MKS 937B - Logarithmic;Linear Analog Output; Combination Analog Output

MKS 937B Operation Manual
83
outputs are processed by the microprocessor, these are updated every 50 msec, regardless of the
number of sensors being connected to the controller.
In addition to these Log/Lin analog outputs, 2 combination analog outputs are also available. Up to 3
sensors can be selected for a combination analog output.
8.4.1 Logarithmic/Linear analog output
There are two types of analog output that can be selected for each channel: logarithmic
(
BpAV  )log( ) or linear ( )pAV

 . Since these analog outputs are determined by the
DACs inside the controller, they can be modified by setting appropriate DAC parameters in the
System Setup screen shown in Figure 6-6.
The default analog output for the 937B controller is logarithmic having a slope of 0.6V per decade and
an offset of 7.2 V (
2.7)(6.0


pLogV ). This covers analog output ranging from 0.6 to 9.6 V
(equivalent to a pressure range from 1X10
-11
to 1X10
4
torr).
For detailed setting of the DAC parameters, refer to System Setup, Section 6.4.
8.4.2 Combination analog output
In addition to the logarithmic analog output for each individual sensor, two combination analog
outputs are available. This allows for wider pressure range coverage since a combination output
combines the measurement ranges of multiple gauges.
When capacitance manometers are used in combination, no smoothing is provided in the overlap
range. The 95% rule is use in switching the capacitance manometers. That is, if the reported pressure
on the lower range manometer is greater than 95% of its full scale, the combined analog output will
be switched to the upper range manometer. In other words, the lower range capacitance manometer
is used as master in gauge switching.
When a capacitance manometer and a Pirani/Convection Pirani are used in combination, if the
Pirani/Convection Pirani reading is greater than 5% of the full scale of the capacitance manometer
(must be >500 torr full scale), the combined analog output will switch to the capacitance manometer.
When a capacitance manometer and an ion gauge are used in combination, the ion gauge pressure
will be used as the combined analog output. The combined output will switch to the capacitance
manometer only when the ion gauge is turned off.
If a Pirani/Convection Pirani and an ion gauges are use in combination, a smoothing formula is used
for the combined analog output where sensor ranges overlap (10
-3
to 10
-4
torr).
To set the combination analog output from the from panel, press the
System
Setup
button, then move the
cursor to change the Set Combination Ch parameter to On. After pressing
Enter
, a setup screen will
appear, as shown below: