Important parameters to select a pressure switch

Accuracy, actuating force and differential are given by membrane surface.

The bigger the surface is, the better the accuracy is, and the lower the differential is. Surface is proportional to the square of diameter. A 45 mm diameter membrane pressure switch will be 4 time more sensitive to pressure than a 22 mm diameter membrane because it will need 4 time less pressure to actuate a mechanism that need the same operating force.

Sensitivity is also given by the membrane hardness, and its thickness. The thinner it is and the softer it is, the more sensitive the pressure switch is. But thin and soft membranes cannot withstand high pressure. Therefore, selecting a device is always a compromise between sensitivity and maximum pressure.

High rating switches need a high force to actuate them. The higher the electrical rating is, the higher the force needed to actuate the contact is. It is very
difficult to actuate high rating switches with low pressure and small membrane surface.

The selection of a pressure switch model will therefore take into account:

• the pressure ranges which must be submitted,
• the fluid or liquid to be monitored,
• the type of contact (NO, NC or SPDT),
• the electrical rating (voltage, amperage),
• whether or not of a setting by the user,
• the use at positive pressure, vacuum or differential,

– its pressure connection (fitting type),

• the environment (protection against water, dust, shock)
• the temperature at which the membrane is exposed.

For example, a small diameter membrane (25mm) is sufficient to actuate a slow break micro switch at 20 millibars with a 1 ampere rating, but it will take a 45 mm membrane to operate at the same pressure a snap action switch with a 15 amperes rating.