What is an Oscilloscope: basics & fundamentals

The oscilloscope is one of the most useful test instruments used for electronics development, manufacture, test, service, and repair.

Oscilloscope Tutorial Includes:
Oscilloscope basics     Oscilloscope types     Specifications     How to use an oscilloscope     Scope triggering     Oscilloscope probes     Oscilloscope probe specifications    

Scope types includes:     Analogue scope     Analogue storage scope     Digital phosphor scope     Digital scope     USB / PC scope     Mixed Signal Oscilloscope MSO    

Oscilloscopes, or scopes are an important tool in the armoury of the electronics engineer or tester. An oscilloscope enables waveforms to be seen and in this way makes it very much easier to see any problems occurring in an electronics circuit.

In view of the advantages which they posses, oscilloscopes are an essential tool for any electronics laboratory or area testing electronics hardware.

The name oscilloscope, comes from the fact that it enables oscillations to be viewed. Sometimes the name cathode-ray oscilloscope, or CRO is used. The reason for this is that cathode ray tubes (CRT) used to be used to enable the waveforms to be displayed.

Nowadays, LCDs, or plasma displays are used as they are smaller, and more convenient to use, especially as the do not require the very high voltages of the old CRTs.

Function of an oscilloscope

The function of an oscilloscope is to be able to display waveforms on some form of display. In the normal mode of operation time is displayed along the X-axis (horizontal axis) and amplitude is displayed along the Y axis (vertical axis). In this way it is possible to see an electronic waveform on an oscilloscope as it may be envisaged. The waveform could be likened to that of the ripples on travelling along the surface of a pond when a stone is dropped into it.

By seeing a waveform in this manner it is possible to see analyse the operation of the circuit and discover why any problems may exist.

Concept of an oscilloscope screen
Basic oscilloscope screen

Key oscilloscope topics

When looking at oscilloscope there are several key topics and areas of interest:

  • Types of oscilloscope:   There are several different types of oscilloscope from analogue to digital and more. The first types of oscilloscope were analogue, but wit the advances in digital technology, most oscilloscopes these days are processor controlled and use digital signal processing to provide excellent displays of the waveforms.

    Not only are there oscilloscopes contained in standard bench style boxes, but some scopes are designed to link to computers, using their display and processing to assist. Often they are connected via USB links but other types are also available.
    Read more about . . . . Oscilloscope types.

  • Scope specifications:   The specifications for oscilloscopes can sometimes be confusing. A basic understanding of the terms and what they mean is very useful. Understanding the basic oscilloscope specifications can provide an understanding of the limitations of any given scope and also help in the selection when one needs to be hired, bought or even booked out of a common store.

    The scope specifications are slightly different between the analogue and digital scopes. Although basic concepts like accuracy, time base range, upper frequencies and the like are essentially the same, digital scopes also have specifications to items like the number of DAC bits, memory depth and the like that are specific to digital oscilloscopes.
    Read more about . . . . Oscilloscope specifications.

  • How to use an oscilloscope:   Although oscilloscopes are easy to use these days, it helps to have an understanding of how to use them. There are very many controls on the front panel, and these days there are even soft keys on the screen, so there is a lot that can be done with all of these controls.

    Normally the most widely used controls are easily available and are quite easy to use. Today’s digital scopes have a lot of functionality built in that makes them very easy to use.
    Read more about . . . . How to Use an Oscilloscope.

  • Oscilloscope triggering:   The trigger function is one of the most important functions on an oscilloscope. The scope trigger enables the timebase to start at the same point on each cycle of the waveform and this enables to be displayed so it appears still on the screen.

    The oscilloscope trigger function has developed considerably since most scopes moved to use digital technology. The digital signal processing available enables the trigger to provide more flexibility and greater functionality so that signals can be investigated more closely to discover problems and issues.
    Read more about . . . . Oscilloscope Triggering.

