Vaisala HMP Series User manual

M212022EN-F
User Guide
Vaisala Indigo compatible
humidity and temperature probes
HMP Series with MMP8 and TMP1

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 2021
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.....................................................................................9
1.1 Version information.......................................................................................... 9
1.2 Related manuals..............................................................................................10
1.3 Documentation conventions..........................................................................10
1.4 Trademarks........................................................................................................ 11
2. Product overview...........................................................................................12
2.1 Probe structure................................................................................................ 12
2.2 Basic features and options............................................................................. 12
2.3 Output parameters..........................................................................................13
2.4 Additional features with Indigo transmitters...............................................14
2.5 Safety................................................................................................................ 15
2.6 ESD protection.................................................................................................15
2.7 Regulatory statements................................................................................... 15
2.7.1 FCC Part 15 compliance statement........................................................ 15
2.7.2 Canada ICES-003 compliance statement............................................. 16
3. Functional description.................................................................................17
3.1 HUMICAP technology......................................................................................17
3.2 Chemical purge................................................................................................17
3.3 Condensation prevention functions..............................................................18
4. Installation.......................................................................................................20
4.1 Probe holder ASM213582................................................................................21
4.1.1 Mounting the probe body using probe holder ASM213582................ 21
4.2 Wiring...............................................................................................................22
4.3 HMP1 probe......................................................................................................23
4.4 HMP3 probe.....................................................................................................24
4.5 HMP4 probe.................................................................................................... 25
4.6 HMP5 probe.....................................................................................................26
4.7 HMP7 probe.....................................................................................................27
4.8 HMP8 probe.................................................................................................... 29
4.8.1 Attaching ball valve kit to process........................................................30
4.9 HMP9 probe......................................................................................................31
4.9.1 Installing HMP9 through a cable gland.................................................32
4.9.2 Overview of HMP9 Duct Installation Kit............................................... 33
4.9.3 Mounting HMP9 probe head with Duct Installation Kit......................34
4.10 MMP8 probe....................................................................................................36
4.11 TMP1 probe...................................................................................................... 37
4.12 DTR502B solar radiation shield.....................................................................37
4.12.1 Mounting probe head inside DTR502B................................................ 38
5. Configuration with Insight software......................................................41
5.1 Vaisala Insight software..................................................................................41
5.2 Connecting to Insight software..................................................................... 41
5.3 Configuration options.................................................................................... 42
Table of contents
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5.4 Configuring condensation prevention.........................................................42
5.5 Diagnostics in Insight.....................................................................................43
6. Using probe with Indigo transmitters..................................................45
6.1 Indigo200 series transmitters...................................................................... 45
6.1.1 Attaching probe to Indigo200 series transmitter............................... 47
6.2 Indigo500 series transmitters...................................................................... 48
7. Maintenance....................................................................................................49
7.1 Cleaning the probe.........................................................................................49
7.1.1 Chemical tolerance................................................................................. 49
7.2 Changing the probe filter.............................................................................. 50
7.3 Replacing the HUMICAPâR2 sensor.......................................................... 50
7.4 Calibration and adjustment...........................................................................52
7.4.1 Adjustment points and requirements...................................................53
7.4.2 HMK15 Humidity Calibrator with HMP Series probes .........................53
7.4.3 Adjusting measurement with Insight software................................... 55
7.4.4 Adjusting measurement with Indigo200 series transmitter..............56
8. Troubleshooting............................................................................................. 61
8.1 Problem situations...........................................................................................61
8.2 Error messages................................................................................................ 61
8.3 Restoring factory default settings................................................................63
9. Technical data................................................................................................64
