EKT 101 Electric Circuit Theory Module 2 UNIVERSITY MALAYSIA PERLIS EKT 101 ELECTRIC CIRCUIT THEORY LABORATORY MODULE 2 SEMESTER I (2012/2013) SCHOOL OF COMPUTER AND COMMUNICATION ENGINEERING SEM I 2012/13 EKT 101 Electric Circuit Theory Module 2 INTRODUCTION TO LABORATORY II BASIC LABORATORY EQUIPMENT OBJECTIVE 1. To introduce student with the basic laboratory equipment 2. Become familiar with the basic operation of a multimeter, oscilloscope and function generator and to gain skill in handling these equipments. 3. Able to perform simple calibration of an oscilloscope. A. MULTIMETER Multimeter is a basic tool in electric and electronic fields. It is a multipurpose device to measure voltage, current and resistance. Basically there are two types of multimeter used either in the education or industrial field based on the electronic circuits inside them: analog and digital meters. The analog meter, broadly known as VOM (volt-ohmmiliammeters) uses a mechanical moving pointer which indicates the measured quantity on a calibrated scale. It requires the user a little practice to interpret the location of the pointer. The digital meter broadly known as DMM (digital multimeter) used number or numerical display to represent the measured quantity. It has high degree of accuracy and can eliminate usual reading errors compared to the analog meters. a) Resistance Measurement For VOM always reset the zero-adjust whenever you change scales. In addition always choose the range setting that will give the best reading of the pointer location. As an example, to measure a 500- resistance, choose function switch resistance with a range setting of X 1k. Finally do not forget to multiply the reading by the proper multiplication factor. If you are not sure about the value always starts with the highest range and going downwards until appropriate scale is chosen. b) Voltage Measurement When measuring voltage levels, make sure the meter is connected in parallel with the SEM I 2012/13 EKT 101 Electric Circuit Theory Module 2 element whose voltage is to be measured. Polarity is important because the reading will indicate up-scale or positive reading for correct connection and down-scale or negative reading if reverse connection of the meter test leads to the resistor’s terminals. Therefore a voltmeter is not only excellent for measuring voltage but also for polarity determination. Choose the correct function switch for example DCV to measure dc voltage and turn to the range switch that has slightly bigger value than the voltage to be measured. c) Current Measurement When measuring current levels, make a series connection between the meter and the component whose current is to be measured. In other words, disconnect the particular branch and insert the ammeter. The ammeter also has polarity marking to indicate the manner they should be hooked-up in the circuit to obtain an up-scale or positive measurement.The connection of the multimeter to measure different electrical quantities is shown in both schematic diagram and real wiring illustration in the laboratory in Figure 1. R Vs V/ A Figure 1: Schematic diagram Figure 2: Real wiring diagram for illustration SEM I 2012/13 EKT 101 Electric Circuit Theory Module 2 B. OSCILLOSCOPE An oscilloscope or better known as scope is the most versatile piece of equipment that displays the variation of voltage with time on a cathode-ray tube (CRT). In other words it can actually draw a graph of voltage direction and amplitude of a signal. The signal can only be measured if its frequency is within the range of the scope’s frequency. In all experiment to follow the type of oscilloscope used will be a dual-trace triggeredsweep scope, model GOS-622G, 20 MHz with two (2) vertical inputs at the sensitivity of 1 mV/cm. The typical scope has four sections/modes as shown in Figure 4. They are vertical; horizontal; trigger or sync; and display. Let us look at each section to learn its purpose and adjustments. Figure 4: Functional block diagram of a general purpose oscilloscope SEM I 2012/13 EKT 101 Electric Circuit Theory Module 2 CONTROL BUTTONS/SWITCH INTENSITY FOCUS VOLT/DIV VERTICAL Y-POSITION VAR SENS VOLT/DIV VERTICAL COUPLING TIME/DIV HORIZONTAL X-POSITION VAR SENS TIME/DIV TRIGGER LEVEL FUNCTION The function of intensity is to control the intensity (brightness) of light or electron beam suitable to the eyes. The electron beam is focused through the grid control in the cathode ray tube. The beam is controlled through this button. This button controls the sensitivity of the input signal at the vertical mode so that a wide range of signals can be displayed. Typically the range varies from a few mV to hundreds of Volts. This button enables the signal displayed to move upwards and downwards. This button enables the adjustment of calibration in terms of VOLT/DIV to be carried out. This button determines the way the signal to be measured is input to the vertical mode. When the switch is set to GND, the signal is shorted to ground. Therefore the signal is not displayed. With AC only the ac signal is allowed to pass through and displayed. With DC both components dc and ac levels are passed to the vertical mode and displayed on the screen. This button is associated to the horizontal mode and is the scale factor for period. As an example if the TIME/DIV is 1 ms means that 1 cm scale on the scope screen is equal to the 1 ms. This button enables the signal to be moved to the right and left horizontally. This button is used to calibrate the period. This button is adjusted until a moving signal on the screen is made stationary. Table 1: Control buttons and its functions of an oscilloscope (a) Amplitude Measurements (Voltage) DC levels: (i) Place DC/AC/GND switch in the GND position to establish the base-line or zero level reference on the screen. (ii) Then switch the DC/AC/GND switch to DC position to measure dc level. In this position the input probe has direct coupling to the internal amplifiers. (iii) Finally place the scope leads across the unknown dc level and use the following equation to