Electromechanical pressure switches

Description

Electromechanical pressure switches

In industrial and automotive applications it is frequently required that the attainment of a pressure value, previously set, be transformed into an electrical signal, used to initiate the machine cycle, or to signal and monitor a certain situation (example: leaks in the system, alarms etc…). These operations are generally handled by components, calibrated according to the application, which take the name of Pressure Switches, Vacuum Switches and Transducers.

With reference to pressure switches, there are basically three types:

• with electrical contacts (SPST) NORMALLY OPEN (N.O.)
• with electrical contacts (SPST) NORMALLY CLOSED (N.C.)
• with electrical contacts in EXCHANGE (SPDT)
• with continuous analog signal (4÷20 mA 0.5÷4.5 V 0÷10 V)

Calibration is by means of an adjusting screw, which, acting on a spring, defines its load.

This spring counteracts the pressure exerted by the fluid on the separating element, (diaphragm or piston), allowing the electrical contact to close or open only when the calibration pressure is reached.

In the NORMALLY OPEN (N.O.) version, the contact is open, that is, there is no passage of current in the absence of pressure. When the set pressure is reached, the electrical contact closes.

In pressure switches with NORMALLY CLOSED (N.C.) contacts we see that, in the absence of pressure the contacts are closed and the signal is present on the external contacts. When the set pressure is reached, the electrical contact rises, interrupting the signal.

In the version with EXCHANGED CONTACTS (SPDT), the pressure exerted by the fluid on the separating element, (diaphragm or piston), determines instead the switching of a microswitch.

In the latter version, either N.C. or N.O. contacts or both can be used indifferently.