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Teledyne API Model 401 O
3
Photometric Calibrator Instruction Manual, 01124, Rev. J2
4.4 Examining The Ozone Formula Slope And Offset
The slope and offset parameters can be examined (or changed) by SETUP-MISC-O3-SLPE or
SETUP-MISC-O3-OFFS. The slope and offset parameters are set only during zero and span
calibration routines. These parameters are used to adjust the span and zero values to their exact
values.
NOTE
Do not change slope or offset value unless it is absolutely necessary
to restore the known original values. Take a note of new slope and
offset values after each bench calibration for reference.
The current value of the ozone reading that is displayed on the front panel and output on the
D/A terminals on the back panel is computed as follows:
1. The Model 401 Analyzer switches into reference mode.
2. The Analyzer waits 2 seconds to purge the sample tube.
3. The instrument measures the intensity of light striking the detector during the next 1.067 sec.
This reading forms the reference intensity I
o
in the ozone concentration equation.
4. The photometer now switches to the sample mode and waits 2 seconds as in step 2 above.
5. The instrument measures the intensity of light striking the detector during the next 1.067 sec.
This reading forms the sample concentration intensity I in the ozone concentration equation.
6. The concentration of ozone is computed using the Beer-Lambert equation corrected for
temperature and pressure.
7. Slope and offset corrections are made to the ozone concentration according to the equation:
OffsetnncentratioMeasuredCoSlopeononcentratiCorrectedC
+
×
=
8. An average of the last 32 samples is computed and converted to the number displayed on the
front panel.
This is the ozone concentration. The number is also routed to the D/A converter and the resulting
voltage is output to the back panel.
4-2