MKS Stabil-Ion 370 Series, Инструкция по эксплуатации, Страница: 104 / 122

6 Theory of Operation and Specifications
6-4
Series 370 Stabil-Ion Instruction Manual - 370119
6.2 Convectron Gauge Theory of Operation
The Convectron Gauge transducer is represented in Figure 6-2 as R1, R2, R3, and R4. These four
resistances form the legs of a bridge circuit, with R1 designating the sensor wire of the transducer.
R2 is a resistive network in the tube that compensates for changes in the ambient temperature. At
bridge null, R1=R2xR3/R4. If there are no changes in ambient temperature, the value of R1 is a
constant and the bridge is balanced.
As the vacuum system pressure is decreased, there are fewer molecules in the system to conduct the
heat away from the sensor wire causing the temperature and resistance of R1 to increase. The
increased resistance of R1 causes the bridge to unbalance and a voltage is developed across the null
terminals. The bridge control circuit senses the null voltage and decreases the voltage across the
bridge until the null voltage is again zero. When the bridge voltage is decreased, the power
dissipated in the sensor wire is decreased causing the resistance of R1 to decrease to its previous
value. The opposite events happen for a pressure increase. The bridge voltage is a non-linear
function of pressure.
All materials have been chosen for ultra high vacuum service, corrosion resistance and bakeability
to 150 °C. The gauge tube envelope is type 304 stainless steel. All metallic joints in the envelope
are TIG welded. No solder is used within the envelope. The following materials are exposed to the
vacuum. Type 304 stainless steel, Carpenter Alloy 52, Kovar
®
, Kapton
®
, gold plated tungsten,
borosilicate glass and Dow-Corning 9015 glass. The blue trim cover is molded of Ultem
®
polyetherimide resin suitable for service to 150 °C.
6.2.1 Convectron Gauge Specifications
Figure 6-2 Simplified Schematic of Convectron Gauge
Measuring range for N2 or Air 1x10
-4
to 999 Torr; 1x10
-2
to 1.33x10
5
Pa; 1x10
-4
to 1.33x10
3
mbar
Mounting position Horizontal preferred, with port down
Sensor material Gold-plated tungsten
Gauge operating temperature 0
o
C to 50
o
C ambient, non-condensing
Gauge bakeout temperature 150
o
C maximum, non-operating, cable removed
Cable bakeout temperature 105
o
C maximum
Maximum gauge cable length 152 meters (500 feet)
NULL
BRIDGE
CONTROL
AMP
-
+
CONVECTRON
GAUGE
TRANSDUCER
R2
R1
R4
R3
V
BR