Analysis with an Oscilloscope

The oscilloscope is an invaluable diagnostic instrument that can be used to troubleshoot problem circuits, verify product design before delivery to consumers, and reverse-engineer products for “hacks”.

We will explore the various uses of an oscilloscope using the Tektronix MDO3104 that was provided by Tektronix. Part 1 will show the versatility of the current generation of oscilloscopes.

Getting a Scope

When preparing articles, we typically provide a link to purchase the parts required from various vendors. Due to the high cost of the machine used in this article, it seemed prudent to find an option for readers to acquire a machine in some other manner. If you cannot afford to purchase a new oscilloscope, you can rent, rent-to-own, lease, finance, or purchase used machines from companies such as Microlease.

A Note Before We Begin

All examples in this article are based on the Tektronix MDO3104 oscilloscope.

While preparing this article I contacted several test instrument makers —Rigol and BK Precision also offered to make test instruments available for this article and I would like to thank all companies for their generosity. They are all world-class instruments.

This article is not intended to be a how-to guide to the Tektronix MDO3104. It is meant to show you the various capabilities and functions of most mid-range oscilloscopes through the use of the Tektronix MDO3104 as an example.

I will show the steps needed to use the machine I have—it is left to the reader to see the documentation on their specific scope for specific key-presses and menu-options. I use bold to indicate physical manipulation of the scope through knob-turn or button-press, and quotation marks to indicate a menu choice.

Oscilloscope Displays

Oscilloscopes allow us to determine relationships between certain variables in electrical circuits. Early oscilloscopes were only able to show the relationship that exists between potential difference and time. Today’s oscilloscopes continue the tradition of measuring voltage vs. time while also providing an extensive collection of sophisticated data-analysis capabilities, display features, and triggering options.

To understand what electrical relationships exist in your circuits, you have to know how to interpret what is presented to you.

This is a typical single waveform display in an oscilloscope, showing the time on the horizontal axis and potential difference on the vertical axis.

In the lower left part of the image, you will see  ① 500mV

That indicates two things:

  • Channel 1 is displayed on the oscilloscope in yellow.
  • For channel one each grid rectangle corresponds to 500 mV in the vertical direction. So we have “500 millivolts per division” with 8 vertical rectangle visible, and thus

    visible in the vertical direction

In the bottom left, you will see another box that says AFG Sine 100.00kHz 1.0000 Vpp:

  • AFG Indicates the Arbitrary Function Generator is active (I used it to create this waveform)
  • Sine is the shape of the waveform
  • 100.000 kHz is the frequency of the waveform: 100,000 cycles each second.
  • 1.0000 Vpp is the amplitude of the transmitted waveform.

In the bottom-center there is another box with:

  4.00 µs                      5.00 GS/s      ① ∫       
  T →▼0.000000 s     1M points      0.00V
  • 4.00 µs is the value of each rectangle in the horizontal direction:  “4 microseconds per division.”  The display includes 10 rectangles, so
    4.00μs1 division×10divisions=40 μs4.00μs1 division×10divisions=40 μs

    of time is visible across the entire screen.

  • The oscilloscope is recording 5.00 GS/s, i.e.,

    samples per second.

  • Channel 1 is used to control the triggering of the waveform.
  • Triggering occurs on the rising edge of the channel 1 waveform.
  • The image is centered at T →▼0.000000 s from the trigger point.
  • 1 million (1 M) data points will be collected.
  • Triggering occurs when a rising signal passes through 0 V.

How to Make Basic Measurements with an Oscilloscope

To illustrate just how far these oscilloscopes have come over the past few decades, I will begin by showing you how many different ways the oscilloscope can be used to make basic measurements of frequency (or period) and peak-to-peak amplitude.

Activate the Arbitrary Function Generator

Begin by connecting oscilloscope channel 1 to the Arbitrary Function Generator (AFG) BNC connector on the back of the scope.  Activate the Arbitrary Function Generator by pressing the AFG button directly above the Channel 1 probe input.  Press the first bottom menu button below “Waveform” and use rotary knob Multipurpose a to select “Ramp.”

Turn on Channel 1

Press the Channel 1 button to activate it.  Rotate the Horizontal Scale knob clockwise to adjust the scale to spread out a complete wave over most of the screen.  Use the Horizontal Position knob to adjust its location on the screen if you like.

Using the Graticule to Make Measurements

The lines on an oscilloscope display are called a graticule.  There are major and minor gridlines (or dots) that are used to measure waveforms.  Major gridlines are displayed as solid or dotted lines that run the width or height of the oscilloscope screen.  The voltage and time that correspond to the divisions formed by the major gridlines are shown at the bottom of the display.  Minor gridlines are subdivisions between major gridlines.  There are usually 4 or 5 subdivisions between gridlines.  In the following example, I used theHorizontal Position rotary dial to move the waveform so that the positive peaks of the waveform line up with major vertical gridlines.