masta@UMICH.EDU on thu 14 aug 03
To actually calibrate a pyrometer you would need something
other than cones, which respond to heat work and not just
temperature. One approach I briefly experimented with uses
the melting point of metal wire, copper in my case .
(1984F, easy to remember!)
What I did was to make a little clay holder that
held a strand of copper wire suspended between two posts.
Ideally these posts should be some high-temperature metal,
stainless steel at least, but I used regular steel nuts and
bolts through a clay base. Then connect a high-temperature
wire to each post and run them separately out of the kiln,
without touching any metal. ( I used plain steel baling
wire for my test. Not recommended, as it oxidized to
dust!)
The idea is that when the copper melts it breaks a circuit
and a light goes out or clock stops or whatever.
You know the temperature at that point in time, so
quickly read the pyrometer. This was enough to show me
that an old type-R thermocouple was kaput, so I haven't
pursued this farther. Possible sources of error would be
different grades of copper with different melting points.
I picked copper as the best bet of readily available metals
that are fairly pure, unlike aluminum or brass, and its
melting point is in a useful range. There may be better
options by buying specialty wire with known melting points.
Since then, I've thought this might be made into a more
permament addition to the kiln, as a way to monitor
thermocouple drift and/or contamination. For that use,
the exact melting point wouldn't be so important, as long
as it was consistent. Using wire from the same spool
would be good enough.
Of course, I'd want something better than watching for a
light to go out, so I'm saving this idea for when I
eventually get the kiln computerized, and can have
the computer monitor both the thermocouple and the
melt-wire, and report on drift directly.
...Some day Real Soon Now....
Robert Masta
dqatech@daqarta.com
D A Q A R T A
Data AcQuisition And Real-Time Analysis
Shareware from Interstellar Research
www.daqarta.com
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