The design principle and material selection of the diaphragm pressure gauges allow them to meet the stringent demands occurring above all in the chemicals and petrochemicals industries. Special corrosion resistant materials protect the wetted parts in service with chemically aggressive media. Open process connections ensure that the gauges are easy to clean with highly viscous or crystallizing process media, thus guaranteeing process reliability.
The diaphragm system makes the gauges extensively insensitive to vibration or jarring, and produces a high level of overpressure protection and actuating force. As a result of the high actuating forces, diaphragm pressure gauges are particularly suitable for connection of electric alarm contacts. Electric alarm contacts open and close circuits in response to the position of the pressure gauge pointer.
Magnetic snap-action electric alarm contacts are predominantly used in adverse operating conditions. The high contact pressure and the selection of various contact materials result in reliable and cost-effective solutions, above all when high currents have to be switched. Signal output can however take place slightly in advance of or lagging slightly behind the motion of the actual value pointer. If the electrical switching capacities of the alarm contacts are exceeded or not reached, a relay is to be used to provide an appropriate current rating.
Inductive electric alarm contacts have an almost unlimited service life, as the signal is switched without physical contact. Closing or opening takes place without any feedback effect on the measuring system, precluding any signal lead or lag. A corresponding control unit is always required for operation. Units with inductive contacts may be operated in areas with potentially explosive atmospheres, assuming compliance with existing specifications.