Temperature reading

[dogfrog]

What instrument is being used to calibrate heaters and controllers to give an accurate temperature reading?

I have 3 different thermometers and non are even close to what I want. I have 2 of the cheep aquarium float ones and a digital cooking one that can go from zero to over 300. The cooking one is about 3 degrees lower then the 2 float ones and they are off by a degree from each other.

I have and ACIII that will be controlling my heater and chiller but I want to make sure its also reading right.

 

[jrgilles]

I work in a lab, and to calibrate thermometers at work I do this:

1. Boil DI water, measure the temperature. It should boil at 100*C (212*F). If the thermometer reads off, such as 98*C. Make a note of that.

2. Put it into ice water (let the ice sit in the water a bit to get it to temperature.) It should read 0*C, or 32*F. If its off, make a note of it. (ie, it reads -3*C.)

Then graph these points, and you'll be able to tell how far off the reading is at different temperatures. (in the above example, it was 3*C off at freezing, 2*C off at boiling, so the degrees off in between those 2 points would be scaled accordingly, such as it would be off 2.5*C at 50*C, etc.

You could probably just calibrate it with ice water and that would be good enough for fish tank temperatures.

Anyway, hope that is clear.

Another way it to measure a temp with a bunch of thermometers, and see if a bunch read the same, then if you made the assumption that the ones that read the same are right, you can mark the thermometers that read off...

rob