oscilloscope modes chop,alternate,add

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Joined Oct 13, 2006
oscilloscope modes terms and skills:

"Add" -the signals of both channels are added before they are displayed on the screen. The sum

"Chop" mode the oscilloscope either draws the signal off the first or the second channel alternating on each sweep of the electronic beam the channel does not alternate during a sweep but during the (invisible) reset of the beam.

Alternate and Chop Display
On analog scopes, multiple channels are displayed using either an alternate or chop mode. (Digital oscilloscopes do not normally use chop or alternate mode.)
Alternate mode draws each channel alternately - the oscilloscope completes one sweep on channel 1, then one sweep on channel 2, a second sweep on channel 1, and so on. Use this mode with medium- to high-speed signals, when the sec/div scale is set to 0.5 ms or faster.
Chop mode causes the oscilloscope to draw small parts of each signal by switching back and forth between them. The switching rate is too fast for you to notice, so the waveform looks whole. You typically use this mode with slow signals requiring sweep speeds of 1 ms per division or less. Figure 3 shows the difference between the two modes. It is often useful to view the signal both ways, to make sure you have the best view.

Channel Invert
Most oscilloscopes have an invert function that allows you to display a signal "upside-down." That is, with low voltage at the top of the screen and high voltage at the bottom.

Math Operations
Your oscilloscope may also have operations to allow you to add waveforms together, creating a new waveform display. Analog oscilloscopes combine the signals while digital oscilloscopes mathematically create new waveforms. Subtracting waveforms is another math operation. Subtraction with analog oscilloscopes is possible by using the channel invert function on one signal and then use the add operation. Digital oscilloscopes typically have a subtraction operation available. a third waveform created by adding two different signals together.

The CHOP mode is therefore better for
slow sweeps because it draws both traces together, although it cannot switch quickly enough to

use ALT mode unless the display is slow enough to
be irritating, and then switch to CHOP. The third setting, "ADD", algebraically adds the input of channel 1 and 2. We will not have much use for this feature.

Alternate Mode – A display mode of operation in which the oscilloscope
completes tracing one channel before beginning to trace another channel.
Chop Mode – A display mode of operation in which small time segments
of each channel are traced sequentially so that more than one waveform
can appear on the screen simultaneously.

On most analog oscilloscope there is chop,Alt,dual,Add,subtract modes i haven't really used them much what can i use theses modes for please some examples?
would help me out alot to know the oscilloscope more thanks


Joined Apr 26, 2005
When synchronizing two signals of the same frequency, inverting a channel and adding, your sum would be zero. I used this many times. It's alot easier to see the signals reduce to zero then to maximum.

Alternate or chop ... you described that pretty well. I used alternate to verify that signal b started x time after signal a. I don't recall using chop very often because of it's limitations [chopping rate].

I'm sure if there weren't enough demand for those functions, they wouldn't be standard on oscilloscopes.

The delay function is useful in finding the time one signal is delayed by another. I've used that alot in the past when looking at signals.

All of those functions were used in maintaining Loran [LOng Range Aid to Navigation] timing and transmitter equipments.

I didn't use those functions as much when maintaining analog communications systems from the 70s and 80s.