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High Bridge Pottery

Home Made Kiln Controller

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It has been a while since I got to dabble with electronics. Looking into automating a gas kiln. Found a ball valve + actuator that needs 0-10v signal sent for how open it is. After some googling I found this op-amp circuit for doing that exact job so set about making it.

 

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Took me a few failed attemps (wired the 24v positive up from actuator up to my raspberry pi and killed it, same with chip) but once I made sure it was the right circuit it all works perfectly.

Realised I never posted the MAX31855 circuit so here is that one too.

 

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Tested it out on the kiln today and it works a treat. Still lots more work for actually programming the thing to do sensible things.

 

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Joe_L, glazenerd and Chilly like this

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Nice work Joel!   I've have been too busy at work to look at my stuff but, hope to return to it shortly;   I did buy some MAX chips to compare against the AD595;  I like the pwm to voltage converter,  thanks for posting the circuits.  

Keep up the progress!
 

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I've decided that doing my own kiln controller would be an interesting project, but too much of a distraction from making pots.

This was exacerbated by my (now ex) kiln controller deciding to overfire to about 1330 (in a kiln rated to 1300!). In the soak, when the elements came on, the temperature readout dropped so they stayed on till it got to the target of 1290, then cut out and the temperature readout immediately jumped up to 1330 and the kiln cooled down to 1285, then the elements came on and the temperature immediately dropped. I guess the elements were causing a voltage drop which then affected the temperature reading.

Kiln survived, though the stoneware in it started bloating as it was an oil spot glaze with a long soak, and a while until I noticed.

Anyway, I've found that the Bentrup TC507 controller does all I need and more, and a lot quicker to get in place than rolling my own. It can also be used to control a gas kiln if you have the right valves, though I just use electric. So I'm wiring it all in, including a couple of thyristors to replace the relays which should give a longer element life.

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Hi;   I found a bit of spare time recently so I added some code to allow the user to add new programmes to the controller;  this took me far longer than I expected, but at least that bit is complete now.

 

to be continued... ;-)

High Bridge Pottery likes this

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I have been doing a bit more work with the home made kiln controller, not too much on the software side but I tried designing some PCB's in Fritzing. It was pretty easy to use but really started going slow with the 0-10v Op Amp circuit. Don't think it's set out for making complicated ones.

 

I sent the PCB's off through the fritzing website and they supplied some mock up images of the board. Now I have to wait 1-2 weeks for the boards :( I still need to find a reliable thermocouple to run along side my board to test how accurate it is, or maybe do something with cones. Not sure on that one. I know it reads temperatures but are they right...

 

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Getting closer to having something that works with a kiln.  Been updating the software a bit so now it resembles something usefulish. It would be interesting to have ideas on features, not that I could add them easily :lol:. Need to order a few more things then I can get it to fire and graph an electric kiln firing.

Joseph F likes this

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One useful feature for the software would be to have one screen option that simply displayed the temperature(s) as big (giant) numbers and nothing else on the screen.  One big number for each thermocouple channel, that the number could be seen and read  easily in all kinds of ambient light from 20 or 30 feet away.   This would make it easy to know the temperature from anywhere in the general vicinity of the kiln (say, down on hands and knees squinting into a porthole) without having to get up and walk over to a pc or laptop and search on a screen.

I am looking for something like this right now to display thermocouple temps for a wood fired kiln and have had no luck so far finding it.  If anyone has any ideas?....

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On 26/09/2017 at 2:35 PM, High Bridge Pottery said:

You can buy this board https://www.adafruit.com/product/3263 Turns out there is a better chip that I should be using that can read all thermocouples. Link it to a pi and you are good to go.

Yeah deffo!   I think I will try and incorporate that chip in the next version of my board, so cheap as well!

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When I looked the better ones were about half price compared to the one I have been using.

picard-facepalm.jpg

Still there was some code set up for doing the linearization software side that I had to copy some figures from here. No idea what it all means but I think it works, magic maths. https://srdata.nist.gov/its90/download/type_S.tab

Edited by High Bridge Pottery

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that facepalm. it is ok. part of learning is doing things wrong. atleast your making progress and doing something awesome. knowledge is power my friend! i can't wait till you open your kiln business. :D

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On 29/09/2017 at 4:14 AM, High Bridge Pottery said:

When I looked the better ones were about half price compared to the one I have been using.

picard-facepalm.jpg

Still there was some code set up for doing the linearization software side that I had to copy some figures from here. No idea what it all means but I think it works, magic maths. https://srdata.nist.gov/its90/download/type_S.tab

That table in your link enables the conversion of millivolts to degrees Celsius.  If you don’t happen to have a proper thermometer to hook up to your thermocouple, you can hook up a multimeter instead and you get a reading in millivolts which, using this table, can be converted to an equivalent in degrees Celsius.   Or maybe you knew that?...  anyway, very handy if you have a spare multimeter lying around.  Your table is for an S type thermocouple, but as you may have seen there are equivalent tables for all other types of thermocouples as well.

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