Calibrating Thermometers

FishTri · 09/17/2007, 06:36 PM

I have two aquarium heaters with digital readouts for the temperature probes, a small digital thermometer with a remote in-water probe, and a larger digital thermometer that reads water temperature and air temperature.

I've got the four probes immersed in my sump at the same location, and I have four different readings!

Heater 1 . . . . . . . . . 81.0

Heater 2 . . . . . . . . . 80.3

Small Digital . . . . . . . 79.2

Large Digital . . . . . . . 78.5

I also have a glass thermometer calibrated in centigrade (high school science vintage) that reads a little higher than 26.5 (I'm guessing 26.7) which equates to a hair over 80 degrees Fahrenheit.

Is there an "best method" for calibrating these thermometers so they all read (pretty close to) the same temperature?

pjf · 09/17/2007, 06:55 PM

Nearly all digital thermometers drift and must be recalibrated. To recalibrate my Medusa temperature controller and Eheim Jager heater, I use a laboratory thermometer, the non-mercury Miller & Weber T-4900/S80F1 â€œPerformaTherm." It is about a foot long and ranges from 66 to 80 degrees Fahrenheit with 0.2 degree increments. The space between increments represents the odd 10th of a degree. There is a review of it in the reviews section of Reef Central. It is sold as the TM-9301 from HMA Lab Supply.

BLockamon · 09/17/2007, 07:10 PM

Unless your heater or temperature sensor have a means of adjusting the output, it can't be calibrated. Most can't.

FWIW, I think your readings are about as close as can be expected. Depending on the type of thermocouple, junction, connector, etc. the stated allowable manufacturing tolerance ranges from 2 F to 4 F. Most are much better, but you're looking at ~1.25 F. That's pretty good.

We have a saying: A man with two watches never knows what time it is.

FishTri · 09/17/2007, 08:27 PM

Quote:

Originally posted by BLockamon
Unless your heater or temperature sensor have a means of adjusting the output, it can't be calibrated.

Exactly. None of these devices include calibration instructions. I'm figuring I have to crack them open and figure out if there's a couple of pots in there for setpoint and slope.

Or should I just make little stickers for each one that shows the correction factor (e.g. "Add 1.5 degrees for correct temperature").

09/17/2007, 06:36 PM	#1
FishTri Registered Member Join Date: Apr 2002 Location: Delaware County, PA Posts: 598	Calibrating Thermometers I have two aquarium heaters with digital readouts for the temperature probes, a small digital thermometer with a remote in-water probe, and a larger digital thermometer that reads water temperature and air temperature. I've got the four probes immersed in my sump at the same location, and I have four different readings! Heater 1 . . . . . . . . . 81.0 Heater 2 . . . . . . . . . 80.3 Small Digital . . . . . . . 79.2 Large Digital . . . . . . . 78.5 I also have a glass thermometer calibrated in centigrade (high school science vintage) that reads a little higher than 26.5 (I'm guessing 26.7) which equates to a hair over 80 degrees Fahrenheit. Is there an "best method" for calibrating these thermometers so they all read (pretty close to) the same temperature? __________________ ...be right there, Honey... Delaware Valley Reef Club (DVRC) Current Tank Info: 210

09/17/2007, 06:55 PM	#2
pjf Premium Member Join Date: May 2005 Location: Colorado Posts: 2,954	Non-Mercury Laboratory Thermometer Nearly all digital thermometers drift and must be recalibrated. To recalibrate my Medusa temperature controller and Eheim Jager heater, I use a laboratory thermometer, the non-mercury Miller & Weber T-4900/S80F1 â€œPerformaTherm." It is about a foot long and ranges from 66 to 80 degrees Fahrenheit with 0.2 degree increments. The space between increments represents the odd 10th of a degree. There is a review of it in the reviews section of Reef Central. It is sold as the TM-9301 from HMA Lab Supply.

09/17/2007, 07:10 PM	#3
BLockamon Registered Member Join Date: May 2005 Posts: 1,104	Unless your heater or temperature sensor have a means of adjusting the output, it can't be calibrated. Most can't. FWIW, I think your readings are about as close as can be expected. Depending on the type of thermocouple, junction, connector, etc. the stated allowable manufacturing tolerance ranges from 2 F to 4 F. Most are much better, but you're looking at ~1.25 F. That's pretty good. We have a saying: A man with two watches never knows what time it is.