9.1 HMP1 specifications........................................................................................64
9.2 HMP3 specifications....................................................................................... 67
9.3 HMP4 specifications.......................................................................................70
9.4 HMP5 specifications....................................................................................... 74
9.5 HMP7 specifications....................................................................................... 77
9.6 HMP8 specifications........................................................................................ 81
9.7 HMP9 specifications.......................................................................................85
9.8 MMP8 specifications...................................................................................... 89
9.9 TMP1 specifications......................................................................................... 91
9.10 Accessories and spare parts......................................................................... 94
Appendix A: Modbus reference.................................................................. 99
A.1 Default communication settings.................................................................. 99
A.2 Function codes............................................................................................... 99
A.3 Data encoding................................................................................................ 99
A.3.1 32-bit floating point or 32-bit integer format................................... 100
A.3.2 16-bit integer format.............................................................................100
A.4 Modbus registers........................................................................................... 101
A.4.1 Measurement data registers..................................................................101
A.4.2 Configuration registers.........................................................................104
A.4.3 Status registers...................................................................................... 107
A.4.4 Test value registers................................................................................108
A.5 Device identification objects.......................................................................108
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A.6 Exception responses.................................................................................... 109
A.7 Modbus communication examples..............................................................110
Maintenance and calibration services........................................................113
Warranty........................................................................................................... 113
Technical support........................................................................................... 113
Recycling...........................................................................................................113
Table of contents
3

List of figures
Figure 1 Probe parts........................................................................................................ 12
Figure 2 Example installation.......................................................................................20
Figure 3 Probe holder ASM213582 dimensions........................................................21
Figure 4 M12 5-pin A-coded male connector pinout............................................. 22
Figure 5 RS-485 wiring.................................................................................................. 23
Figure 6 HMP1 probe dimensions................................................................................23
Figure 7 HMP3 probe dimensions...............................................................................24
Figure 8 HMP4 probe dimensions...............................................................................25
Figure 9 HMP5 probe dimensions...............................................................................26
Figure 10 Optional mounting flange 210696 dimensions...................................... 26
Figure 11 HMP7 probe dimensions...............................................................................27
Figure 12 HMP8 probe dimensions...............................................................................29
Figure 13 HMP9 probe dimensions................................................................................31
Figure 14 Installing HMP9 probe head through a cable gland..............................32
Figure 15 Duct Installation Kit ASM214055 dimensions......................................... 33
Figure 16 Duct installation overview............................................................................34
Figure 17 MMP8 dimensions...........................................................................................36
Figure 18 TMP1 probe dimensions.................................................................................37
Figure 19 DTR502B dimensions.................................................................................... 38
Figure 20 Mounting DTR502B on a pole mast...........................................................39
Figure 21 HMP9 probe head with sensor head support 215130...........................40
Figure 22 Connecting probe to Insight using Indigo USB adapter.......................41
Figure 23 HMP5 in Insight software..............................................................................42
Figure 24 HMP5 diagnostics in Insight (advanced mode)..................................... 44
Figure 25 Probe attached to Indigo200 series transmitter directly....................45
Figure 26 Probe attached to Indigo200 series transmitter with a cable...........46
Figure 27 Attaching the probe to Indigo200 series transmitter.......................... 47
Figure 28 Attaching probes to Indigo500 transmitter........................................... 48
Figure 29 HMP3 probe head with filter removed.......................................................51
Figure 30 HMP5 calibration with HMK15 using 211302SP adapter....................... 54
Figure 31 Using HMP9 calibration adapter with HMK15......................................... 55
Figure 32 Calibration page in the Indigo200 wireless
configuration interface..................................................................................59
Figure 33 HMP1 humidity measurement accuracy as a function of
temperature..................................................................................................... 64
Figure 34 HMP1 temperature measurement accuracy over full range................ 65
Figure 35 HMP1 probe dimensions................................................................................66
Figure 36 HMP3 humidity measurement accuracy as a function of
temperature..................................................................................................... 68
