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Inexpensive handheld thermistor probes?

T

Terran Melconian

Jan 1, 1970
0
I have a handheld thermistor probe. It's a pretty standard 10k NTC
thermistor in a stainless body with a plastic handle and some cable
leading to banana plugs. It came for free with a Radio Shack DMM years
ago and is perfectly functional.

I'd like to get some more similar to it. I thought they would be
trivial to find and cost $10. This has not proved to be the case. In
fact, I have had great difficulty finding any whatsoever.

I have found a lot of industrial ones designed to be permanently mounted
and costing upwards of $50, neither of which are properties I want.
There are also a great lot of thermocouples, and thermocouples are very
nice, but I don't want them for this - I don't need the range and too
many components are required to amplify the signal. It's also easy to
get thermistors, but I have no desire to put my own bodies and handles
on them, either.

Does anybody know where I can get maybe a dozen of the right thing for
under $20 each? If it costs much more than that, I can buy prebuilt
handheld thermometer units and throw out the display.

I am located in the United States.
 
L

Lostgallifreyan

Jan 1, 1970
0
Things.consistent.org:
There are also a great lot of thermocouples, and thermocouples are very
nice, but I don't want them for this - I don't need the range and too
many components are required to amplify the signal. It's also easy to
get thermistors, but I have no desire to put my own bodies and handles
on them, either.

Does anybody know where I can get maybe a dozen of the right thing for
under $20 each? If it costs much more than that, I can buy prebuilt
handheld thermometer units and throw out the display.

As far as I know, the cheap probe thermometers you mention are also
thermocouples, not thermistors. Mine are, anyway.
 
J

Joerg

Jan 1, 1970
0
Lostgallifreyan said:
Things.consistent.org:




As far as I know, the cheap probe thermometers you mention are also
thermocouples, not thermistors. Mine are, anyway.


The ones I took apart over the years had mundane diodes.
 
T

Terran Melconian

Jan 1, 1970
0
As far as I know, the cheap probe thermometers you mention are also
thermocouples, not thermistors. Mine are, anyway.

Interesting. I would have thought that per-unit calibration would be
too costly for a $20-$30 consumer device, but so would opamps with a low
enough input offset voltage to avoid the need for it. Do you recall how
they measured the thermocouple voltage? Perhaps they have some smart
technique I can steal... er, borrow. :)
 
L

Lostgallifreyan

Jan 1, 1970
0
Things.consistent.org:
Interesting. I would have thought that per-unit calibration would be
too costly for a $20-$30 consumer device, but so would opamps with a low
enough input offset voltage to avoid the need for it. Do you recall how
they measured the thermocouple voltage? Perhaps they have some smart
technique I can steal... er, borrow. :)

I think it's likely I was wrong and Joerg is right. Without destroying one,
I can't get at its innards enough even to test it. I was seeing just the
wires to the probe, one is enamelled copper, the other is in what seems to
be a teflon sheath, giving the impression of dissimilar metals. The range
is -50C to +300C, which is definitely NOT a diode, maybe, or even a
thermistor, unless it be PT100 type.

I'd still lay odds on it being a thermocouple, even though I can't prove
it. If you want to buy one to mutilate, go for it. :) They're on eBay,
they're very good for the money, even without yielding their dark secrets.

http://tinyurl.com/2mp95h (eBay listing. I was the buyer on that one.)

There are others similar, many sellers, but I chose these after careful
comparison, and I think I got the best deal by far.

(Off-topic, but I'll take this shameless chance to suggest that if anyone's
looking for an ITX computer, or an FS1R synthesizer (Yamaha), I'm selling
them to raise money for a laser project. ITX machine will go up tomorrow
night, is 1.2 GHz, tiny machine, built to keep, but I really need money
fast to get some optics that won't wait around. I'll say no more here, it's
not the place, but if anyone wants, they can post a question via a
listing..)
 
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