CRO and Cathode Ray Tube Components

A Cathode Ray Oscilloscope (CRO) is an electronic instrument used to visualize varying signal voltages as a two-dimensional plot. The main component responsible for displaying the waveform is the Cathode Ray Tube (CRT).

The CRT is a vacuum tube that generates, accelerates, and deflects an electron beam onto a fluorescent screen, creating a visible spot. The deflection of the spot is controlled by applying voltages to deflection plates.

Parts Located Inside the CRO Cathode Ray Tube

• Electron Gun: This part generates a focused beam of electrons. It typically includes a heater, cathode, grid, and focusing anodes.
• Vertical Deflection Plates: These are a pair of parallel plates oriented horizontally. An input signal voltage applied here causes the electron beam to deflect vertically, corresponding to the signal's instantaneous amplitude.
• Horizontal Deflection Plates: These are another pair of parallel plates oriented vertically. The voltage applied here causes the electron beam to deflect horizontally. In a typical CRO, a sweep voltage (often from the time base generator) is applied here to move the spot across the screen at a constant rate, creating a time axis.
• Fluorescent Screen: The inner surface of the tube's front face is coated with a phosphorescent material that emits light when struck by the electron beam, making the spot visible.

Parts Located Outside the CRO Cathode Ray Tube

While crucial for the operation of the CRO, some components are external circuits that provide the necessary signals and power to the CRT and other parts.

• Time Base Generator: This is an external electronic circuit that produces a sweep voltage, typically a saw-tooth waveform. This voltage is applied to the horizontal deflection plates to sweep the electron beam horizontally across the screen at a constant speed, creating the time axis for displaying waveforms.
• Vertical and Horizontal Amplifiers: These are external circuits that amplify the input signals before they are applied to the vertical and horizontal deflection plates, respectively.
• Power Supply: Provides the necessary high voltage for accelerating the electron beam and lower voltages for the electron gun and amplifier circuits.

Based on the common components of a CRO, the electron gun, vertical deflection plates, and horizontal deflection plates are located inside the cathode ray tube. The time base generator is an external circuit that provides the sweep signal to the horizontal deflection plates.

Therefore, the part that is not located inside the cathode ray tube of the CRO is the time base generator.