Figure 37 HMP3 temperature measurement accuracy over full range............... 68
Figure 38 HMP3 probe dimensions...............................................................................70
Figure 39 HMP4 humidity measurement accuracy as a function of
temperature.......................................................................................................71
Figure 40 HMP4 temperature measurement accuracy over full range................ 71
Figure 41 HMP4 probe dimensions...............................................................................73
HMP Series with MMP8 and TMP1 User Guide M212022EN-F
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Figure 42 HMP5 humidity measurement accuracy as a function of
temperature......................................................................................................75
Figure 43 HMP5 temperature measurement accuracy over full range................75
Figure 44 HMP5 probe dimensions...............................................................................77
Figure 45 HMP7 humidity measurement accuracy as function of
temperature......................................................................................................78
Figure 46 HMP7 temperature measurement accuracy over full range............... 79
Figure 47 HMP7 probe dimensions................................................................................81
Figure 48 HMP8 humidity measurement accuracy as a function of
temperature......................................................................................................82
Figure 49 HMP8 temperature measurement accuracy over full range............... 82
Figure 50 HMP8 probe dimensions...............................................................................84
Figure 51 Optional ball valve installation kit dimensions....................................... 85
Figure 52 HMP9 humidity measurement accuracy as a function of
temperature..................................................................................................... 86
Figure 53 HMP9 temperature measurement accuracy over full range...............86
Figure 54 HMP9 probe dimensions...............................................................................88
Figure 55 MMP8 Awmeasurement accuracy............................................................. 89
Figure 56 MMP8 dimensions............................................................................................91
Figure 57 TMP1 temperature measurement accuracy over full range.................92
Figure 58 TMP1 probe dimensions................................................................................94
Figure 59 Optional duct kit 215003 dimensions....................................................... 94
List of figures
5

List of tables
Table 1 Document versions (English)...........................................................................9
Table 2 Related manuals................................................................................................ 10
Table 3 Availability of output parameters..................................................................13
Table 4 Suitability of cleaning agents........................................................................49
Table 5 Troubleshooting table...................................................................................... 61
Table 6 HMP1 measurement performance................................................................64
Table 7 HMP1 operating environment........................................................................ 65
Table 8 HMP1 inputs and outputs................................................................................65
Table 9 HMP1 output parameters................................................................................ 65
Table 10 HMP1 compliance..............................................................................................66
Table 11 HMP1 mechanical specifications...................................................................66
Table 12 HMP3 measurement performance............................................................... 67
Table 13 HMP3 operating environment....................................................................... 68
Table 14 HMP3 inputs and outputs...............................................................................69
Table 15 HMP3 output parameters............................................................................... 69
Table 16 HMP3 compliance.............................................................................................69
Table 17 HMP3 mechanical specifications..................................................................69
Table 18 HMP4 measurement performance...............................................................70
Table 19 HMP4 operating environment....................................................................... 72
Table 20 HMP4 inputs and outputs............................................................................... 72
Table 21 HMP4 output parameters............................................................................... 72
Table 22 HMP4 compliance............................................................................................. 73
Table 23 HMP4 mechanical specifications.................................................................. 73
Table 24 HMP5 measurement performance............................................................... 74
Table 25 HMP5 operating environment....................................................................... 75
Table 26 HMP5 inputs and outputs............................................................................... 76
Table 27 HMP5 output parameters............................................................................... 76
Table 28 HMP5 compliance............................................................................................. 76
Table 29 HMP5 mechanical specifications.................................................................. 76
Table 30 HMP7 measurement performance............................................................... 77
Table 31 HMP7 operating environment....................................................................... 79
Table 32 HMP7 inputs and outputs............................................................................... 79
Table 33 HMP7 output parameters............................................................................... 79
Table 34 HMP7 compliance.............................................................................................80
Table 35 HMP7 mechanical specifications..................................................................80
Table 36 HMP8 measurement performance................................................................81
Table 37 HMP8 operating environment....................................................................... 83
Table 38 HMP8 inputs and outputs...............................................................................83
