[TheForge] Thermocouple on mig welder

Tue Oct 21 21:33:01 2003

Thanks Mike, so it must be the board then? Did you see my second post, I
measured 15k on the Tc but a short on the board didnt fix the problem....
strange if its meant to be nearly a short at air temp?
----- Original Message -----
From: "Mike Linn" <[email protected]>
To: <[email protected]>
Sent: Wednesday, October 22, 2003 10:46 AM
Subject: Re: [TheForge] Thermocouple on mig welder


> 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
>
>
>
>
>
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