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Teledyne API Model 100AH SO
2
Analyzer Instruction Manual, 02417, Rev. D
5.2.2.4 SO
2
Cal Concentration
Before the M100AH can be spanned, it is necessary to enter the expected span concentrations for
SO
2
. This is done by using CAL-CONC. Concentration values from 10 to 4500 PPM are
accepted. If a value of XXXX is displayed, that indicates an offscale, or invalid reading. The
XXXX value will often be displayed at power-up when there is no data yet available to be
displayed. Certain instrument fault conditions will cause X's to be displayed. This is the same as
the needle being offscale on a analog meter. See the Troubleshooting Section 10.2.8 if this
occurs.
5.2.2.5 Formula Values
The slope and offset terms should be checked after each calibration. The values for these terms
contain important information about the internal health of the analyzer.
To compute the SO
2
concentration, the formula for a straight line is used.
y = mx + b
Where:
y = the SO
2
concentration
m = the slope
x = the conditioned PMT tube output
b = the offset
In comparison with analog analyzers the slope term is equivalent to the "span pot" and the b term
is equivalent to the "zero pot". Again, like an analog analyzer, there is only a limited range of
adjustment allowed for either term, and there are consequences of having the values near the
high or low limits of their respective ranges.
The x term is the conditioned PMT signal. PMT signal is adjusted for the lamp ratio background,
range, temperature, and pressure.
The offset (b) term is the total background light with the zero term subtracted out. The zero term
measures detector dark current and amplifier noise. The b term is composed mostly of the optical
system background.
5-11