With all of my air quality monitor reviews, I’m always looking for sensors that can be used as a baseline. Of course, getting a particulate matter reference sensor costs tens of thousands of dollars and is out of the question. However, without breaking the bank, I’ve been looking for something I can use for temperature and RH comparisons. After some looking, I settled on the Traceable 4040, an inexpensive (although still around $200 where I live) hygrometer that provides relatively accurate temperature and relative humidity readings. Most importantly, each monitor has a lab certificate showing its performance following NIST standards. Below is an image of the certificate that my monitor came with.
What is particularly interesting is that the monitor has a stated accuracy of ± 1°C and ± 5% RH. This is still a very large range, but I figured a monitor such as this could at least indicate how well the temperature and RH sensors in a given air quality monitor are. Anyway, the interesting part is the certificate below.
As you can see from the results above, the ‘as left’ results are far closer to the nominal conditions than the stated accuracy of the device led me to think. While I understand that the accuracy of hygrometers will decrease at higher relative humidity levels (and that’s likely where the large ‘stated range’ really applies), this could turn out to be a better comparison tool than I had anticipated - so long as RH levels are kept in check during testing.
I look forward to testing this more and providing updates.