Exercise 2. Switches EXERCISE OBJECTIVE DISCUSSION OUTLINE DISCUSSION. Introduction to switches. Switch types

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1 Exercise 2 Switches EXERCISE OBJECTIVE When you have completed this exercise, you will be familiar with the operation of switches. You will be introduced to the various types of switches and to the various configurations. You will also be introduced to the Lights, Switches, and Push Buttons modules. DISCUSSION OUTLINE The Discussion of this exercise covers the following points: Introduction to switches Switch types Toggle switch. Push-button switch. Selector switch. Switch configurations Single-pole single-throw switch. Double-pole single-throw switch. Singlepole double-throw switch. Double-pole double-throw switch. Introduction to the indicator light Training system modules Push Buttons module. Switches module. Lights module. DISCUSSION Introduction to switches Switches are one of the basic components of electrical circuits. The main use of switches is to either prevent or allow the flow of electrical current at a particular point of a circuit. When the switch is in open state, it completely prevents the flow of electrical current. In other words, the circuit containing the switch is open. On the other hand, when the switch is in closed state, it allows the flow of electrical current. In this case, the circuit containing the switch is closed. An example of an electrical switch is a standard light switch. When this switch is set to its open state, the light is off. When the switch is set to its closed state, the light is on. Instead of simply preventing the flow of current, some switches also allow the diversion of current. This way, it is possible to use the switch in order to select which load of a circuit is powered on and which is not. Switch types There are many types of switches, classified according to their mechanism of operation. The most common switch types are the toggle switch, push-button switch, and selector switch. These switches are described in the following subsections. Festo Didactic

2 Exercise 2 Switches Discussion Toggle switch The toggle switch is operated manually using a lever or a handle. A toggle switch generally allows selection between only two states, determined by the position of the lever. The most common example of a toggle switch is the light switch. Table 3 shows the circuit diagram symbol for a toggle switch. Table 3. Toggle switch and associated symbol. Component Symbol Push-button switch The push-button switch is operated by a push button. The state of the push button determines the state of the switch. When the button is not pressed, the switch is said to be in normal mode. The normal mode of a push-button switch may be open or closed. When the button of a normally open (NO) push-button switch is not pressed, the switch is open. When the button is pressed, the switch is closed. For example, a car horn is controlled using an NO push-button switch. When the steering wheel button is not pressed, the circuit is open and no current flows in the horn. However, when the push button is pressed, the circuit closes, current flows in the horn and a sound is produced. Table 4 shows an example of a normally open push-button switch, and the associated symbols in closed and open states. Table 4. Normally open push-button switch and associated symbol in open and closed states. Component Symbol Open state Normally open push-button switch Closed state 20 Festo Didactic

3 Exercise 2 Switches Discussion Emergency buttons are examples of an NC pushbutton switch. When the push button is not pressed, the circuit is closed and current flows normally. However, when the push button is pressed (i.e., in the case of an emergency), the circuit becomes open and current ceases to flow in the circuit ( Siemens AG 2014, all rights reserved). When the button of a normally closed (NC) push-button switch is not pressed, the switch is closed (hence the name). When the button is pressed, the switch is open. For example, the light in a refrigerator is activated by an NC push-button switch. When the refrigerator door button is pressed (i.e., when the door is closed), the circuit is open and no current flows in the refrigerator light. However, when it is no longer pressed (i.e., when the door opens), the circuit closes and current flows in the refrigerator light. Table 5 shows an example of a normally closed push-button switch, and the associated symbols in closed and open states. Table 5. Normally closed push-button switch and associated symbol in closed and open states. Component Normally closed push-button switch Symbol Closed state Open state Selector switch The selector switch is manually operated using a rotating knob. It allows selection between two or more positions, with each position making contact at a different branch in the circuit. Table 6 shows an example of a three-position selector switch and the associated symbols. As the symbol shows, from a single circuit branch, the selector switch allows connection to any of three different circuit branches. Table 6. Selector switch and associated symbol. Component Symbol Switch configurations In addition to the different working mechanisms described in the previous section, switches can also be classified according to their configuration. These configurations are differentiated by the number of poles and the number of throws of the switch. The number of poles of a switch indicates the number of circuits that are controlled by the switch. For instance, a single-pole switch controls only one circuit, while a double-pole switch controls two circuits. Basically, a double-pole switch is equivalent to two single-pole switches that are controlled using the same switch mechanism (e.g., lever, push button, and knob). Festo Didactic

