Vaisala GMP252 User manual

M211897EN-E
User Guide
Vaisala CARBOCAPâCarbon Dioxide Probe
GMP252

PUBLISHED BY
Vaisala Oyj
Vanha Nurmijärventie 21, FI‑01670 Vantaa, Finland
P.O. Box 26, FI‑00421 Helsinki, Finland
[phone]
www.vaisala.com
docs.vaisala.com
© Vaisala 2023
No part of this document may be
reproduced, published or publicly
displayed in any form or by any means,
electronic or mechanical (including
photocopying), nor may its contents be
modified, translated, adapted, sold or
disclosed to a third party without prior
written permission of the copyright holder.
Translated documents and translated
portions of multilingual documents are
based on the original English versions. In
ambiguous cases, the English versions are
applicable, not the translations.
The contents of this document are subject
to change without prior notice.
Local rules and regulations may vary and
they shall take precedence over the
information contained in this document.
Vaisala makes no representations on this
document’s compliance with the local
rules and regulations applicable at any
given time, and hereby disclaims any and
all responsibilities related thereto.
This document does not create any legally
binding obligations for Vaisala towards
customers or end users. All legally binding
obligations and agreements are included
exclusively in the applicable supply
contract or the General Conditions of Sale
and General Conditions of Service of
Vaisala.
This product contains software developed
by Vaisala or third parties. Use of the
software is governed by license terms and
conditions included in the applicable
supply contract or, in the absence of
separate license terms and conditions, by
the General License Conditions of Vaisala
Group.

Table of contents
1. About this document.................................................................................... 11
1.1 Version information..........................................................................................11
1.2 Related manuals.............................................................................................. 12
1.3 Documentation conventions.......................................................................... 12
1.4 Trademarks.......................................................................................................13
2. Product overview...........................................................................................14
2.1 Introduction to GMP252 ................................................................................ 14
2.2 Basic features and options............................................................................. 15
2.2.1 Connectivity to Vaisala Insight software............................................... 15
2.2.2 Additional features with Indigo transmitters........................................16
2.2.3 Filter options.............................................................................................17
2.3 Operating principle of CO2measurement....................................................18
2.4 Environmental compensation........................................................................19
2.4.1 Temperature compensation...................................................................20
2.4.2 Pressure compensation........................................................................... 21
2.4.3 Background gas compensation..............................................................21
2.5 Probe startup................................................................................................... 21
2.6 Filtering factor................................................................................................. 21
2.7 Analog output overrange behavior..............................................................22
2.7.1 Analog output overrange example....................................................... 23
2.8 Safety...............................................................................................................24
2.8.1 ESD protection........................................................................................ 24
3. Installation....................................................................................................... 25
3.1 GMP252 probe dimensions............................................................................25
3.2 Recommended installation............................................................................25
3.3 Installation accessories..................................................................................26
3.3.1 243261SP mounting flange.....................................................................27
3.3.2 243257SP mounting clips.......................................................................28
3.3.3 ASM213582 probe holder....................................................................... 28
3.3.4 ASM212017SP spray shield..................................................................... 29
3.3.5 DTR250 radiation shield.........................................................................30
3.3.6 DTR250A pole mounting kit..................................................................30
3.3.7 GMP252 probe handle accessories........................................................ 31
3.4 Power supply...................................................................................................33
3.5 Wiring...............................................................................................................33
4. Vaisala Industrial Protocol........................................................................ 35
4.1 Vaisala Industrial Protocol overview............................................................ 35
4.2 Serial interface settings................................................................................. 35
4.3 Physical interface............................................................................................35
4.4 Connecting with a computer.........................................................................35
4.4.1 Installing driver for the USB service cable........................................... 37
4.5 Accessing serial commands from Modbus or analog mode..................... 38
4.6 Enabling Modbus mode from Vaisala Industrial Protocol......................... 39
Table of contents
3

