Switches - Instrumentation and Control

Switches are one of many instruments used in many control systems. We will introduce some of many different switches used in most control systems. There are many different types of Switches. Below is a list of some of the main different type of switches described by their functionality rather than their brand names.

Toggle switch

An electrical toggle switch requires an external force to change to either the on or off position .The toggle switch implies that there are only two possible position and that you are switching from the current position to the other position. The common lights in household use toggle switches.

Pushbutton switch

Pushbutton switch can be either momentary or latched. Pressing down on the switch or a button will activate the switch and can have an internal spring mechanism to return the button to its original position. Other switches will stay in the position until the button is pulled back out.

Selector switch

This type of switch works with a rotary knob or lever to select one of two or more positions. They can either rest in any of their positions or with spring-return mechanisms return to its central position for momentary operation.

Joystick switch

This switch is actuated by a lever free actuating in many directions with stay put or spring-return operation or combined. Joysticks are typically used for direction control on a wheelchair, scanning devices, crane and robot control.

Proximity switch

These types of switches can be from the simple proximity that use a permanent magnet to a more complex one that work like a metal detector. If a metallic object gets close to the coil, the current will increase, and trip the monitoring circuit.

Another form of proximity switch is the optical switch, which include a light source and photocell. This type of switches is useful to detect personnel entry into a dangerous area.

Pressure switch

The pressure of a piston, diaphragm or bellows can be converted into mechanical force by a pressure switch using Gas or liquid.

Temperature switch

This type of switchs can use a brass bulb filled with liquid or gas or a bimetallic strip. The expansion brass bulb when is heated or cooled, or the bending of the strip actuates the switch mechanisms.

Liquid level switch

This type of switch is used to monitor if a liquid level rises past a certain point. There are level switches designed to detect solid materials level.

Liquid flow switch

these switches are constructed to measure any gas or liquid flow rate usually with a small paddle or vane inserted into a pipe.