The function of Differential Pressure Switches

Differential pressure switches are a particular type of pressure switch that convert a change in the pressure between two systems into an electrical function. The two systems are constantly monitored, and their relative pressure is measured. When one of the two systems experiences a change in pressure, the change in pressure is compared against a set of differential points. If the change in pressure exceeds the allowable levels, the differential pressure switch activates. If the differential pressure switch was set to off, it will turn on, and if it was set to on, it will turn off.

GE-511C Differential Pressure Switches with stainless steel body

Differential pressure switches have many different uses, and are common in multiple industries. Some devices that employ differential pressure switches include fuel cells and refrigeration devices.

The Differential Pressure Switch just like the pressure switch is a simple electro- mechanical device that operates on the basic principles of Levers and opposing forces. They are mainly used for sensing a difference in pressure between two points in a plant or system. Three essential elements in the switch are used in various combinations to manufacture hundreds of variants of differential and pressure switches to suit a variety of industrial applications. These elements are:
(a) Sensing element made either of bellows or diaphragm (metallic or elastomeric)
(b) A stable spring to determine the range set point and
(c) A snap-acting micro-switch available in a wide variety (SPDT, DPDT etc)

Operating Principle:

A differential pressure switch is designed to sense a difference in pressure between two pressure sources in the plant for control purposes. When the pressures from two different sources in a process are connected across the sensing diaphragm, metallic or elastomeric as the case may be, the pressure difference creates a force which then overcomes that of a pre-tensioned spring and in the process moves a balancing arm or mechanism to effect the minimal movement required to actuate the micro-switch(es) of the switch.

High and low pressures are applied on either side of the specially contoured sensing diaphragm. This design feature helps to eliminate errors due to a difference in area which is often a common problem present in twin element pressure differential switches

A particular design of the differential pressure switch is described below to illustrate the principle of operation. Please note that there are various variants of the switch from different manufacturers but the basic principle of operation remains the same.

The adjustment of the switch point or setpoint is made by setpoint screws accessible from the front of the differential pressure switch case. The graduated scales enable a relatively accurate adjustment of the switch points and indicate the setpoint that is momentarily adjusted.

In conclusion, the differential pressure switch essentially works on the basis of a difference in pressure between the high and low pressure ports. This difference in pressure is then converted into axial movement that is used to actuate the contacts of a micro-switch depending on the setpoint(s) of the differential pressure switch



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