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MSOX/DSOX 3000 high-resolution mode

Question asked by jason_s on Jul 22, 2014
Latest reply on Jul 23, 2014 by algoss

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Hi-res mode is my most important feature of an oscilloscope; I've been using it for years on Agilent and Tek scopes. I work with motors and it gives me a way to see the average voltage of PWM waveforms.

I have a MSOX3034A oscilloscope and I went to look at some 20kHz PWM waveforms (50us PWM period) today. I found, to my chagrin, that in order to get averaging over multiple PWM periods, I need to go to really long timescales. Here are the kSa/s readings I get on my scope:

- 1s/div (10s/sweep): 25kSa/s
- 500ms/div ( 5s/sweep): 50kSa/s
- 200ms/div ( 2s/sweep): 125kSa/s
- 100ms/div ( 1s/sweep): 250kSa/s

This tells me that in high-resolution mode, the scope uses an acquisition of 250K samples post-processed from the high-resolution averaging.

*Is there any way to reduce this number, so that for a given post-processing sample rate I can get a faster sweep rate?* I cannot find one. (Please tell me there is.)

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jason_s Jul 22, 2014 10:11 AM

In addition, it looks like if you press Stop to retain acquired data, and you zoom in on the timescale, the effective acquisition rate changes (the raw samples are the same, but the filter used for display changes with the time per division).

>:(

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jason_s Jul 22, 2014 10:49 AM

We also have a MSOX2014A which is not as "bad" and appears to use 25K samples in high-resolution averaging. It also maintains the waveform shape (+ effective acquisition rate) when you zoom in on the timescale. But there doesn't appear to be a way to adjust it.

- 1s/div (10s/sweep): 2.5kSa/s
- 500ms/div ( 5s/sweep): 5kSa/s
- 200ms/div ( 2s/sweep): 12.5kSa/s
- 100ms/div ( 1s/sweep): 25.0kSa/s

I really only need about 1000 samples displayed. The Tek scopes I've used and earlier Agilent scopes (e.g. 54624A) just appeared to combine samples for each screen display point. I wish that behavior were an option with the newer scopes. :(

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algoss

@ jason_s on Jul 23, 2014 4:26 AM

While you may have used "High-resolution" mode in the past to accomplish this task, it was never really the 'right' way to do it. Hi-Res mode is not intended as a filter, although it generally acts as one. It is intended to provide more bits of resolution for constant signals, and it does that quite well. The algorithm is optimized for that purpose, and the implementation is built into an ASIC. In the past, the algorithm was quite different, and while it suited your purposes, it did not accomplish its stated function.

There are other scopes with more capability, including the ability to embed your own algorithm (User-Defined Function) in the processing and display path. You might want to look into one of those.

Al

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jason_s Jul 22, 2014 10:11 AM
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In addition, it looks like if you press Stop to retain acquired data, and you zoom in on the timescale, the effective acquisition rate changes (the raw samples are the same, but the filter used for display changes with the time per division).

>:(
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jason_s Jul 22, 2014 10:49 AM
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We also have a MSOX2014A which is not as "bad" and appears to use 25K samples in high-resolution averaging. It also maintains the waveform shape (+ effective acquisition rate) when you zoom in on the timescale. But there doesn't appear to be a way to adjust it.

- 1s/div (10s/sweep): 2.5kSa/s
- 500ms/div ( 5s/sweep): 5kSa/s
- 200ms/div ( 2s/sweep): 12.5kSa/s
- 100ms/div ( 1s/sweep): 25.0kSa/s

I really only need about 1000 samples displayed. The Tek scopes I've used and earlier Agilent scopes (e.g. 54624A) just appeared to combine samples for each screen display point. I wish that behavior were an option with the newer scopes. :(
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- algoss @ jason_s on Jul 23, 2014 4:26 AM
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  While you may have used "High-resolution" mode in the past to accomplish this task, it was never really the 'right' way to do it. Hi-Res mode is not intended as a filter, although it generally acts as one. It is intended to provide more bits of resolution for constant signals, and it does that quite well. The algorithm is optimized for that purpose, and the implementation is built into an ASIC. In the past, the algorithm was quite different, and while it suited your purposes, it did not accomplish its stated function.
  
  There are other scopes with more capability, including the ability to embed your own algorithm (User-Defined Function) in the processing and display path. You might want to look into one of those.
  
  Al
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MSOX/DSOX 3000 high-resolution mode

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