Vaisala HMP8 Vaisala HMP8
Vaisala HMP8

Vaisala HMP8 Humidity and Temperature Probe for Pressurised Pipelines

Vaisala HMP8 Humidity and Temperature Probe for Pressurised Pipelines

The Vaisala HMP8 provides high-accuracy humidity and temperature measurement in compressed air, refrigerant dryers and pressurised industrial processes up to 40 bar.

  • Humidity accuracy up to ±0.8% RH
  • Operating pressure from vacuum to 40 bar
  • Adjustable insertion depth with two probe lengths
  • Optional ball valve for insertion and removal under process conditions

Vaisala HMP8 Humidity and Temperature Probe for Pressurised Processes

The Vaisala HUMICAP® Humidity and Temperature Probe HMP8 is designed for compressed-air systems, refrigerant dryers and other pressurised industrial processes where adjustable insertion depth and convenient probe removal are important.

The HMP8 measures relative humidity and temperature at operating pressures up to 40 bar absolute. It is available with 268 mm or 454 mm probe-head lengths, allowing the sensing section to be positioned correctly in pipes of different sizes and through varying insulation thicknesses.

When installed with the appropriate optional Vaisala ball-valve assembly, the probe can be inserted into or removed from a pressurised pipeline according to the approved installation procedure. This enables inspection, calibration or replacement without permanently dismantling the process connection.

The probe can operate independently using Modbus RTU over RS-485 or connect to a Vaisala Indigo transmitter for local display, analog outputs, relays, Ethernet and additional automation-system connectivity.

Why Choose the Vaisala HMP8?

  • Pressurised Process Measurement: Designed for applications from vacuum conditions up to 40 bar absolute.
  • Adjustable Insertion Depth: The sliding pressure fitting allows the sensing section to be positioned correctly within the pipeline.
  • Two Probe Lengths: Choose a 268 mm or 454 mm probe according to pipe diameter, insulation thickness and required insertion depth.
  • Optional Ball-Valve Installation: Supports controlled insertion and removal from a pressurised line when the specified procedure and pressure limits are followed.
  • High Measurement Accuracy: Provides humidity accuracy up to ±0.8% RH and temperature accuracy up to ±0.1 °C.
  • Wide Temperature Range: The probe head measures from −70 to +180 °C.
  • Sensor Purge: The HUMICAP R2C option supports chemical purge to reduce contamination effects between calibration intervals.
  • Standalone Modbus RTU: Built-in RS-485 communication allows direct integration with a PLC or automation system.
  • Indigo Compatibility: Add display, analog outputs, relays, Ethernet, Modbus TCP or dual-probe capability using a compatible Indigo transmitter.
  • Traceable Calibration: Supplied with a certificate covering six humidity points and one temperature point.

HMP8 Measurement Performance

Measurement SpecificationPerformance
Relative-Humidity Range 0–100% RH, at a maximum dew-point temperature of +95 °C
RH Accuracy at +23 °C ±0.8% RH from 0–90% RH
RH Factory-Calibration Uncertainty ±0.5% RH from 0–40% RH; ±0.8% RH from 40–95% RH
RH Response Time 15 seconds, T63
Humidity Sensor Options Vaisala HUMICAP® R2 or HUMICAP® R2C
Temperature Range −70 to +180 °C
Temperature Accuracy at +23 °C ±0.1 °C
Temperature Factory-Calibration Uncertainty ±0.1 °C at +23 °C
Temperature Sensor Pt100 RTD Class F0.1 according to IEC 60751

Pressure and Environmental Specifications

Environmental SpecificationOperating Limit
Operating Pressure Below 40 bar absolute, including vacuum applications
Probe-Head Temperature −70 to +180 °C
Probe-Body Temperature −40 to +80 °C
Probe-Head Humidity Limit Maximum +100 °C dew-point temperature
Storage Temperature −40 to +80 °C
Measurement Media Air, nitrogen, hydrogen, argon, helium, oxygen and vacuum; consult Vaisala for other chemicals
Operating Environment Suitable for outdoor use
Probe-Body Protection IP66