  • Oscilloscope probes:   Any oscilloscope will need probes to attach to the unit under test. These probes are key to many measurements.
    Read more about . . . . Scope Probes.

A typical oscilloscope as used in an electronics laboratory
A typical oscilloscope

Development of the oscilloscope

The oscilloscope was developed over many years. It took a large number of new discoveries and inventions for it to arrive at the level of sophistication we see today.

The history of the oscilloscope dates back over 100 years, each step the result of innovation, inspiration and hard work.

Key stages in the Development & History of the Oscilloscope
Date Discovery / Development
1897 Karl Ferdinand Braun invented the first Cathode Ray Tube, CRT. It could display crude figures on the screen controlled by voltages on the plates of the tube.
1899 Jonathan Zenneck improved the basic cathode ray tube by incorporating beam-forming plates and using a magnetic field for sweeping the trace.
1931 V. K. Zworykin improved the cathode ray tube when he detailed a permanently sealed, high-vacuum cathode ray tube with a thermionic emitter. This enabled General Radio to manufacture an oscilloscope that was usable outside a laboratory setting.
Late 1930s The British company A C Cossor invented a dual beam oscilloscope which was widely used during WW2 for servicing electronics equipment and in particular the radar systems.
1946 The triggered sweep oscilloscope was invented by Howard Vollum and Jack Murdock. This made the oscilloscope much easier to use as waveforms were able to be displayed in a steady manner.
1946 Tektronix was founded by Howard Vollum and Jack Murdock.
1963 Tektronix introduced the Direct View Bistable Storage Tube (DVBST). This allowed single pulse waveforms to be displayed rather than just repeating waveforms.
  The Digital Storage Oscilloscope, DSO was invented by Walter LeCroy after producing high-speed digitizers for the research centre CERN in Switzerland. Walter LeCroy later founded the LeCroy Corporation.

Oscilloscope exterior

An oscilloscope will normally have a large array of items on the exterior of the case.

A typical oscilloscope as used in an electronics laboratory
A high performance oscilloscope

The front panel will typically have a number of items on it:

  1. Display   The first things that is noticed on an oscilloscope is the large display that is used for displaying the waveform. This typically may take around a quarter of the space on the front panel or even a little more. It is often good to have a reasonably large display then it is easier to see the various elements of the waveform.
  2. Connectors   There is a variety of different connectors on the front panel. Typically there is an input for each of the channels to be displayed - often an oscilloscope will have more than one channel. Many oscilloscopes are dual channel and can therefore display two signals at the same time, allowing waveforms to be compared. Other inputs may include a trigger input that will enable the trace on the oscilloscope to be triggered according to this signal.
  3. Controls   There is a variety of controls on the oscilloscope:
    • Vertical gain / signal input sensitivity: This is generally calibrated in V/cm, i.e. each vertical division on the scale represents a given number of volts.
    • Timebase: This alters the speed at which the trace crosses the screen horizontally on the oscilloscope. It is calibrated in terms of time / division, e.g. 1ms / cm, assuming the divisions are at one centimetre intervals.
    • Trigger: The controls that are associated with the trigger enable the timebase of the oscilloscope to be triggered in various ways. This enables a still or stable picture to be obtained on the screen of the oscilloscope.

In order to be able to operate the oscilloscope correctly it is necessary to connect the right signals into the inputs, and also to use the controls correctly.

Oscilloscopes are one of the more widely used test instruments. They provide a high level of insight into the operation of a circuit and they are key to finding many issues and resolving them, whether in development, production test, service, repair or even field service.

More Test Topics:
Analogue Multimeter     Digital Multimeter     Oscilloscope     Signal generators     Spectrum analyzer     Frequency counter     LCR meter / bridge     Dip meter, GDO     Logic analyzer     Power meter (RF & microwave)     RF signal generator     Logic probe     Time domain reflectometer, TDR     LabVIEW     PXI     GPIB / IEEE 488     Boundary scan / JTAG    
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