S2 type series Examples of use for two stage pressure switches Pressure monitoring and controlling can be greatly simplified by using pressure monitors with two built-in microswitches which can be made to operate one after the other under rising or falling pressure. For example, minimum and maximum pressure monitoring can be achieved with only one pressure switch, doing away with the need for a second pressure switch (including the cost of installation). Step switching, e.g. pressure-dependent control of a two-stage pump, is of course also possible using this special series. Example 1: Requirement Pressure holding devices and automatic expansion valves usually have a gas cushion whose pressure must be kept constant within a certain range. If the pressure is too low, a compressor is switched on. If the pressure is too high, a solenoid valve must be opened to vent the gas. Between these two levels is a neutral zone, in which the compressor and the solenoid valve are at rest. Solution All pressure switches of types DCM each with additional function ZF217 and switching scheme A 2, are suitable. All pressure ranges listed in the technical documents are possible. Example for ordering: see page 32 Switching function / connection scheme Switch I: With falling pressure, contact 1–2 closes (compressor on) With rising pressure, contact 1–2 opens (compressor off) Switch II: With rising pressure, contact 2–3 closes (valve open) With falling pressure, contact 2–3 opens (valve closed). In between there is a neutral zone in which the compressor is not switched on and the solenoid coil is not energized (off position). Example 2: Requirement In a process engineering system, the pressure in a nitrogen line has to be monitored. A green signal lamp indicates that the pressure in the line is between 2.2 and 2.6 bar. If the pressure goes below 2.2 bar or above 2.6 bar, the indicator lamp goes out and the system shuts down. Solution The first contact of a DCM3–307 pressure switch with 2 microswitches opens under falling pressure at 2.2 bar; the second microswitch opens under rising pressure at 2.6 bar. If the pressure is >2.2 bar or <2.6 bar, the circuit is closed via both microswitches and the signal lamp is lit.