On Oct 9, 2011, at 5:52 PM, Mark Iverson-ZeroPoint wrote:
When you zoom in on the end of the sensor lead wire, where the frayed
insulation is, you clearly see the bare metal thermocouple wires.
And from the length of that section of lead wire (~1.5 to 2
inches), the
most likely location for the actual TC was on one of the flat
surfaces on
the shiny steel nut. They probably laid it on one of the flats,
and wrapped
black tape around the circumference of that shiny nut, more or less
covering
the entire shiny surface.
Horace, I doubt if they would have just assumed the insulation
would hold
the TC against the nut; I vaguely remember reading that "...the TCs
were
held tightly against the outer metal surface by tape". But then,
that would
be one less thing for us to get frustrated about! Can't have that,
now can
we...
-Mark
Well we can always figure out more to worry about! 8^)
Putting a metal thermocouple up against a metal surface sounds like a
prescription for variable but systematic error, depending on
vibrations, touching the wire, humidity, etc. The steel nut can
short out at least some some of the potential. This means requiring
a high bias. However, if the short is removed or reduced, then the
bias is too high. When playing with the bias in my spreadsheet I
settled on 0.8°C. However, it looked as if only one bias was not
sufficient to fit the numbers.
In any case, it seems to me to be just bad technique.
Best regards,
Horace Heffner
http://www.mtaonline.net/~hheffner/