Table 39 HMP8 output parameters............................................................................... 83
Table 40 HMP8 compliance.............................................................................................84
Table 41 HMP8 mechanical specifications..................................................................84
Table 42 HMP9 measurement performance...............................................................85
Table 43 HMP9 operating environment.......................................................................86
Table 44 HMP9 inputs and outputs...............................................................................87
Table 45 HMP9 output parameters............................................................................... 87
HMP Series with MMP8 and TMP1 User Guide M212022EN-F
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Table 46 HMP9 compliance............................................................................................. 87
Table 47 HMP9 mechanical specifications..................................................................88
Table 48 MMP8 measurement performance.............................................................. 89
Table 49 MMP8 operating environment.......................................................................89
Table 50 MMP8 inputs and outputs..............................................................................90
Table 51 MMP8 compliance............................................................................................ 90
Table 52 MMP8 mechanical specifications................................................................. 90
Table 53 TMP1 measurement performance................................................................. 91
Table 54 TMP1 operating environment.........................................................................92
Table 55 TMP1 inputs and outputs.................................................................................92
Table 56 TMP1 compliance...............................................................................................93
Table 57 TMP1 mechanical specifications....................................................................93
Table 58 Connection cables............................................................................................ 95
Table 59 HMP3 accessories............................................................................................. 95
Table 60 HMP3 spare parts..............................................................................................95
Table 61 HMP4 spare parts............................................................................................. 96
Table 62 HMP5 accessories............................................................................................. 96
Table 63 HMP5 spare parts..............................................................................................96
Table 64 HMP7 accessories............................................................................................. 96
Table 65 HMP7 spare parts..............................................................................................97
Table 66 HMP8 accessories............................................................................................. 97
Table 67 HMP8 spare parts..............................................................................................97
Table 68 HMP9 accessories............................................................................................. 97
Table 69 MMP8 accessories.............................................................................................98
Table 70 MMP8 spare parts............................................................................................. 98
Table 71 TMP1 accessories...............................................................................................98
Table 72 Default Modbus serial communication settings.......................................99
Table 73 Modbus function codes...................................................................................99
Table 74 Interpretation of 16-bit signed integer values........................................ 100
Table 75 Floating point measurement data registers (read-only)...................... 101
Table 76 Integer measurement data registers (read-only).................................. 103
Table 77 Modbus configuration data registers (writable).................................... 104
Table 78 Modbus status data registers (read-only)................................................107
Table 79 Error codes in register 0203hex................................................................... 108
Table 80 Modbus test registers (read-only)..............................................................108
Table 81 Device identification objects....................................................................... 108
Table 82 Modbus exception responses...................................................................... 109
List of tables
7

HMP Series with MMP8 and TMP1 User Guide M212022EN-F
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1. About this document
1.1 Version information
This document provides instructions for installing, using, and maintaining Vaisala HUMICAPâ
Humidity and Temperature Probes HMP1, HMP3, HMP4, HMP5, HMP7, HMP8, HMP9, Moisture in
Oil Probe MMP8, and Temperature Probe TMP1.
Table 1 Document versions (English)
Document code Date Description
M212022EN-F March 2021 Applicable from software version 1.2.0 onward. Added
content for HMP1 probe model and updated technical data
for all models.
Added sections:
•HUMICAP technology (page 17)
•Chemical purge (page 17)
•Condensation prevention functions (page 18)
•Mounting the probe body using probe holder
ASM213582 (page 21)
•Configuring condensation prevention (page 42)
•HMK15 Humidity Calibrator with HMP Series probes
(page 53)
Updated sections:
•Product overview (page 12)
•Probe structure (page 12)
•Output parameters (page 13)
•Installation (page 20)
•HMP7 probe (page 27)
•Indigo200 series transmitters (page 45)
•Indigo500 series transmitters (page 48)
•Vaisala Insight software (page 41)
•Problem situations (page 61)
•Restoring factory default settings (page 63)
•Measurement data registers (page 101)
•Configuration registers (page 104)
•Status registers (page 107)
Chapter 1 – About this document
9

Document code Date Description
M212022EN-E June 2020 Added sections:
•DTR502B solar radiation shield (page 37)
•Mounting probe head inside DTR502B (page 38)
•Diagnostics in Insight (page 43)
•Indigo500 series transmitters (page 48)
•Exception responses (page 109)
•Maintenance and calibration services (page 113)
Updated sections:
•Additional features with Indigo transmitters (page 14)
•Using probe with Indigo transmitters (page 45)
• Corrected CRC values in section Modbus communication
examples (page 110)
M212022EN-D March 2020 Added content for HMP3 and MMP8 probe models.
