Equipment Review and Discussion :: Thermometer Reading Variations

[apondfortimmy]

I've been using simple, in-tank thermometers to read the temperature on everything that I've got. I've managed to keep everything balanced in terms of temperature pretty well, and I was proud of myself for getting it right.

Then I thought, "Oh, I'll upgrade to the fancy-schmancy infrared temperature gun thing." I got it yesterday.
I tested all the water today and, for some reason, it's showing QUITE a discrepancy. Like, my little turtle's tank has been steady between 79.1 and 80.3 this whole last couple of weeks. My temp gun shows it (through the glass AND directly onto the water) at 74. The outside tanks have been between 73 (early morning) (yes I am going to put the heater in once I get the filter worked out) and 76 (afternoon) pretty regularly, but the temp gun said they were SIXTY-FIVE.



Cue the worried mother panic mode over here.
I don't have any other thermometers to test with besides my food thermometer, and somebody in the house here would be really mad if I used that one.

NOW WHAT? The turtles don't seem stressed or too cold and everyone's still eating fine and I DON'T KNOW WHAT TO DO.
*flings thermometers*

*quietly goes and picks them back up because she needs them*

[PridgNYC]

Did you read the manufacturers instructions for properly measuring the temp of liquids? IR thermometers detect the emission of infrared light, so don't actually measure the temperature of the water, they measure the temperature of the surface you are pointing it at, so if you measure through the glass, you are measuring the temp of the glass at the outside surface. If you point it at the surface of the water you are measuring the temp of the water vapor that has evaporated from the surface which will be cooler than the actual temp of the water.

[ljapa]

You can also see if the ir gun is calibrated by looking at freezing and boiling.

Throw a bunch of ice in water. Swish it around, let it sit for a while and melt a bit, then swish again. The water should be right at 32 degrees.

Then boil water. Point at the pot of water. It should read 212.

If the thermometer is off, it may not be off by the same amount at each specific temp, but how it reads those should be informative.

EDIT: Just registered that you mentioned food thermometer. If you have one of those fancy, digital, metal probe ones like my wife, it should be pretty accurate.

Fill a glass with water. Use the food probe and compare to the IR gun.

[PridgNYC]

You can also see if the ir gun is calibrated by looking at freezing and boiling.

Throw a bunch of ice in water. Swish it around, let it sit for a while and melt a bit, then swish again. The water should be right at 32 degrees.

Then boil water. Point at the pot of water. It should read 212.

If the thermometer is off, it may not be off by the same amount at each specific temp, but how it reads those should be informative.

EDIT: Just registered that you mentioned food thermometer. If you have one of those fancy, digital, metal probe ones like my wife, it should be pretty accurate.

Fill a glass with water. Use the food probe and compare to the IR gun.

Good way to calibrate it, this way you don't need stick the food probe in turtle water, take a measurement with both and adjust your temp on the infrared by the amount it would take to match the food probe. Add or subtract the same number of degrees when you test the turtle water with the IR.

This is essentially what I did to adjust my heater. I measured the water temp with a lab grade calibrated thermometer and raised the heat so it would stay at the desired temp.

[apondfortimmy]

Oh duh. I don't have to test the TURTLE tank water with my food thermometer. /facepalm

I'll go do this now. It's doing a little better with temperature variation now, but ... yeah, I should go see what the real deal is.

Thanks guys; I feel silly for not having thought of that solution but I was in panic mode.

[steve]

What happened? What brand of temp gun did you use?