Thermocouple

Mazaag

Joined Oct 23, 2004
255
Hi guys,

Does anyone know how a thermocouple works ? (Copper/Constantin) and possibly a more specific explanation on how you can measure the temperature using them ..

Thanks

niftydog

Joined Jun 13, 2007
95
Try this for a start.

Two dissimilar metals are bonded together in the tip of a thermocouple. Each produces a voltage when subjected to a temperature gradient - different metals produce a different voltage. You simply measure the voltage difference between the two dissimilar metals.

Do you want to build something or buy something that will read temperature? Many digital multimeters have thermocouple inputs. There are also many temperature displays or PID temperature controllers to choose from that are relatively inexpensive.

bloguetronica

Joined Apr 27, 2007
1,541
In detail, you have two junctions between two different metals on a thermocouple. Take for example a copper-bismuth thermocouple. You will have a copper-bismuth junction, and a bismuth-copper junction. Through the Seebeck effect, the thermocouple generates an electrical potential based on the temperature difference between the two junctions.
Notice that you will need two junctions for it to work, not just one, or else you would be generating free energy out of plain temperature (instead of temperature difference), and there is no such thing as free energy.

Mazaag

Joined Oct 23, 2004
255
Is it possible to build a circuit that could be used to "simulate" heat for a thermocouple ? as in , provide different CONTROLLED voltages (microvolts) to the thermocouple ?

bloguetronica

Joined Apr 27, 2007
1,541
Is it possible to build a circuit that could be used to "simulate" heat for a thermocouple ? as in , provide different CONTROLLED voltages (microvolts) to the thermocouple ?
I didn't quite got your question.

If you do provide voltage to the thermocouple, it will happen the opposite of the Seebeck effect: you will generate heat difference between the two junctions from a potential differencial. This effect is used on active heatsinks (I don't remember the exact designation of this).

niftydog

Joined Jun 13, 2007
95
Thermocouples generate the voltage, not the other way around.

You could simulate a thermocouple by feeding small voltages into the input of a temperature monitoring device such as a PID controller.

ixisuprflyixi

Joined Sep 16, 2007
52
Since were on the topic of thermocouples, is it possible to get the two dissimilar metals and simply solder them together creating a thermocouple or would the tin/lead solder nullify the seebeck effect? Thanks.

niftydog

Joined Jun 13, 2007
95
Yes you can. It wouldn't nullify the Seebeck effect, but it would alter the characteristics. Commercial high temp thermocouples are cold welded I believe.