determine: DC level (V) = Vert. deflection (div.) X Vert. sensitivity (V/div.) X probe setting SEM I 2012/13 EKT 101 Electric Circuit Theory Module 2 AC level: (i) Place DC/AC/GND switch in the GND position to establish the base-line or zero level reference on the screen. (ii) Then switch the DC/AC/GND switch to AC position to measure ac level. In this mode there is a coupling capacitor between the input probe and the internal amplifiers. This blocks the dc from display and allows the measurement of lowlevel ac signals sitting on the same line as high-level dc voltage. (iii) Finally place the scope leads across the unknown ac voltage level to obtain voltage using the following equation: Vp-pl (V) = Vert. deflection Peak-Peak (div.) X Vert. sensitivity (V/div.) X probe setting C. FUNCTION GENERATOR (i) A function generator is usually a piece of electronic test equipment or software used to generate different types of electrical waveforms over a wide range of frequencies. Some of the most common waveforms produced by the function generator are the sine, square, triangular and sawtooth shapes. (ii) A function generator is a device that can produce various patterns of voltage at a variety of frequencies and amplitudes. It is used to test the response of circuits to common input signals. The electrical leads from the device are attached to the ground and signal input terminals of the device under test. Figure 5: Function Generator SEM I 2012/13 EKT 101 Electric Circuit Theory Module 2 Most function generators allow the user to choose the shape of the output from a small number of options. Square wave - The signal goes directly from high to low voltage. Sine wave - The signal curves like a sinusoid from high to low voltage. Triangle wave - The signal goes from high to low voltage at a fixed rate. The amplitude control on a function generator varies the voltage difference between the high and low voltage of the output signal. The direct current (DC) offset control on a function generator varies the average voltage of a signal relative to the ground. The frequency control of a function generator controls the rate at which output signal oscillates. On some function generators, the frequency control is a combination of different controls. One set of controls chooses the broad frequency range (order of magnitude) and the other selects the precise frequency. This allows the function generator to handle the enormous variation in frequency scale needed for signals. The duty cycle of a signal refers to the ratio of high voltage to low voltage time in a square wave signal How to use Function Generator After powering on the function generator, the output signal needs to be configured to the desired shape. Typically, this means connecting the signal and ground leads to an oscilloscope to check the controls. Adjust the function generator until the output signal is correct, then attach the signal and ground leads from the function generator to the input and ground of the device under test. For some applications, the negative lead of the function generator should attach to a negative input of the device, but usually attaching to ground is sufficient. SEM I 2012/13 EKT 101 Electric Circuit Theory Module 2 Appendix CONTROL BUTTONS/SWICHES OF OSCILLOSCOPE NO 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 SEM I 2012/13 CONTR BUTTONS/SWICHES Calibration Point, CAL Intensity, INTEN Focus Trace Rotation Power ON LED Indicator Power ON/OFF VOLT/DIV AC/DC GND CH1(X) Input Port VAR SENS CH2 (Y) Input Port SWP. UNCAL GND SWP. VAR SLOPE EXT TRIG (EXT HOR) input terminal NO 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 CONTR BUTTONS/SWICHES TIME/DIV TRIG/ALT COUPLING SOURCE X-Y Trigger Mode: NORM/AUTO LOCK TRIGGER LEVEL HOLDOFF Horizontal Position X 10 Magnification CH2 INV CH2 Vertical Position Vertical Mode CH1 Vertical Position CHOP SCREEN – each graticule calibrated in centimeters EKT 101 Electric Circuit Theory Module 2 UNIVERSITY MALAYSIA PERLIS EKT 101 ELECTRIC CIRCUIT THEORY EXERCISE 2 SEMESTER I (2012/2013) SCHOOL OF COMPUTER AND COMMUNICATION ENGINEERING SEM I 2012/13 EKT 101 Electric Circuit Theory Module 2 A. MEASUREMENT USING MULTIMETER (RESISTANCE IN SERIES AND PARALLEL) a) With resistors given, complete Table 1 below. Using multimeter, measure the resistance COLOR BAND No. Band 1 Band 2 Band 3 Band 4 Nominal Value Measured Value 1. 2. 3. 4. b) Construct the circuit as shown in Figure 1 on the breadboard. Note that R1= 1.2 k, R2 = 1 k, R3 = 3.9 k and R4 = 4.7 k. a R1 R2 R3 R4 b Figure 1: Resistor in Series a) Give the equation to CALCULATE of total resistance for the circuit in Figure 1. b) Using multimeter MEASURE the total resistance. SEM I 2012/13 EKT 101 Electric Circuit Theory Module 2 3. Figure 2 show the resistor connected in parallel. R1 R2 R3 R4 Figure 2: Resistor in Parallel a) Give the equation to CALCULATE of total resistance for the circuit in Figure 2. b) Using multimeter MEASURE the total resistance. SEM I 2012/13 EKT 101 Electric Circuit Theory B Module 2 CALIBRATION OF OSCILLOSCOPE 1. Connect a coaxial input signal probe to the BNC jack CH1. 2. Obtain a base-line or zero level horizontal trace by setting the vertical coupling switch to GND and by appropriately adjusting the vertical and horizontal position controls. 3. Calibrate the sensitivity of the instrument by setting the VOLT/DIV switch to the required range. 4. Set the vertical coupling switch to AC (disengage the switch). Set the sweep sensitivity TIME/DIV [ to 0.5 ms. Next, touch the input probe lead to the calibration point, CAL . Make sure that the magnification scales at both scope and probe is X1. 5. OBSERVE the values obtained from the displayed waveform and DRAW the waveform in Figure 6 indicating the important values such as peak-peak value Vpp, Frequency f, VOL/DIV button setting and TIME/DIV button setting. Note: It is very important to make a prior calibration on the scope to ensure a correct and accurate measurement. 6. Draw the waveform signal in graph below. Figure 6: Calibration signal SEM I 2012/13