Moreover, the measuring instrument can also be protected against extremely corrosive media by coating with special material or covering with foil. Wide connection ports, open connection flanges and purging plugs can be integrated for measuring highly viscous, impure or crystallizing media. The capsule element consists of two circular-shaped, convoluted membranes sealed tight around their circumference. The pressure acts on the inside of this capsule and the generated stroke movement is shown by a pointer as measurement of pressure. Pressure gauges with capsule elements are more suitable for gaseous media and relatively low pressures.
Overload protection is possible within certain limits.
These instruments are used where pressures are to be measured independently of the natural fluctuations in atmospheric pressure. As a general rule all the known types of element and measuring principles can be applied. The pressure of the media to be measured is compared against a reference pressure which, at the same time, is absolute zero. For this purpose an absolute vacuum is given as reference pressure in a reference chamber on the side of the measuring element not subject to pressure. This function is achieved by sealing off the appropriate measuring chamber or surrounding case.