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Smart Humidity and Temperature Probe HMP8 for pressurized processes
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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 Specification | Performance |
|---|---|
| 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 Specification | Operating 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 Specification | Limit |
|---|---|
| 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
| Feature | Specification |
|---|---|
| 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 Version | Adjustable Installation Depth | Approximate Weight with 2 m Cable | Recommended 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 Feature | Specification |
|---|---|
| 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 Requirement | Vaisala HMP8 | Vaisala 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?
| Requirement | HMP8 | DMP8 |
|---|---|---|
| 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
| Transmitter | Recommended Configuration | Product 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.
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.
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 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.
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DMP370 availability: Vaisala plans first deliveries for Q1 2027. Contact Seacom for configuration and project lead time.
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The Vaisala Indigo300 is a rugged industrial transmitter for one Vaisala Indigo-compatible smart probe, providing local measurement display and up to three configurable analog outputs.
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Expected availability: early 2027. Enquire with Seacom for configuration and delivery confirmation.
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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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