4.7 Changing from digital output to analog output.........................................39
4.8 Serial commands............................................................................................40
4.9 Device information and status......................................................................42
4.10 Serial line output and communication........................................................ 44
4.11 Analog output..................................................................................................51
4.12 Calibration and adjustment commands...................................................... 56
4.13 Environmental compensation commands.................................................. 60
4.14 Other commands............................................................................................65
5. Modbus............................................................................................................. 66
6. Vaisala Insight PC software...................................................................... 67
6.1 Connecting to Insight software.................................................................... 67
7. Using probe with Indigo200 series transmitters............................ 69
7.1 Introduction to Indigo200 transmitters...................................................... 69
7.2 Connecting probes.........................................................................................70
7.3 Analog output configuration overview.........................................................71
7.3.1 Analog output configuration example..................................................72
7.4 Modbus overview............................................................................................72
7.4.1 Default communication settings........................................................... 74
7.5 Relay configuration overview........................................................................74
7.6 Configuring filtering factor with Insight...................................................... 76
8. Using probe with Indigo80 handheld indicator...............................78
8.1 Indigo80 handheld indicator.........................................................................78
8.1.1 Probe compatibility.................................................................................79
8.1.2 Indigo80 keypad..................................................................................... 79
8.1.3 Indigo80 main menu...............................................................................79
8.2 Connecting probes to Indigo80................................................................... 80
8.3 Configuring probe features with Indigo80 handheld indicator.................81
8.3.1 Example of configuring filtering factor with Indigo80
handheld indicator.................................................................................. 82
8.4 Configuring environment settings with Indigo80 handheld indicator.... 83
9. Operating with MI70 indicator................................................................85
9.1 Overview of MI70 support.............................................................................85
9.1.1 Probe warm-up and MI70 automatic power o..................................85
9.2 Basic display....................................................................................................85
9.3 Graphical display............................................................................................ 86
9.4 Main menu.......................................................................................................86
9.5 Connecting probe to MI70 indicator............................................................86
9.6 MI70 indicator parts....................................................................................... 87
9.7 Holding and saving the display.....................................................................87
9.8 Recording data............................................................................................... 88
9.9 Changing environmental compensation settings with MI70 indicator....88
10. Calibration and adjustment..................................................................... 90
10.1 Calibration setup............................................................................................90
GMP252 User Guide M211897EN-E
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10.2 Eect of environmental compensations...................................................... 91
10.3 Limits of adjustment....................................................................................... 91
10.4 Adjustment types............................................................................................ 91
10.5 DRW244827SP calibration adapter............................................................. 93
10.6 Overview of calibration with Indigo200 using Insight.............................. 94
10.6.1 Environmental compensation................................................................95
10.6.2 CO2probe adjustment example............................................................96
10.7 Performing manual adjustment with Indigo80 handheld indicator.........97
10.8 Restoring factory adjustment with Indigo80 handheld indicator............98
10.9 Calibration and adjustment with MI70 indicator........................................99
10.9.1 1-point adjustment with an MI70-compatible reference probe........ 99
10.9.2 1-point adjustment with a reference gas............................................. 101
11. Maintenance..................................................................................................104
11.1 Cleaning.........................................................................................................104
11.1.1 Chemical tolerance............................................................................... 104
11.2 Changing the filter........................................................................................105
12. Troubleshooting.......................................................................................... 106
12.1 Problem situations........................................................................................106
12.2 Error messages............................................................................................. 106
12.3 Analog output error state............................................................................108
13. Technical data.............................................................................................. 109
13.1 GMP252 specifications.................................................................................109
13.2 Spare parts and accessories......................................................................... 112
13.3 GMP252 probe dimensions........................................................................... 113
13.4 243261SP mounting flange dimensions...................................................... 114
13.5 DRW244827SP calibration adapter dimensions........................................115
13.6 ASM212017SP spray shield dimensions....................................................... 115
13.7 DTR250 radiation shield dimensions........................................................... 117
13.8 DTR250A pole mounting kit dimensions.................................................... 118
Appendix A: Modbus reference..................................................................119
A.1 Default communication settings..................................................................119
A.2 Function codes...............................................................................................119
A.3 Data encoding................................................................................................ 119
A.3.1 32-bit floating point or 32-bit integer format.....................................119
A.3.2 16-bit integer format............................................................................. 120
A.4 Modbus registers.......................................................................................... 120
A.4.1 Measurement data registers..................................................................121
A.4.2 Configuration registers...........................................................................121
A.4.3 Status registers...................................................................................... 123
A.5 Device identification objects....................................................................... 125
A.6 Exception responses.....................................................................................125
A.7 Modbus communication examples............................................................. 126
A.8 Filtering factor...............................................................................................128
Table of contents
5

