Chapter Three: Overview
General Information
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Chapter Three: Overview
General Information
A complete pressure transducer system requires three components to convert pressure to a linear
DC voltage output: a sensor, signal conditioner, and power supply. An analog or digital meter is
required to display the DC output in pressure units.
The 722 transducer contains two of the above components: the sensor and signal conditioner.
An MKS or MKS-compatible power supply is required to complete the pressure to DC voltage
output conversion, and an MKS or MKS-compatible display unit is required for direct pressure
readout. The display unit could be a personal computer, an MKS pressure controller, or an MKS
PDR Series power supply/readout unit.
Sensor
The variable capacitance sensor consists of a pressure inlet tube (port) connected to a small
chamber in the transducer body. One wall of this chamber is a metal diaphragm. The front side
of the diaphragm is exposed to the gas whose pressure is to be measured. The back, or
reference
side of the diaphragm faces a rigidly mounted ceramic disc containing two electrodes. The
diaphragm is positioned opposite the inlet port.
The reference side is permanently evacuated below the resolution of the instrument and its
vacuum is maintained with a chemical getter system.
The diaphragm deflects with changing pressure (force per unit area) independently of the gas
type or composition of the measured gas. This deflection causes an imbalance of the sensor
electrode capacitances since the distance to the diaphragm is now different for each electrode.
Using a precision constant frequency oscillator for excitation, the imbalance of capacitances is
converted to a DC voltage. The resultant signal is then linearized, zeroed, and amplified via the
signal conditioner electronics, to produce a precise output signal scaled to the range of the
transducer.
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