EMI receiver capability?

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Joined: Sun Mar 01, 2009 10:11 pm

EMI receiver capability?

Post by rjm » Mon Aug 07, 2017 1:29 pm

I found the picoscopes (e.g 220x range > 50 MHz) quite suitable for doing precompliance line noise measurements with peak mode and even quite accurately show average measurements using average mode of FFT-display.

However, the software does not provide the capability to display limit curves, e.g. EN 55022 or 55015 (up to now, I use cursors as a limited aid). But in order to improve readability, a dBµV-scale as an extra option would be very helpful!

Further, averaging runs infinite and not as average over e.g. the past second. It would be desirable to have an extra option in the FFT parameter menu. Then one can tweak EMI-performance in real time (e.g. see noise source screening effects immediately while moving a screen around).

Since the Picoscope FFT runs with a high update rate, even a good approximation of a quasi-peak display seems possible.

I'd appreciate any comments about this.

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Joined: Mon Aug 11, 2014 11:14 am

Re: EMI receiver capability?

Post by Gerry » Thu Aug 10, 2017 5:07 pm

Hi rjm,

You can create a 'Mask' for limit testing, and have the data saved to a file if the mask is broken using 'Alarms'. Using masks is pretty straightforward and is described here: https://www.picotech.com/library/oscill ... it-testing. Using Alarms is described below and to save a file when a mask is broken you just need to select 'Mask Fail' as your Alarm 'Event', and then 'Save current Buffer', followed by 'Restart Capture' for your Alarm 'Actions'.

Regarding scaling, if you select the drop down list for 'Logarithmic Unit' in the 'FFT Options', you will find 'Arbitrary dB' at the bottom of the list. This opens a window below allowing you to define the reference voltage for the dB scale, to create any dB..V scale. So, for instance, going from a dBV scale (which is with reference to 1V) to a dbμV scale, if you just type in 1μV as the reference you will see 120dB added to the values of dB's displayed in the Scale for the Spectrum plot (which is obviously correct for a factor or 1,000,000).

Regarding averaging, you can't 'hold the last x buffers of data only' as a running average, but you can automatically wipe the last x buffers and then recapture the next x buffers for continual cyclic averaging over x buffers, or just capture x buffers of data for averaging then stop, and capture the next x buffers manually when ready.
You can do this by setting the number of buffers used for capture in the 'Waveform Buffer' section of the tab opened when you go to the 'Preferences' Menu. For one second intervals you will have to determine the relevant number of buffers that need to be collected for a period of one second, which will depend upon what settings you have for Data Capture and Spectrum Display (the easiest way is to just experiment and time your multi-buffer collection).
Then, if you want to collect buffers of data for an average of plots, and then stop until your next collection, you can go to the 'Alarms' option under the 'Tools' Menu, select 'Buffers Full' in the 'Event' drop down list, and tick the checkbox for it. Then select 'Add' on the right, and select 'Stop Capture' in the 'Action' drop down list, and then, after that has been added, select 'Apply' and 'OK' to close the 'Alarms' window.
If you want to cycle automatically between clearing and collecting buffers of data for new averages (say, every second) then after adding 'Stop Capture' in the 'Action' drop down list, of 'Alarms', you can select 'Add' again to select 'Restart Capture' in the drop down list, and then 'Apply' the actions and exit 'Alarms'.


Technical Specialist

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