Vaisala DRYCAP DMT143 User manual

M211435EN-J
User Guide
Vaisala DRYCAPâDew Point Transmitter
DMT143

PUBLISHED BY
Vaisala Oyj
Vanha Nurmijärventie 21, FI-01670 Vantaa, Finland
P.O. Box 26, FI-00421 Helsinki, Finland
[phone]
Visit our Internet pages at www.vaisala.com.
© Vaisala Oyj 2019
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................................................................................... 7
1.1 Version Information.......................................................................................... 7
1.2 Related Manuals................................................................................................ 7
1.3 Documentation Conventions...........................................................................7
1.4 Trademarks........................................................................................................ 8
2. Product Overview........................................................................................... 9
2.1 Introduction to DMT143 ...................................................................................9
2.2 Basic Features and Options........................................................................... 10
2.2.1 Connectivity to Vaisala Insight Software................................................11
2.3 DMT143 and DMT143L Transmitter Parts...................................................... 12
2.3.1 DMT143 with G1/2” ISO228/1 Thread..................................................... 12
2.3.2 DMT143 with NPT Thread........................................................................ 13
2.3.3 DMT143L with G1/2” ISO228/1 Thread...................................................14
2.4 Loop-powered Display................................................................................... 14
2.5 Connection Cables...........................................................................................15
2.6 Sampling Accessories..................................................................................... 16
2.7 Safety................................................................................................................16
2.7.1 ESD Protection......................................................................................... 16
2.8 Regulatory Compliances.................................................................................17
3. Functional Description................................................................................ 18
3.1 DRYCAPâTechnology....................................................................................18
3.1.1 Autocalibration.........................................................................................18
3.1.2 Sensor Purge.............................................................................................18
3.1.3 Sensor Warming in High Humidities and Freezing Conditions.......... 19
3.2 DMT143 Startup Sequence............................................................................. 19
3.3 Alarm LED....................................................................................................... 20
Table of Contents
1

