CRO block diagram and working

The cathode-ray oscilloscope (CRO) displays a time-varying voltage as a waveform on a screen: voltage on the Y-axis and time on the X-axis.

Block diagram

                  +----------+   +-----------+
 Input signal --->| Attenuator|->| Vertical  |---> Y-plates
                  +----------+   | amplifier |       |
                       |         +-----------+     [CRT]
                  +----v-----+   +-----------+       |
                  | Trigger  |-->| Time-base |---> X-plates
                  | circuit  |   | generator |   (Horizontal
                  +----------+   +-----------+    amplifier)
        Power supply (HV for CRT, LV for circuits)

Working

1. The input signal passes through an attenuator and the vertical amplifier, which raises it to a level high enough to deflect the electron beam; it is then applied to the vertical (Y) deflection plates.
2. The trigger circuit takes a sample of the signal (or an external trigger) and starts the sweep at the same point of each cycle, so the picture is stable.
3. The time base generator produces a sawtooth voltage. After the horizontal amplifier, it goes to the X plates and moves the beam uniformly from left to right, then quickly back.
4. In the CRT, the electron gun emits a focused beam, which strikes the phosphor screen and makes a bright spot. The vertical plates move it up and down with the signal, and the horizontal plates move it across with time. Together, the spot traces the waveform.
5. The power supply gives high voltage (kV) to the CRT and low voltages to the circuits.

Measurements: voltage (amplitude), time period T, frequency f = 1/T, and phase difference.