Specifications

Delayed sweep

Some analog oscilloscopes come with a delayed sweep feature that allows a section of the displayed

waveform to be magnified in the horizontal direction. This lets you see waveform details while at the

same time seeing the whole waveform.

The delayed sweep is a second sawtooth generator that is started an adjustable time after the main

sweep's sawtooth starts its vertical ramp. After the adjustable delay, the delayed sweep is allowed to

control the sweep of the electron beam. As the delayed sweep is set with a sweep time faster than the

main timebase (i.e., smaller time/div setting), the remaining portion of the waveform is expanded.

Adjusting the delay (control number 12 in Figure 5) allows you to choose where to start the horizontally-

expanded display.

The B&K 2125A scope demonstrates its delayed sweep in the following screen photograph (converted

to grayscale):

Figure 12

The bunched waveform on the left was a 1 volt peak-to-peak 10 kHz triangle wave. The main timebase

was set to 1 ms/div, which meant each division held 10 periods of the wave. The expanded section was

created by setting the display mode to MIX and setting the delayed sweep to 50 µs/div. You can see

there are two horizontal divisions between the waveform's peaks in the delayed sweep portion. This

means the period of the waveform is 100 µs, which implies a frequency of 10 kHz.

Some analog oscilloscopes display a second trace for the delayed sweep rather than combine them as

the 2125A does.

Copying/reprinting/republishing without express written consent prohibited.