Impossible humidity measurements using DHT22 and similar sensors

[ccaru]

I am running a luthier's workshop where maintaining a solid 45% humidity is crucial. I've been battling with setting up Domoticz for this purpose for months now, and i'm still finding lots of issues. I run both a Humidifier and dehumidifier both connected as switches - no issues there, but having real challenges with reading the current humidity, particularly as the temperature fluctuates.

One of my more recent experiments was to connect several DHT22's to a single ESP32 microcontroller, and put them in a sealed box with a Potassium Chloride slurry - this should give a constant reading of 44% at 20C and 43% at 25C.

Out of the box, all started off with them giving wildly different readings, which I was kind of expecting since they were not calibrated, so I adjusted the levels so that they all read the same. Being all in the same box, they were all at the same temperature and humidity - at the time it was 20C.

At 25degrees, all of them had completely different humidity levels - from 32% up to 51% (Considering that DHT22's are advertised as having a 3% accuracy this was surprising.).

Over the years i've tried various devices - Netatmo, generic RF sensors, a device from Airthings - and all seem to exhibit the same problem - you put them all in the same box and calibrate them at a particular temperature, then you move away from that temperature and they all seem to go in all sorts of random directions.

Does anybody have a similar experience a could recommend a device which I could rely on?