Thermometers - Mercury vs. Digital TESTED

[cmor1701d]

Some of you may remember my post about the temp difference I was seeing between my mercury thermometers and my digital ones.

I have a lab grade mercury thermo and a cheap plastic one for a tank. Both of them agree on the temperature of a water sample. I have a controller for my heaters and a digital readout on one of the heaters (separate controller).

Both of the digitals read 2 degrees higher than the mercury based thermometers. So which one is correct?

I work at a pharmaceutical company so I asked our metrology department to test one of each of my thermometers. They have a temperature calibrated incubator with a thermometer inside and a canister of some aqueous solution which is used for calibrating thermometers used in manufacturing.

The results PLEASE!!!!!!!!!!!!!!!!!!!!!!!!!!

Well after a careful test of both my digital hand held and my lab grade mercury thermometers, it turns out that the mercury thermometer agrees to the tenth of a degree with the test equipment. The digital reads 2 degrees higher.

So my tank that never varies from 79 degrees is actually a very stable 77 degrees.

 

[mgamer20o0]

also not all digital thermometers are equal. i know the coralife ones are known to be off.... i have 3 of them i got with tanks and other stuff. each one will read a different temp.

 

[neilanh]

Ive gone away from the digital ones for the same reason - they're too inaccurate.

 

[BigJim]

Is the accuracy really that critical?

As long as the thermometer is close to accurate and the water temperature remains steady and within the safe range, I'm happy.

 

[cmor1701d]

It's the safety margin when temps get close to critical (either way).

I have the Pinpoint remote thermometer with 3 units and all three show differnent temps. Anyone want to buy them cheap?