Is there any reason not to use a thermistor in a reflow oven?

[Mechanical Menace]

Well I already have a few highish temp thermistors around and want to get a reflow oven at least working for when my first batch of PCBs arrives from Beta Layout. I've seen a few examples of people doing this and they always seem to use thermocouples so I was wandering if there's a reason not to use a thermistor?


Thanks

[Simon]

At those temperatures you might need to double check that your thermistor can cope. They generally do not do more than 150°C where as thermocouples can go up to 1000°C.

[mikeselectricstuff]

What would you solder it with?

[wraper]

At such temperatures RTD (PT100, PT1000) usually is the best (most accurate) choice. However they cost more than cheap K type thermocouples.

[jamesd168]

Well I already have a few highish temp thermistors around and want to get a reflow oven at least working for when my first batch of PCBs arrives from Beta Layout. I've seen a few examples of people doing this and they always seem to use thermocouples so I was wandering if there's a reason not to use a thermistor?


Thanks

I guess it depends on exact temperature you want to use it for. the oven should tell you what is the highest temperature it will go up to, and your thermistor should also have a temperature rating.

[Simon]

NTC's also have very poor resolution at high temperatures as the curve becomes flatter and flatter.

[Mechanical Menace]

The thermistors I have were meant for a RepRap hotend so are meant to be able to handle 300 degrees.

What would you solder it with?

Wouldn't crimps be OK? Honest question btw.

NTC's also have very poor resolution at high temperatures as the curve becomes flatter and flatter.

This is just a "for now" solution unless it works well and not just well enough.

Thanks everybody.

[Edwin G. Pettis]

While thermistors are rated up to ~150°C, they are only stable, long term, up to 100°C, above that, use should be only intermittent.  Platinum RTDs, particularly the thin film types are accurate and can be found for under $5 and they do require an amplifier stage.  Thermocouples are relatively cheap but require a compensation junction plus amplifier to work as their microvolt output signals are much too low to work with otherwise.  Unless you require very accurate measurement, the RTD interface amplifier can be relatively simple to implement and an RTD has a much higher change per degree than a thermocouple.