4 Exercise 2 Switches Discussion The number of throws of a switch indicates the number of contacts to which the switch can be connected. In other words, it represents the number of circuit paths that the switch can make contact with. For instance, a single-throw switch can make contact with only one circuit path, while a double-throw switch can make contact with two circuit paths. Based on the above notions, the most common switch configurations are described in the following subsections. Single-pole single-throw switch A single-pole single-throw (SPST) switch is the most simple switch configuration. Figure 13 shows an example of an SPST toggle switch. As the figure shows, the switch controls only one circuit and can make contact with only one circuit path. An SPST switch is basically an on/off type of switch allowing the circuit to be either open or closed. SPST toggle switch Power source light Figure 13. Circuit containing an SPST toggle switch. Double-pole single-throw switch A double-pole single-throw (DPST) switch operates just as two SPST switches actuated using the same mechanism operate. Figure 14 shows an example of a DPST toggle switch. The dotted line in the figure is used to indicate that the two switch symbols are in fact a single DPST toggle switch. The figure also shows that the same switch is used to control both indicator lights at the same time. Just like the SPST switch, the DPST switch is basically an on/off switch with the difference being that it controls more than one circuit branch at the same time. 22 Festo Didactic

5 Exercise 2 Switches Discussion DPST toggle switch Power source Figure 14. Circuit containing a DPST toggle switch. Single-pole double-throw switch A single-pole double-throw (SPDT) switch allows selection between two different circuit branches. Figure 15 shows an example of an SPDT toggle switch. As the figure shows, the SPDT switch can make contact with two circuit branches. This means that the SPDT switch can either make contact with the branch containing indicator or with the branch containing indicator, but not with both at the same time. SPDT toggle switch Power source Figure 15. Circuit containing an SPDT toggle switch. Double-pole double-throw switch A double-pole double-throw (DPDT) switch operates just as two SPDT switches actuated using the same mechanism operate. Figure 16 shows an example of a DPDT toggle switch. As the figure shows, when the switch is in its upper position, current flows through indicator lights and, while indicator lights and are off. On the other hand, when the switch is in its lower position, current flows through indicator lights and, while indicator lights and are turned off. Festo Didactic

6 Exercise 2 Switches Discussion DPDT toggle switch Power source Figure 16. Circuit containing a DPDT toggle switch. Introduction to the indicator light An indicator light is a basic type of component often found in electrical circuits. It is designed to produce light from electricity. Table 7 shows a typical incandescent light bulb with its associated symbol (photo courtesy of KMJ). Table 7. light and associated symbol. Component Symbol There are different types of indicator lights, differentiated by the way each type produces light. The most common type is the incandescent indicator light. In this type of indicator light, light is produced by making current flow through the filament wire (usually a tungsten wire) in the indicator light. As the wire heats due to the current flowing through it, it begins to glow. This phenomenon is called incandescence. 24 Festo Didactic

7 Exercise 2 Switches Discussion Training system modules Push Buttons module NO push button NC push button IEC symbols for NO and NC push-button switches Figure 17. Push Buttons module. The Push Buttons module of your training system consists of one normally open (NO) push-button switch and one normally closed (NC) push-button switch. Each push-button switch is designed to operate at either 24 V ac using the 2 mm terminals, or at line voltage using the 4 mm terminals. The Push Buttons module is also equipped with four fault switches and two ground terminals. Switches module DPST toggle switch DPST toggle switch DPDT toggle switch IEC symbols for DPST and DPDT switches Figure 18. Switches module. Festo Didactic

8 Exercise 2 Switches Procedure Outline The Switches module of your training system consists of two double-pole singlethrow (DPST) toggle switches, and one double-pole double-throw (DPDT) toggle switch. Each switch is designed to operate at either 24 V ac using the 2 mm terminals, or at line voltage using the 4 mm terminals. The Switches module is also equipped with four fault switches and two ground terminals. Lights module light 2 mm terminal 4 mm terminal Fault switch Ground terminal IEC symbol for an indicator light Figure 19. Lights module ( V version). The Lights module of your training system has six indicator lights of the incandescent type. The indicator lights at the left are designed to operate at 24 V using the 2 mm terminals, and the indicator lights at the right are designed to operate at line voltage using the 4 mm terminals. The Lights module is also equipped with four fault switches and two ground terminals. The use of the fault switches is explained later in this manual. PROCEDURE OUTLINE The Procedure is divided into the following sections: Setup Push-button switches Normally open push-button switch. Normally closed push-button switch. Toggle switches Single-pole single-throw toggle switch. Single-pole double-throw toggle switch. PROCEDURE High voltages are present in this laboratory exercise. Do not make or modify any banana jack connections with the power on unless otherwise specified. 26 Festo Didactic

9 Exercise 2 Switches Procedure Setup In this section, you will install the equipment required in the workstation. 1. Refer to the Equipment Utilization Chart in Appendix A to obtain the list of equipment required to perform this exercise. Install the equipment required in the workstation as shown in Figure 20. Figure 20. Suggested location of the modules in the workstation ( V version). 2. Make sure that all fault switches are set to the O (off) position. 3. Make sure that the main power switch on the Power Source module is set to the O (off) position, then connect it to an ac power outlet. Push-button switches In this section, you will connect circuits containing push-button switches and indicator lights. In each circuit, you will observe and record the operation of the indicator lights depending on the state of the switches. Normally open push-button switch 4. Set up the circuit shown in Figure 21. The wiring diagram of the circuit is shown in Figure 22. Festo Didactic

