Cathode Ray Oscilloscope

Cathode Ray Oscilloscope Points : cathode ray oscilloscope, introductory information A wide variety of instruments are used in electronics to measure the amplitude and frequency of ac signals. The oscilloscope is one of these instruments. It not only measures amplitude and frequency but in addition, displays the shape (Wave form) of the signal. With an oscilloscope you can check waveforms that are vital to radio, television, high quality sound equipment, computers radar and a host of other devices

The principle components of the oscilloscope are a cathode—ray tube (CRT), horizontal deflection circuit, vertical deflection circuit, and high & low voltage power supplies.

The principle components of the oscilloscope are a cathode—ray tube (CRT), horizontal deflection circuit, vertical deflection circuit, and high & low voltage power supplies.

Basically, the CRT contains an electron gun and sets of horizontal and vertical deflection plates. The electron gun produces and focuses an electron beam on a phosphorescent coating on the inside face of the tube. This causes a visible spot to appear on the face of the tube when viewed from the front. When Voltages are supplied to the deflection plates from the horizontal and vertical deflection circuits, the electron beam, and this is the spot. is made to move by the combined effect of the deflection voltages. The trace appears as a visible pattern on the screen.

The CRT screen is usually covered by a transparent overlay, called a graticule which has a grid pattern graduated in centimeters. Each centimeter represents one division. The two axes (X and Y) of the graticule are used with the horizontal and vertical deflection Circuits to measure time and amplitude directly from the displayed wave form.

The horizontal deflection circuit supplies voltages to the horizontal deflection plates which causes the election beam to move or sweep across the face of the CRT. The circuit includes a calibrated sweep control for adjusting the number of sweeps per second so that time and frequency measurements can be made.

The vertical deflection circuit is the circuit to which the signal to be measured is generally applied. It supplies a voltage to the vertical deflection plates of’ the CRT which causes the trace to move up & down.

A calibrated vertical gain control allows the vertical deflection to be measured. High & low voltage power supplies provide operating voltages for the CRT and the oscilloscope circuits.

Oscilloscopes can be classified as free—running or triggered, with single, dual or multiple — trace capabilities. In the free — running oscilloscope, display stability is achieved by synchronization, whereby a separate signal, usually taken from the vertical deflection circuit, is applied to the horizontal sweep circuit to Cause it to sweep in time with the vertical signal. In the triggered oscilloscope, the horizontal sweep circuits produce a sweep only when triggered. This is usually accomplished by a signal from the vertical deflection circuit, or from an external source related to the signal to be observed which, when applied to the sweep circuit, produces a sweep that coincides with the vertical input signal. Both types of oscilloscope can be used to display waveforms, but the triggered oscilloscope is easier to use since it has a stable display and allows time and frequency measurements to be made.