Corinne Null on fri 20 sep 96
This summer I posted problems with my new Bartlet controller registering
numbers that were low in relation to witness cones, and sitter cones, in my
brand new Bailey electric kiln.
To make a long story short, I just switched both ends of the wire connecting
the controller and the thermocouple, and "voila", my readings are right on
the money! There seemed to be no indication on the wire (unless my
electrician removed it) that one side of the wire was different from the
other side, but there definately is!
Actually, when I first hooked it up, the readings on the controller went
negative. Talk about freaking out! I switched one end, and they went
positive, and I thought all was well, until the sitter cones (^10) turned
the kiln off at 2000 F.
In John's lengthy post on the subject, which I've been studying all summer,
he said:
> the place where you join the thermocouple lead and the copper wire becomes
>another pair of thermocouples!!!These junctions of dis-similar metals will
>create another millivolt signal that will combine with the other "real"
signal >(either plus or minus depending on polarity....or "direction".....
of electon >flow). Worse yet, there will be TWO new thermocouples (each
junction)..... one >Copper / Alumel and one Copper /Chromel each producing
different signals!
And, I got about 300 degrees F. difference in the kiln vs. the controller.
Those little unwanted thermocouples had to be where the heat went!
I've shared this info with Jim Bailey, who was very interested and pleased
to have another bullet with which to problem solve.
Kudo's to John Baymore! It's been a long hard summer worrying this out, and
I feel SO GOOD to have it finally resolved! Wheeeeee!
Corinne Null
Bedford, NH
cnull@mv.mv.com
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