What is Cathode Ray Oscilloscope ( C.R.O ) and C.R.T ? C.R.O working and Applications of C.R.O |


A cathode-ray oscilloscope is an instrument which presents signal wave- forms visually it is also useful for comparing two signal in phase, frequency or amplitude.
A C.R.O can operate up to 50 MHz, can allow viewing of signals within a time span of a few nano seconds and can provide a number of wave form displays simultaneously on the screen. It also has the ability to hold the displays for a short or long time ( or many hours ) so that original signal may be compared with one coming on later.
                                 A block diagram of cathode ray oscilloscope is show in fig.  

Cathode Ray Tube-

A cathode ray tube is the 'Heart' of a oscilloscope and is very similar to the picture tube in a television set.
Fig.b shows the cross - sectional view of a general-purpose electrostatic C.R.T
it has the following four major components :

1. An electronic gun - 

It produces a stream of electrons.

2. Focusing and accelerating anodes-

they produce a narrow and sharply- focused beam of electron.

3. Horizontal and vertical deflecting plates -

for the path of beam.

4. An evacuated glass envelope with a phosphorescent screen -

produces a bright spot when struck by a high velocity electron beam.

  Working of a C.R.O.

When the signal is to be displayed or viewed on the screen it is applied across the Y- plates of a cathode ray tube. But to see its waveform or pattern, it is essential to spread it out horizontally from left to right . this is achieved by applying a saw tooth voltage wave to X- plates. Under these conditions, the electron beam would move uniform from left to right thereby graping vertical variations of the input signal versus time. due to repetitive tracing of the viewed waveform, we get a continuous display because of persistence of vision.
 However, to get a stable stationary display on the screen, it is essential to synchronize the horizontal sweeping of the beam ( sync. ) with the input signal across Y- plates . the signal will be properly synced only when it frequency equal the sweep generator frequency. The usual method of synchronised to the input signal. it is called internal sync because the synchronization is obtained by internal wiring connections as shown in Fig.C

Applications of C.R.O.

  • Tracking of an actual waveform of current or voltage.
  • Determination of amplitude of a variable quantity.
  • comparison or phase and frequency.
  • in televisions.
  • in radar.
  • for finding B.H. curves for hysteresis loop.
  • for engine pressure analysis.
  • for studying the heart beats, nervous reactions e.t.c.
  • for tracing transistor curves. 


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