Setra System Model 760 - Manual (Page 4)

1.0 Introduction
Setra's Vactron Model 760 capacitance manometer is a temperature
compensated, absolute pressure transducer designed for accurate and
repeatable vacuum measurements. Various full scale ranges are available
from 10 Torr up to 1000 Torr. The units of measurement may be specified in
Torr (mmHg), mBar (hPa), kPa or psia.
The Model 760 operates from a
±
15 V DC power supply and provides a 0-
10 V DC or 0-5 V DC signal output that is linear with pressure and indepen-
dent of gas composition. Electrical connections can be either the industry
standard 15 pin D-sub or 6 position terminal strip connector. The Model
760 is pin for pin compatible with other competitive capacitance manom-
eters. Superior EMI/RFI performance is achieved by the use of a metal case
in conjunction with surge and ESD suppression components and RFI
filtering on the inputs and outputs. The Model 760 has an integrated
sliding cover providing easy access to multi-turn potentiometers for fine
zero and span adjustments. Inconel is used for all wetted materials for
compatibility with corrosive gases. A wide range of pressure/vacuum
fittings are available.
The high accuracy pressure sensing element used in the Model 760 is the
Vactron™ sensor, which has been developed from Setra's patented variable
capacitance sensor. A centrally located feedthrough assembly supports a
circular electrode in close proximity to the back surface of the diaphragm.
Together, the electrode and diaphragm form a variable capacitor within a
small reference vacuum chamber. As the pressure increases, the diaphragm
deflects and the gap between the electrode and diaphragm reduces,
causing an increase in the capacitance. This change in capacitance is
detected and converted to a highly accurate linear DC electronic signal by
Setra's unique custom integrated circuit utilizing a patented charge
balance principle.
Excellent zero stability and barometric insensitivity is achieved through the
patented sensor design. The Model 760 sensor contains no fragile or
complex parts as found in ceramic based capacitance manometers. The all
welded construction eliminates stability issues inherent in other designs
due to frictional contact between dissimilar materials.
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