MKS Baratron 122A Series, Manual, Page: 9 / 29

Chapter One: General Information Introduction
3
Chapter One: General Information
Introduction
The MKS Baratron
®
Type 122A Absolute Pressure Transducer marks the beginning of a new era
in low cost pressure measurement. Using a latest-generation single-sided dual-electrode Inconel
®
sensor coupled with a new fixed-frequency bridge signal conditioner, the 122 provides operation
which is inherently temperature stable at zero pressure, capable of withstanding high overpressure
conditions with minimal or no shifts in output over its range, and high resistance to corrosive
environments.
The variable-capacitance sensor is the result of over 25 years of research, development and
customer experience in total pressure measurement. The design incorporates a tensioned metal
diaphragm (Inconel), one side of which is exposed to the gas whose pressure is to be measured.
The other (reference) side of the diaphragm contains a dual electrode assembly (previously found
in premium transducers only) sealed in a high vacuum reference cavity which is maintained by a
chemical getter system.
The signal conditioning electronics board contains a fixed-frequency oscillator, balance-sensing
circuit, linearization circuitry and amplifiers which provide a 0 to 10 Volt DC full scale output.
The signal conditioner is inherently temperature stable at balance (pressure = 0 Torr) and is self-
compensating with temperature changes at other pressures.
A drawn aluminum can forms the protective cover for the transducer and a PC board mounted
removable terminal block allows connections to be easily made for ± 15 VDC power inputs and
the 0 to 10 VDC pressure signal output. In addition, the aluminum cover works in conjunction
with an inner PC shield board with RF bypass capacitors to virtually eliminate RFI and EMI.
Refer to Figure 5, page 12, for a cross sectional view of the 122 transducer.