Teledyne 6400A Instruction Manual page 49

Sulfur dioxide analyzer
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TAI Model 6400A SO
Analyzer Operator Manual, 02164, Rev. G
2
5.2.2.5 Formula Values
The slope and offset terms should be checked after each calibration. The values for these terms
contain valuable information about the internal health of the analyzer. The range of acceptable
values and their meanings is given in Section 7.10.
To compute the SO
concentration, the formula for a straight line is used.
2
=
y
mx
b
Where:
y = the SO
concentration
2
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.
After every zero or span calibration check the QUALITY of the calibration. The calibration of
the 6400A involves balancing several sections of electronics and software to achieve an
optimum balance of accuracy, noise, linearity and dynamic range. See Section 7.10 for the
calibration quality check procedure.
5-11

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