MKS Stabil-Ion 370 Series, Instruction Manual, Page: 89 / 122

4 Preparing the Stabil-Ion System for Operation
4-31
Series 370 Stabil-Ion Instruction Manual - 370119
If the offset has been adjusted to other than 0V at 10
-4
Torr (10
-2
Pa), then the exponent value must
be forced to -4 (-2 for Pa) when the pressure is at 1.0 x 10
-4
Torr (10
-2
Pa) by adding or subtracting a
number other than -4 from the value of V.
For example, if the offset has been adjusted so that the output voltage is -7 V at
10
-4
Torr (10
-2
Pa), then +3 (+5 for Pa) must be used in the equation instead of -4, i.e.,
P = 10
(-7+3)
. Furthermore for the same offset, if the pressure were, say, 10
-2
Torr, then the
output voltage would be -5V. The pressure would be calculated as P = 10
(-5+3)
.
4.11 Preparing for Process Control Operation
4.11.1 Setpoint Display and Adjustment
Setpoints are stored in non-volatile memory, and are specified by a 2-digit mantissa and 2-digit
exponent. They may be set anywhere in the range 1.0 x 10
-12
to 9.9 x 10
+5
. This allows for the
entire pressure range of the Stabil-Ion System and its units of measure to be covered.
The setpoint is compared directly to the display data, so units of measure are implicit. Changing the
units switch on the Controller will not change the stored setpoints. They must be reprogrammed to
the new units of measure.
If a setpoint is set to above atmosphere, then the relay will always be activated (unless its polarity is
reversed, see Section 2.1.3 on page 2-4) except during transient conditions that occur, e.g. when the
Stabil-Ion Gauge is first powered up, or a Convectron Gauge is disconnected. If it is desired that a
process control relay be held in one state, the manual override switch should be used. If the setpoint
is adjusted below 1.0 x 10
-12
to 0.0, then it will always be deactivated (unless polarity is reversed).
4.11.2 To Display a Setpoint
1. Adjust the channel select thumbwheel to the number of the
process control channel for which you wish to display the
setpoint.
2. Press and release either the Up or Down SET button. The
setpoint will appear for 2 seconds in the same display line as
the associated gauge;
■
Setpoints 1 and 2 appear in the IG display line.
■
Setpoints 3 and 4 appear in display line A.
■
Setpoints 5 and 6 appear in display line B.
4.11.3 To Modify a Setpoint
1. Adjust the channel thumbwheel to the number of the channel for which you wish to change a
setpoint.
2. Press and hold the SET button for the direction you wish the setpoint to change;
▲
to raise the
setpoint;
▼
to lower it (see Figure 4-19).
and: the offset is at the factory adjusted 0V at 10
-4
Torr (10
-2
Pa).
Figure 4-19 Electrometer Module Showing
Setpoint Set Buttons and
Channel Select Thumbwheel
Process Control
Off SP On
▲
▲
▲
▲
▲
▲
Off SP On
1
2
3
4
5
6
3
Set