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OM-222 166 Page 21
4-15. Attaching Welded Thermocouples
. Do NOT weld thermocouples while connected to power source.
1. Attach thermocouples using a portable Thermocouple Attachment Unit (TAU). This unit spot welds thermocouple wire directly to the
workpiece. This method of thermocouple attachment ensures accurate temperature measurement.
2. Clean (file or grind) any loose scale or rust from the workpiece at the places where the wires will be attached.
3. Clean the location for the lead magnet to minimize resistance. Place the magnet as near to the thermocouple positions as possible.
4. Strip 1/4 inch of insulation from the thermocouple wires.
5. Set the output variable control of the TAU to about eighty percent (80%).
6. Grasp one of the stripped wires with the tip of the jaws of the application pliers.
. Don’t touch both wires of the thermocouple to the pliers at the same time when energizing the Thermocouple Attachment Unit. This will cause
the thermocouple wire to fuse to the pliers, rather than the workpiece.
7. Press the end of the wire to the workpiece at ninety degrees to the surface, and maintain a firm pressure. Make sure the Thermocouple Attach-
ment Unit is charged and wait for the ready light to glow.
8. Press discharge button, and the wire should weld to the workpiece. There will be a sharp crack and a slight arc flash.
9. Repeat the process with the other wire, placing it approximately 1/4 inch away from the first wire. Attach a spare thermocouple, and support
both thermocouples approximately 18 inches back from the connection with a band or fiber tape.
10. Carefully bend the wire over at right angles. This brings the thermocouple wires out along or parallel to the workpiece. It also tests the strength
of the weld. If the weld shows signs of breaking, remove the wire, restrip the end, and repeat the process.
804 322-A
Thermocouple
Wires
Strap Or Tape