HMP155A-L Temperature and Relative Humidity Probe
Accurate, Wide Temp Range
Higher-end sensor where higher accuracy is required
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The HMP155A, manufactured by Vaisala, monitors relative humidity (RH) for the range of 0 to 100% RH and temperature for the range of -80° to +60°C. It can provide reliable measurements for a wide range of applications, as part of a weather station system or as a single instrument. All Campbell Scientific dataloggers are compatible.

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Benefits and Features

  • Well-suited for long-term, unattended applications
  • Accurate and rugged
  • Mounts to a mast, crossarm, or user-supplied pole
  • Compatible with most Campbell Scientific data loggers


HMP155A-L in a 41005-5 radiation shield and mounted to a pole (items sold separately)

Detailed Description

The HMP155A uses a HUMICAP180R capacitive thin film polymer sensor to measure RH, and a PRT to measure temperature. 

To reduce the current drain, power can be supplied to the HMP155A only during measurement when the sensor is connected to the datalogger’s switched 12 V terminal. Dataloggers that do not have a switched 12 V terminal, such as the CR510 or CR7, can use the SW12V switched 12 V device to switch power to the sensor only during measurement.


Electromagnetic Compatibility Complies with EMC standard EN61326-1 Electromagnetic
Filter Description Sintered PTFE
Housing Body Material PC
Housing Classification IP66
Voltage Output 0 to 1 Vdc
Average Current Consumption ≤ 3 mA (analog output mode)
Operating Voltage 7 to 28 Vdc
Settling Time 2 s (at power up)
Field-Replaceable Chip or Recalibrate Recalibrate
Tip Diameter 1.2 cm (0.5 in.)
Length 27.9 cm (11 in.)
Head Height 4 cm (1.6 in.)
Body Height 2.4 cm (0.9 in.)
Body Width 2.0 cm (0.8 in.)

Relative Humidity

Sensing Element HUMICAP 180R
Measurement Range 0 to 100% RH (non-condensing)
Response Time
  • The response time for the RH specification is for the HUMICAP 180R at 20°C in still air with sintered PTFE filter and a 0 to 75% RH step change.
  • 20 s (63% step change)
  • 60 s (90% step change)
Factory Calibration Uncertainty
  • The factory calibration uncertainty is defined as ±2 standard deviation limits. Uncertainty is at +20°C. Small variations are possible; see also the calibration certificate.
  • ±0.6% RH 0 to 40% RH
  • ±1.0% RH 40 to 97% RH
  • -NOTE- Accuracy specifications include non-linearity, hysteresis, and repeatability.
  • ±1% RH (at 15° to 25°C, 0 to 90% RH)
  • ±1.7% RH (at 15° to 25°C, 90 to 100% RH)
  • ±(1.4 + 0.032 × reading) % RH (at -60° to -40°C)
  • ±(1.2 + 0.012 × reading) % RH (at -40° to -20°C)
  • ±(1.0 + 0.008 × reading) % RH (at -20° to +40°C)
  • ± (1.2 + 0.012 × reading) % RH (at 40° to 60°C)

Air Temperature

Sensing Element PT 100 RTD 1/3 class B IEC 751
Measurement Range -80° to +60°C
  • ±(0.226 - 0.0028 x temperature)°C (-80° to +20°C)
  • ±(0.055 + 0.0057 x temperature)°C (+20° to +60°C)
Entire Temperature Range Refer to graph in probe manual.


Please note: The following shows notable compatibility information. It is not a comprehensive list of all compatible products.


Product Compatible Note
CR1000 (retired)
CR3000 (retired)
CR800 (retired)
CR850 (retired)

Additional Compatibility Information

Sensor Mounts

When exposed to sunlight, the HMP155A must be housed in a 41005-5 or RAD14 14-plate naturally aspirated radiation shield. The 41005-5 and RAD14 attach to a crossarm, mast, or user-supplied pipe with a 2.5 to 5.3 cm (1.0 to 2.1 in.) outer diameter. The RAD14 uses a double-louvered design that offers improved sensor protection from driving rain, snow, and insect intrusion, It also has lower self-heating in bright sunlight combined with higher temperatures (> 24°C [~75°F])
and low wind speeds (< 2 m s-1 [~4.5 mph]), giving a better measurement.


HMP155A Example Programs (4 KB) 15-10-2021

Description: Example CR1000X programs that measure either the analog voltage or RS-485 output of the HMP155A. The analog voltage programs use either the VoltSE or VoltDiff instruction and switch power to the sensor only during measurements. One program also calculates the mean vapor pressure. The RS-485 program measures the RS-485 output with an SDM-SIO1A/SIO4A.  Although these programs are written for the CR1000X, programs for other dataloggers will be similar.

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