Warranty.......................................................................................................... 129
Technical support...........................................................................................129
Recycling..........................................................................................................129
GMP252 User Guide M211897EN-E
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List of figures
Figure 1 GMP252 probe parts.......................................................................................14
Figure 2 ASM212011SP flow-through adapter...........................................................17
Figure 3 Probe cuvette with mirror and sensor chips............................................ 18
Figure 4 CO2 measurement in the measurement cuvette.....................................19
Figure 5 Example of analog output overrange behavior .....................................23
Figure 6 GMP252 dimensions.......................................................................................25
Figure 7 Probe with 243261SP mounting flange.....................................................27
Figure 8 Probe in 243257SP mounting clips............................................................ 28
Figure 9 Probe holder ASM213582 dimensions.......................................................29
Figure 10 Probe with ASM212017SP spray shield..................................................... 29
Figure 11 GMP252 in DTR250 radiation shield..........................................................30
Figure 12 GMP252 installation with DTR250A pole mounting kit.........................31
Figure 13 Fastening magnetic hanger to GMP252 probe handle.........................32
Figure 14 GMP252 probe handle dimensions............................................................ 33
Figure 15 Example of analog output overrange behavior..................................... 55
Figure 16 Connecting probe to Insight........................................................................67
Figure 17 Indigo201 with and without display.......................................................... 69
Figure 18 Connecting probes and cables to Indigo200......................................... 70
Figure 19 Analog output configuration options example in Insight.....................71
Figure 20 Analog output type (current or voltage) selection in Insight.............72
Figure 21 Insight PC software Communication menu view................................... 74
Figure 22 Relay configuration options (CO2 probe example)...............................75
Figure 23 Relay icons on display (relay A active, relay B not active)..................76
Figure 24 Filtering factor setting in Insight................................................................ 76
Figure 25 Indigo80 handheld indicator....................................................................... 78
Figure 26 Indigo80 keypad.............................................................................................79
Figure 27 Indigo80 main menu......................................................................................79
Figure 28 Connecting probes to Indigo80.................................................................80
Figure 29 MI70 basic display.......................................................................................... 85
Figure 30 MI70 indicator parts.......................................................................................87
Figure 31 CO2reading with Tcomp and Pcomp on MI70 screen..........................88
Figure 32 Probe compensation settings on MI70 screen....................................... 89
Figure 33 DRW244827SP calibration adapter with probe inserted....................93
Figure 34 Insight calibration menu main view (CO2probe).................................. 94
Figure 35 Insight Calibrate menu selection................................................................95
Figure 36 Insight Restore factory adjustment selection.........................................95
Figure 37 Insight environmental compensation configuration
example with CO2probe.............................................................................. 96
Figure 38 Opening the filter..........................................................................................105
Figure 39 GMP252 dimensions...................................................................................... 113
Figure 40 243261SP mounting flange dimensions...................................................114
Figure 41 243261SP mounting flange dimensions, cross section........................114
Figure 42 DRW244827SP calibration adapter dimensions................................... 115
List of figures
7