4. Installation....................................................................................................... 22
4.1 Configuring Transmitter Before Installation................................................22
4.2 Selecting the Location................................................................................... 22
4.3 Installing the Transmitter...............................................................................23
4.4 Wiring.............................................................................................................. 24
4.4.1 Power Supply Requirements................................................................. 25
4.5 Sampling from a Process............................................................................... 27
4.6 Sampling Accessories.................................................................................... 28
4.6.1 DMT242SC Sampling Cell.......................................................................28
4.6.2 DMT242SC2 Sampling Cell with Swagelok Connectors..................... 28
4.6.3 DSC74 Sampling Cell with Quick Connector and Leak Screw........... 29
4.6.4 DSC74B Two-Pressure Sampling Cell...................................................30
5. Operation.........................................................................................................36
5.1 Transmitter Start-up.......................................................................................36
5.2 Vaisala Insight Software................................................................................ 36
5.2.1 Connecting to Insight Software.............................................................37
5.3 Operation with DM70 Handheld Dew Point Meter.....................................38
6. Modbus Communication........................................................................... 40
7. Serial Communication................................................................................. 41
7.1 Connecting to the Serial Interface.................................................................41
7.2 Terminal Application Settings........................................................................41
7.3 Accessing Serial Interface in Devices with Modbus Output......................42
7.4 List of Serial Commands................................................................................43
7.5 Device Information.........................................................................................44
7.5.1 Show Device Information.......................................................................44
7.5.2 Show Analog Output Mode................................................................... 45
7.5.3 Show Firmware Version..........................................................................45
7.5.4 Show Firmware Information.................................................................. 45
7.5.5 Show Currently Active Errors................................................................ 46
7.5.6 Show Serial Number...............................................................................46
7.5.7 Show Command List...............................................................................46
7.6 Configuring Analog Output...........................................................................47
7.6.1 Set Analog Output Parameters and Scaling........................................ 47
7.6.2 Set Analog Output Error Notification...................................................48
7.6.3 Extend Analog Output Range............................................................... 49
7.6.4 Test Analog Output.................................................................................49
7.6.5 Enable or Disable Analog Output......................................................... 50
DMT143 User Guide M211435EN-J
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7.7 Serial Line Output Commands..................................................................... 50
7.7.1 Start Measurement Output....................................................................50
7.7.2 Stop Measurement Output.................................................................... 50
7.7.3 Set Output Interval................................................................................. 50
7.7.4 Output a Reading Once...........................................................................51
7.8 Configuring Measurement Parameters......................................................... 51
7.8.1 Set Measurement Output Format.......................................................... 51
7.8.2 Set Measurement Filtering..................................................................... 53
7.8.3 Set Pressure Compensation Value........................................................ 54
7.8.4 Select Unit................................................................................................ 55
7.8.5 View User Adjustment Parameters....................................................... 55
7.8.6 Set User Adjustment Parameters..........................................................56
7.9 Configuring Serial Line Operation................................................................ 57
7.9.1 Set Serial Line Operating Mode............................................................. 57
7.9.2 Set Serial Line Settings........................................................................... 57
7.9.3 Set Transmitter Address.........................................................................58
7.9.4 Set Serial Line Response Time...............................................................59
7.10 Other Commands........................................................................................... 59
7.10.1 Opening the Transmitter in POLL Mode...............................................59
7.10.2 Closing the Connection to a Transmitter in POLL Mode.................... 59
7.10.3 Configure the Alarm LED.......................................................................60
7.10.4 Reset Transmitter..................................................................................... 61
7.10.5 Restore Factory Settings.........................................................................61
8. Maintenance....................................................................................................62
8.1 Periodic Maintenance.....................................................................................62
8.1.1 Cleaning....................................................................................................62
8.1.2 Calibration................................................................................................62
8.1.3 Changing the Filter................................................................................. 62
8.1.4 Field Check Using DM70 Handheld Dew Point Meter.........................63
8.2 Repair Maintenance........................................................................................65
9. Troubleshooting............................................................................................66
9.1 Solving Typical Problems.............................................................................. 66
9.2 Error Messages in Insight Software..............................................................67
9.3 Error Codes in MI70 Handheld Meter...........................................................67
9.4 Unknown Serial Settings............................................................................... 68
10. Technical Data................................................................................................69
10.1 DMT143 Specifications...................................................................................69
10.2 Dimensions...................................................................................................... 72
10.3 Spare Parts and Accessories......................................................................... 73
Table of Contents
3

Appendix A: Modbus Reference................................................................. 75
A.1 Default Communication Settings..................................................................75
A.2 Function Codes............................................................................................... 75
A.3 Data Encoding.................................................................................................75
A.3.1 32-Bit Floating Point Format................................................................. 75
A.3.2 16-Bit Integer Format..............................................................................76
A.4 Modbus Registers........................................................................................... 76
A.4.1 Measurement Data Registers.................................................................77
A.4.2 Status Registers.......................................................................................77
A.4.3 Configuration Registers..........................................................................78
A.4.4 Test Value Registers................................................................................80
A.4.5 Device Identification Objects................................................................ 80
A.5 Modbus Communication Examples...............................................................81
Warranty............................................................................................................ 85
Technical Support............................................................................................85
Recycling........................................................................................................... 85
DMT143 User Guide M211435EN-J
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List of Figures
Figure 1 DMT143 Parts – Model with ISO Thread.....................................................12
Figure 2 DMT143 Parts – Model with NPT Thread....................................................13
Figure 3 DMT143L Parts .................................................................................................14
Figure 4 Nokeval 301 Loop-powered Display........................................................... 15
Figure 5 DMT143 Startup Sequence...........................................................................20
Figure 6 DMT143 Digital and Analog Connectors...................................................25
Figure 7 Wiring the Digital Connector.......................................................................25
Figure 8 Wiring the Analog Connector......................................................................25
Figure 9 Example of Current Consumption During Purge................................... 26
Figure 10 Example of Current Consumption During Autocalibration................. 27
Figure 11 Sampling Cells DMT242SC2 (left) and DMT242SC (right).................. 29
Figure 12 DSC74 Sampling Cell with Accessories.................................................... 30
Figure 13 DSC74B............................................................................................................... 31
Figure 14 Removing the Leak Screw............................................................................ 32
Figure 15 Default Assembly of DSC74C.......................................................................33
Figure 16 Alternative Assembly of DSC74C (for Tight Spaces)............................34
Figure 17 DM240FA with DMT143................................................................................. 35
Figure 18 Settings Menu.................................................................................................. 38
Figure 19 Measurement Settings Menu....................................................................... 38
Figure 20 DMT143 Dimensions – Model with ISO Thread........................................72
Figure 21 DMT143 Dimensions – Model with NPT Thread...................................... 72
Figure 22 DMT143L Dimensions..................................................................................... 73
List of Figures
5

