ThePrincipleandUseof Digital OscilloscopeOscilloscope is an instrument used to display the waveform of signals, which can beused to measure the temporal evolution of shape,frequency,phase difference ofvoltagesignals and so on. Oscilloscope is frequently used to qualitatively observe the dynamicprocess of electrical signals and non-electrical signals (such as speed, pressure, stress,vibration, concentration, sound, magnetism, light, heat, etc.)with different sensors.Digital oscilloscopes have the functions of screenshots, data display, mathematicaloperations, data and waveform storage, which are not available in traditional analogoscilloscopes. Digital oscilloscopes can be connected to networks, USB flash drives,printers, and computers.Nowadays, digital oscilloscopes become the significantequipment in science research and education.In this experiment, students should understand the principle of oscilloscope, andlearn howtooperate theDS2072Adigital oscilloscope.Motivation(1) Understanding how the oscilloscope works(2)Learningtoobservevarioussignalwaveformswithanoscilloscope(3) Measuring the voltage, frequency and phase difference of the signal with anoscilloscopeExperimentalPrinciple1.The operatingprinciple of digital oscilloscopeA schematic diagram of the digital oscilloscope is shown in Figure 53-1. The detectedsignal is firstly delivered to a voltage amplification (or attenuation) circuit, and thesignal will be amplified (or attenuated) to an appropriate value for the subsequentcomponents. Secondly, the continuously variational signals will be sampled at a certainfrequency.Then, the sampled analog quantity is converted into a digital quantity by theanalog-to-digital (A/D) converter, and these digital quantities are stored in the memory.In this way,the stored digital waveform can be displayed on the screen with the help ofCPU and logic control circuit
The Principle and Use of Digital Oscilloscope Oscilloscope is an instrument used to display the waveform of signals, which can be used to measure the temporal evolution of shape, frequency, phase difference of voltage signals and so on. Oscilloscope is frequently used to qualitatively observe the dynamic process of electrical signals and non-electrical signals (such as speed, pressure, stress, vibration, concentration, sound, magnetism, light, heat, etc.) with different sensors. Digital oscilloscopes have the functions of screenshots, data display, mathematical operations, data and waveform storage, which are not available in traditional analog oscilloscopes. Digital oscilloscopes can be connected to networks, USB flash drives, printers, and computers. Nowadays, digital oscilloscopes become the significant equipment in science research and education. In this experiment, students should understand the principle of oscilloscope, and learn how to operate the DS2072A digital oscilloscope. Motivation (1) Understanding how the oscilloscope works (2) Learning to observe various signal waveforms with an oscilloscope (3) Measuring the voltage, frequency and phase difference of the signal with an oscilloscope Experimental Principle 1. The operating principle of digital oscilloscope A schematic diagram of the digital oscilloscope is shown in Figure 53-1. The detected signal is firstly delivered to a voltage amplification (or attenuation) circuit, and the signal will be amplified (or attenuated) to an appropriate value for the subsequent components. Secondly, the continuously variational signals will be sampled at a certain frequency. Then, the sampled analog quantity is converted into a digital quantity by the analog-to-digital (A/D) converter, and these digital quantities are stored in the memory. In this way, the stored digital waveform can be displayed on the screen with the help of CPU and logic control circuit
InputAmplify orSamplingandmemorydisplayattenuateA/DconrsioruniteExternalTriggelLogiccontroltriggerCPUcircuitcircuitInput and outputinterfaceFigure53-1.Schematic diagram of digital oscilloscopeIn order to stably display the real-time waveform of the input signal, the scansignal of oscilloscope must be synchronized to the input signal, and the starting pointof each displayed scan waveform is fixed at the same position on the oscilloscopescreen. If the signals after amplification (or attenuation) is selected as the trigger source,the trigger circuit of oscilloscope will generate a trigger signal when the trigger circuitdetect delivered signal over the set trigger condition (certain level and polarity).Receiving this trigger signal, subsequent logic control circuit start a set of dataprocessing,including ofacquisition, conversion,and memory write processing.Finally,the digital oscilloscope reads the data from the memory and displays it stably on thescreenwiththeparticipationofCPUandthelogiccontrolcircuit.Since the analog signal has been converted into a digital quantity and stored in thememory, the digital oscilloscope can be used to perform some mathematical operations(such as addition,subtraction,multiplication,fastFourier transform)and automaticmeasurement, etc. It also can be used to communicate with computers or otherperipherals through input/output interfaces.2.LissaiousFigureThe default model of waveform display on our oscilloscope is a “Y-T mode, asshown in Figure 53-2(a). The voltage values of the tested signal are sampled follow thesame time interval and displayed after a series of processes. The horizontal axis of thedisplayed waveform is corresponding to time.However, in many cases, it is necessary to compare the signals of two waveforms.For example, we need to observe the change of waveform and phase ofa specific signalbefore and after passing a certain circuit. The“Y-T mode" is very inconvenient.Weusually use the“X-Y mode", in which the X-axis and Y-axis of the displayed curves arethe detected signals of channel 1 and channel 2, respectively.Lissajous figure is defined as a regular and stable closed curve, which is formed by
Figure 53-1. Schematic diagram of digital oscilloscope In order to stably display the real-time waveform of the input signal, the scan signal of oscilloscope must be synchronized to the input signal, and the starting point of each displayed scan waveform is fixed at the same position on the oscilloscope screen. If the signals after amplification (or attenuation) is selected as the trigger source, the trigger circuit of oscilloscope will generate a trigger signal when the trigger circuit detect delivered signal over the set trigger condition (certain level and polarity). Receiving this trigger signal, subsequent logic control circuit start a set of data processing, including of acquisition, conversion, and memory write processing. Finally, the digital oscilloscope reads the data from the memory and displays it stably on the screen with the participation of CPU and the logic control circuit. Since the analog signal has been converted into a digital quantity and stored in the memory, the digital oscilloscope can be used to perform some mathematical operations (such as addition, subtraction, multiplication, fast Fourier transform) and automatic measurement, etc. It also can be used to communicate with computers or other peripherals through input/output interfaces. 2. Lissajous Figure The default model of waveform display on our oscilloscope is a “Y-T mode”, as shown in Figure 53-2(a). The voltage values of the tested signal are sampled follow the same time interval and displayed after a series of processes. The horizontal axis of the displayed waveform is corresponding to time. However, in many cases, it is necessary to compare the signals of two waveforms. For example, we need to observe the change of waveform and phase of a specific signal before and after passing a certain circuit. The “Y-T mode” is very inconvenient. We usually use the “X-Y mode”, in which the X-axis and Y-axis of the displayed curves are the detected signals of channel 1 and channel 2, respectively. Lissajous figure is defined as a regular and stable closed curve, which is formed by
two simpleharmonicvibrationsperpendiculartoeachother,withanintegerratiobetween their frequencies.Different initial phases and different frequency ratios willproducedifferent shapesof Lissajous curves,as shown inFigure53-22=2n=4UaUxit(b)1UUe4C(a)(c)Figure 53-2.Lissajous figure:(a)Different frequencies and phases of Y-axis and X-axis signals.(b)The synthesized Lissajous curvebetween Uxi and Uy.(c)The synthesized Lissajous curvebetween Ux2and UyFig.53-2(b) show the Lissajous figure obtained by taking Uxi and Uy as X-axis and Y-axis, respectively. Fig. 53-2(c) show the Lissajous figure obtained by taking Ux2 and UyasX-axisand Y-axis,respectively.Since theUxiandUx2 signals havethe samefrequency and different phases, the shape of the Lissajous figure is quite different.However, the ratio of the maximum intersections of any horizontal line intersectingwith the Lissajous curve and those of the vertical line with the Lissajous curve is same
two simple harmonic vibrations perpendicular to each other, with an integer ratio between their frequencies. Different initial phases and different frequency ratios will produce different shapes of Lissajous curves, as shown in Figure 53-2. Figure 53-2. Lissajous figure: (a) Different frequencies and phases of Y-axis and X-axis signals. (b) The synthesized Lissajous curve between Ux1 and Uy. (c) The synthesized Lissajous curve between Ux2 and Uy. Fig. 53-2(b) show the Lissajous figure obtained by taking Ux1 and Uy as X-axis and Yaxis, respectively. Fig. 53-2(c) show the Lissajous figure obtained by taking Ux2 and Uy as X-axis and Y-axis, respectively. Since the Ux1 and Ux2 signals have the same frequency and different phases, the shape of the Lissajous figure is quite different. However, the ratio of the maximum intersections of any horizontal line intersecting with the Lissajous curve and those of the vertical line with the Lissajous curve is same t Ux1 a b c d e f g h i t a b c d e f h i Uy g Uy Ux1 a b c d e f g h i nx= 2 ny= 4 t (b) Ux1 g t a b c d e f h i Uy (a) t Ux2 t (c) Ux2 i a b c d e g f h t t a b c d e f h i Uy g Uy a Ux2 c b d e g f h i nx= 1 ny= 2
