[TheForge] Thermocouple on mig welder

[Mike Linn]

A TC should be nearly a dead short. it is NOT a resistive device like an 
RTD or thermistor. T/C operate on the principle of EMF generated by 
dissimilar metals in contact with each other.

If you put a dead short across the input terminals of a compensated t/c 
device it should see/read ambient air temp, uncompensated devices will read 
it as 32 deg F /0 deg C

What the board is looking for is a particular millivolt signal being 
generated by the t/c .

mike


At 06:57 PM 10/21/2003, you wrote:
>My mig has shut itself down with the overheated light on, this is from a
>cold start. I tried short circuiting the thermocouple connection to the pcb
>board but still no go. Does the board look for a certain amount of ohms to
>work?  Can I put a resistior in place of the TC.? I put the multimeter
>across another Tc. I have that is used for measuring temps from a multimeter
>and its 9 ohms at room temp. I dont really want to replace the Tc. on the
>welder, it looks like its buried in the winding and Ive never overheated the
>machine, its 250 amps which has plenty of duty cycle for me so I dont mind
>not having this "feature"...


            Mike Linn
      Artist Blacksmith
          McCalla, AL
        AFC Webmaster
http://afc.abana-chapter.com

"To create is noble, to imitate is dull; a bold experiment which is criticized
   is better than a timid copy which goes unnoticed."
                 Graham Hughes