List of Tables
Table 1 Document Versions (English)...........................................................................7
Table 2 Related Manuals...................................................................................................7
Table 3 Output Parameters of the DMT143.................................................................9
Table 4 Alarm LED States..............................................................................................20
Table 5 Connector Pinouts............................................................................................ 24
Table 6 Default Modbus Serial Communication Settings.....................................40
Table 7 Default Serial Interface Settings....................................................................41
Table 8 List of Serial Commands................................................................................. 43
Table 9 Error Messages on ERRS Command............................................................46
Table 10 FORM Command Parameters ....................................................................... 52
Table 11 FORM Command Modifiers............................................................................ 52
Table 12 Pressure Conversion Coecients................................................................. 55
Table 13 Selection of Output Modes.............................................................................57
Table 14 Troubleshooting Table.....................................................................................66
Table 15 Error Messages in Insight Software..............................................................67
Table 16 Error Codes in MI70..........................................................................................67
Table 17 Measurement Performance............................................................................69
Table 18 Operating Environment...................................................................................70
Table 19 Inputs and Outputs...........................................................................................70
Table 20 Mechanical Specifications................................................................................71
Table 21 Compliance.......................................................................................................... 71
Table 22 Spare Parts and Accessories.......................................................................... 73
Table 23 Default Modbus Serial Communication Settings......................................75
Table 24 Modbus Function Codes..................................................................................75
Table 25 16-bit Signed Integer Format Details...........................................................76
Table 26 Modbus Measurement Data Registers (Read-Only)................................77
Table 27 Modbus Status Registers (Read-Only)........................................................77
Table 28 Error Codes on Modbus Interface.................................................................78
Table 29 Modbus Configuration Data Registers (Writable)................................... 78
Table 30 Modbus Test Registers (Read-Only)........................................................... 80
Table 31 Device Identification Objects........................................................................ 80
DMT143 User Guide M211435EN-J
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1. About This Document
1.1 Version Information
This manual provides information for installing, operating, and maintaining Vaisala DRYCAPâ
Dewpoint Transmitter DMT143.
Table 1 Document Versions (English)
Document Code Date Description
M211435EN-J February 2019 This manual. Modbus protocol added. Added information about
Vaisala Insight PC software. Removed the TIME command.
Added a cautionary note about changing stainless steel filter.
Updated section Troubleshooting. Updated section DMT143
Specifications.
M211435EN-H June 2017 Previous version. DRYCAPâ180S sensor option for DMT143L
added. Analog output accuracy specification added. Accuracy
specification updated for DMT143L variant with DRYCAPâ
180M sensor. Filter spare part information updated.
M211435EN-G January 2017 New probe model DMT143L (DMT242 replacement with
DRYCAPâ180M sensor) added. SF6 gas selections removed.
1.2 Related Manuals
Table 2 Related Manuals
Document Code Name
M010091EN Vaisala DRYCAP
â Handheld Dew Point Meter DM70 User's Guide
M211434EN Vaisala DRYCAP â Dew Point Transmitter DMT143 Quick Guide
M211634EN Nokeval 301/302 Display Wiring Diagram
1.3 Documentation Conventions
Warning 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!
Chapter 1 – About This Document
7