1.2 Related manuals
Table 2 Related manuals
Document code Name
M211982EN HMP Series with MMP8 and TMP1 Quick Guide
M211877EN Indigo201 Analog Output Transmitter User Guide
M211966EN Indigo202 Digital Transmitter User Guide
M212287EN Indigo520 Transmitter User Guide
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!
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!
HMP Series with MMP8 and TMP1 User Guide M212022EN-F
10

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 HUMICAPâare registered trademarks of Vaisala Oyj.
Modbusâis a registered trademark of Schneider Automation Inc.
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
11

2. Product overview
HMP series probes are humidity and temperature measurement probes with a digital output
(Modbusâprotocol). The probes are designed for demanding humidity and temperature
measurement applications. The probes have a two-part structure, with measurement
electronics contained in the probe body and sensor(s) in the probe head. The probe body and
the probe head are connected by a cable, except on the HMP1 model. Length options for this
connecting cable depend on the probe model.
The probes are compatible with Vaisala Indigo transmitters. They can also be connected to
Vaisala Insight software for configuration, calibration, adjustment, diagnostics, and temporary
online monitoring.
2.1 Probe structure
1
2
3
4
5
6
7
8
Figure 1 Probe parts
1Protection cap (remove before use)
25-pin M12 connector
3Probe body with type label
4Status indicator LED:
Green Power on and probe online,
flashes when communicating
Red Error
O Power o, or indicator
disabled
5Probe cable. HMP1 model does not
have a probe cable, as its probe head
is directly attached to the probe body.
6Probe head (HMP7 model shown)
7Location of sensor(s) on the probe
head. Other probe models have a
removable filter over the sensors but
HMP1, HMP9, and TMP1 do not.
8Protection cap (remove before use)
To prevent the warming of the indicator LED from causing a slight measurement
error, HMP1 keeps the indicator normally o (even when power is on). If the probe
is in error state, the red LED is shown.
2.2 Basic features and options
• Comprehensive list of output parameters. See Output parameters (page 13).
HMP Series with MMP8 and TMP1 User Guide M212022EN-F
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• Sensor purge provides superior chemical resistance (HMP models only)
• Condensation prevention feature minimizes condensation on probe (HMP models with
composite sensors only)
• Traceable calibration certificate:
• HMP and MMP models: 6 points for humidity, 1 point for temperature
• TMP1: 2 points for temperature
• Standalone ModbusâRTU over RS-485
• Compatible with Indigo series of transmitters
• Can be connected to Vaisala Insight PC software for configuration, calibration,
diagnostics, and temporary online monitoring
2.3 Output parameters
On HMP probe models, the values of all available output parameters are locked
when the sensor is being warmed by the chemical purge function.
Output parameter is available on this model.
Output parameter is available on this model, but its value is unavailable when
condensation prevention functions are warming the sensor. Writing temperature to
Modbus register 0334hex from an external source makes the output value available during
condensation prevention.
Output parameter is not available on this model.
