Pottery Kiln Automation

I would use an Arduino. There are a plethora of 'shield' boards out there for moisture, temperature...

Or even a PICAXE if he is not very computer savvy, as its even cheaper to buy and all the software and manuals are free to download and use, plus there is a great forum when you meet some really clever people!!

Such ideas are perfect for the fast BASIC PICAXE uses....

What-Is-PICAXE

Picaxeforum.co.uk

Best of luck to the OP and do tell us how you get on no matter what you use!!

I'm not sure checking the humidity will be reliable enough to be worth the effort, but worth some experimentation I guess....To get consistent readings the humidity and cfm flow of the entering air would have to be consistent, I'm not sure that's doable on a hobbyist's budget...you realize the amount of moisture is very small....

http://www.bigceramicstore.com/info/ceramics/tips/tip49_load_fire_kilns_part2.html

A couple of suggestions:

You probably need to arrange for some heat exchange to preheat the incoming air using the exhaust. This will help to minimize cold drafts, thermal shock, saddened pot throwers. A length of coaxial intake and exhaust could be sufficient.

Rather than the entire exhaust, it will be far easier to route a small amount of the exhaust flow to be cooled and measured for water content. No need to admit outside air to cool, just run long enoufh pipe to allow enough heat exchange with ambient.

I have a ceramic potter friend. I don't recall her ever performing a drying cycle as the 'work' was installed in the kiln after being fully air dry.

There may be a initial low temp setting to final dry, but you don't ever put wet clay in the kiln. Your bigger problem is learning the techniques to prevent cracking while drying, as different thickness of the piece will shrink differently pulling the work apart. That is what she fought more then any other problem. She has a Paragon Kiln sitter. This uses cone firing temperature references. They make these to melt at different temperatures. Paragon makes a temperature switch that has 3 fingers that are mechanically connected to a power switch to the heat elements. When the cone melts, the spring loaded fingers move to open the power switch.

Cone 4 through 14 are the typical firing temperatures of clay (Vitrification). Different clay bodies requires different temperatures to melt the glass silicon. As well glazing has it's own cone temps based on the ceramic base piece and proprietary glaze ingredients.

If you fire more then one layer of work, you will need kiln furniture to make use of the volume of the kiln. A solution for my paragon heat treat furnace (a glass makers kiln front load) came with a programmable controller that allows time segments, with temperature and ramp, and hold times.

http://www.paragonweb.com/Sentry_Digital_12-key_Non-Ceramic.cfm

Note this controller has an output to control a kiln vent. The link references a Orton KilnVent.

https://www.dogwoodceramics.com/product/orton/orton-kiln-vents.htm

Both kilns have "Sitters" which cuts power via mechanical switch when the cone melts at its set temperature. We had our first successful bisque firing last night. The Orton kiln vent is what inspired this idea.

My thought is to monitor and automate the process with measurement of the atmospheric conditions inside the kiln. The free water stage is specifically what I was after on this first step. Looking down the road to the vitrification step, I'm imagining an x-ray for density change could work, but not in my basement! The kilns I have max out at 2300F/1260C, so cone 9 is the top of the heat settings.

TE Measurement specialties has a humidity sensor at DigiKey that can handle 140C temperature for $6.46. I've found N-type thermocouples in the $35 range that handle 1287C. I didn't consider flow measurement, (Thanks SolarEagle). A tee fitting with two humidity sensors, one pre kiln input to measure ambient humidity, one post to monitor kiln conditions, The MAF from my van $28, and a temperature probe in the kiln and one in the pipe, post kiln should do it. I will also explore the long pipe/ no mix route, but I'm leary of condensation and time lag.

A raspberry Pi may be the final product, but in the mean time a $150 NI-USB 6008 will allow me to log sensor readings to determine if this is a feasible endeavor.

Andy... A Pic controller is what I used on my senior EE project in college. I interfaced a stationary bicycle with a video game, you had to pedal for the guy to move (PWM the up arrow) and steering was done via the handlebars.

Oh, kiln process is just like drying malt and some crops like rice and wheat.

You can do some hygro calculations and come up with the temperature, the length of kiln, rpm and hot air speed.

Some cement plant use IR monitoring like flir.

Go ahead its doable.

You might want to actually add a small pipe to the kiln to draw air off from the kiln, cool it and measure the humidity rather than monitoring the exhaust. That way you can cool the sample air in a controlled manner and measure the humidity and then just shut off the draw off air with a solenoid valve during high fire.

We used this method on gas-fired heat treating furnaces to monitor and control humidity levels.

That is an excellent idea! Quite surprising no one made that suggestion until now.