Humidity and Air Temperature Probe—Vaisala HMP155

The HMP155 measures ambient air temperature and humidity and provides data to the Sutron 9210B datalogger as analog signals. Here are basic installation and operating guidelines for using the using the HMP155 in LI-COR eddy covariance systems with a biomet system running Biomet_100, Biomet_101, Biomet_102, and Biomet_103 programs.

HMP155 Specifications:
Operating Temperature Range: -40 to +60 °C
Operating Humidity Range: 0 to 100% RH
Voltage Output: 0 to 1 V
Average Current Consumption: <3 mA
Operating Voltage: 7 to 28 VDC

For more information and complete operating instructions see:

Installing the HPM155

  1. Assemble the Humidity and Temperature Probe.
    • Remove the protective yellow cap from the sensor prior to use.
    • Install the HMP155 in the R.M. Young 14-plate radiation shield (7900-135).
    • Loosen the plastic split-nut on the bottom of the radiation shield and insert the sensor into the split-nut and shield. Tighten the split-nut to clasp the sensor.
  2. Siting the Humidity and Temperature Probe.
  3. Figure 1. Install the HMP155 at a minimum distance from nearby obstructions of at least four times the height of the obstruction (H).
    • Place the HMP155 over an open, level area that is free of obstructions.
    • Place it at least 30 m from paved areas.
    • Position the probe as far above vegetation as possible. If you will use the temperature measurement for eddy covariance data processing, position the sensor close to the sonic anemometer but far enough away that it won't obstruct airflow.
  4. Mount the Humidity and Temperature Probe.
    • Wrap the band clamp around a vertical mast.
    • Secure the cable to the tower using zip ties. Avoid bending the cable sharply.
  5. Install the Humidity and Temperature Probe Leads.
  6. The HMP155 is supported by datalogger programs Biomet_100, Biomet_101, Biomet_102, and Biomet_103. For custom programs, use the AT/RH block and configure it as described in Humidity and Temperature Probe (HMP155).
  7. Route cables through an opening in the bottom of the enclosure.Note: Route the sensor cable(s) through an opening in the enclosure prior to installing the leads in the terminal strip.
Figure 2. HMP155 wiring for the Biomet_100 and Biomet_101 programs.
Table 2. HMP155 wiring for the Biomet_100 and Biomet_101 programs.
Description Color Terminal
Temp. Signal (+) White A15 (CH8)
Shield Black A16 (AGND)
RH Signal (+) Yellow A17 (CH9)
Signal Ground Green B14 (GND)
Power Ground Red B14 (GND)
Power (+) Blue B15 (SW'D12)
Not Connected Brown/Gray/Pink None
Figure 3. HMP155 wiring for the Biomet_102 program. Wiring for Biomet_103 is identical, except leads connect to AIO3 rather than AIO2.
Table 3. HMP155 wiring for the Biomet_102 and Biomet_103 programs. For Biomet_102, terminal assignments are for AIO2. For Biomet_103, terminal assignments are for AIO3.
Description Color Terminal
Temp. Signal (+) White 11 (CH8)
Shield Black 12 (AGND)
RH Signal (+) Yellow 13 (CH9)
Signal Ground Green 15 (AGND)
Power Ground Red 17 (GND)
Power (+) Blue 18 (SWBAT)
Not Connected Brown/Gray/Pink None

Retrieving Data

If the system is configured to log biomet data in .ghg files for processing in EddyPro software or the SmartFlux System, data are stored on the removable USB storage device. Refer to the Biomet Instruction Manual for details.


  • Monthly: Check the radiation shield to be sure it is free of debris.
  • Check the probe filter for contaminants. Clean or replace as needed. Replacement filters are available from Vaisala.
  • Clean the probe with a soft, lint free cloth. Use water and mild detergent if needed.
  • In regions near salty bodies of water, salt may accumulate on the radiation shield, sensor, or filter. Salt should be removed by gently rinsing with distilled water.
  • Recalibrate the sensor based on the manufacturer’s recommendations.