Oscilloscope basics

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.

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Oscilloscope exterior

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