CRT OSCILLOSCOPE
VACUUM-TUBE PHYSICS · LIVE SIMULATION
front view
drag to orbit · pinch / ⌘-scroll to zoom
Sawtooth sweep on the H-plates draws the time axis; your signal drives the V-plates. ≈ 4.0 cycles per sweep.
fy : fx
How a CRT oscilloscope works
- Thermionic emission. A filament heats the cathode to ~1000 °C until electrons literally boil off its surface — the orange glow at the back of the tube.
- Control grid. A slightly negative cylinder around the cathode meters how many electrons escape. More negative → fewer electrons → dimmer trace. That's the Intensity knob.
- Electron gun. Anodes at ~+2 kV accelerate the electrons to roughly 10% of light speed (watch the particles speed up), while the focus anode acts as an electrostatic lens squeezing them into a fine spot — the Focus knob.
- Vertical deflection. The input signal is applied to plate pair ④. The electric field between them bends the beam; inside the plates the path is a parabola, after them a straight line. Deflection on screen is exactly proportional to the instantaneous voltage — which is why the trace is a faithful graph.
- Horizontal sweep. A sawtooth voltage drags the spot left→right at constant speed (the time axis), then snaps back during a blanked "flyback". Trigger sync waits for the signal's rising zero-cross before each sweep, so every pass overlays the last → a rock-steady picture. Turn it off and watch the trace drift.
- Phosphor screen. Where electrons strike, the phosphor coating converts their kinetic energy to green light, and its persistence keeps the trace glowing briefly — the fading comet tail you see.
Why the whole beam bends at once: an electron crosses the tube in ~10 nanoseconds — millions of times faster than the signal changes — so the visible beam is effectively a snapshot of "now".
Try: X–Y mode for Lissajous figures (set 2:3 and slide the phase) · defocus the lens · turn intensity to zero · switch trigger off · crank persistence down.
Try: X–Y mode for Lissajous figures (set 2:3 and slide the phase) · defocus the lens · turn intensity to zero · switch trigger off · crank persistence down.
Adjust the signals · drag to orbit · ⌘/Ctrl + scroll to zoom