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Vaisala HMP4 High-Pressure Humidity and Temperature Probe
The Vaisala HMP4 provides high-accuracy humidity and temperature measurement in compressed air, breathing air, industrial gases, vacuum systems and other processes operating at pressures up to 100 bar.
- Operating pressure below 100 bar, including vacuum applications
- Humidity accuracy up to ±0.8% RH
- Temperature range from -70 °C to +180 °C
- Standalone Modbus RTU or connection to an Indigo transmitter
Vaisala HMP4 Humidity and Temperature Probe for High Pressure and Vacuum
The Vaisala HMP4 is a high-accuracy relative-humidity and temperature probe designed for compressed air, breathing air, maritime systems, industrial gases, vacuum chambers and other demanding processes operating at pressures below 100 bar.
The probe combines Vaisala HUMICAP sensor technology, a stainless-steel pressure-tight probe head, ±0.8% RH accuracy and temperature measurement from -70 °C to +180 °C. It can operate as a standalone Modbus RTU device or connect to a Vaisala Indigo200, Indigo300, Indigo510 or Indigo520 transmitter.
Why Choose the Vaisala HMP4?
- High-Pressure Capability: Designed for process pressures below 100 bar and for vacuum measurement.
- High Humidity Accuracy: Provides accuracy up to ±0.8% RH from 0–90% RH at +23 °C.
- Wide Temperature Range: Measures temperature from -70 °C to +180 °C with accuracy up to ±0.1 °C.
- Multiple Gas Applications: Suitable for air, nitrogen, hydrogen, argon, helium, oxygen and vacuum, subject to application and safety review.
- Chemical Resistance: HUMICAP R2 sensor technology and optional sensor purge improve stability in challenging industrial environments.
- Standalone Digital Output: Built-in RS-485 Modbus RTU allows direct connection to compatible automation systems.
- Indigo Compatibility: Add a display, analog outputs, relays, Ethernet or dual-probe operation by selecting the appropriate Indigo transmitter.
- Traceable Calibration: Supplied with a traceable calibration certificate.
HMP4 or HMP8 for a Pressurised Process?
| Selection Requirement | HMP4 | HMP8 |
|---|---|---|
| Maximum Operating Pressure | Below 100 bar | Up to 40 bar |
| Vacuum Applications | Yes | Primarily pressurised pipelines |
| Installation Depth | Fixed pressure-tight probe installation | Adjustable insertion depth |
| Removal Under Pressure | Process should be safely depressurised before removal | Can be removed through the optional ball-valve assembly according to the installation procedure |
| Best Fit | Very high pressure, breathing air, maritime gas systems and vacuum | Compressed-air or dryer pipelines requiring serviceable ball-valve installation |
Selection guidance: Choose HMP4 when pressure may exceed 40 bar or vacuum capability is required. Choose HMP8 when adjustable insertion depth and removal through a ball valve are more important than the higher pressure rating.
Humidity Measurement Performance
| Specification | Performance |
|---|---|
| Measurement Range | 0–100% RH, at a maximum dew-point temperature of +95 °C |
| Accuracy at +23 °C, 0–90% RH | ±0.8% RH |
| Factory Calibration Uncertainty | ±0.5% RH from 0–40% RH; ±0.8% RH from 40–95% RH |
| Typical T63 Response Time | 15 seconds |
| Humidity Sensor Options | Vaisala HUMICAP R2 or HUMICAP R2C |
Temperature Measurement Performance
| Specification | Performance |
|---|---|
| Measurement Range | -70 °C to +180 °C |
| Accuracy | Up to ±0.1 °C under specified conditions |
| Factory Calibration Uncertainty | ±0.1 °C at +23 °C |
| Temperature Sensor | Pt100 RTD Class F0.1 according to IEC 60751 |
Operating Environment
| Environmental Specification | Operating Limit |
|---|---|
| Operational Pressure | Below 100 bar |
| Probe-Head Temperature | -70 °C to +180 °C |
| Probe-Body Temperature | -40 °C to +80 °C |
| Storage Temperature | -40 °C to +80 °C |
| Probe-Head Humidity Limit | Maximum +100 °C dew-point temperature |
| Measurement Media | Air, nitrogen, hydrogen, argon, helium, oxygen and vacuum; consult Vaisala for other chemicals |
| Probe-Body Protection | IP66 |
Pressure Compensation Is Essential
Relative humidity and calculated water-content parameters depend on the process pressure. For the most accurate results, configure the actual process pressure in the HMP4 or continuously update the pressure-compensation value from the control system when pressure varies.
- Enter the correct absolute process pressure, not gauge pressure, when required by the configuration interface.
- Update the compensation value when the process operates across a changing pressure range.
- Confirm the required output parameter and engineering unit before commissioning.
- Review gas compatibility and applicable safety requirements, particularly for oxygen, hydrogen and other flammable or reactive gases.
