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We'd like to use plain automotive connectors to connect our thermocouples.

What we are looking for is the ruggedness and economy of such connectors.

Of course, that brings the problem of material change and cold junction compensation.

Since we already have a gradient between the thermocouple amplifier (ex : INA826) and the real cold junction (entry connector,) I figured we could shift the cold junction all the way to a remote connector and use copper wires from then on. The cold junction temperature would then be sensed by another temperature sensor and the compensation would be made in software between the perceived emf at the In-Amp input and the converted Cj T° to voltage.

Below is a principle schematic for your review:

enter image description here

Does all of this make sense or do you see a flaw in this way of operating?

How about the plating of the pins (tin, gold, or nickel) would that bring yet another error?

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The principle is fine, the devil is in the details. How isothermal you can achieve between junctions and sensor, and whether your connector is reliable with millivolt/microvolt DC signals, in particular. Usually you want to keep the cold junction sensor in the most benign temperature region available, typically close to the amplifier. Remember that the wires themselves conduct substantial heat and so if there are gradients in the vicinity of the connector you’ll have errors.

Plating won’t add error, gold plating is useful to make reliable connections.

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  • \$\begingroup\$ Hi Spehro, Thanks for the answer, Regarding "reliable with millivolt/microvolt", I'm wondering : how could a connector be unreliable with small signals? \$\endgroup\$
    – VoltsAndNuts
    Commented Dec 3, 2021 at 12:54
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    \$\begingroup\$ Many ways- typically to do with a thin film of oxide between contacts that a few volts and hundreds of uA will punch through- search terms “wetting current”, “gas tight” and “wiping”. \$\endgroup\$
    – Spehro 'speff' Pefhany
    Commented Dec 3, 2021 at 12:59
  • \$\begingroup\$ Very interesting, I knew the phenomenon but didn't know its name. Taking a down-to-earth approach : I inted to use Amphenol ATM / Deutsch DTM type connectors. They use nice round pins with several point of contacts. I don't see how it could be worse than the classical "mini" thermocouple connector which is basically a spade sandwiched by two leaf springs. But maybe I'm wrong! \$\endgroup\$
    – VoltsAndNuts
    Commented Dec 6, 2021 at 14:27

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