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937A Multi-Sensor System
Combination Logarithmic Output
A combination sensor is a control sensor with a range that
overlaps the range of the cold cathode sensor. This excludes the
10 and 100 Torr capacitance manometer heads. Refer to page 30
for the selection of control/ combination sensors.
A combination output combines the measurement ranges of a cold
cathode sensor and its combination sensor. For example, if a
Convection Pirani sensor is used as the combination sensor, then the
combination output provides a voltage representing pressures ranging
from 1x10
-11
to 1000 Torr. The combination output is logarithmically
scaled as described in the preceding section . A smoothing formula is
used where sensor ranges overlap.
A combination output is provided for each cold cathode sensor that has a
combination sensor. Pin 1 of the Analog Module rear panel connector is used
for the combination output of the cold cathode sensor in Slot
CC. If there is
no cold cathode in Slot CC, the output will be 10V. The second combination
output will be provided on Pin 9 if a cold cathode sensor is in Slot A and it
has a valid combination sensor.
While the cold cathode sensor is disabled, the combination output will have
the same value as the logarithmic output of the combination sensor. This is
also true for the 3 or 30 second delay immediately after the high voltage is
switched on. When both sensors are operating normally, the combination
output will be determined by the first of the following conditions which is true:
If the combination sensor's pressure is greater than
3.0 x 10
-3
Torr (5.686 V), the combination output will
have the same value as the logarithmic output of the
combination sensor
If the cold cathode sensor's pressure is less than 7.0 x
10
-5
Torr (4.707 V), the combination output will have the
same value as the logarithmic output of the cold cathode sensor
Otherwise, the output will be a processed combination
of the two sensor signals.
If there is no combination sensor or if it is not properly
connected (--- displayed), the combination output will be 10V.
If the combination sensor is inappropriate, the output will be the voltage
corresponding to the ion gauge pressure.
