How to Make Thermocouples

Thermocouples are devices that are used to measure temperature. A thermocouple is a set of two wires welded together at one end, where a junction is formed between the two wires. Because each wire is composed of a different type of metal, each wire reacts differently to the temperature of the junction. Because of this difference, a voltage is generated. The voltage varies consistently with changes in temperature, and so there are devices, such as digital thermometers, that measure the voltage and convert it to a temperature reading.

Difficulty: Moderate

Instructions

Things You'll Need:

• Thermocouple wires
• Wire strippers
• Capacitive discharge welder
• Needle nose pliers

1. Take your thermocouple wire and strip a short length of insulation from one end of each wire.

2. Use needle nose pliers to twist the metal together one time at the end of the wires. Make sure the twist is tight and will not come loose as you handle the wire before welding. If it comes loose, you haven't tightened the wires tight enough. If that's the case, just twist them together again with more force.

3. Turn on your capacitive discharge welder. The twisted metal junction must be welded, not soldered. Solder would inject additional metal components into the junction and destroy the thermocouple properties of the wire.

4. Insert the twisted wire junction into the weld hole of the capacitive discharge welder and weld the junction by pressing the appropriate button on the welder.

5. Remove the completed thermocouple and turn off the welder.

Tips & Warnings

• Different thermocouple wires have different characteristics, which is useful to know for a thermocouple. Because thermocouple wires are color coded, you can check the color code to determine your type of thermocouple.
• Too many twists in the junction can affect the temperature response of the thermocouple.

Resources

• Thermocouple Wire Color Codes
• Capacitive Discharge Welder

[bm10]

on 9/24/2009 Dear Doug,

I like the straight forward way you poited out the most important issues. Just allow me one question:


Your write:

The twisted metal junction must be welded, not soldered. Solder would...

In my understanding the thermoelectric voltge is generated not in the joint, but in the wire with its ends at two different temperatures. The solder joint only is an electrical connection.

A more detailed explanation is given e.g. in


http://electronics-cooling.com/articles/1997/jan/jan97_01.php

I know there is a discussion about this issue, wondering about the Seebeck-effect I can not find any reason wich explains the effect of the quality of the joint.

If you have any argues or even measurements, which compare the two methods, I very much would appreciate to gettin knowledge of it.

Thjanks in advance and best regards,

Benedikt