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I hope this is a proper place to ask the question. I am using two different methods to do a thermal measurement on a flyback power supply that has a planar transformer. First I used FLIR E60 thermal camera and then I did the measurement with OMEGA thermocouples.

My problem is that with thermocouples I obtain temperatures of about 10 degC lower compared to thermal camera. To attach the thermocouples I used a sort of adhesive pads in which I stick the thermocouples.

Did anyone experience anything similar or my method is wrong? To which measurement method can I trust more? My next step would be maybe to stick the thermocouples to my points of interest with a kapton tape (perhaps).

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    \$\begingroup\$ Did you calibrate your thermal camera for the emissivity of whatever material you are measuring? \$\endgroup\$
    – PlasmaHH
    Jun 8, 2017 at 11:44
  • \$\begingroup\$ Well it's a matte solder mask PCB so the emissivity should be 0.95 as by default. The thing is that the transformer PCB is matte while the rest is gloss but in any way I am not interested in the the rest so I guess this value should be good. \$\endgroup\$
    – MarkoP
    Jun 8, 2017 at 12:00
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    \$\begingroup\$ You attached pads, and placed the thermocouples on top? Away from the point of measurement, and exposed to ambient air? Do you have a black-body calibrator? Those are just about required to verify the operation of any type of FLIR vs a thermocouple, thermistor, RTD, whatever. \$\endgroup\$
    – R Drast
    Jun 8, 2017 at 12:00
  • \$\begingroup\$ Yes, that is what I did but I also pushed the TCs inside this adhesive mass. I don't have the calibrator. \$\endgroup\$
    – MarkoP
    Jun 8, 2017 at 12:08
  • \$\begingroup\$ According to Omega, beige masking or drafting tape has an emissivity very close to 0.95. You can stick some onto the glossy surfaces and see if this helps but I suspect that it would make the temperature difference even greater. \$\endgroup\$
    – Transistor
    Jan 31, 2018 at 23:08

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Using thermocouples on switching power supplies is often tricky because of the EMI. Wire loops of the thermocouples tend to pick up noise of the converter and measurements are messy. Try to switch off the converter and check if the readings of the thermocouples don't change apruptly (which would indicate EMI issues).

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