Another newbie oscilloscope question, dual timebases?

[Chris Wilson]

Newbie question again, sorry. From my automotive background I have thought of a potential issue with using a dual or quad channel scope on signals of different frequencies. Let's say I want to use channel one to scope the crank position sensor output which is reading a trigger wheel with 36 less one teeth on an engine turning at 8000 RPM. that's about 4800 Hz I think?
On channel two I want to watch the output of the O2 sensor which cycles a voltage of around 0.9 to 0.1 volts about once second. Would you need a scope with two time bases to see anything worthwhile of both outputs at the same time, or am I misunderstanding it? Is that what dual timebase scopes allow, the watching of two sources of very different frequencies at the same time? Do any USB scopes allow this? Thanks.

[Lightages]

Yes you are right. There are dual trace scopes and dual channel scopes. They differ quite a bit in price.

[amspire]

This is where long memory comes in. You slow the scope down to be able to capture the slowest waveform.  Once the waveform is captured, you can zoom into the trigger wheel waveform at any point of the 0₂ sensor cycle. The bigger the capture memory, the more samples can be captured giving you more high frequency resolution.

For example, with the Rigol DS1052E, if you set the timebase to 200mS/div, and enable long capture memory, then with 2 channels, it is sampling at a bit under 5uS per sample. So that means there will still be about 40 samples per 4800Hz waveform, so that is pretty good. With long memory disabled, the scope would only be sampling at about 3KHz which is useless for the 4800 Hz waveform.

There is also delayed sweep. This is where you trigger off the O₂ sensor waveform, but the scope is set to only show, say, a 1mS window. With the delayed sweep, you can move this 1mS windows backwards and forwards in time so you can investigate both waveforms at any part of the O₂ cycle. This method doesn't need the long memory, but you can still use it. The delayed sweep will give you the best resolution, but you are only able to see one slice at a time.

Richard.

[IanB]

This is where long memory comes in. You slow the scope down to be able to capture the slowest waveform.  Once the waveform is captured, you can zoom into the trigger wheel waveform at any point of the 0₂ sensor cycle. The bigger the capture memory, the more samples can be captured giving you more high frequency resolution.

For example, with the Rigol DS1052E, if you set the timebase to 200mS/div, and enable long capture memory, then with 2 channels, it is sampling at a bit under 5uS per sample. So that means there will still be about 40 samples per 4800Hz waveform, so that is pretty good. With long memory disabled, the scope would only be sampling at about 3KHz which is useless for the 4800 Hz waveform.

There is also delayed sweep. This is where you trigger off the O₂ sensor waveform, but the scope is set to only show, say, a 1mS window. With the delayed sweep, you can move this 1mS windows backwards and forwards in time so you can investigate both waveforms at any part of the O₂ cycle. This method doesn't need the long memory, but you can still use it. The delayed sweep will give you the best resolution, but you are only able to see one slice at a time.

I've just made a post about these features in the other thread:

https://www.eevblog.com/forum/index.php?topic=6239.msg81551#msg81551

I was finding out how they work and thought that others might benefit from some pictures.