MKS Stabil-Ion 370 Series, Instruction Manual, Page: 75 / 122

4 Preparing the Stabil-Ion System for Operation
4-17
Series 370 Stabil-Ion Instruction Manual - 370119
4.5.1 Pressure Indication During Degas
An approximate indication of pressure within the Stabil-Ion Gauge is provided on the digital display
during degas. Observing this pressure indication rise, peak out and then fall is an excellent means
of determining the optimum time of degas. The indication may eventually be unrealistically low due
to a reverse x-ray current effect or temporary gauge pumping. Degassing purposely changes surface
conditions in the gauge. After degassing, permit sufficient time for steady state conditions to be
established before attempting to make measurements.
4.5.2 Degas Power Limiter
For convenience and improved safety, degas power is automatically reduced as gas is liberated to
prevent excessive pressure rise and help reduce the possibility of a gas discharge forming. As the
electrodes clean up, power is increased to a maximum of 40 W. This feature limits the maximum
pressure indication to about 5 x 10
-5
Torr during degas.
4.5.3 Gauge Bakeout
Applying an external heat source to the vacuum system and to the gauge envelope can speed the
removal of contamination from the interior surfaces. Bakeout temperatures between 150 °C and
300 °C are typically adequate. Do not exceed 450 °C at the Stabil-Ion Gauge envelope. Do not
exceed 150 °C at the cable and connector.
4.6 Stabil-Ion Gauge Analog Output Signal
A signal voltage proportional to the logarithm of the Stabil-Ion Gauge pressure indication is
provided on the back of the electrometer module via a standard 1/8 in. miniature phone jack.
Normal Measurement Operation
Pressure indication, P
i
= 10
V-11
Torr or mbar
= 10
V-9
Pascal
When gauge is OFF, V is = 11 volts
This signal voltage is determined by the pressure indicated on the IG display. Thus if the scale-factor
is set correctly for a given gas as specified in Section 4.3.3.3 on page 4-9, the equations above and
curves in Figure 4-8 on page 4-18 still apply for the given gas.
Figure 4-7 Control Unit Rear Panel Showing Location of IG Analog Output
C
G
G
A
U
G
E
R
E
M
O
T
E
C A
X W
8
1 9
15
9 26
1 19
25 13
1 14
9 1
15 8
13 25
1 14
ANALOG
OUTPUT B
ANALOG
RS-232, RS-485,
ELECTROMETER PROCESS CONTROL
REMOTE
OUTPUT
POWER
SUPPLY
GND
ANALOG
OUTPUT A
IG2 COL.
CONVECTRON
OUTPUT
3
7
0
1
0
4
IG1 COL.
or IEEE48