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Looking to make bode plots similar to SysComp's

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Looking to make bode plots similar to SysComp's

Postby Landru » Mon Nov 23, 2015 6:42 pm

Hi, I've been using the SysComp CGR-101 for about a year, and it's been semi-effective for making bode plot measurements of guitar pickups, but I'd like to try an alternative oscilloscope/waveform generator unit with different software.

This is the CGR-101's bode plot interface that I'm using now:

http://www.syscompdesign.com/assets/images/Screenshots/CGR-Screen3.jpg

I'm looking at the Pico product line, and trying to determined which is the lowest priced unit that includes software which duplicates this functionality, and if there is a higher priced unit and software, would the added cost improve accuracy or add useful features?

I found a YouTube video showing frequency analysis with a PicoScope 4262



but this appears to record peaks in an FFT breakdown rather than measure one frequency at a time and plot the amplitude of each. Is this the closest the PicoScope software comes to create a bode plot graph, or does it also have a function similar to the CGR-101's UI above?

Thanks for your help!
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Re: Looking to make bode plots similar to SysComp's

Postby Martyn » Mon Nov 23, 2015 9:50 pm

Have you looked at Hexamer's thread
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Re: Looking to make bode plots similar to SysComp's

Postby hexamer » Tue Nov 24, 2015 4:32 am

Landru wrote:I'm looking at the Pico product line, and trying to determined which is the lowest priced unit that includes software which duplicates this functionality, and if there is a higher priced unit and software, would the added cost improve accuracy or add useful features?


If you decide the FRA application would meet your needs, here are some points to consider:

1) I can confirm that it works on the PS2204A (since I own one and regularly test with it). The PS2204A is one of the lower priced oscilloscopes offered by Pico (perhaps the lowest?) - a great value in my opinion.

2) What scope you ultimately choose for FRA depends on your application. While I have not tried yet, I strongly suspect a scope like the PS2204A would struggle to do SMPS stability analysis. SMPS stability analysis is very challenging because you're looking for a very low amplitude signal buried in much higher amplitude ripple noise. For this task, you'd probably want a scope with much larger dynamic range, and much larger buffer. E.g. something like the PS5000A is ideal for dynamic range with 15 bits of precision and +/- 10mV to +/- 20V range. The buffer size will drive the low end of testable frequencies. I have been using my PS5444A for SMPS analysis and it works well - I can get it to match published Bode plots over the relevant range for several power supplies. Keep in mind for this task, you'll also need an isolation transformer.

3) If you're doing FRA work primarily in the audio band and below, almost any PicoScope will work well. For audio band work, if you want greater accuracy in higher attenuation portions of filters, a higher resolution scope like 4262 might be helpful.

4) Consistent with (3), an important scope characteristic impacting FRA capability is the signal generator range. Make sure to buy one that handles the frequency range and amplitude you need. The scope's bandwidth will naturally be designed to handle the full range of the generator.

5) Assuming you may use the scope for more than FRA, of course there are many other things to consider. Most obvious is bandwidth and sampling rate. But there are plenty of others. E.g. one reason I opted for a 4 channel scope is to be able to decode serial data streams requiring more than 2 channels. And, while I don't have one, I've always thought the MSO scopes would be really handy for combined analog and digital work.
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Re: Looking to make bode plots similar to SysComp's

Postby Landru » Tue Nov 24, 2015 8:50 pm

Thanks a lot for the info! If I can get hexamer's program working on Windows 10, I'll go ahead with the 4262.
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Re: Looking to make bode plots similar to SysComp's

Postby hexamer » Tue Nov 24, 2015 10:00 pm

Landru wrote:Thanks a lot for the info! If I can get hexamer's program working on Windows 10, I'll go ahead with the 4262.


No problem, glad to help. FYI - I've been testing the program on Windows 10 and so far I have noticed no issues.
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