Caution 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.
Lists tools needed to perform the task.
Indicates that you need to take some notes during the task.
1.4 Trademarks
Vaisalaâand DRYCAPâare 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.
DMT143 User Guide M211435EN-J
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2. Product Overview
2.1 Introduction to DMT143
Vaisala DRYCAPâDew Point Transmitter DMT143 is a small and lightweight dew point
transmitter suitable for a wide range of OEM applications. DMT143 is easy to install and the
mechanics have been designed for harsh environments requiring protection against dust, dirt
and splashed water.
There are 2 variants of the DMT143 transmitter, DMT143 and DMT143L. DMT143 and DMT143L
oer dierent sensor, installation and output options to meet the requirements of varying dew
point measurement applications.
• DMT143 with DRYCAPâ180D sensor
• either G1/2” ISO228/1 or NPT1/2” mechanical connection
• measurement range -70 ... +60 °C (-94 ... +140 °F)
• operating pressure up to 50 bara (725 psia)
•voltage (V) or current (mA) analog output 1)
• RS-485 digital output with Modbus RTU support
• DMT143L with DRYCAPâ180M sensor
• G1/2” ISO228/1 mechanical connection
• measurement range -70 ... + 60 °C° (-94 ... +140 °F)
• operating pressure 0 ... 20 bara(0 ... 290 psia)
•current (mA) analog output 1)
• RS-485 digital output with Modbus RTU support
• DMT143L with DRYCAPâ180S sensor
• G1/2” ISO228/1 mechanical connection
• measurement range -50 ... + 60 °C° (-58 ... +140 °F)
• operating pressure 0 ... 20 bara(0 ... 290 psia)
• current (mA) analog output 1)
• RS-485 digital output with Modbus RTU support
The accuracies of the dierent sensors used in DMT143 and DMT143L have been optimized for
dierent parts of the sensors’ measurement ranges.
DMT143 transmitters use the Vaisala DRYCAPâpolymer sensor for dew point measurement.
DRYCAPâtechnology has low maintenance needs due to its excellent long term stability and
durability against condensation. The calibration interval of DMT143 transmitters is 2 years.
Table 3 Output Parameters of the DMT143
Parameter Abbreviation Metric Unit Non-Metric Unit
Dew point/frost point temperature Td/f °C °F
Dew point/frost point temperature,
converted to atmospheric pressure
Td/fatm °C °F
1) The analog output is not available in devices ordered with digital output only.
Chapter 2 – Product Overview
9

Parameter Abbreviation Metric Unit Non-Metric Unit
ppm moisture, by volume H20 ppm ppm
When dew point is below 0 °C, the transmitter outputs frost point for Td.
Dew point temperature in atmospheric pressure (Td/f atm) is a calculated parameter that
presents the dew point the gas would have at atmospheric pressure. For this calculation to
provide accurate results, it is important to have the correct pressure setting stored in the
transmitter. This setting is specified on the order form, and it can be changed using the RS-485
line or DM70 handheld dew point meter.
More Information
‣DMT143 and DMT143L Transmitter Parts (page 12)
‣DMT143 Specifications (page 69)
2.2 Basic Features and Options
• Maximum dew point measurement range of -70 ... + 60 °C (-94 ... +140 °F)
• Dew point measurement accuracy up to ±2 °C (±5.4 °F) Td in air or N2
• Operating pressure range:
• DMT143: 0 ... 50 bara(725 psia)
• DMT143L: 0 ... 20 bara(0 ... 290 psia)
•Configurable for optimum dew point measurement accuracy: Pressure compensation
(fixed pressure setting or live pressure input through RS-485)
• Analog output: one output channel, selectable from:
• 0 ... 1 V (DMT143 only)
• 0 ... 5 V (DMT143 only)
• 1 ... 5 V (DMT143 only)
• 4 ... 20 mA (DMT143 and DMT143L)
• None (DMT143 and DMT143L, digital output only)
• Digital output: RS-485 (non-isolated). The following protocols are supported:
• Modbus RTU
• Vaisala Industrial Protocol
• LED for dew point level alarm and transmitter diagnostics
• DRYCAPâpolymer sensor:
• Autocalibration ensures accuracy in changing measurement conditions
• Sensor warming keeps the sensor dry in high humidity
• Sensor purge ensures long term stability
• NIST traceable (certificate included)
• Field check suitability with DM70 handheld dew point meter
DMT143 User Guide M211435EN-J
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• Optional accessories:
• Stainless steel grid filter for vacuum applications
• Sampling cells with various installation options
• Loop-powered external display
• Connection cable for DM70 handheld dew point meter
• Plastic shipping case to avoid contamination during shipping
More Information
‣Operation with DM70 Handheld Dew Point Meter (page 38)
‣Modbus Communication (page 40)
‣Connecting to the Serial Interface (page 41)
‣DMT143 Specifications (page 69)
2.2.1 Connectivity to Vaisala Insight Software
The transmitter can be connected to Vaisala Insight software using a Vaisala USB cable (order
code 219690). With the Insight software, you can:
• See device information and status.
• See real-time measurement.
•Configure serial communication settings, filtering factor, alarm LED, and analog output
parameters and scaling.
More Information
‣Connecting to Insight Software (page 37)
Chapter 2 – Product Overview
11