Figure 43 ASM212017SP spray shield dimensions....................................................115
Figure 44 GMP252 spray shield cross section........................................................... 116
Figure 45 DTR250 radiation shield dimensions (mm)............................................ 117
Figure 46 DTR250A pole mounting kit dimensions (in mm [inch])....................118
GMP252 User Guide M211897EN-E
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List of tables
Table 1 Document versions (English).......................................................................... 11
Table 2 Related manuals.................................................................................................12
Table 3 Analog output overrange clipping and error limits.................................22
Table 4 M12 male connector..........................................................................................33
Table 5 Default serial interface settings.................................................................... 35
Table 6 Basic serial commands................................................................................... 40
Table 7 Advanced serial commands............................................................................41
Table 8 ? command.........................................................................................................42
Table 9 errs command....................................................................................................42
Table 10 help command...................................................................................................42
Table 11 snum command.................................................................................................43
Table 12 system command..............................................................................................43
Table 13 time command.................................................................................................. 44
Table 14 vers command...................................................................................................44
Table 15 addr command..................................................................................................44
Table 16 close command................................................................................................. 45
Table 17 form command..................................................................................................45
Table 18 Output parameters for form command......................................................46
Table 19 Modifiers for form command........................................................................ 46
Table 20 intv command....................................................................................................47
Table 21 open command................................................................................................. 48
Table 22 r command......................................................................................................... 48
Table 23 s command......................................................................................................... 48
Table 24 sdelay command...............................................................................................49
Table 25 send command..................................................................................................49
Table 26 seri command.................................................................................................... 50
Table 27 smode command..............................................................................................50
Table 28 amode command...............................................................................................51
Table 29 aover command.................................................................................................52
Table 30 asel command....................................................................................................55
Table 31 adate command................................................................................................ 56
Table 32 atext command..................................................................................................57
Table 33 cdate command.................................................................................................57
Table 34 ctext command..................................................................................................57
Table 35 cco2 command.................................................................................................. 58
Table 36 env command....................................................................................................60
Table 37 o2cmode command......................................................................................... 62
Table 38 pcmode command........................................................................................... 63
Table 39 rhcmode command..........................................................................................63
Table 40 tcmode command............................................................................................ 64
Table 41 frestore command............................................................................................ 65
Table 42 pass command...................................................................................................65
Table 43 reset command..................................................................................................65
Table 44 Default Modbus serial communication settings.......................................66
Table 45 Indigo202 Modbus registers.......................................................................... 73
List of tables
9

Table 46 Default Modbus serial communication settings....................................... 74
Table 47 GMP252 measurement performance.........................................................109
Table 48 GMP252 operating environment..................................................................110
Table 49 GMP252 inputs and outputs...........................................................................111
Table 50 GMP252 mechanical specifications.............................................................. 111
Table 51 GMP252 compliance........................................................................................ 112
Table 52 GMP252 spare parts and accessories..........................................................112
Table 53 Default Modbus serial communication settings...................................... 119
Table 54 Modbus function codes.................................................................................. 119
Table 55 Interpretation of 16-bit signed integer values.........................................120
Table 56 Modbus measurement data registers (read-only).................................. 121
Table 57 Modbus configuration data registers (writable)......................................121
Table 58 Modbus status registers (read-only)..........................................................123
Table 59 Error codes in register 0803hex................................................................... 124
Table 60 Device identification objects........................................................................125
Table 61 Modbus exception responses.......................................................................125
GMP252 User Guide M211897EN-E
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1. About this document
1.1 Version information
Table 1 Document versions (English)
Document code Date Description
M211897EN-E July 2023 This manual.
• Added information on using the GMP252 probe with the Indigo80
handheld indicator.
• References to Indigo200 transmitters' wireless configuration
interface replaced with information about the new Indigo200
transmitters that have a USB-C interface. For instructions on
configuring GMP252 probes with the earlier wireless configuration
interface, see GMP252 User Guide revision M211897EN-E, available
at docs.vaisala.com.
• Added sections ASM213582 probe holder (page 28) and GMP252
probe handle accessories (page 31).
• Updated sections:
•Recommended installation (page 25)
•DTR250 radiation shield (page 30)
•DTR250A pole mounting kit (page 30)
•Environmental compensation commands (page 60)
•Error messages (page 106)
•GMP252 specifications (page 109)
•Spare parts and accessories (page 112)
•Status registers (page 123).
• Removed section Patent notice.
M211897EN-D March
2018
Previous version.
• Added information about using the probe with Vaisala Insight PC
software.
• PuTTy terminal settings instructions updated.
• Calibration uncertainty specification updated.
• DTR250A radiation shield pole mounting kit added.
• Added recommendation to disable MI70 indicator's automatic
power o feature when used with GMP252.
• Updated instructions on using MI70 to configure environmental
compensations.
• Default device address in serial line communication corrected
(240).
• Corrected the unit information of sdelay command.
• Added a note about maximum voltage output to analog error
state output configuration.
• Information on Modbus register numbers updated.
Chapter 1 – About this document
11

