Introduction
Advanced electronics labs use both oscilloscopes and function generators. A function generator produces signals that provide a specifiable voltage applied over a particular time, such as sine wave or triangular wave signal. Signals generated by the device are used to control other devices to, for instance, vary magnetic field, send radioactive source back and forth, or act as a timing signal. An oscilloscope is used as a signal analyzer: they show the picture of the signal usually in the form of voltage versus time. The experimenter learns about the amplitude, frequency, and the shape of the signal. The tow devices are highly sophisticated (Loyd, 42).
A function generator has a collection of features, whether the analog type or the new digital ones: firstly, a way to select the type of a waveform, whether sine, square and triangle; others give ramps, pulses, noises or enable the user to program a specific arbitrary shape. Secondly, a way to select the amplitude and frequency of the waveform; typical frequency range is 0.01Hz to 10Mz. Thirdly, at least, two output ports; the main output port where the desired waveform is tapped has a typical maximum voltage of 20 volts, that is, volts range; and an impedance of 50 ohms. The second output (Sync, Aux or TTL) produces a square wave with 0 and 5-volt digital signal levels (Loyd, 23).
The function generator produces a time varying voltage signal. The three controls adjust the amplitude, frequency and shape features of the waveform. Frequency is the repetition of a definite period; F= 1/T, where f is the frequency in Hertz (Hz), and T is a period in seconds (sec). Figure 1 below shows the front panel view of a function generator.
Figure 1. The front panel of a function generator.
An oscilloscope has the screen on which the signal produces the moving dot or the trace in analog cathode ray models. In digital scopes, the screen resembles the monitor. On it, the signal is displayed in voltage versus time graph. The monitor has a graticule of about 1 cm squares. An oscilloscope has, at least, two input ports (channels), referred to as “CH1”, “CH2”, “CH3” and so on. Also, it has an external trigger input referred to as “EXT TRIG”. Also, an oscilloscope has a collection of controls associated with vertical section of the display related to the input signals. They control the coupling to the input, direct - “DC”, through capacitors – “AC” or disconnected – “GROUND”. Amplification applied to the signal is controlled by a knob specified regarding screen units, 10mV/div setting. It has controls related to the horizontal section of the display. Horizontal controls set the time axis. They are calibrated in sec/div, for instance, 1microsec/div. Trigger control is used to synchronize (match) the input signal to the horizontal signal.
Figures 2 a) and b) below shows the two front view of an oscilloscope.
Figure 2 a) front panel layout of a digital oscilloscope
Figure 2 b) front panel layout of an analog oscilloscope
Aims and objectives
Look at the different types of signals available from the function generator and explore the major controls of the oscilloscope and the generator.
Procedure
A BNC cable was connected from the output of the function generator to the input of the oscilloscope at channel “A”. The “third thought experiment” was done; figure 3 below shows how third thought experiment works.
Figure 3. Third thought experiment.
A graph of the voltage across the resistor versus time was completed in DATA SHEET #1. The period, frequency, and peak-to-peak voltage were recorded.
Part 1. Formation of the square wave.
The third though the experiment was repeated 1000 times faster. A function generator on the CGR 101 was used to switch the wires back and forth. A square waveform was created with the CGR 101 Waveform generator of T=2.0 milliseconds. Volts peak-to-peak voltage was selected.
The waveform was made to display on the oscilloscope screen by connecting the BNC cable from the output port of the function generator to the Channel “A” input of the oscilloscope. The values of frequency and amplitude were recorded on DATA SHEET #2. The shape of the waveform was as well drawn.
Part 2 creation of custom wave
The Timebase controls were adjusted to find the period, T., at least, three periods were observed on the screen. The number of horizontal divisions taken to match the period of the signal to one-tenth of a division was counted. The period was calculated as (#sec/divisions)*(#divisions). For instance, T= (20microsec/div)*(6.5div) = 1.3*10-4 s.
Results
DATA SHEET #1
3RD thought experiment #1
Figure 4 a) shape of the waveform in 3RD thought experiment #1
3RD thought experiment #2
Figure 4 b) shape of the waveform in 3RD thought experiment #2
3RD thought experiment #3
Figure 4 c) shape of the waveform in 3RD thought experiment #3
DATA SHEET #2
Square wave: measurement using oscilloscope.
The figure 5: below shows the square waveform displayed on the oscilloscope
Figure 5: Square Waveform on the oscilloscope display.
Custom wave: measurement using oscilloscope.
The figure 6: below shows the custom waveform displayed on the oscilloscope
Figure 6: Custom Waveform on the oscilloscope display.
DATA SHEET #3
Part 1: spectrum display for sine wave:
When the given amplitude of the sine wave is reduced by half, the peak on the spectrum as well reduces by half. When the spectrum analysis graph indicates a peak at 500 kHz, the frequency of the sine wave is also 500 kHz.
Part 2: spectrum display for custom wave:
Frequency values seen on the spectrum display from customWaveform1.
Frequency values seen on the spectrum display from customWaveform2.
Comments:
The signals on the spectrum display in customWaveform1 and customwaveform2 are the same.
The two signals on the oscilloscope display are not the same.
The actual shape of the wave information is not included in the spectrum display.
Part 3: Comparing the audio files of custom waveforms
There was no difference between customWaveform1Song.wav and customWaveform2Song.wav. No sound difference was noted. Neither the ear nor the brain could differentiate the two audio files.
DATA SHEET #4
Questions and answers
The amplitude adjustments and vertical controls from channels A and B affect the vertical size of the waveform. The amplitude control changes the amplitude of the waveform whereas vertical control zooms the waveform.
Frequency adjustments and Timebase controls alter the horizontal axis of the waveform. Frequency adjustments alter the wave whereas the Timebase controls the zoom.
The number of the waveforms, the name, and the color are aspects that are only controlled by the function generator. The oscilloscope only displays the final wave, the other properties of the signal are controlled by the generator.
Discussions
The digital oscilloscope on the other part provided the means for making an observation of the periodic waveforms of the signals produced by the generator. From the display, the horizontal axis represented the time variable, and the vertical axis represented the voltage. The rate of sweep and scale factor were selected directly. Taking data from the oscilloscope (amplitude, frequency, and peak-to-peak voltage values) involved directly reading the values displayed on the oscilloscope monitor.
The objective of learning the operation of an oscilloscope begun by knowing the basics of pressing the RUN/STOP button to start and discontinue an analysis as the words suggest, adjusting the signal vertically and horizontally on the display, as well as storing the waveforms on a floppy disc. In both devices, controls are combined in the front panel as knobs and buttons. Knobs are used to control a continuous property of the signal whereas the buttons involve a distinct property of the signal.
Conclusion
Modern physics and engineering labs employ the use of function generator and oscilloscopes to synthesize and read the different types of waveforms. Digital oscilloscopes have a broad range of advantages compared with the analog ones. We got to learn the working of these gadgets and their precision was highly appreciated. From this experiment, it would be much honest to say that the exercise was successful.
Work Cited
Loyd, David H. Physics Laboratory Manual. Boston: Brooks/Cole, 2013. Print.
Loyd, David H. Physics Laboratory Manual. Belmont, CA: Thomson Brooks/Cole, 2008. Print.
