Double Beam Oscilloscope

Multi-Input OscilloscopeOscilloscopes can have multiple input and display facilities.

The most common one is of-TWO INPUTS.

Single beam oscilloscopeDouble beam oscilloscope

There are primary two types of multi input oscilloscope

How a double beam oscilloscope looks like

The double beam analog oscilloscope can display two signals simultaneously.

A special dual beam CRT generates and deflects two beams separately.

Unlike an ordinary Dual trace oscilloscope which time shared a single electron beam, thus loosing about 50% of each signal, a dual beam oscilloscope simultaneously produced two separate electron beams capturing the entirely of both signals.

Also Dual trace oscilloscope cannot capture two fast transient events, as it cannot switch quickly enough between traces.so to avoid these problems Dual Beam Oscilloscope is used.

Dual Beam Oscilloscope

constructionThe dual beam oscilloscope has two separate electron beams and therefore two completely separate vertical channels.each channel consists of a preamplifier and attenuator.

There is single set of horizontal plates and single time base circuit.

The sweep generator drives the horizontal amplifier which in turn drives the plates.

The horizontal plates sweep both the beams across the screen at the same rate.

AttenuatorAnd

preamplifier

AttenuatorAnd

Preamplifier

Delay line

Vertical amplifier

Trigger

Vertical amplifier

Delay line

Trigger Sweep generator

Sweep generator

Horizontal amplifier

Horizontal amplifier

Vertical deflection plate

Vertical deflection plate

Horizontal deflection plate

Channel A

Channel B

External

Line

Dual Beam Oscilloscope with independent time base

Horizontal amplifier

Main vertical

amplifier

Main vertical

amplifier

Delay line

Delay line

Sweep generator

Trigger circuit

Preamplifier and

attenuator

Preamplifier and

attenuator

Signal A

Signal B

Two sets of Y-deflection plates

X deflection plates

line

Dual beam oscilloscope with common time base

SB

Exit

There are two methods of used for generating the two electron beams within the CRT.

1) Double gun tube

2) Split beam

Modes of operation:

A. Double gun tube: method allows the brightness and focus of each beam to be controlled separately but it is bulkier than a split beam.

B. Split beam : In this method a single electron gun is used.

A horizontal splitter plate is placed between the last anode and the Y deflection plate.

This plate is held at the same potential as the anode, and it goes along the length of tube,between the two vertical deflection plates which isolates the channels.

Disadvantages:

This arrangement has half the brightness of single beam.

The two display may have noticeably different brightness .

THANK YOU….