# 5 Using Cathode Ray Oscilloscope

### Using CRO

Function
1. Power switch To switch on and off of the oscilloscope
2. Focus controlTo control the focus of the spot on the screen.
3. Intensity controlTo control the brightness of the spot on the screen.
4. X-offset
5. Y-offset
Y-offset moves the whole trace vertically up and down on the screen, while X-offset moves the whole trace from side to side on the screen.
6. Timebase control

Whenever we switch on the time-base, we are actually applying a sawtooth voltage to the X-plates (Figure below).

* This makes the electron beam sweep across the screen at a constant speed.
* By knowing the period of each cycle, T, we can then know how fast the beam is sweeping across the screen. The time-base is thus a measure of time for the oscilloscope.

7. Y gain control* the “Volts/Div.” wheels amplify an input signal so that for a division a given voltage level is invalid. A “division” is a segment, a square on the screen of the oscilloscope.
* A setting of “.5” i.e. means, that the height of a single square equals a voltage of 0.5 V. An amplitude of 1 V would have a size of two divisions vertical to the abscissa.
8. d.c./a.c. switchd.c. – d.c. and a.c. voltage displayed.
a.c. – only a.c. voltage displayed.
9. X-input and Y-inputElectric input connects to the X-plate and Y-plate.

Example
The table below shows the sample display of direct current and alternating current when the time base is switched ON and OFF.

Direct Current (Time Base Switched Off) Direct Current (Time Base Switched On)
Alternating Current (Time Base Switched Off) Alternating Current (Time Base Switched On)