What is Oscilloscope?

What is an Oscilloscope?

Oscilloscope Definition

An oscilloscope is a piece of laboratory equipment that is often used to display and study the waveform of electronic signals. In practice, the device makes a graph that shows how the instantaneous signal voltage changes over time.

A typical oscilloscope can display waveforms of direct current (DC) or alternating current (AC) with a frequency as low as about 1 hertz (Hz) or as high as several megahertz (MHz). High-end oscilloscopes can display signals with frequencies of up to several hundred gigahertz (GHz). The display is divided into what are called horizontal divisions (hor div) and vertical divisions (vert div). The time is shown on a horizontal scale from left to right. The vertical scale shows the instantaneous voltage, with positive values going up and negative values going down.

The cathode-ray oscilloscope is the oldest type of oscilloscope and is still used in some labs today. It makes an image by making a focused electron beam move across the face of a cathode ray tube in a pattern (CRT). Modern oscilloscopes mimic the CRT's action electronically by using a liquid crystal display (LCD) like the ones found on notebook computers. The most advanced oscilloscopes use computers to process waveforms and show them on the screen. All kinds of displays, like CRT, LCD, and gas plasma, can be used with these computers.

The horizontal sweep of an oscilloscope is measured in seconds per division, milliseconds per division, microseconds per division, or nanoseconds per division. Volts per division (V/div), millivolts per division (mV/div), or microvolts per division (?V/div) are used to measure vertical deflection. Almost all oscilloscopes have horizontal sweep and vertical deflection settings that can be changed.

Oscilloscope Graph

The picture shows how two common waveforms might look when shown on an oscilloscope screen. The top signal is a sine wave, and the bottom signal is a ramp wave. This graph shows that the frequencies of both signals are the same or very close to the same. They are also about the same size from peak to peak. Let's say that the horizontal sweep rate is 1 s/div in this case. Then, each of these waves goes through a full cycle every 2 s. This means that their frequencies are both about 0.5 MHz, or 500 kilohertz (kHz). If the vertical deflection is set to 0.5 mV/div, then both waves’ peak-to-peak heights are about 2 mV.

Digital devices make up most high-end oscilloscopes these days. They hook up to personal computers and use the displays on those computers. Even though these machines don't use scanning electron beams like the old cathode-ray "scope" did to make pictures of waveforms, the basic idea is the same. Software controls the sweep rate, the vertical deflection, and a lot of other features, which can include:

  • Storage of waveforms for future reference and comparison
  • Display of several waveforms simultaneously
  • Spectral analysis
  • Portability
  • Battery power option
  • Usability with all popular operating platforms
  • Zoom-in and zoom-out
  • Multi-color displays
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