Table 3 Availability of output parameters
Output parameter Output unit HMP1, 3, 4, 5,
7, 8, and 9
MMP8 TMP1
Absolute humidity g/m3
Absolute humidity at NTP g/m3
Dew/frost point temperature °C
Dew/frost point temperature at 1 atm °C
Dew point temperature °C
Dew point temperature at 1 atm °C
Dew point temperature dierence °C
Enthalpy kJ/kg
Mixing ratio g/kg
Relative humidity %RH
Relative humidity (dew/frost) %RH
Relative saturation %RS
Chapter 2 – Product overview
13

Output parameter Output unit HMP1, 3, 4, 5,
7, 8, and 9
MMP8 TMP1
Temperature °C
Water activity -
Water concentration ppmv
Water concentration in oil ppmv
Water concentration (wet basis) vol-%
Water mass fraction ppmw
Wet-bulb temperature °C
Water vapor pressure hPa
Water vapor saturation pressure hPa
2.4 Additional features with Indigo 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 Indigo500 series transmitters:
• Touchscreen display for real-time data viewing and configuration
• Support for 2 probes simultaneously
• 4 configurable analog outputs
• 2 configurable relays
• Ethernet connection with web interface for remote access
• Modbus TCP/IP protocol
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
• Wireless browser-based configuration interface for mobile devices and computers (IEEE
802.11 b/g/n WLAN)
Available features vary depending on the Indigo transmitter model. For more
information on Indigo transmitters, see www.vaisala.com/indigo.
HMP Series with MMP8 and TMP1 User Guide M212022EN-F
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2.5 Safety
When returning a product for calibration or repair, make sure it
has not been exposed to dangerous contamination, and is safe to handle
without special precautions.
WARNING!
Do not attempt to open the probe body. There are no user
serviceable parts inside the probe body.
CAUTION!
Do not touch the probe head with your bare hands. Touching will
deposit impurities on the probe head.
CAUTION!
Be aware that the probe head may become hot to touch when
condensation prevention heating or chemical purge functions are active.
CAUTION!
2.6 ESD protection
Electrostatic discharge (ESD) can cause immediate or latent damage to electronic circuits.
Vaisala products are adequately protected against ESD for their intended use. However, it is
possible to damage the product by delivering an electrostatic discharge when touching,
removing or inserting any objects inside the equipment housing.
Avoid touching component contacts or connectors when working with the device.
2.7 Regulatory statements
2.7.1 FCC Part 15 compliance statement
This equipment has been tested and found to comply with the limits for a Class B digital
device, pursuant to Part 15 of the FCC rules. These limits are designed to provide reasonable
protection against harmful interference in a residential installation. This equipment generates,
uses and can radiate radio frequency energy and, if not installed and used in accordance with
the instructions, may cause harmful interference to radio communications. However, there is
no guarantee that the interference will not occur in a particular installation. If this equipment
does cause harmful interference to radio or television reception, which can be determined by
turning the equipment o and on, the user is encouraged to try to correct the interference by
one or more of the following measures:
• Reorient or relocate the receiving antenna.
Chapter 2 – Product overview
15

• Increase the separation between the equipment and receiver.
• Connect the equipment into an outlet on a circuit dierent from that to which the receiver
is connected.
• Consult the dealer or an experienced radio/TV technician for help.
Changes or modifications to this equipment not expressly approved
by the party responsible for compliance could void the user's authority to
operate the equipment.
CAUTION!
This device complies with part 15 of the FCC Rules. Operation is subject to the
following two conditions: (1) This device may not cause harmful interference, and
(2) this device must accept any interference received, including interference that
may cause undesired operation.
2.7.2 Canada ICES-003 compliance statement
This Class B digital apparatus complies with Canadian ICES‑003.
Cet appareil numerique de la classe B est conforme a la norme NMB‑003 du Canada.
HMP Series with MMP8 and TMP1 User Guide M212022EN-F
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3. Functional description
3.1 HUMICAP technology
Vaisala HUMICAPâis a capacitive thin-film polymer sensor consisting of a substrate on which
a thin film of polymer is deposited between two conductive electrodes. The sensing surface is
coated with a porous metal electrode to protect it from contamination and exposure to
condensation. The substrate is typically glass or ceramic.
