Switches and Sensors – Working Principles, Applications, and Wiring

Understanding how human being functions will help you understand automation. Having a brain is not enough for a human being to operate. Sight, hearing, touch, and smell are required to provide information about the environment for the brain to process. Similarly, switches and sensors provide information about the environment for a controller to process. The result of processing determines the actions that will be carried out by an actuator, which will be discussed in the next chapter. This chapter is specifically reserved for switches and sensors to enable us to discuss actuators in depth. Just like sight, hearing, touch, and smell are important for humans to function, switches and sensors are important components that are required to automate an industrial process.

In this chapter, we are going to cover the following main topics:

• Introducing switches and sensors
• Describing manually operated switches...

2 Switches and Sensors – Working Principles, Applications, and Wiring

Understanding how human being functions will help you understand automation. Having a brain is not enough for a human being to operate. Eyes, ears, touch, and smell are required to provide information about the environment for the brain to process. Similarly, switches and sensors provide information about the environment for a controller to process. The result of processing determines the actions that will be carried out by an actuator, which will be discussed in the next chapter. This chapter is specifically reserved for switches and sensors to enable us to discuss actuators in depth. Just like the eyes, ears, touch, and smell are important for humans to function, switches and sensors are important components that are required to automate an industrial process.

In this chapter, we are going to cover the following main topics:

• Introducing switches and sensors
• Describing manually operated switches
• Describing...

Introducing switches and sensors

A switch is an electrical component that connects or disconnects a signal path in an electrical circuit. It is used to make or break an electrical circuit. A switch has two states: an ON state and an OFF state. In an electrical circuit, the current will flow when the switch is in the ON state. When in the OFF state, the current will not flow. Hence, the ON state will connect a signal path, while the OFF state will disconnect a signal path. A switch can be referred to as a device that’s used to turn equipment ON or OFF.

Switches can be categorized as follows:

• Manually operated switch
• Mechanically operated switch

Sensors are devices that detect or sense the presence or absence of objects. A sensor can be thought of as an automatic switch. They gather information from their environment and convert it into a form of signal that can be read and/or seen by an observer or equipment. In a human being, their eyes, nose, ears, tongue, and skin can be referred...

Describing manually operated switches

In manufacturing, there is always the need for an operator to start or stop a machine and there could be needed to manually perform some other form of control aside from starting and stopping. These usually require switches that can be operated by hand. Switches that are operated by hand are referred to as manually operated switches. Some examples are as follows:

• Push button
• Rocker switch
• Toggle switch
• Selector switch
• Knife switch

We will explore each of these in the following sections.

Push button

A push button is a type of switch that closes or opens a circuit when a button is pressed or depressed. The button is designed to operate in two states (that is, ON or OFF). When it's in the ON position, an internal metal spring contacts the two terminals of the switch, allowing the current to flow. When ot#s in the OFF position, the internal switch retracts and the current will stop flowing.

Push buttons exist as normally open or normally closed...

Describing mechanically operated switches

A mechanically operated switch is controlled automatically by factors such as pressure, position, or temperature. This differs from a manually operated switch, which is operated by hand or by a human operator. They are used in situations where automatic control is required. The switch operates automatically by pressure, temperature, or position via a mechanism in the switch. They can also be referred to as sensors.

A mechanically operated switch takes the place of a human operator. Some examples of this type of switch are as follows:

• Limit switch
• Level switch
• Pressure switch
• Temperature switch

Let’s have a look at each.

Limit switches

This is a switch that is operated by the motion of a machine part. It operates when a predetermined limit is reached. The standard limit switch is a mechanical device that uses physical contact to detect the presence or absence of an object. It consists of a switch body, an actuator, and an operating head...

Understanding proximity sensors (capacitive, inductive, and photoelectric)

Proximity sensors are commonly used in industrial applications. Knowledge of proximity sensors can help you understand other types of sensors.

Proximity sensors detect the presence or absence of objects using electromagnetic fields, light, or sound. There are various types, each suited to a specific environment or application.

The available types of proximity sensors are as follows:

• Inductive proximity sensors
• Capacitive proximity sensors
• Photoelectric proximity sensors

In the next few sections, we are going to discover each of these proximity sensors.

Inductive proximity sensor

This is a non-contact sensor that detects ferrous metals, such as carbon steel, stainless steel, and cast iron.

An inductive proximity sensor consists of a coil, oscillator, detection circuit, and output. The oscillator provides an oscillating magnetic field that radiates around the winding of the coil, which is located at the sensor...

Summary

Congratulations on completing this chapter! You should now be able to explain switches and sensors, describe manually operated switches and their various types, describe mechanically operated switches and their various types, and describe proximity sensors and their various types. You should also be able to identify the symbols for various switches and understand how they are wired to perform control functions.

The topics that were covered in this chapter are relevant for automation engineers and will help you understand the next chapter, Actuators and their Application in Industrial Automation.