Oscilloscopes

An oscilloscope is used as a fault diagnostic instrument for electronic devices. It has a display unit with a moving dot (trace) that gives a representation of the voltage versus time for an electronic device. An oscilloscope creates a visible two-dimensional graph of one or more electrical potential differences. The horizontal axis of the display typically represents time, which makes the instrument useful for displaying periodic signals. The vertical axis usually shows voltage.

A typical oscilloscope is shaped like a rectangular box which has a small screen with several input connectors, control knobs and buttons on the front panel. To aid in the measurement, a grid called the graticule is drawn on the face of the screen. Each square in the graticule is known as a division. In its most basic mode, an oscilloscope repeatedly draws a horizontal line, which is called the trace, across the middle of the screen from left to right.

The oscilloscope’s time base control sets the speed at which the line is drawn, and calibrates it in seconds per division. If the input voltage originates from zero, the trace is deflected either upwards or downwards. The machine’s vertical control sets the scale of the vertical deflection and is calibrated in volts per division. The trace that is produced is a graph of voltage against time.

If the input signal is periodic, then a nearly stable trace can be produced just by setting the time base to match the frequency of the input signal. For example, if the input signal is a 50 Hz sine wave, then its period is 20 ms, so the time base should be changed so that the time between successive horizontal sweeps is 20 ms. This mode is called continual sweep. However, an oscilloscope's time base is not usually accurate, and the frequency of the input signal isn’t perfectly stable, so the trace will often drift across the screen making measurements difficult to read.

The basic types of oscilloscopes are:

  • Cathode ray oscilloscopes with a CRT display.
  • Analog storage type, where the trace does not quickly decay, but is retained on the screen for some time.
  • Digital storage type, which stores the wave formations in digital format.
  • PC based oscilloscope which has an analog-to-digital converter attached to a PC.

You need to consider the following while selecting an oscilloscope such as: bandwidth (the range of frequencies that are met), the communication channels hosted, like: serial port, parallel port, SCSI, Ethernet, modem, RAM available, hard disk capacity, nonvolatile memory required, number of input channels, attachments like data logger/ chart recorder/ strip chart, sweep range, input voltage/current and operating temperature.

Oscilloscopes can be either handheld or bench mounted devices.

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