10 Exercise 2 Switches Procedure a In this exercise, the circuits that you need to set up are given as both a wiring diagram and a circuit diagram. This is done to allow familiarization with the use of circuit diagrams. Note, however, that in later exercises, only circuit diagrams are given. NO push-button switch 24 V light 0 V Figure 21. Circuit diagram of a power source supplying power to an indicator light controlled using an NO push-button switch. (a) Wiring diagram (120 V). (b) Wiring diagram ( V). Figure 22. Wiring diagram of the circuit in Figure Festo Didactic

11 Exercise 2 Switches Procedure To reduce the risk of electrical shock, connect all ground (green) terminals of the modules in series with the ground (green) terminal of the power source. 5. Turn the power source on. Press on the push button for about five seconds, then release it. Observe what happens as you do so. Repeat this step a few times. 6. Describe the indicator light operation depending on the state of the NO pushbutton switch. Indicate for each state of the switch whether the resulting circuit is open or closed. 7. Turn the power source off. Normally closed push-button switch 8. In the circuit of Figure 21, replace the NO push-button switch with a normally closed (NC) push-button switch. This results in the circuit shown in Figure 23 and Figure 24. NC push-button switch 24 V light 0 V Figure 23. Circuit diagram of a power source supplying power to an indicator light controlled using an NC push-button switch. Festo Didactic

12 Exercise 2 Switches Procedure (a) Wiring diagram (120 V). (b) Wiring diagram ( V). Figure 24. Wiring diagram of the circuit in Figure Turn the power source on. Press on the push button for about five seconds, then release it. Observe what happens as you do so. Repeat this step a few times. 10. Describe the indicator light operation depending on the state of the NC pushbutton switch. Indicate for each state of the switch whether the resulting circuit is open or closed. 30 Festo Didactic

13 Exercise 2 Switches Procedure 11. Briefly explain how the circuit in Figure 23 operates just like the circuit for the light in a refrigerator. 12. Turn the power source off. Toggle switches In this section, you will connect circuits containing toggle switches and indicator lights. In each circuit, you will observe and record the operation of the indicator lights depending on the state of the switches. Single-pole single-throw toggle switch 13. Replace the Push Buttons module with the Switches module. 14. Set up the circuit shown in Figure 25. When you connect the SPST toggle switch, make sure that it is in its open state (O position). SPST toggle switch 24 V light 0 V Figure 25. Circuit diagram of a power source supplying power to an indicator light controlled using an SPST toggle switch. Festo Didactic

14 Exercise 2 Switches Procedure (a) Wiring diagram (120 V). (b) Wiring diagram ( V). Figure 26. Wiring diagram of the circuit in Figure Turn the power source on. Toggle the SPST toggle switch between its open state and its closed state, waiting a few seconds before each change. Observe what happens as you do so. Repeat this step a few times. 16. Describe the indicator light operation depending on the state of the SPST toggle switch. Indicate for each state of the switch whether the resulting circuit is open or closed. 17. Turn the power source off. 32 Festo Didactic

15 Exercise 2 Switches Procedure Single-pole double-throw toggle switch 18. Set up the circuit shown in Figure 27. In this circuit, the SPST toggle switch is replaced by a single-pole double-throw (SPDT) toggle switch and a second branch (also containing an indicator light) is added. When you connect the SPDT toggle switch, make sure that it is in the A position. SPDT toggle switch 24 V 0 V Figure 27. Circuit diagram of a power source supplying power to two indicator lights controlled using an SPDT toggle switch. (a) Wiring diagram (120 V). (b) Wiring diagram ( V). Figure 28. Wiring diagram of the circuit in Figure 27. Festo Didactic

16 Exercise 2 Switches Conclusion 19. Turn the power source on. Switch the SPDT toggle switch back and forth between the A position and the B position, waiting a few seconds before each change. Observe what happens as you do so. 20. Describe the operation of indicator and indicator depending on the position of the SPDT toggle switch. 21. Turn the power source off. Disconnect your circuit. Return the leads to their storage location. CONCLUSION In this exercise, you became familiar with the use of switches in electrical circuits, as well as with the most common types of switches. You learned the possible configurations of switches in electrical circuits. You were introduced to the Push Buttons, Switches, and Lights modules. REVIEW QUESTIONS 1. What is the main use of switches in electrical circuits? 2. Name one example of a common toggle switch. What happens when this toggle switch is in its open state or its closed state? 3. Explain the operation of a normally open (NO) push-button switch. When is it open and when is it closed? 34 Festo Didactic

17 Exercise 2 Switches Review Questions 4. Explain the operation of a single-pole double-throw (SPDT) switch. 5. Of what type are the indicator lights included in the training system? How does this type of lamp operate? Briefly explain. Festo Didactic