What Is a Temperature and Humidity Meter (Thermohygrometer)? Types and Selection Criteria
A temperature and humidity meter (thermohygrometer) is a digital instrument that measures the air temperature and relative humidity around it and shows both on its display.
A temperature and humidity meter (thermohygrometer) is a digital measuring instrument that measures the air temperature and relative humidity of its surroundings together and shows them on its display. It is used to monitor ambient conditions in panel and server rooms, warehouses, archives, greenhouses and production areas, and when adjusting air conditioning and ventilation. It does not measure the moisture inside materials such as wood, plaster or concrete; that requires a material moisture meter.
Types of temperature and humidity meters
| Type | Feature | Models in the catalog |
|---|---|---|
| Handheld meter | Instant measurement; MAX/MIN and data hold | UNI-T UT333, UT333S |
| Handheld meter with Bluetooth | Sends measurements to an app on the phone | UNI-T UT333BT |
| Logging (USB) meter | Stores measurements in memory and transfers them to a computer over USB; also shows dew point and wet-bulb temperature | UNI-T UT331+, UT332+ |
| Digital ambient display | Shows ambient values continuously; the A13T also has a clock | Unit A12T, A13T |
Selection criteria
- Measuring range: According to the manufacturer, the UT333 and UT333BT measure from -10 °C to 60 °C and 0–100 % relative humidity. If you will use the meter in a cold room or outdoors, check the lower limit in the datasheet.
- Accuracy: The UT333 and UT333BT give ±1 °C and ±5 % relative humidity; for temperature, the UT331+ gives ±0.5 °C and the UT332+ ±0.3 °C. Humidity accuracy is usually stated for a certain range; the error grows at the very dry and very humid ends.
- Logging and transfer: A handheld meter without logging is enough for spot checks. To document measurements, choose the UT331+ and UT332+ (USB) or the UT333BT (Bluetooth). For monitoring that lasts days, temperature and humidity data loggers are more suitable.
- Calculated values: Dew point helps assess the risk of condensation in panels and warehouses; wet-bulb temperature helps with HVAC adjustment. Choose the UT331+ or UT332+ for these values.
- Permanent monitoring: If the value is to be sent to a PLC or building automation system, a humidity and temperature transmitter is used instead of a handheld instrument.
Common mistakes
- Reading right after changing environment: The value keeps changing until the humidity sensor adapts to the new environment; wait until the reading settles.
- Holding the meter in your palm or close to your face: Hand heat and breath raise both temperature and humidity.
- Measuring next to a heat source: Sunlight, a heater or an air conditioning outlet gives a value that does not reflect the room as a whole.
- Trying to measure material moisture with a thermohygrometer: For wall, wood or concrete moisture, use a material moisture meter.
Temperature and humidity meters in the catalog
The Temperature and Humidity Meters category has 7 active products, all from Unit (UNI-T): UT331+, UT332+, UT333, UT333S, UT333BT, A12T and A13T. All are sold by the piece and listed with a price.
Frequently asked questions
What is relative humidity?
It is the ratio of the water vapour in the air to the maximum amount of water vapour the air can hold at that temperature. As the same air warms, relative humidity falls; as it cools, relative humidity rises.
Why does dew point matter?
If the temperature of a surface falls below the dew point, condensation forms on it. Condensation inside a panel can cause corrosion and insulation faults.
What is the difference between a thermohygrometer and a material moisture meter?
A thermohygrometer measures the temperature and relative humidity of the air. A material moisture meter shows the moisture content inside a material such as wood, plaster or concrete.
How are measurements transferred to a computer or phone?
The UT331+ and UT332+ transfer their records to a computer over USB. The UT333BT sends measurements via Bluetooth to the manufacturer's mobile app.