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CATHODE RAY OSCILLOSCOPE CRO

It is generally referred to as oscilloscope or scope and is the basic tool of an electronic engineer and technician as voltmeter; ammeter and watt meter are those of an electrical engineer or electrician. The CRO provides a two-dimensional visual display of the signal wave shape on a screen thereby allowing an electronic engineer to ‘see’ the signal in various parts of the circuit.

It, in effect, gives the electronic engineer an eye to ‘see’ what is happening inside the circuit itself. It is only by ‘seeing’ the signal wave forms that he/she can correct errors, understand mistakes in the circuit design and thus make suitable adjustments.


An oscilloscope can display and also measure many electrical quantities like ac/dc voltage, time, phase relationships, frequency and a wide range of waveform characteristics like rise-time, fall-time and overshoot etc. Non-electrical quantities like pressure, strain, temperature and acceleration etc. can also be measured by using different transducers to first convert them into an equivalent voltage.

figure 1
As seen from the block diagram of an oscilloscope (Figure 1), it consists of the following major sub-systems:

1. Cathode Ray Tube (CRT): it displays the quantity being measured.
2. VERTICAL AMPLIFIER: it amplifies the signal waveform to be viewed.
3. HORIZONTAL AMPLIFIER: it is fed with a saw-tooth voltage which is then applied to the X-plates.
4. SWEEP GENERATOR: produces saw-tooth voltage waveform used for horizontal deflection of the electron beam.
5. TRIGGER CIRCUIT: produces trigger pulses to start horizontal sweep.
6. High and low-voltage power supply.

The operating controls of a basic oscilloscope are shown in Figure 2.  The different terminals provide.

1. Horizontal amplifier input,
2. Vertical amplifier input,
3. Sync. input,
4. Z-axis input,
5. External sweep input.

As seen, different controls permit adjustment of

1. INTENSITY: for correct brightness of the trace on the screen,
2. FOCUS: for sharp focus of the trace.
3. HORIZONTAL CENTERING: for moving the pattern right and left on the screen.
4. VERTICAL CENTERING: for moving the pattern up and down on the screen.
5. HORIZONTAL GAIN (also Time/div or Time/cm): for adjusting pattern width.
6. VERTICAL GAIN (also volt/div or volt/cm): for adjusting pattern height.
7. SWEEP FREQUENCY: for selecting number of cycles in the pattern.
8. SYNC. VOLTAGE AMPLITUDE: for locking the pattern.

The different switches permit selection of:

1. Sweep type,
2. Sweep range,
3. Sync. type

Figure 2

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