The cathode-ray oscilloscope (CRO) provides accurate time and amplitude measurements of voltage signals having wide range of frequencies. CRO is the most suitable laboratory instrument. The cathode-ray tube is the heart of the CRO.
Above Figure shows the cathode ray tube of CRO. The cathode ray beam of electrons emitted by the heating the cathode and moved towards the fluorescent screen. The setup of cathode, intensity grid, focus grid, and accelerating anode is known as electron gun. Its 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 thus referred to as the horizontal and vertical deflection plates. In oscilloscope the signal is first amplified and applied to the vertical plate to deflect the beam vertically and at the same time a voltage that increases linearly with time is applied to the horizontal plate. Hence the signal applied to verical plate is displayed on screen as a function of time.