I’ve had one of these in service in my greenhouse for a few years, and I brought it inside recently to finally design a proper case for it. (It’s at https://www.thingiverse.com/thing:4693294 if you want to check it out!)
While testing things, I noticed that the readings I was getting were hotter than I expected. I assumed it was because of the design of the case, so I did some testing in the open air and the readings are still high.
I happened to have a spare on hand, so I swapped my Particle Photon over to it and tested again and it’s giving me the same high values. I set it next to an ecobee sensor and a watch that has a temp sensor in it. After an hour of settling time after being handled, both of those are reading about 69 degrees F, whereas this is reporting about 76 F.
I updated the photon to be running current OS (2.0.1) and I updated the sensor lib to current as well (1.1.3) and the offset remains. Any suggestions? Has anyone else seen something similar? I looked at the library code, and while I can’t say I fully grok it, the calcs being done in there seem about right? Later I intend to dive into that more deeply to make absolutely sure there’s not a problem there, but I would be surprised if that were the case.
The Photon gets a bit warm and inside an enclosure that could be throwing off your temperature measurements. If it’s consistently 7 degrees warm, you could just subtract 7 from any reading you’re getting as a simple fix though.
Yeah, I’ve thought about doing that, but I haven’t for a couple reasons:
-
It doesn’t seem to be exactly 7 degrees
-
It does the same thing inside the case or outside
-
It does it with two different weather shield boards
All that makes me think it’s some underlying thing that needs to be addressed.
Has anyone else done some calibration against other sensors? Oh, it’s also worth noting that I’m getting the same readings from both the onboard temp sensors.
I’ve done some more testing here, and the amount it’s off seems to vary with the temperature. Right now, I have ambient at about 73 degrees, and the weather shield is reading about 82, or 9 degrees high. If I reduce the ambient, the difference gets smaller.
I’ve also done some more testing to see the impact of having the station inside and outside of the case. So far, it only accounts for about 1 degree of change.
The Photon itself generates heat that can influence the sensor readings, you might consider an external temperature sensor that’s 6" to 12" away from any heat sources if you need accurate temperature without accounting for the readings in code.