Lesley Alexander on fri 19 jan 01
Dave Finkelnberg says, "What you do need to do is have the TI calibrated
on a periodic basis, using your TC. " Can that be explained? Lesley
Dave Finkelnburg on fri 19 jan 01
Lesley,
There are two ways to calibrate a temperature indication.
One is to generate a millivolt signal and send it to the two input
terminals of the temperature indicator (TI). Then you adjust the indicated
temperature, if needed, to correspond to the low voltage signal value. The
math is a little complex, but a particular type of thermocouple of a
particular diameter wire will produce a particular number of millivolts when
exposed to a particular temperature. Sending an equivalent voltage to the
TI has a similar effect to putting the thermocouple (TC) in a heated area.
This is especially handy for calibrating a TI at, say, 1,000 degrees C when
the kiln is off. Any good instrument technician should be able to do this
for you.
The other method of calibrating a TI is to put the sensing end of the TC
into a source of heat or cold, such as a pan of boiling water, which at sea
level will be 212 degrees F for pure water. Then adjust the temperature
indication, if needed, to read 212. The trouble with this method, of
course, is there's no handy reference for the temperatures we like to work
at and where an indication is most critical--from 1,800 to 2,350 degrees F.
:-( In fact, a big error on the low end isn't very critical most times,
but on the high end it can be disaster!
I hope this helps.
Dave Finkelnburg
From: Lesley Alexander
>Dave Finkelnberg says, "What you do need to do is have the TI calibrated
>on a periodic basis, using your TC. " Can that be explained? Lesley
David Woodin on sat 20 jan 01
I don't think Dave Finkelnberg meant to say the diameter of the wire had
anything to do with the millvolt output of a thermocouple. There are
millivolt tables for each type of themocouple J,K,T,R,S etc. The newer
calbiation equipment has all of the tables in memory and has an automatic
cold junction so you need no math at all to calibrate digital indicators.
However the old analog type requires a different method to calibrate it. You
do need the proper wire for each thermocouple input. If you question the
accuracy of your digital pyrometer send it back to the manufacturer.
David
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