FYI: I tested the remote sensor head at work today, my findings are:

1. It's a Negative Temperature Coefficient thermistor, with a value of 10,000 ohms (10K) @ 25șC.

2. It's resistance falls with increasing temperature at a rate of -4%/șC

A fairly standard device to measure temperature, not linear but can be easily calibrated with a lookup table (temperature v resistance) or an equation that yields a rough approximation. You can buy these off the shelf at most electronic component suppliers if you ever need to, example: