Overview
This lecture explains the major components and functions of the cathode ray oscilloscope (CRO), focusing on the electron gun, deflecting plates, fluorescent screen, and their roles.
Main Components of Cathode Ray Oscilloscope
- The CRO consists of an electron gun, deflecting plates, and a fluorescent screen.
- The entire CRO tube is maintained as a vacuum to prevent electron collisions with air particles.
Electron Gun Structure and Functions
- The electron gun includes the heating filament, cathode, control grid, focusing anode, and accelerating anode.
- The heating filament (usually tungsten) heats the cathode to release electrons.
- The cathode emits electrons when heated by the filament.
- The control grid, connected to a negative potential, controls electron flow and thus the screen brightness.
- The focusing anode focuses the electron (cathode ray) beam into a fine spot on the screen.
- The accelerating anode increases the speed of electrons for a straight, fast beam.
Deflecting System
- The deflecting system consists of X and Y plates.
- Y plates move the electron beam up and down (vertical direction).
- X plates move the electron beam left and right (horizontal direction).
- Beam deflection occurs because electrons are negatively charged and move toward positive plates.
Fluorescent Screen and Graphite Layer
- The fluorescent screen absorbs electron energy and emits light to create a visible spot.
- A graphite layer is present on the screen to conduct electrons to the Earth, preventing charge buildup.
- Removing accumulated electrons avoids a negatively charged screen, which could repel incoming electrons.
Key Terms & Definitions
- Cathode Ray Oscilloscope (CRO) — an instrument displaying electrical signals as visual patterns.
- Electron Gun — assembly that produces and accelerates the electron beam.
- Fluorescent Screen — coated surface where electron impacts produce visible light spots.
- Control Grid — component controlling beam intensity and brightness.
- Focusing Anode — narrows and focuses the electron beam.
- Accelerating Anode — increases electron velocity.
- Deflecting Plates (X, Y) — plates that steer the electron beam horizontally (X) and vertically (Y).
- Graphite Layer — conductive layer directing excess electrons to the Earth.
Action Items / Next Steps
- Review the structure and function of each CRO component.
- Prepare for questions on the purpose of the graphite layer and deflecting plates.