Dave Finkelnburg on thu 18 jan 01
Faye,
For the type of firing you are doing (macrocrystalline glazes) you need
to be using a Type-S thermocouple. I get by fine with a Type-K because it's
accurate enough, and I can fire by watching my cones but it's not nearly as
good as the Type-S. A good temperature indication somewhat more objective
than watching a cone, and you need it anyway while controlling your cooling
cycle and soak periods. You still want to have a cone pack to avoid
overfiring and as a witness record.
The thermocouple is a bimetallic wire sensor placed into the hot part of
the kiln. The temperature indication (TI) is a meter which responds to the
very low-voltage signal from the TC. As the surface of the TC oxidizes, the
junctions between the TC wire and the meter corrode, etc, the indicated
temperature can change from what it was for exactly the same temperature
when the system was new.
What you do need to do is have the TI calibrated on a periodic basis,
using your TC. Do this before you experience problems. I am no instrument
technician, but I do know that TI's begin to drift, slowly as you note in a
later post. You can't tolerate that for the kind of work you are doing.
You want to find out from some instrumentation folks how many hours you
can expect to fire before you need to recalibrate. I would expect it would
be less frequently than once/year, depends on how often you fire, and how
long, possibly every two or three years. By checking and recalibrating your
TC indication BEFORE it goes very bad on you, the indication will safely
stay accurate to within 5 degrees F or so all the time.
Good glazing!
Dave Finkelnburg
Idaho Fire Pottery
| |
|
