Mechanically Operated switch

A mechanically operated switch is controlled automatically by factors such as pressure, position, or temperature. The limit switch, shown in image , is a very common industrial control device. Limit switches are designed to operate only when a predetermined limit is reached, and they are usually actuated by contact with an object such as a cam. These devices take the place of a human operator. They are often used in the control circuits of machine processes to govern the starting, stopping, or reversal of motors.

The temperature switch, or thermostat, shown in image is used to sense temperature changes. Although there are many types available, they are all actuated by some specific environmental temperature change.Temperature switches open or close when a designated temperature is reached. Industrial applications for these devices include maintaining the desired temperature range of air, gases, liquids, or solids.

Pressure switches, such as that shown in image , are used to control the pressure of liquids and gases. Although many different types are available, they are all basically designed to actuate (open or close) their contacts when a specified pressure is reached. Pressure switches can be pneumatically (air) or hydraulically (liquid) operated switches. Generally, bellows or a diaphragm presses up against a small micro switch and causes it to open or close.

Level switches are used to sense liquid levels in vessels and provide automatic control for motors that transfer liquids from sumps or into tanks. They are also used to open or close piping solenoid valves to control fluids. The float switch shown in image is a type of level switch. This
switch is weighted so that as the liquid rises the switch float and turns upside down, actuating its internal contacts.