Document code Date Description
M211897EN-C June
2017
• Added information about using the probe with Vaisala Indigo
transmitters.
• Added flow-through adapter accessory ASM212011SP, spray shield
accessory ASM212017SP, and radiation shield accessory DTR250.
• Modbus status register information updated.
• Calibration adapter order code corrected.
1.2 Related manuals
For the latest versions of these documents, see docs.vaisala.com.
Table 2 Related manuals
Document code Description
M211799EN Vaisala GMP251 Carbon Dioxide Probe User Guide
M211798EN Vaisala GMP251 Carbon Dioxide Probe Quick Guide
M211893EN Vaisala GMP252 Carbon Dioxide Probe Quick Guide
M212842EN Vaisala Indigo201 Analog Output Transmitter User Guide
M212815EN Vaisala Indigo201 Analog Output Transmitter Quick Guide
M212843EN Vaisala Indigo202 Digital Transmitter User Guide
M212816EN Vaisala Indigo202 Digital Transmitter Quick Guide
M212887EN Using GMP252 Probe with Probe Handle Accessory
GMP252HANDLESP or ASM214342SP Quick Guide
M211986EN Vaisala DTR250 Radiation Shield Quick Guide
M212041EN Vaisala DTR250A Radiation Shield Installation Kit Quick Guide
1.3 Documentation conventions
alerts you to a serious hazard. If you do not read and follow
instructions carefully at this point, there is a risk of injury or even death.
WARNING!
GMP252 User Guide M211897EN-E
12

warns you of a potential hazard. If you do not read and follow
instructions carefully at this point, the product could be damaged or important
data could be lost.
CAUTION!
Note highlights important information on using the product.
Tip gives information for using the product more eciently.
1.4 Trademarks
Vaisalaâand CARBOCAPâare registered trademarks of Vaisala Oyj.
Windowsâis either a registered trademark or trademark of Microsoft Corporation in the
United States and other countries.
All other product or company names that may be mentioned in this publication are trade
names, trademarks, or registered trademarks of their respective owners.
Chapter 1 – About this document
13

