On 25 Dec 2006 07:04:25 -0800, "Davis Salks"
wrote:

Dear fellow potters,

I just purchased and installed a three zone controller for my kiln. I
would like to warn anyone who is considering doing this.

I am generally satisfied with the controller itself, and the company
provided me with responsive and competent technical support. But they
did not guide me in determining whther my kiln would be sufficiently
powerful enough, and I am disappointerd with this.

So here is my advise. There is one major thing that you must consider
before retrofitting a 3-zone controller to your kiln. Your kiln must
have considerable surplus power to reach your highest working cone. And
I do mean considerable.

Here's why. When you run your kiln manually, and let's say your reach
your cone in the last half hour at a rate of 108 DegF\Hr. Then,
assuming that you are running at full capacity to achieve this, then
you will certainly not be able to maintain this same rate with the kiln
controller. The controller will be switching your elements on and off
as it tries to maintain even heat, so only a percentage of your kiln's
capacity will be used. Consequently, it will not be able to maintain
your intended rate of heating and may not even be able to reach your
cone.


Perhaps I misunderstand your problem, but the above doesn't
make sense.

The controller does indeed switch your elements on and off, but
there should be no loss of maximum performance. It's like your
kitchen oven: when the current temperature is below the setpoint,
there is maximum power to the element(s). Only when it reaches the
setpoint does it start cutting back, in order to maintain whatever
temperature you set. The difference with a digital controller is that
there is not just one simple setpoint like your oven, more like a
schedule of setpoints that it sets one after the other.

Yes, it's true that when you set a slow ramp-up, the kiln does not
heat as fast... it's just doing what you told it! This is certainly
not a fault of the controller. It's also possible to set a ramp
that is so steep that the kiln can't meet it even running flat-out.
So you do need to have some experience with your kiln to know
what is possible as far as rise rates go.

But there should never be a problem such as you describe.
You don't need any surplus power at all if you have set your
schedule to be similar to your original uncontrolled rate.
In that case, the controller will not be doing much of anything
until you hit the setpoint. Only then does it start cutting back
on the power in order to hold that temperature.

I am not an expert, so I can't give you any kind of formula to use for
determining this. However, it would seem that if you can reach your
cone reasonably by running at, say, only two-thirds of your full power
(such as running with only 4 elemnts out of 6 total), then it might
work out okay.

If not, you'll still be able to run your kiln unattended, but you will
not be able to get uniformly heated zones at the end of your fire.

Again, perhaps I have misunderstood your problem, but my
suspicion is that you have simply set an unreasonable schedule.
One thing you might consider is running the kiln the old way
and recording the temperatures every hour, then use that data
to set a controller schedule that comes close to the "natural"
kiln performance. The difference is that once you reach the
cone setting, you will now be able to hold that for as long as
you want, or to cut back to a somewhat lower setting for
crystal growth, etc.

Once you have this base ramp -up information, you can
feel free to set slower ramps over any temperature region.

Best regards,


Bob Masta
dqatechATdaqartaDOTcom

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