Cathode Ray Oscilloscope (CRO): Working and Applications

Cathode Ray Oscilloscope:

The Cathode Ray Oscilloscope (CRO) is an equipment that displays, measures, and analyzes different waveforms of electrical circuits. A cathode ray oscilloscope is a high-speed X-Y plotter (a plotter that operates on two axes of motion) that may display an input signal vs time or another signal.


Cathode ray oscilloscopes work with light points that are produced by striking the electron beam. This light point moves in response to the variation of the input quantity. Why are we using only one electron beam? The reason for this is the low effect of the electron beam which can be used to track changes in the instantaneous values ​​of the rapidly changing input quantity. The general forms of cathode ray oscilloscopes operate on voltages.

How to measure


It’s simple to measure voltages using an oscilloscope; all you have to do is count the number of vertical divisions the signal takes up on the screen. By adjusting the signal with the horizontal positioning knob we can use the subdivisions of the grid to make a more precise measurement. (Remember that a subdivision is generally equivalent to 1/5 of what a complete division represents). It is important that the signal occupies the maximum space on the screen for reliable measurements.

Time and Frequency:

The horizontal scale of the oscilloscope is used to perform time measurements. This includes the measurement of periods, pulse width, and pulse rise and fall times. Frequency is an indirect measure and is made by calculating the inverse of the period. As with voltages, the time measurement will be more accurate if the time to object of measurement occupies most of the screen, for this we will act on the time base switch. If we center the signal using the vertical positioning knob we can use the subdivisions to make a more precise measurement.

Measurement of rise and fall times of the pulses:

The standard measurements in a pulse are its width and the rise and fall times. The rise time of a pulse is the transition from low level to high voltage level. Normally the time is measured between the moment the pulse reaches 10% of the total voltage until it reaches 90%. This eliminates irregularities at the edges of the impulse. This explains the markings seen on some scopes (sometimes just dotted lines).


CRO applications are mainly involved in radio, TV receivers, also in laboratory work involving research and design. In modern electronics, the CRO plays an important role in electronic circuits.

Differences between dual trace and dual beam

Dual Trace:

1. A single beam is used to produce two different waveforms.

2. You cannot capture two fast transient events.

3. Loss of signal in case of double trace CRO about 50% of each signal.

4. Two modes of operation in this CRO, alternate and cut.

Dual Beam:

1. Two separate electron beams are used to produce different waveforms.

2. It can capture two fast transient events as it can display two signals simultaneously.

3. There is no loss during dual-beam viewing.

4. Two modes of operation under this CRO, double gun tube and split beam.

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