(1: 2).So it is follow the relation as:n,:n,=f,:f,(53-1)Figure53-3showstheLissajousfiguresforseveraldifferentfrequencyratiosDt(d) O(e) J.2I.Figure 53-3.Lissajous figures of several frequency ratiosExperimental Instruments1.DS2072AdigitaloscilloscopeFigure53-4 shows the operation panel of the DS2072Adigital oscilloscope.The signalsare input to the oscilloscope through the two input channels (CH1 and CH2).Table 53-1 shows thefunction introductionoftheoscilloscope.If you want toknowthedetailedfunction of one button during operation, you can press the "Help" button firstly, andthen press the button. Then the function introduction of this button will be displayed onthe oscilloscope screen
(1: 2). So it is follow the relation as: x y y x n : n = f : f （53-1） Figure 53-3 shows the Lissajous figures for several different frequency ratios. Experimental Instruments 1. DS2072A digital oscilloscope Figure 53-4 shows the operation panel of the DS2072A digital oscilloscope. The signals are input to the oscilloscope through the two input channels (CH1 and CH2). Table 53- 1 shows the function introduction of the oscilloscope. If you want to know the detailed function of one button during operation, you can press the “Help” button firstly, and then press the button. Then the function introduction of this button will be displayed on the oscilloscope screen. (a) (b) (c) (d) (e) (f) Figure 53-3. Lissajous figures of several frequency ratios
QuickFunctionOperationMulti-functionScreenmenuknobcontrol areacontrol areaselection buttonmeasurementaQAADaHelp/printE一ParametersettingbuttonOHorizontalcontrol area口WaveformrecordingareaTrigger control areaProbe compensation endExternal trigger inputchannel zoneVertical controlSwitchUSB interfaceSignal inputFigure 53-4.Schematic diagram of the operation panel of the DS2072A digital oscilloscopeTable 53-1.Functions of the DS2072ADigital OscilloscopeNameAreaFunctionAutomatically detect the signal input channel, automaticallyAUTObuttonselect the appropriate measurement range, period, trigger, anddisplay the detected signal in Y-T mode.RUN/STOPDisplaythereal-timewaveform/displaythewaveformbeforeOperationbuttoncontrolpressingthestopbutton.(Screenshot)AreaThe singletriggerbutton:theoscilloscopewillbetriggeredbyanSINGLEbuttonappropriate signal satisfiedthe certain requestcondition anddisplays the signal.CLEAR buttonIn the case ofa single trigger mode, it will clear the screen.Press helpbuttonfirstly,andthenpress anotherbuttontodisplayHelp buttonHelpthefunction of that button.printPrint buttonSave screen data to a USB flash drive or print itCHI buttonDisplay / (stop display) CH1 channel signal and operation menu.VerticalCH2 buttonDisplay / (stop display) CH2 channel signal and operation menu.controlAccording to selected function, display the results of adding.AreaMATHbuttonsubtracting, multiplying and FFT (fast Fourier transform)operations of CHI signal and CH2channel signal
Table 53-1. Functions of the DS2072A Digital Oscilloscope Area Name Function Operation control Area AUTO button Automatically detect the signal input channel, automatically select the appropriate measurement range, period, trigger, and display the detected signal in Y-T mode. RUN/STOP button Display the real-time waveform / display the waveform before pressing the stop button. (Screenshot) SINGLE button The single trigger button: the oscilloscope will be triggered by an appropriate signal satisfied the certain request condition and displays the signal. CLEAR button In the case of a single trigger mode, it will clear the screen. Help print Help button Press help button firstly, and then press another button to display the function of that button. Print button Save screen data to a USB flash drive or print it. Vertical control Area CH1 button Display / (stop display) CH1 channel signal and operation menu. CH2 button Display / (stop display) CH2 channel signal and operation menu. MATH button According to selected function, display the results of adding, subtracting, multiplying and FFT (fast Fourier transform) operations of CH1 signal and CH2 channel signal. Help/print Parameter setting button Probe compensation end Screen menu selection button Multi-function knob Function control area Operation control area Switch USB interface Vertical control zone Signal input channel Quick measurement button Figure 53-4. Schematic diagram of the operation panel of the DS2072A digital oscilloscope Horizontal control area Waveform recording area Trigger control area CLEA AUT SINGL Measur Acquire Storage Cursor Display Utility Help Print MENU SCALE C 1 C 2 MATH REF Decode Decode MOD MEN FORC POSITI SCALE CH1 CH2 External trigger input channel zone