Sections
Check of Calibration of Cheap Temperature Humidity Sensors
Comparison of readings from common Chinese sensors with a reliable reference
Chinese sensors for temperature and humidity like the one in the photo are very common and found also inside other devices, since they are extremely cheap and quite compact. They are even available with large digit temperature, or viceversa with large digits humidity.
I started doubting about the reliability when I noticed it was sensing 25% humidity at my workplace, while I was not feeling the usual symptoms of dry air.
I decided to compare the readings with a TFA Dostmann 30.5011 Digital Thermo Hygrometer Comfort Control which is explicitly calibrated in the range 1-99% with 5% accuracy.
I collected readings at different temperatures and humidities for the TFS Dostmann and for two Chinese sensors.
| TFA | Chinese 1 | Chinese 2 | |||
|---|---|---|---|---|---|
| T | H | T | H | T | H |
| 17.1 | 71.2 | 17.4 | 72.0 | 17.4 | 72.0 |
| 18.6 | 67.0 | 19.1 | 66.0 | 19.0 | 67.0 |
| 18.4 | 67.0 | 18.8 | 66.0 | 18.8 | 67.0 |
| 17.4 | 60.4 | 17.6 | 58.0 | 17.5 | 62.0 |
| 18.0 | 54.3 | 18.5 | 53.0 | 18.6 | 52.0 |
| 19.7 | 53.4 | 20.9 | 51.0 | 20.6 | 54.0 |
| 19.4 | 51.9 | 19.8 | 52.0 | 19.9 | 51.0 |
| 16.2 | 47.0 | 16.7 | 46.0 | 16.6 | 50.0 |
| 18.6 | 44.0 | 19.5 | 44.0 | 19.4 | 46.0 |
| 19.3 | 43.0 | 19.6 | 42.0 | 19.4 | 46.0 |
| 21.5 | 38.0 | 22.1 | 33.0 | 21.9 | 36.0 |
| 22.1 | 38.0 | 22.6 | 30.0 | 22.4 | 34.0 |
| 22.8 | 37.0 | 23.2 | 28.0 | 23.0 | 30.0 |
| 23.9 | 37.0 | 24.1 | 25.0 | 24.1 | 27.0 |
| 24.4 | 36.4 | 24.7 | 24.0 | 24.7 | 26.0 |
| 25.1 | 35.7 | 25.3 | 24.0 | 25.3 | 25.0 |
| 25.3 | 35.7 | 25.6 | 21.0 | 25.4 | 23.0 |
| 26.4 | 35.3 | 26.5 | 22.0 | 26.6 | 24.0 |
| 26.1 | 35.3 | 26.6 | 21.0 | 26.4 | 23.0 |
| 27.8 | 35.2 | 27.9 | 22.0 | 27.9 | 24.0 |
| 27.0 | 34.9 | 27.0 | 24.0 | 27.1 | 25.0 |
It looks like my Chinese sensors match the German one down to 42%. Below that, the discrepancies explode. Basically they are reliable only in the "healthy" humidity range (40% and up). Using these sensors for other purposes is pointless.
I checked another Chinese sensor, a Xiaomi Zigbee one and it matches the German reference. But it costs 10 Euro a piece, not 50 cents.
Summary: if you care about the values, you have to pay for them. Cheap humidity sensors are unlikely to be reliable. Humidity sensing is not that easy, even TFS Dostmann doesn't calibrate all sensors in such a wide range 1-99%: Digitales Thermo-Hygrometer MOXX is rated 20-99%.
Author: Olaf Marzocchi
First revision: 2023-07-23.
Last revision: 2023-07-23.