another mystery object

Anyone know what this is? I'm guessing it is some kind of temperature sensor. It has ND/LS/89 engraved on the side, I've tried Google, no joy

Hi Duncan

Think its either a J or K type Thermocouple

the red/white cable denotes its type and temp range

cheers

Looks like a type J.

Wire colours - **LINK**

Thanks Trevorh, to check your suggestion I connected it to a multimeter set on mV and plunged it into a nice hot cup of tea, no output. However if I set it on ohms it measures 110 at room temp and increases by a few ohms at tea temp.

Edited By duncan webster on 12/07/2018 15:42:55

It's the detonator from a Blue Bunny 10 kiloton nuclear land-mine. Usual bomb-disposal rules apply - don't cut the red wire!  Under no circumstances plunge it into a hot cup of tea; that starts the firing sequence...

Edited By SillyOldDuffer on 12/07/2018 15:48:32

I agree it looks like a thermocouple to measure temperature - your ohms readings are unusual though.

But if it is something you have just come across remember it is not necessarily a working thermocouple.... !

It is a temperature probe but its not a thermocouple.

It is a PRT (Platinum Resistance Thermometer), most probably a PRT100 which is 100 Ohms (not sure at what standard temp) but its resistance change with temperature is very predictable and at lower temperatures (say below 200C) is far more accurate than a thermocouple.

Ian P

Nice one!

PRTs usually have 3 wires.

Rod

Industry standard PT100 prt's have a 100 ohm resistance at 0 deg C.....at 100 deg C  I'd expect it to read 138.5 ohms....

There are look up tables for the various resistances expected at a given temperature...temperature transmitters using a PT100 sensor are usually calibrated using a decade resistance box....

Edited By John Rudd on 12/07/2018 18:59:03

They also usually have 4 wires!

The basic platinum element has only two connections but bringing out extra wires allows the wire resistance to be compensated for. Two of the wires carry the current that passes through the sensor and the other two are used to measure the voltage at the sensor itself. Current in a circuit is the same at every point in the loop so is 'known' by the reading circuitry which then measures the voltage across the PRT and translates it to the temperature display etc.

Ian P

Thanks for4 the replies chaps, I looked up the resistance/temperature chart for a PRT100 and then immersed the end of the probe in boiling water. It behaves as predicted. Now I know what it is I'll have to think of a use for it! Bit OTT for a workshop thermometer. Perhaps I'll have to fit a feed water heater to my loco then I'd have something to measure.