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another mystery object

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duncan webster12/07/2018 14:53:45
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1631 forum posts
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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 joyimg_3317 (small).jpg

Trevorh12/07/2018 14:56:59
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238 forum posts
41 photos

Hi Duncan

Think its either a J or K type Thermocouple

the red/white cable denotes its type and temp range

cheers

Brian Sweeting12/07/2018 15:40:22
271 forum posts
1 photos

Looks like a type J.

Wire colours - **LINK**

duncan webster12/07/2018 15:42:32
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1631 forum posts
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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

SillyOldDuffer12/07/2018 15:47:05
3193 forum posts
651 photos

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

Nick Clarke 312/07/2018 17:21:59
66 forum posts
1 photos

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.... !

Ian P12/07/2018 17:30:25
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1924 forum posts
81 photos

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

Vic12/07/2018 18:25:51
1694 forum posts
10 photos
Posted by SillyOldDuffer on 12/07/2018 15:47:05:

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

Nice one! smiley

Roderick Jenkins12/07/2018 18:46:09
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1611 forum posts
406 photos

PRTs usually have 3 wires.

Rod

John Rudd12/07/2018 18:57:38
1179 forum posts
56 photos

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

Ian P12/07/2018 20:09:53
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1924 forum posts
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Posted by Roderick Jenkins on 12/07/2018 18:46:09:

PRTs usually have 3 wires.

Rod

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

duncan webster13/07/2018 11:49:15
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1631 forum posts
18 photos

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.

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