MANUAL P/N 316005 REV: B
15
Figure 1-6 Control Unit Front Panel
NOTE: Display units are set separately on the Convectron or thermocouple gauge modules.
Adjustments must be made to both gauge modules to avoid confusion. Be certain to update
the label to reflect any change of units.
1.6 Theory of Operation
More detailed explanations of the theory of operation of the Convectron, thermocouple and capacitance
manometer gauges is provided in sections 2.6, 3.6, and 4.6 respectively.
1.6.1 Microcontrollers and Bus Structure
Each module in the 316 VGC has a dedicated microcontroller with internal ROM, RAM, timing, and interrupt
management functions. This architecture provides high-performance at low cost with greater reliability and
noise immunity.
Each microcontroller is equipped with a watchdog timer, which automatically generates a reset if the
processor fails to fulfill timing "checkpoints" within its code.
Inter-processor communication is accomplished via the display bus. These lines carry BCD-format pressure
data which is used to generate the 316 VGC display. The bus is updated once per millisecond. Fifteen cycles
are used for display data. Modules that require pressure data, such as process control and computer
interface, take it directly from the display update cycles.
1.6.2 Convectron Gauge Theory
Both the Convectron gauge and the thermocouple gauge are heat loss transducers. This causes the
response of the gauges to be gas type dependent and non-linear. The Convectron gauge uses feedback
amplifier circuitry to maintain the sensor at a constant temperature thus providing greater resolution over a
wider pressure range. The thermocouple gauge heater is supplied a constant voltage, thus allowing
temperature variation over the pressure range.
1.6.3 Capacitance Manometer Theory
Within the capacitance manometer, a diaphragm is distorted by the pressure of the gas in the system under
measurement. This diaphragm forms part of a capacitor, and its deflection causes changes in capacitance.
Thus, the electrically measured capacitance is a measure of pressure. The device is very sensitive to the
Содержание Granville-Phillips Convectron 316 Series
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