Choose a temperature and humidity data logger around your monitoring decision. Verify the actual temperature/RH range, accuracy at expected conditions, sample interval, data capacity, method of retrieval, battery behavior and required records. A device with an app is not automatically suitable for a regulated monitoring system.
A data logger cannot repair a poor measurement location
Placing a capable recorder near a door, warm compressor or humidifier may produce precise data about the wrong location. Choose representative mounting points, document environmental exposure and test a complete logging cycle before deployment. For regulated storage, match the monitoring plan and sensor calibration to the applicable procedure.
Match the device to the environment
| Application | Questions before purchase |
|---|---|
| Office or archive | Is long-term RH drift important? Will the sensor be disturbed by sunlight or vents? |
| Refrigerated goods | Does the probe measure air or product? What happens during door openings or power loss? |
| Warehouse | Are several positions needed to map local conditions? |
| Quality-controlled process | Are calibrated records, user roles, alarms or audit trails required? |
Humidity accuracy has conditions
Relative-humidity accuracy varies with temperature, RH range, sensor state and calibration history. A published ±RH figure must be read with the conditions stated in the datasheet. Hygrometers may need longer to stabilize after moving into a very different environment. Condensing atmospheres require special care because water on the sensor can affect readings. If two instruments disagree, see the guide to comparing hygrometer readings.
Worked example: schedule and memory
Hypothetical: one temperature/RH pair saved every 10 minutes creates 144 pairs/day. If the chosen logger actually stores 16,000 pairs, theoretical capacity is 16,000 ÷ 144 = 111.1 days. Confirm whether the manual counts pairs, values or memory slots and whether logging stops or overwrites when full. For practical guidance on sampling intervals and storage, see the data-logging guide.
Testo model and configuration checks
The testo 174 H (USB-C version) measures both temperature and RH with local data storage and PC transfer. The testo 605i instead serves live air-temperature and humidity spot measurements through the Smart App; it should not be described as an autonomous long-duration logger with the same memory and retrieval behavior. If remote alarms or regulatory audit features matter, verify those capabilities in the chosen system rather than inferring them from Bluetooth connectivity.
Deployment procedure
- Define the threshold or trend of interest and the monitoring duration.
- Choose representative locations, possibly using a preliminary spatial mapping study.
- Synchronize timestamps and set the interval before deployment.
- Record serial numbers, installed locations and sensor-check evidence.
- Review data for gaps, condensation, excursions and maintenance events.
- Archive original exports and actions taken in response to excursions.
Common buying mistakes
Do not select a logger solely by memory size, advertised connectivity or minimum displayed increment. Confirm sensor performance across the actual humidity range, including near extremes, and match data integrity to the intended business or regulatory decision.