Ball-Valve Operating Limits

Ball-Valve SpecificationLimit
Maximum Operating Pressure 40 bar absolute
Maximum Operating Temperature +100 °C
Installation Method Use the approved Vaisala ball-valve kit and follow the applicable insertion and removal procedure
Safety Requirement Only trained personnel should insert or remove the probe from a pressurised process
Safety note: A 40 bar probe rating does not mean that the probe may be inserted or removed freely at any pressure. Follow the ball-valve kit instructions, site permit requirements and the specified safe insertion/removal procedure.

Pressure Compensation Is Essential

Relative humidity and several calculated water-content parameters depend on process pressure. Configure the actual absolute pressure in the HMP8 or compatible Indigo transmitter for accurate results.

  • Use absolute pressure rather than gauge pressure when required by the configuration interface.
  • Update the compensation value whenever the operating pressure changes significantly.
  • For processes with continuously changing pressure, update the compensation value from the automation system when supported.
  • Confirm the selected humidity parameter and engineering unit before commissioning.
  • Review chemical compatibility and safety requirements for hydrogen, oxygen and other reactive or flammable gases.

Electrical and Communication Specifications

FeatureSpecification
Operating Voltage 15–30 V DC
Typical Current Consumption 10 mA
Maximum Current Consumption 500 mA
Digital Interface RS-485, non-isolated
Communication Protocol Modbus RTU
Electrical Connector M12 five-pin A-coded male

HMP8 Probe Lengths and Installation Depth

Probe VersionAdjustable Installation DepthApproximate Weight with 2 m CableRecommended Use
268 mm HMP8 41–199 mm 512 g Standard pipes and process connections
454 mm HMP8 41–385 mm 612 g Large pipes, thick insulation or deeper insertion requirements

Mechanical Specifications

Mechanical FeatureSpecification
Pressure-Fitting Options ISO ½-inch and NPT ½-inch fitting bodies included
Probe Diameter 12 mm
Probe Material AISI 316L stainless steel
Probe-Body Material AISI 316L stainless steel
Cable Jacket FEP
Available Cable Lengths 2 m or 10 m
Optional Ball-Valve Kit Vaisala BALLVALVE-1 or other compatible kit selected for the process connection

Measured and Calculated Parameters

  • Relative humidity
  • Temperature
  • Absolute humidity
  • Dew point and dew/frost point temperature
  • Wet-bulb temperature
  • Enthalpy
  • Mixing ratio
  • Water-vapour pressure
  • Water concentration and water mass fraction

HMP8 or HMP4 for a Pressurised Process?

Selection RequirementVaisala HMP8Vaisala HMP4
Maximum Operating Pressure Below 40 bar Below 100 bar
Installation Depth Adjustable Fixed pressure-tight installation
Probe Length Options 268 mm or 454 mm Fixed probe construction
Removal from Pressurised Line Supported with optional ball-valve assembly and correct procedure Process should normally be safely depressurised before removal
Vacuum Measurement Supported within specifications Supported and preferred for demanding vacuum applications
Best Fit Serviceable compressed-air and dryer pipeline installation Very high pressure, breathing air, maritime gases and vacuum

Compare the Vaisala HMP4 High-Pressure Probe

HMP8 or DMP8 for Compressed Air?