Digital Output and Electrical Specifications
| Feature | Specification |
|---|---|
| Operating Voltage | 15–30 V DC |
| Typical Current Consumption | 10 mA |
| Digital Interface | RS-485, non-isolated |
| Communication Protocol | Modbus RTU |
| Electrical Connector | M12, five-pin, A-coded male |
Calculated Humidity Parameters
In addition to relative humidity and temperature, HMP4 can provide several calculated parameters depending on configuration:
- Dew point and frost point temperature
- Absolute humidity
- Mixing ratio
- Wet-bulb temperature
- Enthalpy
- Water vapour pressure
- Water concentration in ppm or volume percentage
- Water mass fraction
Selecting an Indigo Transmitter for HMP4
| Transmitter | Position | Recommended When |
|---|---|---|
| Indigo200 | Standard | Normal single-probe analog or Modbus RTU integration is required |
| Indigo300 | Rugged intermediate | An IP66 metal transmitter with three analog outputs is preferred |
| Indigo510 | Simplified flagship | One probe, isolated outputs, Ethernet, web access and Modbus TCP are required |
| Indigo520 | Full flagship | HMP4 must operate with a second probe, four outputs or two relays |
Mechanical and Process Connection
| Feature | Specification |
|---|---|
| Probe Material | AISI 316 stainless steel |
| Process Fitting | M22 × 1.5 or 1/2-inch NPT |
| Standard Probe Cable | Approximately 2 m |
| Cable Jacket | FEP |
| Approximate Weight | 530 g with 2 m cable |
Installation and Safety Considerations
- Confirm that the selected process fitting, sealing method and pressure rating are suitable for the process.
- Depressurise and isolate the process safely before installing or removing HMP4.
- Keep the probe body within its -40 °C to +80 °C operating range even when the probe head is exposed to higher temperatures.
- Use a representative measurement location with adequate gas circulation.
- Configure pressure compensation and the required calculated parameters during commissioning.
- Follow all site procedures for pressure systems, breathing air, oxygen service, hydrogen and other hazardous gases.
Common HMP4 Applications
Use Vaisala HMP Probes with Indigo80
Vaisala HMP1, HMP3, HMP4, HMP5, HMP7, HMP8 and HMP9 can be connected to the Vaisala Indigo80 Handheld Indicator using a compatible connection cable.
Portable measurement and field servicing: use Indigo80 to display live humidity and temperature readings, record measurement data, check probe performance, configure settings, and perform field calibration and adjustment. The same Indigo80 can support different compatible probes, making it practical for servicing multiple measurement points.
Which Vaisala HMP Probe Should You Choose?
Vaisala Indigo-compatible HMP probes share the same measurement platform, but their mechanical design and installation method suit different conditions. Use the table below to identify the best starting point for your application.
| Probe | Main strength | Recommended application | Product |
|---|---|---|---|
| HMP1 | Compact wall-mounted probe for indoor environments | Cleanrooms, laboratories, data centres, warehouses and demanding HVAC | Vaisala HMP1 |
| HMP3 | Field-maintainable general-purpose 12 mm probe | Ducts, chambers, paint booths, air-handling units and industrial HVAC | Vaisala HMP3 |
| HMP4 | High-pressure measurement up to 100 bar | Compressed air, breathing air, industrial gases and vacuum systems | Vaisala HMP4 |
| HMP5 | Long probe for high temperatures up to +180 °C | Ovens, kilns, baking processes and high-temperature dryers | Vaisala HMP5 |
| HMP7 | Heated probe for continuous high humidity | Near-condensing chambers, humidifiers, drying processes and other persistently humid conditions | Vaisala HMP7 |
| HMP8 | Adjustable-depth probe for pressurised pipelines | Compressed-air lines, refrigerant dryers and industrial pipelines requiring easy probe removal | Vaisala HMP8 |
| HMP9 | Compact 5 mm probe head with fast response | Tight spaces, rapidly changing air, compact equipment, ducts and data centres | Vaisala HMP9 |
Vaisala HMP4 Supplier in Malaysia
Seacom Process Instruments supplies and supports the Vaisala HMP4 high-pressure humidity and temperature probe in Malaysia. Our team can assist with process compatibility, pressure range, fitting selection, calculated parameters, Indigo transmitter selection, cabling, installation and commissioning.
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The Vaisala HMP5 provides high-accuracy humidity and temperature measurement in ovens, dryers, kilns and other processes operating at temperatures up to +180 °C.
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- Standalone Modbus RTU or Vaisala Indigo transmitter operation
The Vaisala Indigo500 Series provides flagship industrial measurement integration: choose Indigo510 for a simplified single-probe system or Indigo520 for full dual-probe capability.
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The Vaisala HMT120 and HMT130 provide accurate, stable humidity and temperature measurement for cleanrooms, laboratories, data centres and demanding HVAC applications.
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