Re: Would you calibrate this instrument?
My simple answer to your question is YES. Have it calibrated. The long answer follows:
Have you ever had to stop painiting parts because the temperature or humidity was out of the range? If yes, then it is good that you are recording it. If not, what is the point of recording it?
If the temp or humidity is out of spec, what does it do to the product and would this be caught by some other quality inspection. (ie, the paint goes on poorly and you do a visual check at the end for surface finish or you do some other test to the part). If this is the case, then you may not need to record it.
Let's assume that you have to record it and none of the questions above gave reason to stop recording it (or the president of the comapny wants you to record it and he is the boss so you are going to do it.)
My question would be : Do you need to calibrate the one you have to make sure that it has been good for all of the years that you have used it? OR do you want to get it calibrated for the furture? What will you do if it is found to be bad? Most likely, you will just do nothing and buy a new one.
All of that being said, ISO 17025 accredited calibration of a temperature/humidity meter is about $85. A new meter can be purchased from Fisher Scientific with an accredited certificate that has a two year due date for about $50-$60. Go to
www.fishersci.com and search for "traceable temperature humidity". With the tolerances you have, you could buy a new gage fro fisher and do a single point comparison between the new gage and the old gage to confirm that the old gage was actually working for the past few years. Note also, that if you send the gage out, someone will ask, "how did you record temperature and humidity when the gage was out for service?"
Knowing that you can buy a new one with a cert for less than the cost of calibrating the old one, please do not make the mistake of just buying a new one with a cert every year or two. Remember, there are two points to having something calibrated: 1.) to have confidene that it is making a good measurment now 2.) to know that is has probably made good measurements since the last time it was calibrated.
Joe