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Temp probe specs for possible generic replacements

post #1 of 2
Thread Starter 

WARNING:  Science Ahead!!!

 

I will get to the good stuff, but first some background:

I was playing around with the temp probes that I currently have getting ready to build my own super thermometer and I found a few things.

 

Most the of the thermometer probes are called "thermistors", which are heat dependent resistors.  This broken into three categories

negative temp coefficient (NTC) - NTC is that the resistance goes down as the temp goes up.

positive temp coefficient (PTC) - PTC is when the resistance goes up as the temp goes up.

resistance temperature detector (RTD) - RTD - This is like a PTC, but the rate of resistance is more linear than a standard PTC

 

Another common type is the thermocoupler, these produce millivolts as the temp goes up.  These are the common K,J,T and E type of temp probes.

 

There are other types that I may have missed but these are the most common that I have ran into.

 

The thermistors and thermocouplers have there advantages and disadvantages.  Some can handle higher temps, other are better for lower temp and some are extremely accurate, but at a cost.  One area that of this that I ran into with my probes is that since thermistors are based on resistance, the greater the tolerance of the resistor used can cause your temp to way out of whack.  All resistors have a tolerance marked as +/-1%, 5%, 10% or even 20%.  The cheaper the resistor the greater the tolerance (but manufacturers will rarely tell you the tolerance of the thermistor that they used).  In trying to make new probes I have come across some thermistors that have 0.1% tolerance, which can make your probe very accurate but at a higher price.

 

 

 

Now, with the science out of the way, here is what I have found.  I hope that these can help you if you are looking for.

 

  Resistance @ 0C Resistance @ 25C Resistance @ 100C Type
Cheap $20 store Probe  169K Ohms 50K Ohms 3.6 Ohms NTC
ET-732 Meat Probe 3,500,000 Ohms 1,000,000 Ohms 45,000 Ohms NTC
ET-732 Smoker Probe 4,000,000 Ohms 1,000,000 Ohms 45,000 Ohms NTC
Green Mtn Grill Meat Probe 100 Ohms 110 Ohms 139 Ohms PTC

 

0C = 32F

25C = 77F

100C = 212F

 

When looking for thermistor probes most of them are noted for their resistance value at 25C.  Any probe that matches these values should be a good candidate as a replacement.

 

Hope this helps.

post #2 of 2

Thanks, I always wondered about the 2 ET-732 probes reading close but different when switched around.

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