The Vaisala Humicap HMP155 humidity and temperature probe provides reliable humidity and temperature measurement. The HMP155 has a new generation Vaisala Humicap®180R sensor that has excellent stability and withstands harsh environments. The probe structure is solid and the sensor is protected with a sintered teflon filter, which gives maximum protection against liquid water, dust, and dirt.

Measuring humidity reliably is challenging in environments where humidity is near saturation. Measurements may be corrupted by fog, mist, rain, and heavy dew. A wet probe may not give an accurate measurement in the ambient air.

This is an environment to which Vaisala has designed a patented, warmed probe for reliable measuring. As the sensor head is warmed continuously, the humidity level inside it stays below the ambient level. Thus, it also reduces the risk of condensation forming on the probe.

The HMP155 is especially designed for use in meteorological applications, such as synoptic and hydrological weather stations, aviation, and road weather.

Technical Specifications

Relative Humidity

Measurement range0 - 100 %RH
Accuracy (incl. non-linearity, hysteresis and repeatability) at
+15 to +25 °C (+59 to +77 °F)
-20 to+40 °C (-4 to 104 °F)
-40 to -20 °C (-40 to -4 °F)
+40 to +60 °C (+104 to +140 °F)
-60 to -40 °C (-76 to -40 °F)
Factory calibration
uncertainty (+20 °C /+68 °F)

±1 %RH (0 - 90 %RH)
±1.7 %RH (90 - 100 %RH)
±(1.0 + 0.008 x reading) %RH
±(1.2 + 0.012 x reading) %RH
±(1.2 + 0.012 x reading) %RH
±(1.4 + 0.032 x reading) %RH
±0.6 %RH (0 to 40 %RH)*
±1.0 %RH (40 ... 97 %RH)*
Response time at +20 °C in still air with a sintered PTFE filter

20 s
60 s


Measurement range-80 °C to +60 °C (-112 °F to +140 °F)
Accuracy with voltage output at
-80 to +20 °C
+20 to +60 °C
passive (resistive) output
according to IEC 751 1/3 Class B
RS485 output
-80 to +20 °C
+20 to +60 °C

±(0.226 - 0.0028 x temperature) °C
±(0.055 + 0.0057 x temperature) °C
±(0.1 + 0.00167 x |temperature|)°C
±(0.176 - 0.0028 x temperature) °C
±(0.07 + 0.0025 x temperature) °C
Temperature sensorPt100 RTD Class F0.1 IEC 60751
Response time with additional temperature probe in 3 m/s air flow

20 s
35 s


Operating temperature range-80 °C to +60 °C (-112 °F to +140 °F)
Storage temperature range-80 °C to +60 °C (-112 °F to +140 °F)
Connection8-pin male M12 connector
Connection cables3.5, 10, and 30 m
Cable materialPUR
Wire sizeAWG26
Service cablesUSB connection cable
MI70 connection cable
Additional T probe cable length2 m
Housing materialPC
Housing classificationIP66
Sensor protectionsintered PTFE
optional membrane filter
Weight (probe)86 g
Dimensions267 mm L x 40 mm Ø
Electromagnetic compatibilityComplies with the EMC standard EN61326-1, Electrical equipment for measurement control and laboratory use - EMC requirement for use in industrial locations

Inputs and outputs

Operating voltage7 to 28 VDC
Note: minimum operating voltage 12 V with 0 to 5 V output and 16 V with 0 to 10 V output, probe heating, chemical purge or XHEAT.
Outputsvoltage output (0 - 1 V, 0 - 5 V, 0 - 10 V)
resistive Pt100 (4-wire connection)
Average current consumption (+15 VDC, load 100 kOhm)

0 to 1 V output

0 to 10 V output


during chemical purge

with warmed probe

3 mA
+0.5 mA
4 mA
max 110 mA
max. 150 mA
Settling time at power-up
voltage output

2 s


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