RequirementHMP8DMP8
Primary Measurement Relative humidity and temperature Low dew point and temperature
Best Humidity Region Moderate to high humidity Very dry compressed air and industrial gases
Typical Application Refrigerant dryers and humid pressurised processes Desiccant dryers, dry gases and low-dew-point systems
Operating Pressure Up to 40 bar Up to 40 bar
Adjustable Insertion Yes Yes

View the Vaisala DMP8 Dew-Point Probe

Compatible Vaisala Indigo Transmitters

TransmitterRecommended ConfigurationProduct Link
Indigo200 Series Standard single-probe transmitter with display and analog, relay or Modbus options Vaisala Indigo200
Indigo300 Rugged IP66 metal transmitter for one probe with up to three analog outputs Vaisala Indigo300
Indigo510 Simplified flagship for one probe with isolated outputs, Ethernet and Modbus TCP Vaisala Indigo510
Indigo520 Full dual-probe flagship with four outputs, two relays, Ethernet and Modbus TCP Vaisala Indigo520

The cable distance between the HMP8 and compatible Indigo transmitters can be extended to a total of approximately 30 m using the correct Vaisala connection arrangement.

View the Vaisala Indigo80 Portable Meter

Common HMP8 Applications

  • Compressed-Air Systems: Relative-humidity and temperature monitoring in pressurised distribution lines.
  • Refrigerant Dryers: Monitoring dryer performance where humidity is higher than typical low-dew-point desiccant-dryer applications.
  • Industrial Gas Pipelines: Measurement in compatible pressurised gases following application and safety review.
  • Breathing-Air Systems: Process humidity measurement within the HMP8 pressure range and applicable regulatory requirements.
  • Vacuum Processes: Humidity measurement when adjustable insertion depth and serviceability are required.
  • Test Systems: Measurement in pressure vessels, chambers and research equipment.
  • Process Drying: Monitoring pressurised drying or conditioning systems.

Installation Guidance

  • Select the probe length that places the sensing section sufficiently inside the main gas flow.
  • Avoid installing the probe in a dead leg, low-flow pocket or location where condensate can collect.
  • Seal the ISO or NPT fitting using a suitable process-compatible thread sealant.
  • Use the correct tools on the fitting body and clasp nut; do not rotate the probe body or cable.
  • Configure the actual absolute process pressure before commissioning.
  • Keep the probe electronics body within its specified temperature range.
  • Follow all approved safety instructions before inserting or removing a probe from a pressurised line.

Other Vaisala Indigo-Compatible Probes

RequirementProbeProduct Link
Indoor wall monitoring HMP1 Vaisala HMP1
General process humidity HMP3 Vaisala HMP3
Pressure up to 100 bar HMP4 Vaisala HMP4
High-temperature process HMP5 Vaisala HMP5
Continuous high humidity HMP7 Vaisala HMP7
Compact, fast-response measurement HMP9 Vaisala HMP9
Temperature only TMP1 Vaisala TMP1
Low dew point in pressurised pipeline DMP8 Vaisala DMP8
Moisture in oil MMP8 Vaisala MMP8

Calibration and Maintenance

The HMP8 is calibrated and adjusted before delivery. Calibration and adjustment can be performed using Vaisala Insight PC software, a compatible Indigo transmitter or an Indigo80 handheld indicator.

The ball-valve installation can simplify planned calibration by allowing controlled probe removal without dismantling the permanent process fitting. Calibration frequency should be determined according to the gas, contamination level, process criticality and quality requirements.

Vaisala HMP8 Supplier in Malaysia

Seacom Process Instruments supplies and supports the Vaisala HMP8 humidity and temperature probe in Malaysia for compressed air, refrigerant dryers, industrial gas pipelines, vacuum equipment and other pressurised processes.

Our team can assist with selecting the probe length, insertion depth, ISO or NPT fitting, ball-valve kit, cable length, humidity sensor and Indigo transmitter required for the application.

Contact Seacom for Vaisala HMP8 Selection

Download

  HMP8 Catalogue - Smart Humidity and Temperature Probe HMP8 for pressurized processes (192.46k)
  Indigo200 Catalogue - Indigo200 Series Transmitters for Vaisala smart probes for Vaisala Smart Probes (204.62k)
  Indigo 500 Catalogue - Indigo500 Series Transmitters for Vaisala smart probes (581.96k)

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