Hello Bob,
The Omega SA1-RTD sensor you provided a link to is a standard 100 ohm RTD (IEC60751, also referred to as Pt100) which seems like it should work for auxiliary temperature measurement using the MISC TEMP inputs on the GEA 24.
RTD stands for
resistance temperature detector. You can think of an RTD as simply a resistor that changes its resistance with changing temperature. An RTD is not the same as a
thermistor - they both indicate changing temperature with changing resistance, but an RTD typically has a wider operating range and an essentially linear R-T curve which is much nicer to work with.
In its simplest form, an RTD is a two-terminal device, similar to a rheostat. Three- and four-wire RTDs exist in order to help cancel out effects of sense wire resistance when using long cable runs (click
here and
here for a discussion of the theory if you're interested). Since we don't need laboratory accuracy and our wire runs are relatively short compared to an industrial setting, you should be able to ignore the extra third wire and treat your RTD as a two-wire sensor, exactly like the UMA RTD you are already using for the oil temperature sensor in your G3X system.
I don't know for sure which wire on that Omega RTD is which, but I would guess that it follows the color conventions shown in the diagram below. If it does, you should be able to clip the extra black wire, but first use your ohm meter to be sure. If you can find a pair of wires between which the measured resistance is approximately 110 ohms at room temperature, then you have found the right wires and you can ignore whatever is left over.
RTDs are non-polarized devices, so it doesn't matter which side connects to MISC TEMP HI or MISC TEMP LO... however I would still follow the "red to HI, black to LO" convention for clarity if nothing else.
good luck,
- Matt
Cheers Capt Bob....
