Rescuing messed-up dial thermometers

[Jordan]

Darkroom experts,

I have a couple of dial-type darkroom thermometers that for one reason or another no longer work correctly. One "reads high" by about 3-4C, where as the other is close to stuck on one temperature and responds very slowly to changes. Both started out life working just fine.

Is there any way to "rescue" these thermometers, e.g. by putting them in a very hot or cold solution for a while (as one might do to fix gaps in the mercury column of a conventional thermometer?)

Thanks!

 

[mgb74]

Some, typically with a nut just underneath the dial at the top of the tube, allow you to adjust by holding the nut and turning the dial part. Essentially the temp reading function stays the same, you are just adjusting the what the dial indicates.

Others may have a small setscrew somewhere that performs the same function.

 

[Jordan]

Regrettably, I don't think either of the thermometers have calibration or set-screws. (At least the one in front of me right now, doesn't).

 

[mgb74]

Then what I do, if I don't want to toss them, is calibrate against a quality mercury thermometer (that I use just for this purpose) and mark on the dial where the needle reads 68 degrees F. So I know if I'm over, under, or at 68 deg.

I've also done this with the small inexpensive meat thermometers I use for cooking (though not at 68 deg of course).

 

[Photo Engineer]

Jordan;

I have heard of some being rescued the same way as a bad mercury thermometer. You cool to the lower limit and then abruptly heat to the upper limit. If this does not work, repeat the cycle several times. It serves to loosen and reset the needle.

It is not as reliable as the same method with a separated mercury thermometer. That latter always seems to work for me.

PE