That thermocouple would be either Type J or Type K.  The voltage to temp 
profiles are inherent to the type and not dependent on the mfg.  You can 
look them up.

The voltage is low and requires a low offset amplifier to read.

A thermocouple creates a voltage based only on a temp difference between 
the hot junction and the "cold junction" where the special alloy wires 
meet copper wires or PCB traces.  Typically the controller has a 
thermistor or diode or whatever to read the absolute cold side temp to 
accurately gauge what the hot side temp is.  Otherwise you have to just 
assume the cold side is 72F or whatever which may be far off at times.  
The board heats up from the oven heat and the room temp will fluctuate too.

Danny

Dr Skip wrote:
> I'm having a creative thought blockage to what should be an easy EE problem....
>
> I have an kitchen oven (with range top) that is electronically controlled and 
> 20 years old. It consists of a control board with the only real chip on it 
> looking like it's the display controller, not a general micro. It has the 
> thermocouple input, 3v and 23v AC inputs and 4 outputs to control a relay board 
> for 2 elements, a fan, and a door lock (self clean).
>
> Early on the unit was flaky, often quiting with odd codes. Kicking it would 
> help... Turned out a row of solder joints were cracked on the connector of the 
> relay board. After resoldering, all has been fine for years. Seems it gets hot 
> in there. ;) Until yesterday. The error code during use implied a bad 
> controller board once, but that was just once. Even cold, it now says the 
> thermocouple is out of range. It isn't, I tested. Wiring is fine too.
>
> I'm also getting some flickering segments on the display. It is probably the 
> controller, although nothing seems visibly awry. No board schematics, and it's 
> several boards mounted in a sandwich with almost all discretes.
>
> Before one thinks I'm looking for a repairman, I've always thought of 
> re-designing the controller, since it has a separate relay board and low 
> voltage control to it. I haven't had a chance to study the extras, like cycling 
> during self cleaning, etc. Unfortunately, now it HAS to be done and time is 
> important.
>
> So the question: given I've got a good thermocouple, but without knowing its 
> temperature curve, and that I can get at controlling the elements, what would 
> be the quickest, simplest, most creative way one could control oven temp with 
> these resources? My PIC skills are not fast enough, and the time pressure has 
> blunted my creativity. I'm hoping I'm overlooking a simple analog design that 
> will allow me to control the elements to temperature using the current 
> thermocouple or another component (to 550F approx or better). Time is urgent it 
> seems (a hungry family), so parts count and availability are important.
>
> Any ideas?
>
> TIA, Skip
>
>
>
>   

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