Question on this '1625' Thermistor


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rogerdw
Guru

Joined: 22/10/2019
Location: Australia
Posts: 818
Posted: 01:20am 27 Jul 2023      

Hi guys, I have a device that uses a thermistor approx 10cm long and with the number '1625' stamped on one end. I haven't been able to find any details in searching, so am hoping for some help please.

It sits alongside a heating element in a grease trap and is supposed to tell the relay to turn on at 49 degrees C and off at 54 degrees.

This one measures ~12 ohms despite temp being hot or cold  ...  and substituting a decade box sees the relay switching on at anything above about 60kohm and off around 50kohm.

I found a similar manual, but it shows the thermistor comes with the pcb!!! and chances of finding that is probably more remote. Thanks.



phil99

Guru

Joined: 11/02/2018
Location: Australia
Posts: 1853
Posted: 03:41am 27 Jul 2023      

Using your decade box test results my guess is the NTC thermistor is likely to have a nominal value of 100k @ 25C.

The '1025' marking on it, however suggests 10k @ 25C. Worth testing again and then reading the decade box with a multimeter, to ensure it isn't 10 x too high.

Edit. In the photo it looks like 1025 but have no idea what it means if it is 1625.
Edited 2023-07-27 23:27 by phil99

rogerdw
Guru

Joined: 22/10/2019
Location: Australia
Posts: 818
Posted: 12:54am 28 Jul 2023      

Thanks Phil  ...  yeah it's definitely 1625. I'll have another look and see what I find with the decade box. The board doesn't have any trim pots for fine tuning and I don't expect it's really all that critical  ...  although having an out of control heater in a bucket of grease could end up pretty nasty.

I do have a packet with a selection of thermistors here  ...  I could hook a few up and then see where they switch. Once I'm confident of the value, then I'll chase up one in a suitable sheath. Thanks again.