4-wire RJ (?) connector into 2-wire sensor input

[Shtukka]

I'm replacing my solar thermal controller SMT300 with a Resol CS4, having cast around to find a suitable replacement for some time. The temperature sensor connectors have me flummoxed as they're 4 wire and I can't find a reference for how they can be connected to the 2 pin input for each sensor on the Resol. Currently the 4 wires are fitted into a small RJ connector, possibly RJ14 but hard to tell. I'd expect to strip the connector off but don't know how to combine the wires.

Grateful for any pointers!.

[LucMan]

Ohm out the wires and see what you get, then compare to a thermister chart.

[Shtukka]

Finally - done ! I get 127 Ohms for a ~50 Tank which tells me the sensor is pt100 (based on https://blog.wika.com/knowhow/pt100-...uring-element/). So I'm stuck as my new Resol controller is pt1000 (2 wire). Is there such a widget that takes a 4 wire pt100 and can output 2 wire pt1000 ? As ever, any pointers gratefuuly received!

[bob-n]

Is it possible to remove the PT100 sensor and replace it with a PT1000? That would be the easiest and most effective solution.

If you must have a converter, you can build one, but it will take more work to know exactly what the Resol needs. Either the Resol will force a constant current into the sensor or will use it as an element in a voltage divider. The converter design will be different based on what you learn. To measure the Resol, you need a variable resistor and a voltmeter. Connect the resistor to the Resol. Vary the resistor from 200 ohms to 5000 ohms and measure the voltage across the resistor at each resistance. Then you wire an op amp to give you that same response from the PT100 sensor.

[LucMan]

Much easier to just replace the sensor. Solder the wires from the new sensor to the cable running to the old sensor, use heat shrink tubing to seal out the elements.