Donald P. Chitwood/Jane Peterson on sat 1 jun 96
Several months ago I described problems my wife was having with a new kiln
and its built-in programmable controller. Since that original posting,
we've learned a lot and the problems have been resolved. I wanted to share
the results with the rest of you. First, let me describe the situation
again.
My wife and ceramic artist, Jane, bought a new-model programmable kiln from
a major brand kilnmaker about 2 years ago. Both of us have engineering
backgrounds and have used industrial electronic temperature controllers
before. So we were intrigued when we saw a pottery kiln equipped with one.
Modern controllers are versatile, easy to use. If done right, they can
give excellent control on equipment like kilns.
This controller is very user friendly. It is easy to program and has two
different firing modes. The first is called CONE FIRE MODE. It works just
like it sounds, i.e. you simply enter the cone number you want to fire to
and off you go. The controller has built-in data tables that mimic the
firing schedules that Orton specifies with its cones. You can select from
three firing rates: slow, medium, and fast.
The second mode is called RAMP-HOLD MODE. This mode gives you total
control over the ramp rates and soak times. You figure out all the values
on paper, then manually enter the values in the keypad. It's really pretty
easy to do.
From the very start, Jane had problems with the kiln and controller. Her
firing losses, related to the controller alone, were about 50%. In some
cases, the controller wouldn't do what the manual said it would do.
First, it wouldn't candle her work. As you know candling requires a very
slow ramp-up to a very low temperature. The controller wouldn't ramp this
slowly without shutting itself off with an error message (even though the
manual said it would ramp this slowly).
The second problem came when using the cone fire mode. The SLOW mode fired
too rapidly and cracked a lot of her thicker, more sculptural ware. To get
a slower rate and save her work, Jane had no choice but to use the
ramp-soak mode.
This mode was the source of her greatest frustration. Using witness cones
to monitor the upper temperature range, she quickly learned that the
temperature readout and the witness cones didn't agree from run to run.
This required her to be the cone-sitter and decide when to manually stop
the program.
In the best of all possible worlds, an ideal controller would allow you to
change the program at any time to correct problems and fine tune the final
temperature. This controller did not allow changes during a firing. To
make a program change at a critical point, she had to stop the run, enter a
new program, then restart. During this time, the kiln would lose heat, of
course. So she would have to take heat loss into account while
reprogramming. All this fooling around subjected the work to unknown
work-heat, so it quickly became a crap-shoot.
Needless to say, this is a crazy-making situation. She complained to the
factory right after she got it and they replaced a faulty chip for no
charge. The new chip didn't help. Her problems were based on the
fundamental controller design and built-in limitations. After suffering
lots of firing losses right before a major show last year, she decided it
was an expensive piece of junk. It was time to pursue finding something
better. So I began looking for a suitable industrial controller.
I researched many controllers, and talked to factory reps and technical
people. There were numerous controllers that would work fine. But before
we spent the big bucks for a new unit, Jane suggested I call the kiln
manufacturer on the off chance they may have a solution. When I contacted
them, they were very sympathetic and concerned. I was quite frank about
our problems and said we were fed up with their controller. They asked me
to bring the controller to the factory to see how they could help.
Luckily, the factory is in town. When I arrived, the production manager
listened to my complaints. Eventually, he offered to swap our old
controller circuit board with the latest upgraded version. This sounded
reasonable to me. To sweeten the deal, the new version came with some
valuable new features including 8 instead of 6 program steps, a 6 program
memory (for example, you can program a bisque fire, several glaze fires,
etc. and store them for future use), and a SKIP feature. More about that
later.
The manager installed a new circuit board, plugged it in, and ran through
the programming to check it out and show me the new features. He gave us a
new manual plus technical information that wasn't printed anywhere. This
didn't cost me a cent, even though the warranty had lapsed more than a year
ago. I got a new thermocouple, too, because the old one was almost shot.
In return, he asked for feedback on how it works for us which we will do.
All in all, we were quite impressed with the manufacturer's response. The
manufacturer is Skutt. The company showed real concern with our problems
and backed it up by offering us the best solution they could. I received a
tutorial on programmable kiln operation that few people get. It was also
clear that the new features were improvements based on customer feedback.
Jane used the new controller to fire all her ware for the 14th Annual
Ceramics Showcase scheduled for April 26-28. (This is the biggest ceramics
show in Oregon, if not the Pacific Northwest, and is very well attended.
It is put on and run by the Oregon Potters Association.) It candled her
work just fine. Every firing was successful as far as the kiln is
concerned. Repeatability has improved and she has learned to trust it.
Jane has a shelf covered with fired cone-packs that look almost identical.
That's impressive!
Before I conclude my story, I want to describe the SKIP feature on the new
controller. It is a major improvement and one of Jane's most appreciated
features. Here's what it does. During a firing, it allows you to skip
from the current program step to the next step. Very simple. It's a
partial solution to the problem of changing the program at a critical point
if necessary.
Here's a real-life example. Let's say you're doing a cone 5 glaze firing
and you've programmed a maximum temperature that should be close to where
cone 5 drops. Then, as the kiln approaches this temperature, you peek at
the cones and notice that cone 5 is almost down. You know from experience
that if the temperature continues to rise and reaches the programmed value,
cone 5 will be history and cone 6 will start to bend. Not only that, but
you know this glaze responds well to a slow cooling ("firing down"). You
don't want to simply turn the power off to avoid overfiring. Here's where
the SKIP feature works well. You simply press the SKIP button and the
controller immediately goes to your controlled cool-down step. Of course,
skipping is a benefit only if you've anticipated the problem and programmed
the next step to solve your problem. With experience, you can anticipate
what you'll likely need. It works great for Jane. She rarely uses it now
because firings are so repeatable.
The final verdict on the replacement Skutt controller is this: it now
candles OK; and the SKIP feature gives control over achieving the desired
maximum temperature and allowing firing down. Using the same program with
roughly similar kiln loads, the results have been very consistent among 5
or more firings. It is a distinct improvement over the original
controller. We are also very pleased with the support from Skutt Kilns and
recommend them highly. Our plans to buy an industrial temperature
controller are on the shelf. The money saved will probably go
into.........MORE CLAY!!
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