Introduction to CATHODE-RAY OSCILLOSCOPE/ (CRO)

What do you know about cathode-ray oscilloscope ?

Ans: As we know that, we can say,The cathode-ray oscilloscope (CRO) is a common instrument for laboratory and industrial.its provide measurements of accurate time and amplitude voltage signals over a wide range of frequencies and troubleshooting ,falt detection in industries.
It suitable as a general purpose laboratory instrument.
cathode-ray tube is also called The main part as we can say it a heart of the CRO.

the beam of electrons which are emitted by the heated cathode (negative electrode) . The assembly of the cathode, intensity grid, focus grid, and accelerating anode (positive electrode) is called an electron gun.

the purpose is to generate the electron beam and control its intensity and focus between the electron gun and the fluorescent screen are two pair of metal plates - one oriented to provide horizontal deflection of the beam and one pair oriented ot give vertical deflection to the beam. These plates are referred to as the horizontal and vertical deflection plates. The combination of these two deflections allows the beam to reach any portion of the fluorescent screen. the when electron beam hits the screen, the phosphor is excited and light is emitted from that point. This conversion of electron energy into light allows us to write with points or lines of light on an otherwise darkened screen.

In the most common use of the oscilloscope the signal to be studied is first amplified and then applied to the vertical (deflection) plates to deflect the beam vertically and at the same time a voltage that increases linearly with time is applied to the horizontal (deflection) plates thus causing the beam to be deflected horizontally at a uniform ,The signal applied to the vertical plates is displayed on the screen as a function of time. The horizontal axis serves as a uniform time scale.

The linear deflection or sweep of the beam horizontally is accomplished by use of a sweep generator that is incorporated in the oscilloscope circuitry.

The voltage output of such a sweep generator is that of a saw tooth wave

CRO Operation:

A part of the signal in the vertical amplifier is applied to the sweep trigger as a triggering signal. The sweep trigger it generates a pulse coincident with a selected point in the cycle of the triggering signal. This pulse turns on the sweep generator, initiating in the saw tooth wave form. The saw tooth wave is amplified by the horizontal amplifier and applied to the horizontal deflection plates.

The signal to be displayed is amplified by the vertical amplifier and applied to the vertical deflection plates of the CRT.

Usually, additional provisions signal are made for applying an external triggering signal or utilizing the 60 Hz line for triggering. Also the sweep generator may be bypassed and an external signal applied directly to the horizontal amplifier.