Can a thermocouple give the temp of a metal surface?

[Peabody]

Or does the fact that it's touching metal mess up the reading?  So if I wanted to measure the temperature of a hotplate for reflow purposes, could I use a thermocouple?

[ogden]

Or does the fact that it's touching metal mess up the reading?  So if I wanted to measure the temperature of a hotplate for reflow purposes, could I use a thermocouple?

Indeed. Just make good thermal, not galvanic connection.

[Teledog]

Quick & dirty: ..I use a non-contact IR/laser thermometer
It's best if you paint the surface flat black first though (hi-temp/ BBQ paint)

[Wan Huang Luo]

Or does the fact that it's touching metal mess up the reading?  So if I wanted to measure the temperature of a hotplate for reflow purposes, could I use a thermocouple?

yes a thermocouple shouldn’t get messed up by a reflow hot plate so you’re good to go

[Peabody]

I had thought about using an IR thermometer, but my understanding is that it would need to be adjustable as to the emissivity of the surface, and one that would do that would be a lot more expensive than a thermocouple meter (such at the TM-902C).

So there appears to be a difference of opinion.  One says the contact has to be non-galvanic, but the other says it's ok.  Maybe the metal contact would be non-galvanic if no current actually flows.  Well I guess high-temp epoxy would make the question moot.

[Ian.M]

If the thermometer is battery powered and not grounded, it doesn't matter if the thermocouple tip makes electrical contact with the hotplate.  If however any part of the thermometer circuit is grounded, then you have to consider the effect of contact on its input circuit a lot more carefully, and need detailed knowledge of the input circuit used, which may be an issue if you want to use a non-isolated thermocouple as the sensor for an off-the-shelf controller for the hotplate.

[Peabody]

If the thermometer is battery powered and not grounded, it doesn't matter if the thermocouple tip makes electrical contact with the hotplate.  If however any part of the thermometer circuit is grounded, then you have to consider the effect of contact on its input circuit a lot more carefully, and need detailed knowledge of the input circuit used, which may be an issue if you want to use a non-isolated thermocouple as the sensor for an off-the-shelf controller for the hotplate.

In this case the TM-902C is self-contained and battery powered, so it should be ok.  The idea is to control the temperature manually based on the temperature display, so there is no contoller circuit.  Of course it remains to be seen whether this will work, but it seems it should with a little practice.  It seems most people use an IR thermometer, but it looks like a thermocouple would give more accurate readings.

Thanks very much.


Thanks very much.