Granville-Phillips Series 330, Инструкция по эксплуатации, Страница: 56 / 76

5 Convectron Gauge Module
56
Series 330 Vacuum Gauge Controller
Instruction Manual - 330004 - Rev. 02
5.5 Convectron Gauge Theory of Operation
The Convectron transducer is represented in Figure 5-13 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 which compensates for changes in the ambient temperature. At
bridge null, R1 = R2 x R3/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 ºC. 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
• Dow-Corning 9015 glass
The blue trim cover is molded of polysulfone thermoplastic suitable for service to 150 ºC.
Figure 5-13 Convectron Gauge Schematic