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Southern Luzon State UniversityCOLLEGE OF ENGINEERING

ECE Department

SWITCH Activity No. 1

Submitted by:

Member:

ALFUERTO, Joel M.CONDES, Mary RoseMACALE, ChesterUMALI, Armida Brin S.

ECE - V

Rating:

Engr. Renante D. AbuyanInstructor

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SWITCHESActivity No.1

OBJECTIVES

1. To know how to use ohmmeter for checking the condition of a switch.2. To learn how to use the voltmeter for testing and measuring the voltage across

the switch terminals.

BRIEF INTRODUCTION

In electronics, a switch is an electrical component that can break an electricalcircuit, interrupting the current or diverting it from one conductor to another .[1][2] Themost familiar form of switch is a manually operated electromechanical device with one

or more sets of electrical contacts. Each set of contacts can be in one of two states:either 'closed' meaning the contacts are touching and electricity can flow between them,or 'open', meaning t he contacts are separated and non-conducting.

Figure 1 Sample switch

A switch may be directly manipulated by a human as a control signal to a system,such as a computer keyboard button, or to control power flow in a circuit, such as a lightswitch. Automatically-operated switches can be used to control the motions of

machines, for example, to indicate that a garage door has reached its full open positionor that a machine tool is in a position to accept another work piece. Switches may beoperated by process variables such as pressure, temperature, flow, current, voltage,and force, acting as sensors in a process and used to automatically control a system.For example, a thermostat is an automatically-operated switch used to control a heatingprocess. A switch that is operated by another electrical circuit is called a relay. Largeswitches may be remotely operated by a motor drive mechanism. Some switches areused to isolate electric power from a system, providing a visible point of isolation that

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can be pad-locked if necessary to prevent accidental operation of a machine duringmaintenance, or to prevent electric shock.

Figure 2 Symbol for SPST switch

Switch is a manually operated device capable of making, breaking or changingthe connections in an electronics or electrical circuit. A switch connected in series withone of the connecting wires of a simple circuit affords a means of controlling the currentin the circuit. Usually, switches are used to open or close a circuit.

MATERIALS REQUIRED

Equipment: VOM or equivalent; Power supplySwitch: Assorted types (good or defective)

PROCEDURES

NOTE: To check the switch with an ohmmeter, turn the power “off” or remove theswitch from the circuit.

A. OHMMETER TEST:1. Set the VOM at R x 1. Set the pointer exactly at zero by shooting the test

leads together and adjusting the Zero-Ohm control.2. Simply connect the test leads to the switch terminals. Write the result in figure

A as per instruction.

B. VOLTMETER TEST:1. Again, set the VOM at 50v ac range. (NOTE: Be certain that no terminals are

short- circuited.)2. Insert the power plug of the power supply to the ac line outlet.3. POWER ON: Carefully touch or connect the test leads to the switch terminals.

Write the result to figure B.4. Repeat the procedure Nos. 1 to 5 for the other switch. Fill up the needed

information or data.

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DATA RESULTS

A. Checking a switch with an ohmmeter

OHMMETER TEST

RANGE RX1

CLOSED“on” 0

OPEN“off”

CONDITION Good

TYPE SPST

B. Checking a switch with a voltmeter

VOLTMETER TEST

RANGE 50VAC

CLOSED“on” 0V

OPEN“off” 50V

CONDITION Good

TYPE SPST

C. Checking a switch with an ohmmeter

OHMMETER TEST

RANGE RX1

CLOSED“on”

a. 0

b. 0 c. 0 d. 0

CONDITION Good

TYPE DPST

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D. Checking a switch with a voltmeter

VOLTMETER TEST

RANGE 50VACCLOSED

“on” OPEN

“off”

a. 0Vb. 0Vc. 0Vd. 0V

CONDITION Good

TYPE DPST

E. Checking a switch with an ohmmeter

OHMMETER TEST

RANGE RX1

CLOSED“on”

a. 0 b. 0

OPEN“off”

a. b.

CONDITION Good

TYPE Mainswitch

G. Checking a switch with a voltmeter

VOLTMETER TEST

RANGE 250v (AC)

CLOSED“on”

a. 0 b. 0

OPEN“off”

a. b.

CONDITION Good

TYPE Mainswitch

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CONCLUSIONS

In view of this activity, the following are concluded by the group:When checking the switch with an ammeter we always unplug the entire unitfrom the source, while by using a DC or AC voltmeter a switch must be with the

power “on” in the circuit. A good switch has a zero resistance when it is on the “on” position. The resistance of a switch is high or infinite, and no current flows when it is onthe “off” position. A good switch has a zero voltage across its two terminals, simply because thereis no voltage drop, when it is on the “on” position. The voltage drop across the terminals is equal to the voltage source if the switchis on the “off” position. Last, and most importantly in order to determine if the switch is defective onegood way is to substitute a good one or simply connect a jumper wire on bothterminals termporarily.

TEST REVIEW EXERCISES

1. Usually, the switch is electrically connected in series with the voltage source andits load.

2. When the switch is on , the electrons find an uninterrupted path in the circuit.3. The troubles arising in the switch fall into two main categories, electrical and

mechanical .4. When the switch is open or defective, the resistance is high or infinite, and no

current will flow in the circuit.5. Open is the off position of the switch, while closed is the on position.

QUESTIONS

1. How much is the resistance reading of a good switch?Ans: zero resistance

2. How many connections are required for a double- pole, double- throw switch?Ans:

3. How much is the voltage (IR) drop across a closed (good) switch?

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ASSIGNMENT

1. 3-way switch

-using 2 SPDT (J1 & J2) and a DPDT (S1)

2. Jeepney passenger’s alarm system

-using five push-button switch (J1-J5)

V1

120 V60 Hz0Deg

J1

Key = Space

J2

Key = Space

S1

Key = Space

1

2

3

4

X1

5V_1W

5

6

7

U1

SONALERT200 Hz

J1

Key = SpaceJ2

Key = SpaceJ3

Key = SpaceJ4

Key = SpaceJ5

Key = Space

V112 V

1 2

0