NEWS | May 26, 2021

Soldier Safety: Wet Bulb Checks Humidity

If you’ve seen Soldiers setting up what appears to be some kind of equipment on a tripod, and it’s not a camera, look closer. It could be a wet bulb thermometer (also called a hygrometer).

Wet bulb thermometers measure relative humidity. Relative humidity is often used with the local temperature to ensure a safe work environment, because humidity affects the body’s ability to cool itself.

The wet bulb measurement compares the temperature of a “dry” thermometer to the temperature of a thermometer covered in a cloth or sock that has been moistened with water. As air is passed over the wet thermometer, the moisture in the sock evaporates and cools the thermometer.

The drier the air, the faster the evaporation and the cooler the reading will be. The wet and dry thermometer temperatures are then compared, and the temperature difference is converted into an approximate relative humidity reading.

Wet bulb thermometers are considered Test, Measurement, and Diagnostic Equipment (TMDE). They should be periodically calibrated to ensure they give correct readings.

In no case should a unit attempt calibration. Your local TMDE support activity can calibrate wet bulb thermometers or arrange for support.

Contact your local TMDE support coordinator to ensure your wet bulb thermometer is supported correctly and giving accurate readings. If your specific model is not already listed in TB 43-180, Calibration and Repair Requirements for the Maintenance of Army Materiel (updated monthly), ask your TMDE support activity how to get it added.

Questions? Email the USATA Enterprise Support Directorate at: