- Double Beam Oscilloscope Definition: A double beam oscilloscope uses two electron beams to display signals on a single screen simultaneously.
- Construction: It has two separate vertical channels with individual attenuators and pre-amplifiers for each beam.
- Time Base Circuits: These oscilloscopes can have common or independent time base circuits, allowing different sweep rates.
- Split Beam Method: In this method, a single electron gun is used, but the beam is split into two, resulting in reduced brightness.
- Dual Beam vs. Dual Trace: Dual beam oscilloscopes use two electron guns, while dual trace oscilloscopes split a single beam, affecting their ability to capture fast events and their brightness.
A dual beam oscilloscope is an analogue cathode-ray-tube instrument that forms two electron beams and displays both traces on one phosphor screen. Separate vertical systems can control the two beams, while the horizontal sweep may be shared or independent. This specialised CRT and its supporting circuits are more complex than a conventional single-beam design.
A double beam oscilloscope is therefore different from an analogue dual-trace oscilloscope, which switches two input channels into one vertical deflection path and uses one electron beam. Modern digital oscilloscopes instead sample each input channel and render the acquired waveform data on a display. They do not split an electron beam into channels.
Construction of Double Beam Oscilloscope
Each input has its own attenuator and vertical preamplifier. The amplified signals drive separate vertical-deflection systems, so the position and amplitude of one trace can be adjusted without routing its signal through the other channel.
Some designs use one time base and a common horizontal-deflection system for both beams. Others provide separate time bases or horizontal systems so the traces can use different sweep rates. The exact arrangement depends on the CRT and instrument architecture.
A dual beam oscilloscope can use two electron-gun assemblies within one cathode-ray tube. Each beam has its own intensity, focus and vertical-deflection controls. A shared horizontal sweep moves both beams across the same screen in the common-time-base arrangement shown.
Another historical construction uses one electron source with electrodes that divide the beam into two paths. A splitter plate isolates the two vertical-deflection regions, while later accelerating and horizontal-deflection elements can be common. Dividing the available beam current reduces the intensity available to each trace. A two-gun CRT avoids that particular trade-off but requires more internal electrodes and control circuitry.
Difference between Dual Beam and Dual Trace Oscilloscope
A dual-beam oscilloscope has two physical beam paths and separate vertical-deflection channels. A dual-trace analogue oscilloscope has two input channels but channel-switching logic feeds their signals to one vertical output amplifier and one CRT beam.
A dual-trace CRO normally uses alternate mode at faster sweep rates or chopped mode at slower sweep rates. Because the display is time-shared, two unrelated one-shot events are not acquired independently in the way two true beams can display them.
Trace brightness depends on beam current, sweep speed, repetition rate and the selected display mode. Two traces using widely different sweep rates can therefore appear unequal in either architecture.
A dual-trace display is not inherently half as bright as a dual-beam display. Its visible intensity depends on how much display time each channel receives and how often the waveform repeats.
