Hi,
I would like to measure the humidity in the cellar.
To do this, I have placed an Aqara sensor and a Sonoff sensor next to each other in the cellar.
To my astonishment, they both show different values.
They are about 5% (!!!) apart, here an comparison of the last 6 hours:
Which one is measuring correctly? Can I somehow carry out a calibration or something similar?
Many thanks for any ideas and help!
Neither. If you add more sensors you might find even higher spread, 10% wouldn’t be surprise. Expect 3% even from same brand/model.
Yes, you can do that quite easily in Z2MQTT. I doubt you can in ZHA though.
However at this point, you don’t know which of these devices is incorrect. You’d need a (professionally) calibrated humidity sensor to get the correct value at a given point in time. Worst case scenario is that both are reading 2.5% humidity too high/low.
Either way, those readings shouldn’t make too much of a difference to you. Whatever sensor you use, the ideal way to trigger is on the change, not on the absolute value - use something like the Trend integration to accomplish this.
I would not be too worried about a 5% difference. Once calibrated against a reliable reference device, the trend or change should be what you are after to trigger automations.
Btw unless it’s a temporary spike, I would be concerned about a 72%+ humidity level in your cellar.
I’m surprised you found only 5% difference. Humidity is difficult to get accurate in the best devices. Even after calibrating, it drifts for a variety of reasons. Best is to look at trends instead of the value itself to indicate a problem.
Thanks, how I can do calibration using Z2MQTT?
BTW. the cellar is more or less a garage without a garage door close to my house with a door inbetween. In the winter season the humidity is almost around 70% due to high humidiuty outside.
It is device specific but generally found under: “Settings (specific)”
You need to compare the value against a reliable source and apply an offset.
