Vaisala HMP9 Compact Humidity & Temperature Probe


  • Miniature probe head with low thermal mass for superior response time
  • RH accuracy up to 0.8 %RH
  • Temperature accuracy up to 0.1 °C (0.18 °F)
  • Temperature measurement range: −40 … +120 °C (−40 … +248 °F)
  • Sensor purge provides superior chemical resistance
  • Modbusâ RTU over RS-485
  • Compatible with Indigo transmitters and Insight PC software
  • Traceable calibration certificate: 6 points for humidity, 1 point for temperature
  • M10×1.5 cable gland included for mounting the probe head

Dpstar is a leading supplier of environmental measurement sensors for temperature, relative humidity, pressure, dew point, CO2, and other environmental condition monitoring for industrial process application and research. Since the ’90s, we earned a reputation as a trusted partner to our clients through our commitment and dedication. We are an authorized distributor and supplier of measuring sensors solutions from renowned manufacturers Vaisala. Vaisala is a global leader in environmental and industrial measurement. Building on 80 years of experience, Vaisala provides observations for a better world. Vaisala is a reliable partner for customers around the world, offering a comprehensive range of innovative observation and measurement products and services.

The Vaisala temperature Probe HMP9 and Vaisala HUMICAP Humidity are designed for easy installation in environments that change quickly, where a fast response time, accurate measurements, and chemical tolerance are important. Their small size allows installation even in tight spaces, with the probe head just 5 mm (0.2 in) in diameter. For duct and chamber installations, a duct installation kit is available. The HMP9 is a great fit for the Indigo product family and works well for applications like monitoring in dryers, air handling units, data centers, and other humidity measurement tasks where temperatures stay under 120°C (248°F), and there’s no high pressure or prolonged exposure to condensation. It’s compatible with Indigo500 series transmitters and Insight PC Software.


Key Benefits

  • Miniature probe head
    The 5 mm diameter probe head contains a new-generation HUMICAP sensor that provides industry-standard humidity measurement performance. Vaisala HMP9 is a stable instrument with a fast response time and low hysteresis in a wide range of applications.
  • Minimized effects of contaminants
    In environments with high concentrations of chemicals and cleaning agents, the chemical purge option heats the sensor to remove harmful chemicals, helping to maintain measurement accuracy between calibration intervals. The chemical purge process can be initiated manually or programmed to take place at set intervals.
  • Flexible connectivity
    The probe is plug-and-play compatible with the Vaisala Indigo series transmitters, which offer a variety of connectivity options through analog signals or digital outputs, configurable relays, and a wireless (WLAN) configuration interface. It can also be used as a standalone digital Modbus RTU transmitter over RS-485 serial bus. For easy-to-use access to field calibration, device analytics, and configuration functionality, the probe can be connected to Vaisala Insight software (for Windows 7, 8.1, and 10; see


Measurement Performance
Relative Humidity
Measurement range 0 … 100 %RH
Accuracy at +23 °C (+73.4 °F) 1) ±0.8 %RH (0 … 90 %RH)
Factory calibration uncertainty 2) ±0.7 %RH (0 … 40 %RH)
±1 %RH (40 … 95 %RH)
T63 response time 3) 15 s
Measurement range −40 … +120 °C (−40 … +248 °F)
Accuracy at +23 °C (+73.4 °F) 1) ±0.1 °C (±0.18 °F)
Factory calibration uncertainty 2) ±0.1 °C (±0.18 °F) at +23 °C (+73.4 °F)
T63 response time 3) 70 s
1) Defined against calibration reference. Including non-linearity, hysteresis, and repeatability.
2) Defined as ±2 standard deviation limits. Small variations possible; see calibration certificate.
3) In still air.
Operating Environment
Operating temperature of probe body −40 … +60 °C (−40 … +140 °F)
Operating temperature of probe head −40 … +120 °C (−40 … +248 °F)
Storage temperature −40 … +60 °C (−40 … +140 °F)
Operating environment Suitable for outdoor use when protected from rain
Measurement environment For air, nitrogen, hydrogen, argon,
helium, and oxygen 1)
IP rating of probe body IP65
1) Consult Vaisala if other chemicals are present. Consider safety regulations with flammable gases
Inputs & Outputs
Operating voltage 15 … 30 V DC
Current consumption 5 mA typical, 400 mA max.
Digital output RS-485, non-isolated
Default serial settings 19200 bps N 8 2
Protocol Modbus RTU
Output Parameters
Absolute humidity (g/m3) Relative humidity (%RH)
Absolute humidity at NTP (g/m3) Relative humidity (dew/frost) (%RH)
Dew point temperature (°C) Temperature (°C)
Dew/frost point temperature (°C) Water concentration (ppmv)
Dew/frost point temperature at 1 atm
Water concentration (wet basis)
(vol %)
Dew point temperature at 1 atm (°C) Water mass fraction (ppmw)
Dew point temperature difference (°C) Water vapor pressure (hPa)
Enthalpy (kJ/kg) Water vapor saturation pressure (hPa)
Mixing ratio (g/kg) Wet-bulb temperature (°C)
EU directives EMC Directive (2014/30/EU)
RoHS Directive (2011/65/EU)
EMC compatibility EN 61326 1, industrial environment
Compliance marks CE, China RoHS, RCM, WEEE
Mechanical Specifications
Connector M12 5-pin A-coded male
Weight 68 g (2.40 oz)
Probe AISI 316L
Probe body PBT
Cable overmolds FEP
HMP9 calibration adapter for HMK15 ASM213801
HMP9 duct installation kit ASM214055
Solar radiation shield DTR502B with sensor head support 215130 DTR502B and 215130
Indigo USB adapter 1) USB2


Vaisala HMP9 Compact Humidity & Temperature Probe_DpstarGroup