DUAL Thermocouple for PID controlled convection oven?

[rototerrier]

Anyone aware of a way to hook up a dual thermocouple, maybe one at the top and one at the bottom and it average the temps?

Since having one TC in an oven is just going to measure that one spot, wouldn't having 2 that average give you a more accurate temperature over the entire oven?

Just curious if this has been done or am I thinking wrong?

[oteroman]

No need.
Unless you have element on top you want to use a separate PID on.


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[rototerrier]

Correct. I have a dual element and find the temp on the top rack to always be higher than the bottom, even with convection. I can only use the top rack to be sure I'm at the right temp. I suppose a dual pid would work.

[Mike W1]

The PID's I've seen only have one input for a TC so you'd need 2 PID's. Some genius might be able to come up with a way to average the temperature but I'm not a genius. Suppose there's probably an industrial version that could do it but it'd likely be out of our price range for casting.

[Ausglock]

If the airflow in the oven is adequate, only 1 probe is needed and placed in the centre of the oven.
Mine is under the centre of the middle rack.

[dikman]

Interesting idea, but I don't think it would work too well. I reckon you'd still end up with hot spots at the top of the oven. Effective circulation is the only way to keep a constant even temp, but using a small oven, with the elements close to the top and bottom, makes it difficult. If you can boost the air circulation that might help?

[LabGuy]

Money and time would be better spent on verifying circulation.

[Mike W1]

Looking thru some PID manuals tonight and noticed something. Have no idea if it would work for this but there's an illustration on page 7 of Auber's manual showing 2 TC's hooked up to maintain a temperature difference. Their tech staff is pretty sharp so you might want to get hold of them and tell them what you have in mind. Bet they'd have an answer one way or the other if it's feasible.

[ebruce]

An average temperature can be read by wiring two or more thermocouples in parallel into the same input of your PID controller. You won't know individual temperatures this way, just the average.

http://www.dugantech.com/Product_Group-Temperature/Technical%20Articles/TE-Series%20and%20Parallel%20TC%20Measurements.pdf

Whether it is needed or not is debatable.