2. Product overview
2.1 Introduction to GMP252
GMP252 is designed for CO2measurement in demanding applications that require reliable and
accurate performance. The measurement range is 0 ... 10 000 ppmCO2(measurements can be
carried out in the 10 000 ... 30 000 ppmCO2range with reduced accuracy).
The probe is based on Vaisala’s patented 2nd generation CARBOCAPâtechnology and
equipped with Vaisala's Microglow infrared light source. The probe is easy to install with a
plug-in/plug-out M12 connection.
GMP252 is able to compensate for temperature, pressure and background gas. For
temperature compensation purposes, the probe includes an internal temperature sensor that
allows measurement compensation according to ambient temperature. As dust and most
chemicals do not aect the measurement, and the eect of temperature, pressure and
background gas can be compensated for, GMP252 can provide accurate and stable
measurements in a wide range of applications.
12 3 4 5
Figure 1 GMP252 probe parts
15-pin M12 connector. For pinout, see Wiring (page 33).
2Probe name and orientation mark for Vaisala transmitter installations (front) and laser-
printed type label (back).
3Probe body. Contains the main component board.
4Measurement cuvette with optics and CARBOCAPâCO2sensor.
5Filter (sintered, PTFE: see also Filter options (page 17)).
GMP252 User Guide M211897EN-E
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Do not attempt to open the probe body. There are no user
serviceable parts inside the probe body.
CAUTION!
2.2 Basic features and options
• CO2measurement range 0 … 10 000 ppmCO2.
• Measurement up to 30 000 ppmCO2with reduced accuracy.
• Operating temperature range -40 … +60 °C (-40 … +140 °F).
• Vaisala CARBOCAPâCO2sensor with excellent long-term stability.
• Measurement compensated for eects of temperature, pressure, and background gas. The
temperature compensation can be based on an integrated temperature sensor or use a
set temperature. Pressure and background gas parameters can be set to the probe.
• Heating to avoid condensation on optical elements.
• Digital output with RS-485:
• Modbus RTU
• Vaisala Industrial Protocol
• Analog output:
• Current output (0 … 20 mA or 4 … 20 mA)
• Voltage output (0 … 5 V or 0 … 10 V)
• Can be used as a standalone probe or with Vaisala Indigo transmitters
• Compatible with Indigo80 handheld indicator and MI70 handheld indicator
• Can be connected to Vaisala Insight PC software for configuration, diagnostics, and
temporary online monitoring
• Easy plug-in, plug-out.
More information
‣Operating principle of CO2 measurement (page 18)
‣Environmental compensation (page 19)
‣Vaisala Industrial Protocol overview (page 35)
‣Modbus (page 66)
‣Vaisala Insight PC software (page 67)
‣Introduction to Indigo200 transmitters (page 69)
‣Indigo80 handheld indicator (page 78)
‣Overview of MI70 support (page 85)
‣GMP252 specifications (page 109)
2.2.1 Connectivity to Vaisala Insight software
The probe can be connected to Vaisala Insight software using a Vaisala USB cable (item code
242659) or Vaisala Indigo USB adapter (item code USB2). With the Insight software, you can:
• Calibrate and adjust the measurement.
• See device information and status.
• See real-time measurement.
Chapter 2 – Product overview
15

•Configure serial communication settings, purge settings, filtering factor, and analog
output parameters and scaling.
More information
‣Connecting to Insight software (page 67)
2.2.2 Additional features with Indigo transmitters
GMP252 probes manufactured from 2017 onwards are compatible with Vaisala Indigo200
transmitters.
Connecting the probe to an Indigo transmitter provides a wide range of additional options for
outputs, measurement viewing, status monitoring, and configuration interface access.
Examples of additional features available with Indigo520 transmitters:
• Touchscreen display for real-time data viewing and configuration
• Support for 2 probes simultaneously
• 4 configurable analog outputs
• 2 configurable relays
• 2-wire current loop analog input
• Barometer module for barometric pressure measurement (optional module)
• Ethernet connection with web interface for remote access
• Modbus TCP/IP protocol
• Service port for connecting to Indigo80 handheld indicator
Examples of additional features available with Indigo200 series transmitters:
• 3.5” TFT LCD color display or non-display model with LED indicator
• Digital output or 3 analog outputs (depending on the transmitter model)
• 2 configurable relays
• USB-C connection to Vaisala Insight PC software for easy configuration access
Available features vary depending on the Indigo transmitter model. For more
information on Indigo transmitters, see www.vaisala.com/indigo.
GMP252 User Guide M211897EN-E
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2.2.3 Filter options
Figure 2 ASM212011SP flow-through adapter
The GMP252 flow-through adapter (item code ASM212011SP) has two gas ports for controlled
gas feed (port outer diameter 4.6 mm, port hole inner diameter 2 mm, suitable for tubing with
4 mm inner diameter). For information on ordering accessories and spare parts, see Spare
parts and accessories (page 112).
Chapter 2 – Product overview
17

