Diagram:
Explanation: The single beam dual trace CRO consists of one electron gun, an electronic switch which switches the two signals to a single vertical amplifier and a single pair of horizontal deflection plates, as compared to a dual beam CRO. The block diagram of a Dual Trace CRO is shown in fig. It consists of a single electron gun, whose electron beam is split into two by an electronic switch. There is one control for focus and another for intensity. The two signals are displayed simultaneously. The signals pass through identical vertical channels or vertical amplifiers. Each channel has its own calibrated input attenuator and positioning control so that the amplitude of each signal can be independently adjusted. As shown in fig., two channels A and B are used. Signals from A and B are applied through a pre-amplifier and attenuator, which brings the signal within an acceptable level for amplification. It is then passed through a delay line, to delay the signal to the vertical section so that the sweep or the horizontal section can start well in advance. The output from both channels A and B are applied to an electronic switch, which operates in two modes, alternate and chop mode. In the alternate mode, signals from the two channels are applied alternately to the VDP and in the chop mode, small segments of the signal from the two channels are applied alternately to a single pair of VDPs. The dual trace CRO operates in two modes, the alternate and the chop mode. A mode control switch on the front panel enables the electronic switch to operate in two modes. When the switch is in the ALTERNATE position, the electronic switch feeds each signal alternately to the vertical amplifier. The electronic switch alternately connects the main vertical amplifier to channels A and B and at same time adds a different DC component to each signal. This DC component directs the beam alternately to the upper or lower half of the screen. When the switch is in the CHOP mode position, the electronic switch is free and running at the rate of 100- 500 KHz, entirely independent of the frequency of the Sweep Generator. The switch successively connects small segments of A and B waveforms to the main vertical amplifier at a relatively fast chopping rate of 500 KHz. In the X-Y mode of operation, the Sweep Generator is disconnected and channel B is connected to the Horizontal Amplifier. Since both pre-Amplifier are identical & have the same delay time, accurate X-Y measurements can be taken.