How to calibrate a thermometer?.

printer said:

Your first idea of using a meat thermometer and calibrate with the ice/boiling water method and using it as a reference would be my way to go. I bought a couple of meat probe thermometers and they seemed pretty accurate. But back to calibrating other thermometers using your reference, I would slap together a wooden box with a door and a hole to stick the reference probe through, seal the hole. Stick the thermometers in an wait. After a length of time (Depending how accurate you want it and your setup) take the readings and compare.

We used to have our students do labs calibrating with the boiling water/ice point method. On using the transfer method for the others using your 'reference' thermometer, I did many hundreds of calibrations this way.

Click to expand...

I wasn't sure if the meat therm would be usable. I read a little saying that while it may be calibrated ok at the extreme ends it doesn't mean it's a linear scale across mid temp readings. It was enough to put me off although in hindsight I guess the possible inaccuracy is probably meaningless for my needs.

Never the less I went with the lab therm/closed box and a bovida pack/sealed tub. It put things in a decent enough range for me to feel quite certain. On the pluss side humidity at it's worse reading was about 7% out while temp calibration was within 5%F if I recall. Still, it's peace of mind that RH/temps are accurate enough that I can get a base line for vpd nutrient strength. I realised that without being certain of these aspects and only paying superficial attention to vpd I may have been running in circles with nutrient transition adjustments, particularly with N.

I would highly recommend people calibrate therm/humidity read outs when you can. During the process of doing all this I seen some horror comments of new hygrometers being way off, 10-15%. That will definately make a difference if you strugle with various issues like pm etc. All in it cost about £10 - $15 and 30min of putting things together. Some people seemed happy with trusting de-huey read out or an expensive RH read out and to be honest I think that's a big mistake. I've been in that same boat too, just trusting the units are correct out of the box, never dawned on me they are likely not.

The meat thermometer usually uses a thermistor as a temperature source, they are pretty linear. I have some cheap temp/humidity sensors and they (mine) are pretty accurate. But if the temperature reading is inaccurate it throws off the humidity readings as they depend on what the temperature is. I had access to some pretty good temperature and humidity instruments at work, I will probably have to check my instruments at some point again. Calibration was part of the field I worked in.