Table #2
the atmosphere is so small, it has a very small impact on the overall TC
of air.
Note that as the numbers increase, the TC of the gasses increase,
with Hydrogen (H
2
) and Helium (He) being the most thermally
conductive. It’s this distinction between the TC of CDA as compared to
the TC of hydrogen or helium that we are interested in.
Our MGD-2002 is designed with two ranges. The low range detects
gas between 25 and 20,000 parts per milion (PPM) in increments of 25
ppm. Mathematically, 20,000 ppm is a concentration of 2%.
The high range is between 2% and 100%. Calibration of the MGD is
accomplished via the microprocessor. Initially when the sample air
contains no (zero) tracer gas, it will draw in 100% CDA. The micro-
processor is then told that the reading it’s getting is to be refered to as
“Zero”. Using a known controlled volume of CDA, 2% tracer gas (Scientific
grade) is injected into a closed loop. The accuracy of the gas is 2.00%,
and the detector should read 2.00%. This setting is then stored in
memory. The last calibration
point is to draw in 100%
scientific grade tracer gas,
and the reading stored in
memory. Since the TC of the
tracer gas is constant, the
readings observed are
directly proportional to the
concentration received.
Another way to state this is
that two points make a
straight line, and the more
points given, the more
accurate the straight line will
be. After the calibration
process, any concentration
sampled will fall on the line.
TESTING THE THEORY:
We at the manfacturing
facility have the capacity to
mix any concentration of gas
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