissivities are a
factor, please contact your sales representative.
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Emissivity
Definition
The intensity of infrared radiation, which is emitted by each body, depends on the temperature as well as on
the radiation features of the surface material of the measuring object. The emissivity (ε – Epsilon) is used as
a material constant factor to describe the ability of the body to emit infrared energy. It can range between 0
and 100 %. A “blackbody” is the ideal radiation source with an emissivity of 1,0 whereas a mirror shows an
emissivity of 0,1.
If the emissivity chosen is too high, the infrared thermometer may display a temperature value which is much
lower than the real temperature – assuming the measuring object is warmer than its surroundings. A low
emissivity (reflective surfaces) carries the risk of inaccurate measuring results by interfering infrared radiation
emitted by background objects (flames, heating systems, chamottes). To minimize measuring errors in such
cases, the handling should be performed very carefully and the unit should be protected against reflecting
radiation sources.
Determination of unknown Emissivities
► First, determine the actual temperature of the measuring object with a thermocouple or contact sensor.
Second, measure the temperature with the infrared thermometer and modify the emissivity until the
displayed result corresponds to the actual temperature.
► If you monitor temperatures of up to 380°C you may place a special plastic sticker (emissivity dots – part
number: ACLSED) onto the measuring object, which covers it completely. Now set the emissivity to 0,95
and take the temperature of the sticker. Afterwards, determine the temperature of the adjacent area on
the measuring object and adjust the emissivity according to the value of the temperature of the sticker.
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► Cove a part of the surface of the measuring object with a black, flat paint with an emissivity of 0,98. Adjust
the emissivity of your infrared thermometer to 0,98 and take the temperature of the colored surface.
Afterwards, determine the temperature of a directly adjacent area and modify the emissivity until the
measured value corresponds to the temperature of the colored surface.
CAUTION: On all three methods the object temperature must be different from ambient temperature.
Characteristic Emissivities
In case none of the methods mentioned above help to determine the emissivity you may use the emissivity
tables ►Appendix A and B. These are average values, only. The actual emissivity of a material depends on
the following factors:
 temperature
 measuring angle
 geometry of the surface
 thickness of the material
 constitution of the surface (polished, oxidized, rough, sandblast)
 spectral range of the measurement
 transmissivity (e.g. with thin films)
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Characteristic Slope Values
The slope is the quotient of the emissivities of both of the overlapping wavelength bands. The factory default
value for the slope is 1,000. The following slopes are typical reference values. The real slope can vary
depending on the metal alloy and surface finish.
Cobalt, Iron, Nickel, Stainless steel, Steel
► oxidized surfaces
Slope: 1,000
Cobalt, Iron (solid, molten), Molybdenum,
Nickel, Platinum, Rhodium, Stainless steel,
Steel, Tantalum, Tungsten, Wolfram
► unoxidized surfaces
Slope: 1,060
Determination of unknown Slope values
Basically you can use the same methods to determine an unknown slope as described under
► Determination of unknown Emissivities. As the CTratio is dedicated for high temperature applications,
only the first method may be practically applicable (use of a t/c or other contact probe).
Attenuation
The CTratio is able to measure the temperature of targets smaller than the field of view (FOV). If the target
size is smaller than the FOV (and thus attenuating the signal) this may cause a small inaccuracy of the
reading. The inaccuracy is dependent on the object temperature and value of attenuation. The higher the
object temperature and attenuation the higher the inaccuracy of the sensor.
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This figure is showing the typical temperature reading of a ratio thermometer optris CT ratio in both the 1color- and the 2-color-mode in addiction of increasing contamination of the optical transmission path inbetween the target and the ratio thermometer. Due to the ratio principle the 2 channel signal (upper curve)
stays very stable over a wide range of attenuation up to over 90%. The signal of the 1 channel mode (lower
curve), acting like in a standard pyrometer with one measuring wavelength only, is decreasing rapidly with
the contamination of the transmission path.
