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937A Multi-Sensor System
When using a control set point near the lower limit,
check the zero calibration and correct if necessary
(see page 49).
If a control set point is used, disable the protection set point or set it to a
higher value than the control set point. Otherwise, the protection set point will
override the control set point, preventing automatic start-up of the cold
cathode sensor when the pressure falls back below either set point.
When a protection and a control set point are used together, consider their
interaction with one another when choosing their values. If,
the two sensors measure the same pressure and are
properly calibrated,
the pressure never changes rapidly, and
the cold cathode sensor is never turned on when the
pressure is too high
then only the lower of the two set points will ever operate. If any of these
conditions are not true, both set points might be active at different times.
See page 48 for information on setting protection and control set points.
Information Update Rate
The A/D converter has a conversion time of 50 msec. The total pressure
update cycle in either
Pressure or Leak Test modes is the number of sensors
multiplied by 50 msec, e.g., if 5 sensors are operating, the display and the
logarithmic output for each sensor are updated every 250 msec.
When the Controller is in a mode other than
Pressure or Leak Test, the update
rate is 100 msec per sensor rather than 50 msec. Therefore, it is preferable to
leave the Controller in
Pressure mode.
The sensor update rate may be suspended briefly while the Controller is self-
calibrating, while rotary switches are turned or buttons are pressed, and while
entering calibration values into nonvolatile memory. These time suspensions
are infrequent and always less than a second.
Outputs will remain at the present value for a few hundred milliseconds until
sampling resumes.
These time suspensions do not apply to the buffered analog output or to the
relay set points, which are not affected by the update rate.
While reviewing or changing front panel lock status, all software driven
Controller functions are suspended (see Front Panel Control Lock, page 44).
Relay set points and buffered analog output continue to function normally.