Temperature Sensing Probe

It all depends on the nature of the "Gel"

If it is a viscous liquid (usually white to beige to grey in colour) then it is as described previously - A material conducive to the conduction of heat though most commecrial probes avoid such materials as "filler".

If the gel is a solid then it is more likely a silicon based potting compound to mechanically hold the sensor in place and protect it to some degree. This is most often found in low cost probes and pretty much standard for most thermistor probes.

As to probe type the usual method of deduction is as follows.

4 wires, 3 of one colour and a forth of an other - usually an RTD

3 wires, 2 of one colour and one of a third - usually an RTD

2 wires of two colours - RTD, TC or thermistor - The colours used help narrow things down. RTDs are usually red/white and white jacket. TCs are usually Red/Blue and blue jacket T-type, Red/Yellow Yellow jacket K-type, Red/White black jacket J-type.

To verify the sensor type you could use a very sensitive multimeter and a sensor handbook, but a meter designed for reading an RTD/TC is a better bet. Just connect the sensor to the appropriate terminals of the meter and check if you get a reading and if it is reasonably close to correct.

If it turns out your sensor is not a TC or an RTD then it most likely is a Thermistor or some form of integrated sensor.

Hope this helps deduce what you are looking at.

So if at first you don't succeed, read the manual.