What type of sensor this probe uses ?

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Externet
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What type of sensor this probe uses ?

Post by Externet » Fri Jan 25, 2013 10:22 am

Hi all.
This thermometer : http://www.chefsresource.com/cdn-progra ... timer.html
Works to 'high' temperatures, as in grilling.

This thermometer : http://www.chefsresource.com/rf-02.html
Works for 'low' temperatures, as refrigeration.

(They are two conductor probes)

Ignoring the probe enclosure; are they sensors thermocouples, thermistors, or something else ? Are they interchangeable, and the range of readings are a 'voltmeter' type of scaling in the electronics ?
- Abolish the deciBel ! -

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Lenp
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Re: What type of sensor this probe uses ?

Post by Lenp » Fri Jan 25, 2013 3:33 pm

Hi Externet...

Most likely they are thermistors (temp sensitive resistors, that can be either positive or negative coefficients). They are cheap, small, responsive and there is a wide range of resistance values, usually rated at 25°C. It is unlikely they are interchangeable, even between the same models. I use thermistor probe thermometers and they are laser trimmed to match the unit's sensor. For best interchangeability use thermocouples or PTD sensors. Thermocouples are robust, cheap and quite easy to make if you have the thermocouple wire, but they do get tricky if there is any switching or other connections of dissimilar metals.

Len
Len

“To invent, you need a good imagination and a big pile of junk.” (T. Edison)
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Dean Huster
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Re: What type of sensor this probe uses ?

Post by Dean Huster » Fri Feb 01, 2013 5:04 pm

Trouble with thermistors is that they tend to melt down at higher temps such as "grilling" temps. These days, temp sensors tend to be thermocouples for really extreme temps in industry; RTDs or transistors are used more with us common folk; thermistors for temps that we can bodily stand for a short time.
Dean Huster, Electronics Curmudgeon
Contributing Editor emeritus, "Q & A", of the former "Poptronics" magazine (formerly "Popular Electronics" and "Electronics Now" magazines).

R.I.P.

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Lenp
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Re: What type of sensor this probe uses ?

Post by Lenp » Sat Feb 02, 2013 8:02 am

Dean,
When I first looked at the post, I looked at the refrigerator / freezer unit, which is most likely to be a thermistor probe.
Certainly the other one, designed for grilling, is a thermocouple.

TC's are more handy than most people realize. Like batteries, placing them in series increases the voltage. Kilns years ago used a thermocouple driving a milliviolt meter movement directly to monitor the firing temperature, no batteries required!
Many gas burner safety devices still use thermocouples to prove that the pilot is lit and to and keep the gas valve in the ready position.

If you have some thermocouple wire, twisting the two wires together, applying a bit of brazing flux and heating it to form a small bead will make a quite accurate thermocouple at low cost.

Len
Len

“To invent, you need a good imagination and a big pile of junk.” (T. Edison)
"I must be on the way to success since I already have the junk". (Me)

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