Hi guys,
I recently purchased 3 Aqara Temperature and humidity sensors.
I put them into the fridge to test their accuracy. This is the result:
I think the result is pretty bad - you can clearly see that there is a temp difference of more than 1°C
That seems like a lot to me, or am I too eager? They were literaly lying right next to each other.
Anyone else with this problem?
How is it inn higer temperature, if there is an constant offset this can be adjusted. I think this is quite useual for cheap sensors
The specs are telling: “The measuring accuracy is -0.3 to +0.3 degrees. Also, the humidity sensor has a high accuracy. The tolerance range is only 3%.”…
–> max difference of 0.6 degrees!
I could see in your graph a maximum difference of approx. 0.8 °C at 9:00 o’clock…
It’s not so bad, I think. Maybe you can calibrate them?
I wouldn’t know how. Probably an offset with a rule would be a possibility.
There is an old saying which I wish I could remember where I first heard it.
“If you have one thermometer you know the temperature. If you have two or more you have confusion.” You need to spend really big money to buy thermometers that have very precise measurements and those need to be precisely calibrated.
Based on what Alex says, these seem to be performing within their published specifications, maybe just a tad worse.
If you do write a Rule, pay attention to what Jostein asked. Are they consistently off? For example, is Sensor3 always .5 lower than Sensor1 no matter where you are in the temperature range? Based on that graph I’m not so sure they are.
If being up to 1 degree off from each other is meaningful in your use case then you need to get more precise sensors or just pick one sensor. If not, just be sure you configure your hysteresis and remember when you look at the data that they have a range of uncertainty.
Maybe with the MiHome App?
I wouldn’t be able to check unfortunately. My sensors are connected to a CC2531 with zigbee2mqtt.
Then you better use a rule. E.g. sensor2 (-0.3) and sensor3 (+0.3).
Use the offset profile
That was introduced with openhab 2.4, correct?
Is there a turorial out there?
Example:
Number:Temperature Sensor2Temp "Temperature [%.1f °C]" <temperature> { channel="your-channel" [profile="offset", offset="0.3"] }It’s already in the docs! Wow. Last time I checked it was not there. So thank you. I have to keep checking the Docs more often. Or look at a changelook or something.
Also if you haven’t seen or figured it out: use a container of ice water for calibration, as the ice water will be at 32F / 0C, versus a random cold temperature in your freezer or refrigerator.