# Temperature Probe



## SergeMarx (28/6/14)

I've looked through a few threads on here, but couldn't find a definitive answer... the temp probe for my temperature controller is too short, and needs lengthening. Should I open the box and rewire a new longer probe in there if so, where to get one, or can i just patch in some wire to the existing probe? 

Some people said to have done this, but others say it affects the accuracy... some clues?


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## QldKev (28/6/14)

Is the probe itself or is it the wire too short?

Without knowing which type of probe you are running we cannot comment about if it is ok to lengthen the wires.


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## SergeMarx (28/6/14)

just the wire too short - it's about 1m, with a metal cap about 2 cm at the end


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## QldKev (28/6/14)

I'm guessing it is a thermistor, what is it plugged into?

If it is, then generally you will get away with lengthening the cable. Just ensure the cable you use to lengthen it has a low resistance. After you lengthen it you will need to check the calibration. I've used OFC speaker cable as it was what I had sitting around, and for a 0.5m I found there was no difference in the calibration.


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## Logan_01 (28/6/14)

If the probe is a thermocouple you cannot just extend it with normal copper wire. If it is a resistance type probe, ie PT100 or thermistor than extending it a couple of meters or so will likely add very little error, none if it is a 3 or 4 wire PT100.

If it is a thermocouple, you can buy the extention cables cheap as chips off ebay, you just need to know what type of thermocouple, but 99% seem to be K type. You also need the terminals to match the cable.

One way to determine what probe you have is first by how many wires. If it has more than 2, it is not a thermocouple. If it has only 2, measure the resistance between them. If it is very low, like <10 ohms it is probably a thermocouple. If it is around 100 ohms it is a PT100 and if it is 1000, 5000 ,10000 ohms or near enough it is a thermistor.


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