Vacuum switches

Description

 Vacuum switches

Industrial and automotive applications frequently require that the attainment of a pressure value, previously set, be transformed into an electrical signal, used to initiate the machine cycle or to signal a certain situation (e.g., leaks in the system, alarms, etc.).

These operations are generally handled by components, calibrated according to the application, which are called vacuum-stats.

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).

Calibration is done by means of an adjusting screw that, acting on a spring, defines the load of the spring. 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.) Fig. 1 version, the contact is open, i.e., there is no passage of current in the absence of pressure. When the set pressure is reached, the electrical contact closes.
• The representation in Fig. 2 shows a pressure switch with NORMALLY CLOSED (N.C.) contacts in the absence of pressure. In fact, 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) of Fig. 3, 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.