[TheForge] Thermocouple on mig welder

Tue Oct 21 23:37:00 2003

A problem on the board might cause the TC to go out. Though unlikely.

In my experience either a TC works or it doesn't. When you measured the
TC was it COMPLETELY disconnected from the board? if not the TC is open
and your reading resistances back through he board. 

If it was the TC is still bad, anything other than approximately 0 ohms
is a bad TC. 

Either way the TC seems to have issues...

If the board isnt compensated it will read the short as 32 deg F, it may
have a low temp limit... but whatever took out the tc could have taken
out the board..

just a thought...

mike

At 07:28 PM 10/21/2003, shannell wrote:

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: {quot}Mike Linn{quot} <[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 {quot}feature{quot}...
>
>
>            
Mike Linn

>       Artist Blacksmith
>           McCalla,
AL

>         AFC Webmaster
>
http://afc.abana-chapter.com

>
> {quot}To create is noble, to imitate is dull; a bold experiment
which is

criticized

>    is better than a timid copy which goes
unnoticed.{quot}
>                 
Graham Hughes

>
>
>
>
>
> _______________________________________________
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Login:  [email protected]
password:  anvil
___________

           Mike
Linn

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

{quot}To create is noble, to imitate is dull; a
bold experiment which is criticized 

  is better than a timid copy which goes unnoticed.{quot}
                Graham
Hughes

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