Lab 04: Function Generator and Oscilloscope
Objectives
Equipment
- Function Generator
- Digital Multimeter
- Resistors: 1M, 1K,
Background
Procedure
Exp #1: Output Resistance of the Function Generator
Connect a Digital Multimeter to the Function Generator. In the function generator, set the frequency to 1 kHz and the output voltage to 1.0 Vrms (read on the Multimeter). Then connect a fixed resistor across (i.e. in parallel with) the output of the Function Generator. Change the resistance until the output voltage is down to about one-half of its original value. Record the voltage and resistance values.
Figure 1: The Output Resistance of the Function Generator Measurement
Calculate the output resistance of the Function Generator. Compare with the specification.
Exp #2: Oscilloscope
Connect the Function Generator's main output to the Channel 1 input of the oscilloscope and to a DMM (all in parallel). Connect the Function Generator sync (synchronization) output to the Channel 2 input of the oscilloscope. On the oscilloscope set the trigger signal source on channel 2, and the trigger slope to a positive slope.
Figure 2: The Connection for Exp #2, #3, #4 and #5
- Set the Function Generator to give a sine wave output at a frequency = 1 KHz. Adjust the amplitude to give a peak-to-peak voltage of 2 V as observed on the oscilloscope. Press the Auto-Scale button on the oscilloscope for the initial settings. Then display only the sine wave on Channel 1.
- Import oscilloscope display to computer: you have to save the oscilloscope screen to the USB flash drive, and paste it in your report.
- Compare the peak-to-peak voltage as measured by counting divisions and using the voltage/DIV scale to that obtained from the oscilloscope direct voltage measurement.
- Record the RMS voltage as observed on the DMM. Compare that to the RMS voltage as measured by the oscilloscope.
- Compare the RMS voltage with the expected value based on the peak-to-peak voltage.
- Measure the period of the waveform by counting divisions and using the time/DIV scale. Find the frequency and compare to the expected value.
- Obtain the period of the waveform using the oscilloscope direct measurement. Compare to the value obtained by counting divisions and using the time/DIV scale.
- Obtain the frequency of the waveform using the oscilloscope direct measurement. Compare with the value set on the Function Generator.
Function Generator Settings - Frequency: 1KHz, Waveform: Sine Wave, VPP: 2V
- Set the Function Generator to give a square wave output at a frequency = 1 KHz with an amplitude of 2 V peak-to-peak voltage as observed on the oscilloscope. Repeat the above steps a. to g. again.
Function Generator Settings - Frequency: 1KHz, Waveform: Square wave, VPP: 2V - Set the Function Generator to give a triangle wave output at a frequency = 1 KHz with an amplitude of 2 V peak-to-peak voltage as observed on the oscilloscope. Repeat the above steps a. to g. again.
Function Generator Settings - Frequency: 1KHz, Waveform: Triangle Wave, VPP: 2V
Exp #3: DC Offset
- Same connection as the Exp#2 in Figure 2.
- Set the DMM to read DC volts. Turn on the DC OFFSET control on the Function Generator and rotate it to give a DC offset of +1 V. Measure the shift in the DC level on the oscilloscope and compare it with the value of DC voltage indicated by the DMM. Set the DMM to read AC volts. What is the change in the DMM AC voltage reading as the DC offset is changed from zero to +1 V?
- Repeat the previous procedure with a DC offset of -1 V.
- Change the input coupling switch to AC and now observe what happens.
Exp #4: Trigger Slope
- Set the Function Generator back to a SINE WAVE output. On the oscilloscope, change the Trigger slope to NEGATIVE SLOPE and observe what happens. Now change the TRIGGER SLOPE to POSITIVE SLOPE and observe the result.
Exp #5: Sweep Speed
- Change the sweep speed control (TlME/DlV) to 0.5 ms/DIV. Measure the period and compare with the previous result.
- Repeat the previous procedure for sweep speeds (TIME/DIV) of 1.0 ms/DIV, 2.0 ms/DIV, and 0.1 ms/DIV.
- Set sweep speed to 0.1 ms/DIV. Measure the period for the following frequencies and compare with the expected values: 2 KHz, 4 KHz, and 10 KHz.
Questions
- What value of output resistance would the "ideal" Function Generator have? Explain.
- A Function Generator is adjusted to give a no-load (open-circuit) voltage of 1.0 V. When a 1 KΩ load is placed across the output terminals of the Function Generator the output voltage drops to 0.8 V. Find the output resistance of the Function Generator.
- Voltage Ratio in decibels \((dB) = 20{\log _{10}}\left( {\frac{{{V_1}}}{{{V_2}}}} \right)\)
- Express the following ratios in decibels (dB):
- V1 / V2 = 100
- V1 / V2 = 0.1
- Change these dB values to voltage ratios:
- -10 dB
- 3 dB
- Express the following ratios in decibels (dB):
- A Function Generator has a specification that the variation in the output voltage with frequency will remain flat to within ±1 dB over the frequency range of 10 Hz to 100 kHz. Find the corresponding maximum percentage variation in the output voltage over this frequency range.