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Appendix A – Emissivity Table Metals
Material
Aluminium
Brass
Copper
Spectral response
non oxidized
polished
roughened
oxidized
polished
roughened
oxidized
polished
roughened
oxidized
Chrome
Gold
Haynes
Inconel
Iron
Iron, casted
alloy
electro polished
sandblast
oxidized
non oxidized
rusted
oxidized
forged, blunt
molten
non oxidized
oxidized
typical Emissivity
1,0 µm
0,1-0,2
0,1-0,2
0,2-0,8
0,4
0,35
0,65
0,6
0,05
0,05-0,2
0,2-0,8
0,4
0,3
0,5-0,9
0,2-0,5
0,3-0,4
0,4-0,9
0,35
0,7-0,9
0,9
0,35
0,35
0,9
1,6 µm
0,02-0,2
0,02-0,1
0,2-0,6
0,4
0,01-0,05
0,4
0,6
0,03
0,05-0,2
0,2-0,9
0,4
0,01-0,1
0,6-0,9
0,25
0,3-0,6
0,6-0,9
0,1-0,3
0,6-0,9
0,5-0,9
0,9
0,4-0,6
0,3
0,7-0,9
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5,1 µm
0,02-0,2
0,02-0,1
0,1-0,4
0,2-0,4
0,01-0,05
0,3
0,5
0,03
0,05-0,15
0,5-0,8
0,03-0,3
0,01-0,1
0,3-0,8
0,15
0,3-0,6
0,6-0,9
0,05-0,25
0,5-0,8
0,6-0,9
0,9
8-14 µm
0,02-0,1
0,02-0,1
0,1-0,3
0,2-0,4
0,01-0,05
0,3
0,5
0,03
0,05-0,1
0,4-0,8
0,02-0,2
0,01-0,1
0,3-0,8
0,15
0,3-0,6
0,7-0,95
0,05-0,2
0,5-0,7
0,5-0,9
0,9
0,25
0,65-0,95
0,2
0,6-0,95
Material
Spectral response
Lead
polished
roughened
oxidized
Magnesium
Mercury
Molybdenum
non oxidized
oxidized
Monel (Ni-Cu)
Nickel
electrolytic
oxidized
Platinum
black
Silver
Steel
polished plate
rustless
heavy plate
cold-rolled
oxidized
Tin
non oxidized
Titanium
polished
oxidized
Wolfram
polished
Zinc
polished
oxidized
typical Emissivity
1,0 µm
0,35
0,65
0,3-0,8
0,25-0,35
0,5-0,9
0,3
0,2-0,4
0,8-0,9
0,04
0,35
0,35
0,8-0,9
0,8-0,9
0,25
0,5-0,75
0,35-0,4
0,5
0,6
1,6 µm
0,05-0,2
0,6
0,3-0,7
0,05-0,3
0,05-0,15
0,1-0,3
0,4-0,9
0,2-0,6
0,1-0,3
0,4-0,7
0,95
0,02
0,25
0,2-0,9
0,8-0,9
0,8-0,9
0,1-0,3
0,3-0,5
0,6-0,8
0,1-0,3
0,05
0,15
5,1 µm
0,05-0,2
0,4
0,2-0,7
0,03-0,15
0,05-0,15
0,1-0,15
0,3-0,7
0,1-0,5
0,1-0,15
0,3-0,6
0,9
0,02
0,1
0,15-0,8
0,5-0,7
0,8-0,9
0,7-0,9
0,05
0,1-0,3
0,5-0,7
0,05-0,25
0,03
0,1
8-14 µm
0,05-0,1
0,4
0,2-0,6
0,02-0,1
0,05-0,15
0,1
0,2-0,6
0,1-0,14
0,05-0,15
0,2-0,5
0,9
0,02
0,1
0,1-0,8
0,4-0,6
0,7-0,9
0,7-0,9
0,05
0,05-0,2
0,5-0,6
0,03-0,1
0,02
0,1
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Appendix B – Emissivity Table Non Metals
Material
Spectral response
Asbestos
Asphalt
Basalt
Carbon
Carborundum
Ceramic
Concrete
Glass
Grit
Gypsum
Ice
Limestone
Paint
Paper
Plastic >50 µm
Rubber
Sand
Snow
Soil
Textiles
Water
Wood
typical Emissivity
1,0 µm
0,9
non oxidized
graphite
0,4
0,65
plate
melt
2,2 µm
0,8
0,8-0,9
0,8-0,9
0,95
0,8-0,95
0,9
0,2
0,4-0,9
0,4-0,98
non alkaline
any color
non transparent
0,95
0,95
0,9
0,9
0,95
natural
0,9-0,95
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5,1 µm
0,9
0,95
0,7
0,8-0,9
0,7-0,9
0,9
0,8-0,95
0,9
0,98
0,9
0,95
0,4-0,97
8-14 µm
0,95
0,95
0,7
0,8-0,9
0,7-0,8
0,9
0,95
0,95
0,85
0,95
0,8-0,95
0,98
0,98
0,9-0,95
0,95
0,95
0,95
0,9
0,9
0,9-0,98
0,95
0,93
0,9-0,95
Appendix C – Smart Averaging
The average function is generally used to smoothen the output signal. With the adjustable parameter time
this function can be optimal adjusted to the respective application. One disadvantage of the average function
is that fast temperature peaks which are caused by dynamic events are subjected to the same averaging
time. Therefore those peaks can only be seen with a delay on the signal output.
The function Smart Averaging eliminates this disadvantage by passing those fast events without averaging
directly through to the signal output.
Signal graph with Smart Averaging function
Signal graph without Smart Averaging function
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