chosen to balance strength and life expectancy against compatibility with process fluids. For example, rubber diaphragms are commonly used in contact with water, but would quickly degrade if used in a system containing mineral oil. Switches designed for use in hazardous areas with flammable gas have enclosure to prevent an arc at the contacts from igniting the surrounding gas. Switch enclosures may also be required to be weatherproof, corrosion resistant, or submersible. An electronic pressure switch incorporates some variety of pressure transducer (strain gauge, capacitive element, or other) and an internal circuit to compare the measured pressure to a set point. Such devices may provide improved repeatability, accuracy and precision over a mechanical switch. Pneumatic Uses of pneumatic pressure switches include: Switch a household well water pump automatically when water is drawn from the pressure tank. Switching off an electrically driven gas compressor when a set pressure is achieved in the reservoir Switching off a gas compressor, whenever there is no feed in the suction stage. in-cell charge control in a battery Switching on an alarm light in the cockpit of an aircraft if cabin pressure (based on altitude) is critically low. Air filled hoses that activate switches when vehicles drive over them. Common for counting traffic and at gas stations. Hydraulic Hydraulic pressure switches have various uses in automobiles, for example, to warn if the engine's oil pressure falls below a safe level, or to control automatic transmission torque converter lock-up. Prior to the 1960s, a pressure switch was used in the hydraulic braking circuit to control power to the brake lights; more recent automobiles use a switch directly activated by the brake pedal. In dust control systems (bag filter), a pressure switch is mounted on the header which will raise an alarm when air pressure in the header is less than necessary. A differential pressure switch may be installed across a filter element to sense increased pressure drop, indicating the need for filter cleaning or replacement. Examples Pressure sensitive mat A pressure sensitive mat provides a contact signal when force is applied anywhere within the area of the mat. Some mats provide a single signal, while others can resolve the position of the applied force within the mat. Pressure sensitive mats can be used to operate electrically operated doors, or as part of an interlock system to ensure machine operators are clear of dangerous areas of a process