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Old 09-29-13, 09:40 AM   #9
stevehull
Steve Hull
 
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Location: hilly, tree covered Arcadia, OK USA
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Electronically, there are two different ways of measuring temperature with a contact probe. One is with thermistors and the other is with thermocouples.

Thermistors have a VERY rapid response as they are tiny. They are a device that changes resistance (non linear) with temperature. In the absence of a thermal mass around them, their response time is in the msec. The electronics to display the non-linear resistance change is a bit tricky, so their accuracy is low compared with their inherent precision.

Thermocouples are larger and have a much longer time constant, but in this application, a few msec compared to a couple hundred msec is irrelevant. These have characteristics of both high precision and high accuracy. Any degradation of the signal reflect the electronics and not the probe.

Thermocouples put out a voltage linear with temperature change and the electronics to display this is easy.

I suspect that cheap meters have cheap electronics that have offset voltages that degrade both precision and accuracy in both cases.

A microprocessor is not necessarily more "accurate" as the A/D converter (even "double precision") still relies on some electronic analog formatting - and that is where degradation typically occurs.

I think AC's suggestion of getting multiple measurements on an identical surface is a good one. Years ago, I would do this by starting with nearly frozen water in a beaker on a stir plate so that the entire volume of water was at an identical temp. Probes were placed in the water right next to one another and I plotted the curves as the water warmed up.

Didn't have to worry about contact issues as the probe was submerged.

It is frustrating to buy a temperature meter and not have it display the right temp . . . .

Steve
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