2.3 Operating principle of CO2measurement
1
2
3
The Vaisala CARBOCAPâsensor used in
the probe is a silicon-based, nondispersive
infrared (NDIR) sensor for measurement of
gaseous carbon dioxide in air-like gases.
Figure 3 Probe cuvette with mirror and
sensor chips
1Mirror
2Cuvette
3Sensor chips under TO5 package
The sensitivity to carbon dioxide is based on absorption of infrared light at a characteristic
wavelength. During measurement, infrared light is routed through the cuvette that contains
the gas to be measured. A mirror reflects the light from the cuvette to a thermopile detector
that measures the light intensity at a wavelength determined by a Fabry–Pérot interferometer
(FPI) and a band pass filter.
The carbon dioxide measurement consists of two steps: first, the FPI is electrically tuned so
that its pass band coincides with the characteristic absorption wavelength of carbon dioxide
and the signal is recorded. Second, the pass band is shifted to a wavelength where no
absorption occurs in order to get a reference signal. The ratio of these two signals, one at the
absorption wavelength and the other at the reference wavelength, gives the fraction of light
absorption from which the carbon dioxide concentration is calculated. Measuring the reference
signal compensates the possible eects of sensor aging and signal attenuation due to dirt on
optical surfaces, making the sensor very stable over time.
TO5 packages with hermetic windows are used to protect the sensor chips from moisture and
contamination. A heater chip is utilized to prevent condensation in normal operation.
GMP252 User Guide M211897EN-E
18

1
2
3
4
6
7
5
Figure 4 CO2 measurement in the
measurement cuvette
1Gold-plated mirror
2Light absorbed by CO2in the
measured gas
3Hermetic window
4Fabry-Pérot interferometer
5Light source (Microglow)
6Hermetic window
7Thermopile detector
2.4 Environmental compensation
When necessary, various environmental compensations can be applied to improve the CO2
measurement accuracy of the probe.
The probe can compensate for the eects of the following parameters:
• Temperature
• Pressure
• Background gas oxygen (O2) content
• Background gas relative humidity (%RH)
To apply an accurate relative humidity compensation, make sure that also the
temperature compensation and pressure compensation configurations match the
measurement environment.
The probe has an on-board temperature sensor that can be used to compensate for
temperature. Additionally, if the probe is integrated in a system that measures one or more of
the compensation parameters (T, P, RH, O2), they can be updated to the probe continuously.
Chapter 2 – Product overview
19

Compensation parameters are configured on the order form when ordering the probe, and can
later be updated using Vaisala Industrial Protocol or Modbus protocol.
You can also turn o any of the compensations. In that case, the probe uses the default
compensation value that is mathematically neutral for the probe’s internal compensation
model.
You can configure the environmental compensation settings with any of the following options:
• Vaisala Industrial Protocol serial commands
• Vaisala Insight software
• Modbus configuration registers
• MI70 handheld indicator
• Indigo80 handheld indicator
The environmental compensation configuration options available in the MI70
handheld indicator are not compatible with the probe. Using MI70 to configure
the environmental compensation settings of the probe can decrease
measurement accuracy.
More information
‣Environmental compensation commands (page 60)
‣Vaisala Insight PC software (page 67)
‣Configuring environment settings with Indigo80 handheld indicator (page 83)
‣Changing environmental compensation settings with MI70 indicator (page 88)
‣Eect of environmental compensations (page 91)
‣Configuration registers (page 121)
2.4.1 Temperature compensation
The probe can measure the approximate temperature of the CARBOCAPâsensor for
compensation, or use a fixed setpoint. Unless a dedicated temperature measurement is
available and can be regularly updated to the probe, it is strongly recommended to use the
probe's internal temperature compensation to ensure real-time accurate measurements. If the
measurement is made in a constant temperature, the constant temperature can be set as the
compensation value (fixed setpoint option).
If temperature compensation is turned o, the probe uses the default value of +25 °C (+77 °F).
When the probe is installed through a flange and part of the probe and the cable
is left outside the measuring environment, it is possible that temperature
conduction from the probe body and cable outside the measurement
environment aects the temperature compensation and decreases measurement
accuracy.
GMP252 User Guide M211897EN-E
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