Is the thermistor NTC? PTC? just by looking?

[eccerr0r]

I suppose this can be deduced when in circuit, but if an out of circuit or questionable connectivity thermistor is handed to you, is it possible to tell whether or not the thermistor is PTC or NTC, if you're not allowed to touch it, never mind measure it with a heater or chill spray?

I don't even have a picture of the questionable thermistor, but currently guessing it's PTC. But it's just a guess.

[eccerr0r]

Re: Is the thermistor NTC? PTC? just by looking?

Here are two samples, though there's another that a friend of mine was wondering, no pictures available...

NTC? PTC?

[R_J]

Re: Is the thermistor NTC? PTC? just by looking?

Check the resistance with your meter, then apply some heat and see which way the resistance changes. If they are inrush thermistors they are likely ntc, if they are for, example in a crt degausing circuit, they are likely ptc

[eccerr0r]

Re: Is the thermistor NTC? PTC? just by looking?

Err... the premise is that you can't touch. Can look, but not touch - so no heating or resistance measurements.

Actually why can't touch... assume the part is actually damaged beyond recognition and all you have is a photograph of someone else's identical device but can't tell what's connected to what. The device is supposedly around 19mm in diameter - larger than these I have pictured - but I think thinner. Likewise they have no markings on them.

[eccerr0r]

Re: Is the thermistor NTC? PTC? just by looking?

of these I do have in hand, intact, and OOC, left appears to be an ntc 25 ohm, other appears to be a ptc 20 ohm I think...

[R_J]

Re: Is the thermistor NTC? PTC? just by looking?

Err... the premise is that you can't touch. Can look, but not touch - so no heating or resistance measurements.

Actually why can't touch... assume the part is actually damaged beyond recognition and all you have is a photograph of someone else's identical device but can't tell what's connected to what. The device is supposedly around 19mm in diameter - larger than these I have pictured - but I think thinner. Likewise they have no markings on them.

Then the correct answer is you can not tell the difference.

[eccerr0r]

Re: Is the thermistor NTC? PTC? just by looking?

Okay. Was hoping someone could tell after going through enough of them.

Hate it when parts aren't marked with something that can lead back to a datasheet somewhere...

[R_J]

Re: Is the thermistor NTC? PTC? just by looking?

The ones you have pictured do look like ptc's used in old crt degaussing circuits.

[budm]

Re: Is the thermistor NTC? PTC? just by looking?

the ones you have pictured do look like ptc's used in old crt degaussing circuits.

+1

[eccerr0r]

Re: Is the thermistor NTC? PTC? just by looking?

It's very possible the PTC on the right was indeed used from a degausser, but not the NTC on the left... I believe the NTC was from a SMPS.

Either way, I hate unmarked devices. And yes they apparently do still sell these without a coating, don't know if they were meant for temperature sensing versus inrush protection...