Vaisala HMP9 Compact Humidity and Temperature Probe
The Vaisala HUMICAP® Humidity and Temperature Probe HMP9 is designed for tight spaces and rapidly changing environments where fast response, compact installation, measurement accuracy and chemical tolerance are essential.
Its defining feature is a miniature probe head measuring only 5 mm in diameter. The low thermal mass enables the sensor to respond quickly to changing air temperature while preserving Vaisala HUMICAP humidity-measurement stability and low hysteresis.
The HMP9 is suitable for air-handling units, data centres, industrial dryers, test chambers, environmental chambers, glove boxes, incubators, machinery and other installations where a conventional industrial probe is physically too large or responds too slowly.
Built-in RS-485 Modbus RTU enables standalone operation. The probe can also connect to a Vaisala Indigo transmitter for local display, analog outputs, relays, Ethernet connectivity and additional automation-system integration.
Why Choose the Vaisala HMP9?
- Miniature Probe Head: The 5 mm diameter sensing head fits into confined spaces, small ducts and compact equipment.
- Low Thermal Mass: The lightweight probe head responds quickly when air temperature changes rapidly.
- High Measurement Accuracy: Provides relative-humidity accuracy up to ±0.8% RH and temperature accuracy up to ±0.1 °C.
- Wide Temperature Range: The probe head measures from −40 to +120 °C.
- Sensor Purge: Chemical purge helps reduce the effects of contaminants and cleaning agents on long-term measurement stability.
- Standalone Modbus RTU: Connect directly to a PLC, data-acquisition system or building-management system through RS-485.
- Indigo Compatibility: Add display, analog outputs, relays, Ethernet, Modbus TCP or dual-probe capability by selecting a compatible Indigo transmitter.
- Traceable Calibration: Supplied with a calibration certificate covering six humidity points and one temperature point.
- Simple Process Mounting: An M10 × 1.5 cable gland is included for mounting the miniature probe head.
HMP9 Measurement Performance
Operating Environment
Temperature-limit note: The +120 °C rating applies to the miniature probe head. The HMP9 electronics body must remain within its −40 to +60 °C operating range.
Condensation and Liquid-Water Exposure
The HMP9 can be used where occasional condensation may occur, provided that the probe is protected from direct exposure to liquid water. It is not the preferred probe for continuously condensing conditions.
For persistent high humidity, repeated condensation or applications that require active probe heating, select the Vaisala HMP7 high-humidity probe.
Electrical and Communication Specifications
Mechanical Specifications
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
Compatible Vaisala Indigo Transmitters
View the Vaisala Indigo80 Portable Meter
HMP9 for Data-Centre Environmental Monitoring
The HMP9 is well suited to measurement points where available space is limited or environmental conditions change quickly, including air-handling units, cooling equipment, server racks and airflow paths. Its low thermal mass reduces lag when cooling load or airflow changes.
For broader guidance on probe placement, room monitoring, chilled-water measurement and data-centre cooling control, see Seacom’s Vaisala Data Centre Environmental Monitoring Guide.
Common HMP9 Applications
- Air-Handling Units: Fast measurement in restricted internal spaces and rapidly changing airflow.
- Data Centres: Monitoring around racks, cooling equipment, air paths and other space-constrained locations.
- Industrial Dryers: Measuring inlet, exhaust or recirculation air where response speed is important.
- Environmental Chambers: Monitoring changing conditions in compact test volumes.
- Glove Boxes: Compact humidity and temperature measurement where installation space is limited.
- Incubators: Measurement inside equipment when a small sensor head is required.
- Machinery and Equipment: Integration into enclosed systems with limited clearance.
- Outdoor Measurement: Use with the appropriate DTR502B radiation shield and rain protection.
Installation Accessories
Calibration and Maintenance
The HMP9 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.
Because the miniature sensor head does not use the heavier replaceable filters found on some other HMP probes, it should be protected from mechanical damage and direct contamination. Calibration frequency should be determined according to process criticality, operating conditions and quality-system 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.
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.
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HMP9 Catalogue
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