Lab 1: Oscilloscope Fundamental (Tones)

PHYS 471, Spring 2023

We begin by looking at several of the most common pieces of lab equipment. The goal of this lab is to become not just acquainted with them, but to really become an expert user of oscilloscopes, function generators and DMMs. These tools will be used all semester so its worth spending some time getting to know them now, rather than during the physics experiments.

This lab consists of 3 Exercises and 1 Experiment

The Function Generator

The Function Generator

This is the Function Generator. It is used to generate wave forms of specific frequencies and amplitudes. For example, if you needed a sinusoidally varying voltage, you would use this instrument to generate that. The frequency and amplitude can be selected from the front panel options. It will output the voltage on the BNC Connector plug on the front.

Exercise 1:

  1. Make sure nothing is connected to the front panel. Turn on the function generator. Press the SHIFT + DEFAULT button to return the unit to the normal default operating mode. This will set it to generating a 10 kHz sine function.

  2. Make sure the amplitude knob is all the way to the lowest setting. Connect the speaker to the Waveform Output plug using the BNC adaptor on the bench. Adjust the AMPL knob until you can hear the tone.

  3. Use the front panel keys to enter a frequency of 440 Hz.

  4. Try pressing the WAVE button to change the output to square and triangle waves. Notice the difference in how these waves sounds.

  5. Use the knob to change the frequency of the output. Familiarize yourself with the left and right arrow buttons to change the position of the cursor on the display.

  6. Can you hear the difference between 440 and 441 Hertz?

  7. You can turn down the output amplitude now and let's take a look at the oscilloscope.

Oscilloscope

A two channel oscilloscope

Here is a basic digital oscilloscope. These are among the most important pieces of lab equipment. At the most basic level, they are used to quickly look at an electronic signal but can also be used in the acquisition of data.

Exercise 2:

In this exercise we will use the oscilloscope to look at the signal from the function generator.

  1. Turn on the oscilloscope. It will take a few seconds to warm up and turn on. Leave the language interface set to English.

  2. Connect the Waveform Output of the function generator to the CH 1 input on the oscilloscope using a short BNC cable.

    connect Function Generator to Oscilloscope

  3. Set the Function Generator to output a 440 Hz sine function.

  4. At this point, you might see a signal on the oscilloscope screen. But, you will likely need to play with the knobs and settings a bit to make it good.

    Vertical and Horizontal Knobs

  5. Here is the desired screen you should try to obtain. It shows the 440 Hz sine function with a Peak to Peak amplitude of 1 V.

    440 Hz signal

  6. Press the MEASURE button. Now you can use the two cursor lines to measure features of the incoming signal.

    Time and Voltage Measurements

  7. Adjust the settings of the function generator to change the wave form. Try to different frequencies (over several orders of magnitude) and use the oscilloscope knobs to make sure you can display the signals nicely.

Exercise 3: Get a spectrum

Math FFT

  1. Use the MATH MENU button to tell the oscilloscope to start doing some math. We will do a Fast Fourier Transform (FFT) of our signal. (Reset the FG to create a 440 Hz sine function.)

    FFT settings

  2. Use the operation button to select FFT. There are other options like, Ch1-Ch2, which can be used to find the different between two signals, but we won't use those at the moment.

  3. Experiment with the FFT settings until you can see a screen similar to one shown in the image above, with a peak that clearly identifies the 440 Hz signal.

  4. FFT settings

    Setting the FFT Cursor

    Use the cursor function to identify the peak. You might want to try adjusting the FFT zoom setting and using the Horizontal position knob to center in on the peak.

  5. If you did the same operation with a triangle wave, you should be able to detect more peaks in the signal. The spacing of the peaks will match the fourier series for a triangle wave. (Simulated here: Triangle Wave additive → )

    FFT settings

Experiment 1: Obtain the Spectrum from a Tuning Fork

The experiment will seek to obtain the spectrum from a tuning fork. We'll build a simple circuit that has a microphone and hook the microphone up to the oscilloscope.

    electric microphone circuit

    A circuit to build!

  1. Using the parts and breadboard available, build the circuit shown here and connect it to CH1 input of the oscilloscope.

  2. Start the tuning fork oscillating: Hold it by the wooden handle and give it a quick tap with the mallet. (Do not just whack it against the table). Bring it close to the microphone and you should be able to see the waveform on the screen of the oscilloscope if you have things set up correctly.

  3. Use the FFT function of the oscilloscope to generate a spectrum of the recorded audio.

  4. You might want to investigate the ACQUIRE menu and then use the SINGLE SEQ function to record a average of say, 8 or 16 samples.

  5. Save your data as a csv (raw data) and eps (just an image format) to the Compact Flash card. (There is manual on the bench that you consult about the steps needed to save a file. Give it a look!)

  6. Retrieve your data from the Compact Flash card using the card reader and another computer.

    7. electric microphone circuit

    FFT data output.

  7. Your FFT output data should stored in a csv with some settings and parameters in the first few columns, then two large columns showing the frequency and level of the Spectrum.

  8. Prepare a plot showing your FFT from one of the metal tuning forks. Here is an example Colab document to help you get started. Example FFT Plot →

  9. When you are done, make sure to put everything back, and please erase/format the Compact Flash card using the Utility button on the oscilloscope.

    10. Example:

Report to submit:

Please type up a short 1-2 page report that shows your FFT plot of the spectrum of the tuning fork.

You will need to make your own plot of the data obtained from the oscilloscope. (i.e. export it as shown above and replot the data using a scientific computing application, i.e. Python/Colab)

Look up an equation for the analytical expectation of the resonance frequency of a tuning fork. Assume the one the desk is made of steel (but you might not know what kind of steel it is.) Make a theoretical estimate of the resonance frequency of the fork based on the physical parameters. Yes, you will need to measure the geometry of the fork.

Include:

  1. Brief Introduction
  2. Visual schematic of the experiment
  3. Plot of the FFT
  4. Comparison to theoretical prediction
  5. Links to your data online
  6. Links to your analysis code online
  7. References in proper format for any external sources you used.