The thin-film polymer either absorbs or releases water vapor as the relative humidity of the
measurement environment rises or falls. The dielectric properties of the polymer film depend
on the amount of absorbed water. As the relative humidity around the sensor changes, the
dielectric properties of the polymer film change, and so does the capacitance of the sensor.
Capacitance is converted into a humidity reading. The HUMICAP sensor is complemented by a
temperature sensor, which is bonded together with the capacitive polymer on some of the
sensor variants. Additional output parameters such as dew point are calculated from the
readings measured by the sensors.
HUMICAP sensors with bonded temperature sensors are also known as composite sensors.
Probes with composite sensors can use the chemical purge function to maintain sensor
performance. They also implement condensation prevention functions that are a key element
in achieving an excellent stability and good condensation resistance in high humidity
applications.
The integrated sensor arrangement on the HMP1 and HMP9 probes is dierent from the
composite sensors used in the other HMP probes. However, they are also capable of using
condensation prevention heating and chemical purge.
3.2 Chemical purge
Chemical purge heats the sensor to a high temperature, which evaporates excess molecules
out of the sensor polymer. This minimizes the drift at the wet end of humidity readings, and
removes contaminants from the sensor element. The heating phase is followed by a cooling
phase where the sensor cools down to ambient temperature.
During chemical purge the values of the output parameters stay frozen at their last measured
values. Chemical purge takes a few minutes to complete, after which measurement continues
normally and updated values of output parameters are again available.
When ordered with chemical purge enabled, HMP model probes perform the purge at one day
intervals (known as interval purge). If desired, chemical purge can also be performed when
the probe is powered on (known as startup purge). Purge settings can be configured with
Insight software or using Modbus protocol.
To allow the chemical purge to be completed in a reasonable time, it will not be
started if the ambient temperature is below 0 °C (+32 °F).
Chapter 3 – Functional description
17

3.3 Condensation prevention functions
Condensation prevention heating prevents water from condensing on the sensor and
interfering with humidity measurement. Use of condensation prevention is controlled by a
single setting that can be changed with Insight software or using Modbus protocol. The setting
is only available if your probe supports condensation prevention.
By default, condensation prevention is o. However, the HMP7 model can be ordered from
Vaisala with the feature enabled.
When condensation prevention is enabled, the probe will automatically use its available
condensation prevention functions. When warming is active, values of output parameters that
depend on temperature measurement (for example, relative humidity) are unavailable unless
temperature is written to register 0334hex from an external source. Output parameters that can
be measured or calculated without this external temperature information, such as dew point
temperature, are available even without the temperature input.
Sensor warming
Sensor warming is available to all HMP series probes with composite sensors, HMP1, and HMP9.
Warms the humidity sensor when necessary to keep its temperature above the dew point of
the measurement environment. When sensor warming is activated, all temperature dependent
output parameters become unavailable unless external temperature information is provided to
the probe. The output parameters become available again 4 minutes after the warming is
stopped.
Sensor warming is intended for improving the condensation tolerance of the
probe in measurement environments that may occasionally cause condensation
to form. It is not intended for environments where continous warming is needed.
Probe heating
Probe heating is available on HMP7 model only. Probe heating warms up the entire probe head
instead of just the sensor. It is intended for use in challenging measurement environments
where condensation on the probe would otherwise present a problem.
Probe heating always applies some heating power even when the sensor is not near
condensation, so temperature-dependent output parameters are permanently unavailable
when probe heating is used, unless external temperature information is provided to the probe.
If the ambient dew point rises close to current sensor temperature, the heating power is
increased to avoid condensation. Heating power also increases as supply voltage increases.
If you use probe heating, be sure to mount the HMP7 probe head in a way that
prevents the heat from being conducted away from the probe. Tightly connecting
the HMP7 probe head to a metal structure may prevent the probe from
maintaining probe temperature above the dew point. It will also heat the structure
which may be undesirable.
HMP Series with MMP8 and TMP1 User Guide M212022EN-F
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