Thursday, March 24, 2022

Sensor Bias And Noise

My second SensorPush hygrometer arrived in the mail yesterday and I immediately hooked it up. I'm going to start my tobacco experiments tonight, but first I needed to see if the two sensors agreed with one another. Here's the applicable chart.

Click on the image for a readable version.

The first thing to notice is that the Y scale is deceptive, particularly with regards to humidity. By compressing it to the max and min readings for the time frame, it emphasizes the differences in the two sensors. In any case, it looks like the two of them agree quite nicely on temperature. I'm willing to accept a ±0.2 degrees accuracy.

As far as the humidity goes, it looks like it's ±4%. That's good enough. If I give my feedback look for the tobacco fermentation coffin a 10% window, perhaps biasing it down so that it's not trying to hit 90% humidity when the sensor can't read that high, that should be fine. As far as fermentation goes, I can't believe that 80% humidity in the chamber will be all that different from 90%.

Today, I'm going to take one of them and mount it in a sealed contained with water at the bottom and post the other one directly outside said chamber. I want to see what happens to the humidity with a reservoir only. I'll have to run this same experiment twice, exchanging the sensor positions to further test their accuracy.

1 comment:

tim eisele said...

I'm actually impressed that your humidity sensors agree that closely. In my experience, humidity sensors are not particularly precise, and +/-4% is actually pretty good.