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In this Article we will discuss To be Familiar with the basic knobs of Oscilloscope,How to measure Voltage,Frequency and different signals from Oscilloscope, Complete Lab reports and Lab Video of how to use Oscilloscope and Function generator.
Oscilloscope and Function Generator Lab Video:
Oscilloscope and Function Generator Lab Manual:
- To become familiar with the basic operating controls of a CRO.
- To use the oscilloscope to observe the wave-form and to measure the value of
- An A.C. Voltage.
- A D.C. Voltage.
- To use the oscilloscope to observe the wave-form and to measure the current flowing in a resistor when energized from
- An alternating current supply;
- A direct current supply.
To oscilloscope is one of the most versatile and widely used instruments found in modern laboratories. It can be used to measure frequency, phase, and peak value of ac wave-form, as well as dc value, transients, and many special characteristics of electronic components. It provides an especially vivid means for studying and understanding circuit behavior, and is an indispensable tool in research, and design activities, as for trouble shooting complex circuit.
The many practical uses of an oscilloscope are derived from its ability to display a time varying waveform that is a plot, or graph, of voltage versus time. The display is created by a beam of electrons in a cathode ray tube (CRT). When beam strikes the phosphorescent screen in the CRT, light is emitted, and the path of the beam as it moves across the screen, called a trace, is clearly visible. Electronic circuitry in the oscilloscope causes the beam to sweep across the screen from left to right, so the horizontal position of the beam is proportional to time. The wave-form to be displayed causes the beam to move up and down as it is being swept from left to right, so the vertical position of the beam, at any instant of time is proportional to the instantaneous value of the wave-form at that time. Causing the beam to move is called deflecting it. The horizontal deflection, proportional to time, and the vertical deflection, proportional to the value of the waveform, create a waveform plot versus time.
The laboratory grade oscilloscopes, generally, have calibrated controls that allow the user to adjust the size of the display and to make accurate measurement from it. The screen has a gratitude, which, like the graph paper, has divisions that from a measurement grid. Adjusting front-panel controls sets scale factors. A calibrated control called vertical sensitive adjusts the scale factor along the vertical axis and is therefore used to measure magnitudes, or the instantaneous values, of the waveform. The vertical sensitivity, or the scale factor, on a typical oscilloscope can be adjusted from a few mill volts per division to 100 or more volts per division.
The horizontal axis of a waveform display represents time, so the horizontal sensitivity, called the time base, is the oscilloscope control used to set the scale factor for measuring increments of time. Adjusting the time base alters the frequency of the internally generated sweep. The time base of a typical oscilloscope can be adjusted from less than 1μs to several seconds per division. Since time can be measured with an oscilloscope, we can find the period of a waveform and hence its frequency. Most laboratory grade oscilloscopes can display two waveforms simultaneously and are therefore called dual-trace oscilloscopes. By measuring the time interval between corresponding points of two wave-forms, time shift between them can be determined.
- Cathode-ray oscilloscope;
- C. variable-voltage supply of mains frequency;
- C. variable-voltage supply;
- C. Voltmeter;
- C. Ammeter;
- C. Voltmeter;
- C. Ammeter;
- Resistors: R1, 680 ohm, R2, 6800 ohms.
To set up the oscilloscope:
- Locate the following controls on the front panel of the oscilloscope and adjust each one to the position nominated.
- There are many makes and model of oscilloscopes and the controls may be defined differently. However, the controls and their names listed above are most commonly used for Dual-channel oscilloscopes. If there is any doubt, ask your teacher for clarification.
- Ensure that other equipment on the bench does not obstruct the ventilation to the oscilloscope. Do not place books or other items on top of it.
- Switch on the oscilloscope by putting the ON-OFF control to ON, and wait a few
- Minute for the instrument to warm up.
- Adjust the intensity control until the trace appears. Do not operate the oscilloscope with excessive brilliance as this can damage the screen.
- Center the trace on the screen by means of the Horizontal and Vertical Shift controls.
The oscilloscope is now ready for use.
- Turn the AC\GND\DC control to AC.
- Connect an alternating voltage of mains frequency and about 5 volts (rms) to the CH1 input.
- Adjust the CH1 Volts/Div control so that whole of the waveform can be seen within the graticule markings of the screen.
- If necessary, adjust the sweep Time/Div control to obtain two complete cycles on the screen.
- Slowly adjust the following controls in turn and observe the effect on the trace.
- Each control should be returned as near as possible to its former position.
- CH1 Position control
- CH1 Volts/Div switch
- Y Position control
- Sweep Time/Div Control
- VAR Sweep Control
- X Position Control
To use the Oscilloscope to measure a voltage:
- Connect an alternating voltage of mains frequency to the CH1 input and adjust the input to 10 volts (rms).
- Read the peak-to-peak height of the trace on the screen from the graticule Markings.
- Convert this value to peak-to-peak volts by applying the correct scale factor.
- Convert this value to the root mean square value as follows:
- Volts (rms) =Volts (PK-PK)/2√2
Compare this value with the voltmeter reading.
- Replace the A.C. supply with a D.C. supply.
- Adjust the AC/GND/DC switch to DC.
- Note the zero signal vertical position of the trace.
- If necessary, adjust it to coincide with one of the horizontal graticule lines.
- Switch on the D.C. supply and adjust it to 10 volts.
- Adjust the CH1 Volts/Div control to obtain a satisfactory defection of the trace.
- Read the deflection of the trace and convert this distance into volts by applying
- the correct scale factor.
Compare this with the voltmeter reading.
To use the oscilloscope to measure current:
- Connect up the circuit as shown in the current measuring diagram.
- Set the CH1 AC/GND/DC switch to AC.
- Adjust the output of the AC supply until the ammeter reads 4mA (rms).
- Set the CH1 Volts/Div switch as required to obtain satisfactory trace.
- Read the peak-to-peak height of the waveform and convert it to root-mean-square Voltage.
- Calculate the rms current from I=E/R1
- Compare this current with the ammeter reading.
- Replace the AC voltage supply with one of direct voltage.
- Set the CH1 AC/GND/DC switch to DC
- Note the vertical position of the trace on the graticule scale and if necessary adjust it to coincide with one of the horizontal lines.
- Adjust the output of the supply until the ammeter reads 4ma.
- Set the CH1 Volts/Div switch to obtain a satisfactory deflection of the trace.
- Read the trace deflection and convert it to voltage. Calculate the current from I=E/R1
- Compare this current with the ammeter reading.
ANALYSIS, DEDUCTIONS AND CONCLUSIONS:
- Have the objectives of the experiment been achieved?
- For what purpose, other than those carried out in this experiment, may the oscilloscope be used?
- For what purpose may the double-beam oscilloscope be particularly useful?
- In what situations may the control of triggering point be useful?
- Is the oscilloscope an effective means of measuring voltage and current? What facts indicate this?
- In what situations would the oscilloscope be used to measure voltage or current in preference to a voltmeter or an ammeter?