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Thermocouples
tegwin - 18/2/12 at 12:50 PM

Anyone understand thermocouples?

I have this multimeter HERE

It came with (what I assume) is a thermocouple. I have now lost it....

Any idea what type of thermocouple I can replace it with? I know there are varaious types J,k etc... but no idea which I need to order?!

Ideally I need a tiny tiny thermocouple for testing some electrical stuff....

Madinventions - 18/2/12 at 01:01 PM

Give Rapid a quick call? They're open on Saturdays, and should be able to give you the information you need.

Ed.

wylliezx9r - 18/2/12 at 01:16 PM

Thermocouples use 2 similar metals to produce a voltage when there's a change in temp. The metals also have to be matched by the wiring that goes to the meter. So you are going to need the specific thermocouple for your meter or the read out will be incorrect. Best to contact manufacturer.

ATH Dan

Confused but excited. - 18/2/12 at 02:22 PM

quote:
Originally posted by wylliezx9r
Thermocouples use 2 similar metals to produce a voltage when there's a change in temp. The metals also have to be matched by the wiring that goes to the meter. So you are going to need the specific thermocouple for your meter or the read out will be incorrect. Best to contact manufacturer.

ATH Dan


That would be two dissimilar metals, ie; iron/constantan for lower temp ranges, platinum/rhodium for higher ranges etc.

Marcus - 18/2/12 at 02:26 PM

The vast majority of these are k type. All the multimeters and temperature loggers at work use k type.

tegwin - 18/2/12 at 02:30 PM

quote:
Originally posted by Marcus
The vast majority of these are k type. All the multimeters and temperature loggers at work use k type.


That is the impression I am getting from my googling... Are all K type thermocouples the same? (appart from size) so I can just use any K type?


Rapids technical guys dont work at weekends, the people on today cant help me.

Paul_C - 18/2/12 at 03:10 PM

My understanding is that all K type thermocouples are the same. The K means that the junction is chromel / nickel according to Wikipedia.
There is at least one standard for the type of connector that uses the same material as the thermocouple because any dissimilar metal junction causes some voltage which will change the reading. If it has one of those (available from RS Stock No. 455-9534 amongst others) then it's clear what the multimeter uses.

I'm guessing that the standard multimeter terminals are used to connect the temperature sensor. If so it's possible that your meter came with a thermistor which allows a cheaper internal circuit and possibly greater accuracy but with disadvantages as well. Unfortunately they aren't standard.

britishtrident - 18/2/12 at 03:57 PM

Easier to use one of these http://www.maplin.co.uk/handheld-non-contact-thermometer-590711

tegwin - 18/2/12 at 03:58 PM

quote:
Originally posted by britishtrident
Easier to use one of these http://www.maplin.co.uk/handheld-non-contact-thermometer-590711


I have something similar to that... But not suitable for this application. I need to glue a very small thermocouple onto a tiny pad on a circuitboard and measure the temp in that specific area.... Should allow me to calculate junction temperatures. :-)