Inside the Vaccum Sensor
The sensor capsule contains the diaphragm and the metal-on-ceramic electrode structure. The reference side (backside) of the diaphragm is evacuated to a very high vacuum, much lower than the pressures that are to be measured. The high vacuum on the reference side is maintained over the life of the manometer by means of an internal chemical getter pump. The sensors are made of Inconel® all-welded construction for ruggedness and compatibility with process environments.
Pressure is determined by measuring the change in capacitance between the metal diaphragm and an adjacent, fixed dual electrode. The radially tensioned diaphragm provides very low hysteresis, excellent repeatability, remarkably high resolution (1x10-5 of Full Scale), fast response, and the ability to measure extremely low pressures. If a high overpressure is applied to the manometer, the diaphragm will bottom out on the electrode substrate, preventing permanent damage to the sensor.
Most MKS Baratron® capacitance manometers have an overpressure rating of 45 psia or 2-times the Full Scale range, whichever is greater. Pressures of greater than the allowable rating can cause internal mechanical failure or significant changes in the zero.