how to choose a thermistor?

[jarthel]

as title. thank you.

ps. the thermistor will connected on the primary side of the transformer.

 

[stevesurf]

Thermistor applications and product choices are well summarized by Omega Engineering. Thermistors provide an accurate but a relatively low resistance change with temperature and are best used as a leg of a Wheatstone Bridge circuit. Useable temperature range, ability to stick to a surface or measurement of ambient temperatures are all considerations when a thermistor is selected. If you have a selection question, just call Omega's group of application engineers.

 

[splaz]

^ How much did you get paid to say that... ?

Well what is the application ?

Is it going to be over-heat protection ?

I also found a web pagethat that a thermistor can be used instead of a dropper resistor in tube gear to help reduce surge current when the heaters are cold. So maybe that ?

First thing to consider would be which temperature coefficient you desire.

PTC, Positive temperature coefficient - Resistance increases with an increase in temperature.

NTC, Negative temperature coefficient - Resistance decreases with an increase in temperature.

and obviously the opposite for a temperature decrease. I believe if this is meant as some sort of over-heat protection you'd be after a PTC thermistor.

Now I'm not an expert but there are some important specs I wouldn't completely understand so someone else maybe able to explain help you with.

The thermistor should have a specified resistance at 25C or around that. It should also have specs for how much it's resistance changes with temperature. Also I'm not sure but I think that with each type of resistor, PTC and NTC, that if a certain temperature is reached they'll be almost no resistance or extremely high resistance depending on type. Might want to double check though. Might be other specs but I think those are most important, not sure what they're proper names and calculations use would be.

Then also like has been said then you need to think about what sort of package you'll need.

I've used thermistors in the past, specific parts were worked out by someone else though, they're were just bead type clipped onto a heatsink.

I can't really get anything else so I just make do but I'm sure there'd be an ideal package, like if you want to stick on the transformer.

Well hope I've been of some help, I have an electronics book now, so hopefully less dumb questions from me

, anyway I may see if that has anything on the subject.

 

[stevesurf]

Quote:

Originally Posted by splaz ^ How much did you get paid to say that... ?

LOL, I guess it did sound like a testimonial. Well, here's a confession: I actually worked there about 20 years ago and their support today is just as good as when I was an Appl. Engineer. In fact, last year I bought a PLC from them and they knew exactly what it would do.

...you know, come to think of it, why not use an RTD instead