Exercise 1: Identify Types of Switches

Transcription

1 Exercise 1: Identify Types of Switches EXERCISE OBJECTIVE When you have completed this exercise, you will be able to identify switch functions by using a multimeter. You will verify your results with information found in this exercise. DISCUSSION All switches contain one or more poles. A pole consists of one complete set of contacts that opens or closes one electric circuit. The schematic symbol for a single-pole switch in its normally open position is shown below. When the switch contacts provide an open and close position for one circuit, the switch is called a singlepole single-throw (SPST) switch. A double-pole switch (two poles) controls two circuits or both sides of one circuit, as shown below. When the switch can simultaneously open and close two isolated contacts, the switch is called a doublepole single-throw (DPST) switch. 80 FACET by Lab-Volt

2 Switches and Switching Concepts The connection between poles is only mechanical, not electrical. a. SPST and DPST with shorted poles b. SPST and DPST c. SPST and SPDT with independent poles A double-throw switch controls two circuit loads. To control one conductor in the circuit, use a single-pole double-throw (SPDT To control two conductors in two circuit loads, use a double-pole double-throw (DPDT) switch, shown in FACET by Lab-Volt 81

3 represented? a. SPST b. DPST c. DPDT Pushbutton switches can have normally open (PBNO) or normally closed (PBNC) contacts. The slide switch has a mechanism that actually slides back and forth in a track, causing the switch contacts to make or break a circuit connection. Slide switches are available with single or multiple poles and in normally open or normally closed S1 and S2 represent which types of switches, respectively? a. normally closed and normally open pushbuttons b. slide switch with isolated poles c. double-pole toggle switch 82 FACET by Lab-Volt

4 Switches and Switching Concepts PROCEDURE Locate the SWITCHES circuit block on the DC FUNDAMENTALS circuit board. Locate S3 in the SWITCHES circuit block. Place the handle of S3 in the UP position (toward the ZIF connector). Select the ohms function on your multimeter. Measure the resistance between each set of contacts (upper and lower) of S3. Based on your measurement, which of the following is correct? a. One set of contacts is closed while the other is open. The closed side indicates 0. The b. c. Both sets of contacts are closed and indicate 0. Place the handle of S3 in the DOWN position (toward you). Measure the resistance between each set of contacts of S3. Based on your measurements, which of the following is correct? a. The upper contacts are open and the lower contacts are closed. b.. c. All of the above. On the SWITCHES circuit block, locate S1 and S2. Based on the silkscreened switch symbols, which of the following statements is correct? a. S1 and S2 are PBNO switches. b. S1 is a PBNC switch and S2 is a PBNO switch. c. S1 and S2 are PBNC switches. FACET by Lab-Volt 83

5 Use your ohmmeter to measure the switch resistance of S1. Repeat the measurement when you depress the switch button. Based on the meter indication, which statement is correct? a. The initial resistance of S1 is 0 activated (pressed down). b. The initial resistance of S1 is 0. Its resistance does not change when the S1 pushbutton is c. when the S1 pushbutton is Use your ohmmeter to measure the switch resistance of S2. Repeat the measurement when you depress the switch button. Based on the meter indication, which statement is correct? a. The initial resistance of S2 is 0 b. is c. when the S2 pushbutton is Locate S4 in the SWITCHES circuit block. What type of switch is S4? a. DPDT toggle switch b. DPDT pushbutton switch c. DPDT slide switch 84 FACET by Lab-Volt

6 Switches and Switching Concepts Place slide switch S4 in the UP position (toward the ZIF connector). Use your ohmmeter to measure the resistance of each contact pair. Based on your measurements, which statement is correct? a. The lower set of contacts of each pole are made. No electrical connection is indicated between the poles of S4. b. The upper set of contacts of each pole are made. No electrical connection is indicated between the poles of S4. c. The upper set of contacts of each pole are made. Both switch poles are electrically connected and all four made contacts are shorted together. CONCLUSION Switches possess one or more poles that make or break a pair of contacts. A closed switch exhibits a resistance of near 0 and makes a circuit. single-pole single-throw (SPST) switch has one pole and one position. Switches are normally open or normally closed. REVIEW QUESTIONS 1. In electrical circuits, switches a. b. open circuits. c. close circuits. d. All of the above. 2. The switch that controls one conductor with two loads is a(n) a. SPST switch. b. SPDT switch. c. rotary switch. d. DIP switch. FACET by Lab-Volt 85

7 Use the circuit in this image to answer the following questions. 3. In the circuit, a switch that opens a circuit when pressed is a. S1. b. S2. c. S3. d. S4. 4. In the circuit, the DPDT switch controls a. one conductor in one circuit. b. one conductor in two circuits. c. two conductors in two circuits. d. two conductors in one circuit. 5. a. S1. b. S2. c. S3. d. S4. 86 FACET by Lab-Volt