Practical Electronics - Example

Name Course Institution Instructor Experimental Date Submission Date Abstract This report is a description of how a cathode ray oscilloscope (CRO) can be used to measure voltage of an alternating current and the frequency or period of A.C. signal input. It involves the use of a function generator that produces sinusoidal waveforms of various frequencies and amplitudes. The function generator is adjusted to give various waveforms. Similarly, adjustments were made on the CRO to give a fine sinusoidal wave that covers a considerable screen area. With the help of CRO screen calibrations, the amplitude and period of resultant sinusoidal wave form was measured. The resultant value of amplitude was used to calculate the effective or Rms voltage (Vrms). To ascertain the calculated effective voltage, the result was compared to what was measured on the multimeter. A cathode ray oscilloscope can be used to measure voltage of an A.C. signal input. Table of Contents Table of Contents 3 1.0 Introduction 4 1.1 Aims 4 2.0 Cathode Ray Oscilloscope 4 2.1 AC Voltage 5 2.3 Measurement of frequency 6 3.0 Materials and Method 6 3.1 Apparatus 6 3.2 Procedure 6 3.3 Results and Calculations 7 4.0 Task 2: Graph 7 4.1Results and Calculations 8 5.0 References 9 1.0 Introduction A CRO is a crucial laboratory apparatus that can be used for diverse functions. Being knowledgeable about its operation is therefore an important idea. The experiment began with familiarization of different control mechanisms such as TIME/DIV control and VOLTS/DIV control. The wave form produced on the screen is dependent on the signal connected to the input terminals. The wave form was used to calculate the input voltage. Verification was possible through the comparison of the calculated values and measured values from digital multimeter. 1.1 Aims The purpose of this experiment was to: Familiarize with the use of a function generator to produce sinusoidal waveforms of various frequencies and amplitudes. Familiarize with the use of a cathode ray oscilloscope to measure the period/frequency and the amplitude of sinusoidal waveforms. Know how to use a CRO to measure voltage Know how to use a digital multimeter to measure voltage. 2.0 Cathode Ray Oscilloscope A cathode ray oscilloscope is a laboratory apparatus that enables signal voltages to be observed in form of a two dimensional graph. The axes of the graph represent voltage and time. A CRO can be used to measure voltage, frequency and amplitude. It has a lot of advantages compared to DC meters. One of the advantages is that it has the capability of measuring very high voltages with high accuracy. A CRO has various controls that are used to adjust the sinusoidal waveform both in horizontal and vertical scales. The TIME/DIV control or time-base band switch that is connected to the X-plates is used for navigation along the horizontal scale. The VOLTS/DIV control or voltage sensitivity band that is connected to the Y-plated is used for navigation along the vertical scale. There are other important controls such as INTENSITY, FOCUS, Y-POS and CH 1. 2.1 AC Voltage When an alternating current signal is connected to a CRO, a sinusoidal waveform appears on the screen. This is due to the fact that alternating current is always changing in both the magnitude and direction after a very short period. Sinusoidal waveforms are described by the equation below and it is represented as shown in fig 1 below; or where or is the peak voltage. Fig 1 To determine the voltage of an alternating current, the function generator producing a sinusoidal waveform is connected to the CRO. The peak voltage or can be determined from peak to peak height. When peak to peak height is multiplied by voltage sensitivity (VOLT/DIV) value, we obtain which is twice the peak voltage. From this, the peak voltage can be determined by using; Where; is the rms voltage or effective voltage is the peak voltage. The rms voltage is the value that is measured by a multimeter. The calculated value of rms from the CRO can be verified by comparing it with the measured value from the digital multimeter. 2.3 Measurement of frequency To measure the frequency of an AC signal, the function generator is connected to Y-plates sensitivity band of the CRO. The X-plates are connected to the time base signal. The result is a progressive sinusoidal waveform having alternating peaks. The distance between two alternating peaks can be measured in terms of divisions. Multiplying the resultant value with time base or SEC/DIV value used gives the period () in seconds. The reciprocal of the period gives the frequency; 3.0 Materials and Method 3.1 Apparatus Function generator Digital multimeter (DMM) Hameg HM 203-6 cathode ray oscilloscope 3.2 Procedure Task 1: Using a cathode ray oscilloscope to measure the voltage of an AC signal To determine the voltage of an AC signal from the function generator, the circuit components were connected as shown below; Function generator CRO 1. With the amplitude at mid position, the function generator was set up to produce a sine wave of frequency of approximately 1 kHz. 2. The output of the function generator was then connected to channel 1 input of the CRO. 3. The horizontal control or time base band switch of the CRO was then set at 0.2 ms/Div while the vertical control or voltage sensitivity band switch was adjusted such that the displayed waveform occupies most of the screen of the CRO. 4. From the CRO screen, the period and amplitude of the resultant waveform was then measured and recorded. 5. A digital multimeter (DMM) was then used to measure the voltage output from the function generator and recorded. N/B: The variable voltage output from the function generator was kept at zero and its power switched off when the circuits were being connected up. 3.3 Results and Calculations Period = Amplitude = DMM reading ()= 2.51 V. But = 4.0 Task 2: Graph Procedure The same circuit set up was used. 1. The output frequency of the function generator was adjusted to 400kHz. 2. The controls on the CRO were changed such that two cycles were shown on the screen with the timebase set at 0.5 µs/cm. 3. The period and amplitude on the CRO screen was recorded. 4. The output voltage signal of the function generator was connected to DMM and the resultant voltage recorded. N/B: The variable voltage output from the function generator was kept at zero and its power switched off when the circuits were being connected up. 4.1 Results and Calculations Period = Amplitude = DMM reading (Vrms) = CRO DMM CRO Timebase Divs Period(timebase×divs) VPkPk VPk Vrms Divs Period f(HZ) 20 ms 5 0.1 2.59 0.1 10 20 ms 2.5 0.05 2.6 0.05 20 5 ms 4 0.02 2.6 0.02 50 5 ms 2 0.01 2.61 0.01 100 2 ms 2.5 0.05 2.6 0.05 200 1 ms 2 0.002 2.57 0.002 500 0.5ms 2 0.001 2.52 0.001 1000 0.2ms 2.5 0.0005 2.43 0.0005 2000 0.1ms 2 0.0002 2.24 0.0002 5000 20 μs 5 0.0001 2.16 0.0001 10000 20 μs 2.5 0.00005 2.52 0.00005 20000 10 μs 2 0.00002 3.31 0.00002 50000 5 μs 2 0.00001 1.34 0.00001 100000 2 μs 2.5 0.000005 0.06 0.000005 200000 1 μs 2 0.000002 0.00 0.000002 500000 5.0 References Nath, D.K. Practical Electronics. New York: Academic Publishers, 1995. Read More