banorkin on mon 24 jan 00
In my last letter i forgot to mention that my kilns are located outdoors in
a metal shed open to the weather. With the thermocouple assembly and lead
wire configured the way I described, I get the same results regardless of
the seasonal weather. Inbetween my house and the shed, i run the
compensated extension wire through a common garden hose to provide
protection against the weather.
I also forgot to mention that the electrical noise that can be picked up by
the tc and the compensated lead wire is generated from a phase angle power
controller. This type of power controller delivers an analog(continuous)
non pulsing output to the electric heaters. There is another type of power
controller, distributed zero crossover where a 100 percent on or completely
off output is delivered to the heaters. The on off cycling is achieved by
distributing the on off siginals equally over time allowing for 30 percent
on and 70 percent off, in other words the equivalent of a 30 percent output
from the controller. other outputs would involve lets say 40 percent full
on and 60 percent full off resulting in a fourty percent output.
But the siginal is a pulsing one. When this type of power controller
is used with smaller gague kanthal wire, Im not sure where the cut off
point is in gague size, the controller delivers a pulsing siginal that
causes the heaters to pulse. I have used both types of firing circuits and
have found that the distributed zero crossover board resulted in very tiny
crystal aggregates all over the vase. With the other firing circuit, very
large aggregates of crystals can be achieved. The advantage of using a
distributed zero crossover firing circuit is that it generates no electrical
noise.
I have searched the web for a company that makes a controller that shows a
1/10 degree increment in the process temperature and allows for the
programming of temperature in one tenth of a degree increments with
temperature profiles that can have a great many segments for curve fitting
or simply to experiment with the firing cycle. This is the Yokogowa
Company. If you read their specs, when you look at stability, you will see
that in order to stabalize the controller for really precice control that it
too has to be kept at a constant temperature.
Sorry for the omissions and again. Good luck.
Bevan Norkin
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