Oven controller (arduino based)

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David Jupp:
Just a brief point - may not be critical for this project.

K type thermocouples are widely used, but can suffer problems - ageing/drift for example. More modern alternative constructions tend to suffer less problems.

rschilp:
David, what other kinds are available? and are they affordable for a project like this?

Thanks,

Rob

David Jupp:
There are several other types - N,T,S,J,R and others. Some have limited useful temperature range, or might be more or less suitable for particular duty. Check the web or speak to thermocouple vendor for more information.

If a few degrees of error isn't a major problem, then type K should be OK - after all they are still very widely used. If you need very precise measurement, there are potential subtle calibration/stability issues that you should look into. The issues can be overcome, but doing so tends to drive up the cost of the element.

I wouldn't expect cost to be a big factor when purchasing say 1 or 2 quantity of differing types - availability may drive your choice though.

You might also want to look into cold junction compensation (potentially a bigger issue than the type K foibles).

rschilp:
Hooked the thing up yesterday and it works great. I used the switching circuit of the oven to control it, just like the factory controller would.

The k-type thermocouple did produce a few stray readings, but with some minor code adjustments these are now no longer an impact.

Did a simple program yesterday getting the oven up to 955c (1751f) and letting it cool down after, this was to bake some ceramics to the biscuit stage.

Have a few updates to make to the code to clean up some screen artifacts, change the time display to hh:mm format and some other minor interface issues, but overall a very successful project. I'm going to make an enclosure for the arduino and screen without the relays and thermocouple parts and make those external with easy connectors so I can use the arduino for other projects and keep the enclosure as small as possible.

pardydon:
I have done a very similar project. I use it for pottery. I have it working now. I am interested in your approach to the programming. I have simply used the same approach as it was used manually. My glaze firings are very successful.
I noticed your comment about some problems with the thermocouple readings. I had some problems with my thermal couple readings above 1600 F and I discovered that they went away when I power the Arduino and the max chip from a separate power supply. When I was using my laptop to power the Arduino I got random readings of 0 mixed in with the proper readings. I got no further bad readings when I used a small power supply to directly power the Arduino and the max chip. I can see from your photo that you have almost the identical hardware that I am using. I'm very glad to see someone else doing the same things I am.

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