Elastic diaphragm pressure

Elastic-Element Methods Elastic-element pressure-measuring devices are those in which the measured pressure deforms some elastic material (usually metallic) within its elastic limit, the magnitude of the deformation being approximately proportional to the applied pressure. These devices may be loosely classified into three types Bourdon tube, bellows, and diaphragm. 

In the elastic diaphragm gauge, the pressure-induced motions of a diaphragm are detected either optically or by changes in the electrical impedance. 

Most fluid pressure transducers are of the elastic type, in which the fluid is confined in a chamber with at least one elastic wall, and the deflection of the elastic wall is taken as an indication of the pressure. The Bourdon tube and the bellows are examples of elastic pressure transducers, which are used in laboratory-grade transducers and in some industrial process control applications. The fluid pressure transducer depicted in Fig. 18.7, which uses an elastic diaphragm to separate two chambers, is the type most frequentlyencountered in industrial process control. Diaphragms are constructed from one of a variety of elastic materials ranging from thin metal to polymerized fabric. 

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. 

For nonnewtonian fluids, pressure readings with taps may also be low because of fluid-elasticity effects. This error can be largely eliminated by using flush-mounted diaphragms. 

Due to the limited elastic deformability of the diaphragm only a comparatively low pumping speed is obtained. In the case of this pumping principle a volume remains at the upper dead center - the so called dead space - from where the gases can not be moved to the exhaust line. The quantity of gas which remains at the exhaust pressure expands into the... 

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). 

Those that are based on the measurement of the distortion of an elastic pressure chamber (mechanical pressure gauges such as Bourdon-tube gauges and diaphragm gauges)... 

Elastic elements such as diaphragms and capsules are used as sensing elements in combination with different displacement transducers (e.g. inductive, potentiometric, etc.) for low/medium vacuum measurements down to about 1 torr. Elastic elements have been employed in conjunction with capacitive transducers for the measurement of pressures as low as 10 5 torr. 

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