2.3 DMT143 and DMT143L Transmitter Parts
2.3.1 DMT143 with G1/2” ISO228/1 Thread
1
2
3
4
5
6
7
8
Figure 1 DMT143 Parts – Model with ISO Thread
1Transmitter body. Type label is applied here.
2Digital output: non-isolated RS-485
3Alarm LED
4Analog output
5Sealing ring. Must be used with the G1/2” ISO228/1 connection thread.
624 mm nut
7Connection thread: G1/2" ISO228/1
8DRYCAPâ180D sensor protected with sintered filter
When the transmitter is delivered, the filter is protected by a yellow transport
protection cap that keeps the sensor dry. The transport protection cap should be
left on the transmitter during storage. Remove the transport protection cap
before installing the transmitter.
DMT143 User Guide M211435EN-J
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2.3.2 DMT143 with NPT Thread
1
2
3
4
5
6
7
Figure 2 DMT143 Parts – Model with NPT Thread
1Transmitter body. Type label is applied here.
2Digital output: non-isolated RS-485
3Alarm LED
4Analog output
530 mm nut
6Connection thread: NPT 1/2"
7DRYCAPâ180D sensor protected with sintered filter
Chapter 2 – Product Overview
13

2.3.3 DMT143L with G1/2” ISO228/1 Thread
1
2
3
4
5
6
7
8
Figure 3 DMT143L Parts
1Transmitter body. Type label is applied here.
2Digital output: non-isolated RS-485
3Alarm LED
4Analog output
5Sealing ring. Must be used with the G1/2” ISO228/1 connection thread.
624 mm nut
7Connection thread: G1/2" ISO228/1
8DRYCAPâ180M or DRYCAPâ180S sensor protected with sintered filter
2.4 Loop-powered Display
DMT143 can be connected to a loop-powered external LED display. The display provides a
reading of the output parameter. The display is powered by the 4 ... 20 mA current signal, so
there is no need for an external power supply.
DMT143 User Guide M211435EN-J
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Two models are available:
• Nokeval 301
• Nokeval 302 (with alarm relays)
The display is delivered at its default settings. Configure the display functions and scaling
according to the documentation delivered with the display. For a wiring example, see Nokeval
301/302 Display Wiring Diagram (document code M211634EN).
Figure 4 Nokeval 301 Loop-powered Display
The loop resistance of the display must be included in the loop resistance
calculation for the complete current loop. For the loop resistance of the display,
refer to the manufacturer’s documentation.
More Information
‣Spare Parts and Accessories (page 73)
2.5 Connection Cables
Vaisala supplies shielded cables with M8 female straight threaded connector. Standard cables
are available in four lengths:
• 0.3 m (1.0 ft)
• 3 m (9.8 ft)
• 5 m (16.4 ft)
• 10 m (32.8 ft)
Chapter 2 – Product Overview
15

