Diaphragm vacuum gauges

Vacuum gauges with pressure reading that is independent of the type of gas 

Mechanical vacuum gauges measure the pressure directly by recording the force which the particles (molecules and atoms) in a gas-filled space exert on a surface by virtue of their thermal velocity. 

The interior of a tube bent into a circular arc (so-called Bourdon tube) (3) is connected to the vessel to be evacuated (Fig. 3.2). Through the effect of the external air pressure the end of the tube is deflected to a greater or lesser extent during evacuation and the attached pointer mechanism (4) and (2) is actuated. Since the pressure reading depends on the external atmospheric pressure, it is accurate only to approximately 10 mbar, provided that the change in the ambient atmospheric pressure is not corrected. 

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The best-known design of a diaphragm vacuum gauge is a barometer with an aneroid capsule as the measuring system. It contains a hermetically sealed, evacuated, thin-walled diaphragm capsule made of a copper-beryllium alloy. As the pressure drops, the capsule diaphragm expands. 

Many control problems can be better solved with a diaphragm controller. The function of the diaphragm controller (see Fig. 3.27) can be easily derived from that of a diaphragm vacuum gauge the blunt end of a tube or pipe is either closed off by means of an elastic rubber diaphragm (for reference pressure > process pressure) or released (for reference pressure < process pressure) so that in the latter case, a connection is established between the process side and the vacuum pump. This elegant and more or less automatic regulation system has excellent control characteristics (see Fig. 3.28). 

Bourdon vacuum gauge Diaphragm vacuum gauge... 

Diaphragm vacuum gauges where the deflection of the diaphragm is not detected mechanically but by strain gauges are called electromechanical transducers. In a strain gauge a thin element (wire or foil) is stressed by tension or pressure. 

Diaphragm gauges are also commonly used, particularly as vacuum gauges. They employ a thin, flexible diaphragm which is pushed outwards when pressure is applied the movement is shown by an indicating pointer (Fig. 5.3). 

In directly measuring vacuum gauges, the elastic restoring force of a spring element (diaphragm) or of gravitation (liquid column) is used for pressure measurement. 

In a diaphragm pressure gauge the elastic deflection of a circularly clamped metal disk is transferred to a pointer. Such devices are suitable for measuring ranges of 0-0.5 mbar and 0-70 bar [3]. For vacuum applications the range is 0-0.5 mbar and 0-1 bar vacuum. They are also suitable for differential pressure measurement if both sides of the diaphragm are connected with the respective measuring points. 

Capacitance manometer (vacuum technology) A vacuum gauge that uses the deflection of a diaphragm, as measured by the changing capacitance (distance) between surfaces, as an indicator of the pressure differential across the diaphragm, the pressure on one side being a known value. See also Vacuum gauge. 

Gauges. Because there is no way to measure and/or distinguish molecular vacuum environment except in terms of its use, readings related to gas-phase concentration ate provided by diaphragm, McCleod, thermocouple, Pitani gauges, and hot and cold cathode ionization gauges (manometers). 

Strain-gauge pressure transducers are manufactured in many forms for measuring gauge, absolute, and differential pressures and vacuum. Full-scale ranges from 25.4 mm of water to 10,134 MPa are available. Strain gauges bonded direc tly to a diaphragm pressure-sensitive element usually have an extremely fast response time and are suitable for high-frequency dynamic-pressure measurements. 

Bourdon and diaphragm gauges that show both pressure and vacuum indications on the same dial are called compound gauges. 

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