Internal UV Ozone Photometer Page 9-
Start out with the Derivative term set to zero. It is
possible (and simpler) to tune the servo loop using only the
Proportional and Integral terms. If there is a slight
overshoot, however, the Derivative term can sometimes be
increased slightly to eliminate the overshoot, rather than
decreasing the Integral term, resulting in an improved
response time.
Start out by selecting the factory default Proportional and
Integral terms (about .4 and .2, respectively). With the
Proportional constant remaining fixed, increase the Integral
constant if the photometer takes too long to reach the
setpoint value and decrease it if there is overshoot or
oscillation. The best Proportional constant value can be
found by trying different values, but for each new
Proportional constant, the Integral constant bust be
readjusted to compensate for undershoot or overshoot.
After setting the constants using the Fake Hardware mode,
resume normal mode (by entering ALT-H) and run tests with the
real Photometer and Ozone Generator. Be sure to restore the
original Sample Hold and Measure times. The response may be
somewhat different than that while using the simulated
Photometer, requiring additional adjustment of the PID
constants. Test that the servo control operates properly even
when the photometer calibration is high or low.
Routine Maintenance
The Model 2010D's Photometer is designed to operate with minimal
maintenance, however periodic maintenance will ensure that the
Photometer continues to operate in the optimum condition. In
addition, there are several components in the Photometer that
should be considered expendable and that will need periodic
replacement. This section describes the common maintenance
items, beginning with those requiring the most frequent
attention.
Calibration
In order to ensure the accuracy of the 2010D's Photometer, it
should be calibrated periodically by comparing it to an ozone
reference standard. This will not only ensure that the
Photometer's measurements are accurate, but will also point
out when there is a problem and maintenance is needed. The
sub-section entitled "Photometer Calibration" beginning on
Page 9-17 describes how to calibrate the 2010D's Photometer.
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