Taking humidity readings: newbie question

[midgk0]

Hi there,
I hope this question hasn't already been asked: I did search and couldn't find anything. I've just started a job that involves measuring the temperature and humidity of various spaces. I've been given a Precision Gold N21FR multimeter to take spot readings, though I am thinking of proposing we buy some recording thermohygrometers for longer-term readings. Anyway, when I use the spot meter in some of the spaces, the humidity reading just keeps dropping. Sometimes this will be quite quick and it will level out, but other times I can wait 15 minutes and it still keeps dropping by 0.1% every 30 seconds or so. I was wondering whether I should try to wait for it to stop dropping, but perhaps that won't happen? Or should I choose an amount of time with a stopwatch and take a reading after the time has elapsed, regardless of whether it is still dropping or not? Sorry if this is a daft question, I just want to make sure that the data I'm logging is actually useful!

Many thanks,

Katherine

[IanB]

Bear in mind that that meter is not a precision instrument, so the readings will not be highly accurate.

I found what looks like the manual online and it seems that for relative humidity readings the accuracy is about plus/minus 5% and you should wait up to 15 minutes for the reading to settle before taking a measurement.

https://maplindownloads.s3-eu-west-1.amazonaws.com/N21FR-8667.pdf

[midgk0]

That's what I thought: it would be better to use the spot meter to supplement the readings of a recording thermo-hygrometer. I will try leaving it for 15 minutes, to see if that makes a difference. Thanks for your help!

[mzzj]

Hi there,
I hope this question hasn't already been asked: I did search and couldn't find anything. I've just started a job that involves measuring the temperature and humidity of various spaces. I've been given a Precision Gold N21FR multimeter to take spot readings, though I am thinking of proposing we buy some recording thermohygrometers for longer-term readings. Anyway, when I use the spot meter in some of the spaces, the humidity reading just keeps dropping. Sometimes this will be quite quick and it will level out, but other times I can wait 15 minutes and it still keeps dropping by 0.1% every 30 seconds or so. I was wondering whether I should try to wait for it to stop dropping, but perhaps that won't happen? Or should I choose an amount of time with a stopwatch and take a reading after the time has elapsed, regardless of whether it is still dropping or not? Sorry if this is a daft question, I just want to make sure that the data I'm logging is actually useful!

Many thanks,

Katherine

Cheapest, crappiest humidity sensors behave pretty much like you describe, settling time can be several days! to last 1-2% vs 15 minutes with a "proper"* good humidity sensor.

Low humidity is typically the problematic area for cheapest sensors/meters, your meter has NO response time specification whatsoever below 45% RH 

*) humidity meters from manufacturers like Vaisala, Rotronic and E+E



 

[midgk0]

Thank you, good to get some advice about a better brand! I thought as much due to the vagueness of the instruction manual and the fact that it measures *everything*, never a good sign...