I need to measure the voltage across the leads of a thermocouple, the thermocouple being physically connected to a 600 Vdc terminal.

The instrument which measures the thermal couple (thermometer) will not withstand a 600 Vdc input.

How can I read the differential voltage across the leads of the thermocouple? I am considering an isolation amplifier, but the problem I have at the moment is I do not know how to power the high voltage side as most are limited to ~20 Vdc.

  • 1
    \$\begingroup\$ I would isolate and communicate over optics \$\endgroup\$
    – PlasmaHH
    Commented Sep 13, 2018 at 13:54
  • \$\begingroup\$ Continuous measurement 24/7 or just for a brief test? \$\endgroup\$ Commented Sep 13, 2018 at 17:51
  • \$\begingroup\$ Able to elaborate on each case, continuous and momentary? \$\endgroup\$
    – A.S.
    Commented Sep 13, 2018 at 21:03

1 Answer 1


The high voltage AC (assuming..) common mode voltage on the thermocouple will cause problems for most signal conditioners.

You can power the high side signal conditioner (maybe ADC too if you want) with a step-down transformer from 600VAC and a small power supply (won't be very cheap or very small), then use some form of isolation to get the signal down. I did this one time for 100kV using fiber. At 600V you may be able to get away with a commercial process signal isolator. Make sure the latter is rated for continuous operation with 600VAC and follow their instructions as to grounding etc.

  • \$\begingroup\$ The terminal is at 600 Vdc. I will edit the question to specify, my mistake and thank you for your feedback. \$\endgroup\$
    – A.S.
    Commented Sep 13, 2018 at 16:01
  • \$\begingroup\$ I will modify my answer. \$\endgroup\$ Commented Sep 13, 2018 at 16:21

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