Heavy duty cables are available in two lengths:
• 1.5 m (4.9 ft)
• 3 m (9.8 ft)
Also available are the following cables for service and field check use:
• USB service cable
• MI70 connection cable
More Information
‣Spare Parts and Accessories (page 73)
2.6 Sampling Accessories
DMT143 is compatible with various sampling accessories.
More Information
‣Sampling Accessories (page 28)
‣Spare Parts and Accessories (page 73)
2.7 Safety
This product has been tested for safety. Note the following precautions:
Do not modify the unit. Improper modification can damage the
product or lead to malfunction.
CAUTION!
The transmitter body does not have user serviceable parts inside,
and is not designed to be opened. Opening the transmitter will void the
warranty.
CAUTION!
2.7.1 ESD Protection
Electrostatic Discharge (ESD) can damage electronic circuits. Vaisala products are adequately
protected against ESD for their intended use. However, it is possible to damage the product by
delivering electrostatic discharges when touching, removing, or inserting any objects in the
equipment housing.
To avoid delivering high static voltages to the product:
• Handle ESD-sensitive components on a properly grounded and protected ESD workbench
or by grounding yourself to the equipment chassis with a wrist strap and a resistive
connection cord.
DMT143 User Guide M211435EN-J
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• If you are unable to take either precaution, touch a conductive part of the equipment
chassis with your other hand before touching ESD-sensitive components.
• Hold component boards by the edges and avoid touching component contacts.
2.8 Regulatory Compliances
This product is in conformity with the provisions of the following EU directives:
• EMC-Directive
• RoHS-Directive
Conformity is shown by compliance with the following standards:
• EN 61326-1: Electrical equipment for measurement, control, and laboratory use – EMC
requirements – for use in industrial locations.
• EN 550022: Information technology equipment – Radio disturbance characteristics –
Limits and methods of measurement
Chapter 2 – Product Overview
17

3. Functional Description
3.1 DRYCAP Technology
Vaisala DRYCAPâdew point measurement technology ensures accurate measurement with
excellent long term stability. This results in very low maintenance requirements for the
transmitter. The lasting performance is achieved with microprocessor technology and software
that automatically performs self-diagnostic functions in addition to the normal dew point
measurement. The self-diagnostic procedures that are conducted are called autocalibration,
sensor purge, and sensor warming.
DMT143 and DMT143L use dierent versions of the Vaisala DRYCAPâsensor:
• DMT143 uses the DRYCAPâ180D sensor designed for applications such as plastic dryers
and small industrial compressed air dryer (sensor filter length 22.5 mm, probe length 91.6
mm).
• DMT143L can be ordered with two versions of the DRYCAPâ180 sensor: either the 180M
sensor designed for standard dry gas and desiccant dryer applications, or the 180S sensor
designed for more humid applications such as refrigeration dryers. The sensor filter length
of both DMT143L variants is 51 mm, probe length 120 mm.
3.1.1 Autocalibration
The autocalibration feature of the DMT143 transmitter is an automatic procedure which greatly
reduces the possible drift in the dry end of the dew point measurement. It is performed at 1-
hour intervals, and when the power is switched on. When measuring very dry conditions, the
transmitter performs the autocalibration at shorter intervals. A significant change in dew point
or temperature may also trigger the autocalibration.
During autocalibration the sensor is warmed for a short period (< 1 min) and the sensor
capacitance values are evaluated at the elevated temperature. The possible dry end drift is
then corrected to correspond to the calibrated values. During the autocalibration the
transmitter outputs the Tdvalue prior to the procedure.
Autocalibration is carried out only if several criteria for the measurement environment are
fulfilled. This ensures the reliability of the adjustments, and maintains the excellent long term
stability that the patented technology oers. These criteria include for example a stable
enough moisture level in the measured atmosphere. If the conditions are not fulfilled, the
autocalibration function is postponed until satisfactory conditions are reached.
3.1.2 Sensor Purge
Sensor purge is also an automatic procedure that minimizes the drift at the wet end readings
of the dew point measurement. Sensor purge is performed once a day or when the power is
switched on. The sensor is heated for several minutes which will then evaporate all excess
molecules out of the sensor polymer. This, together with autocalibration, results in a very small
drift of the sensor due to the very linear behaviour of the polymer technology. During the
sensor purge the transmitter outputs the Tdvalue prior to the procedure.
DMT143 User Guide M211435EN-J
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