resolution enhancement

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Dook000
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resolution enhancement

Post by Dook000 » Mon Nov 26, 2018 5:13 pm

I have just taken delivery of a 2406B unit. I want to use the resolution enhancement described on page 25 of the training manual but the drop down box doesn't contain the option. Any suggestions?
Regards,
Duncan

Martyn
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Re: resolution enhancement

Post by Martyn » Mon Dec 03, 2018 8:04 am

This feature should be in the software, can you go to Help->About and post the text from the box so we can see what versions you have.
Martyn
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Dook000
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Re: resolution enhancement

Post by Dook000 » Mon Dec 03, 2018 8:49 pm

PicoScope® 6 - PC Oscilloscope software version: 6.13.6.3775
Copyright © 1995-2018, Pico Technology Ltd.

Model: Demo
Serial Number: Demo
Driver Version: 6.13.6.3775

The problem seems to appear only when a spectrum is displayed. I can get resolution enhancement when only a scope display is present.

Gerry
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Re: resolution enhancement

Post by Gerry » Tue Dec 04, 2018 4:05 pm

Hi Duncan,


When using our PicoScope 6 software in Scope Mode, Resolution Enhancement replaces a number of time domain samples with a single time averaged sample that is equivalent to the average value of the many samples it is replacing. This is done using a filter that sweeps across the collected samples (i.e. a moving average filter), and has the added effect of smoothing out the signal variation, i.e. reducing the noise. As the noise masks some of the lower level signals that you might want to measure, reducing it is actually revealing more of the resolution that you already have.

To put it another way, if you start out with 8-bit resolution, the noise level may be reducing that to an effective resolution of, say, 6-bits. Adding 4-bits of Resolution Enhancement may then remove, say, 1.5 bits of noise, and gain you 4 extra bits of resolution, changing your original effective vertical resolution of 6-bits to a new effective vertical resolution of 11.5 bits. To do this though you would lose some horizontal resolution.

In Spectrum Mode, because the level variation of the higher harmonic content of a signal is so small in comparison to the lower harmonic content, most displays are plotted using a logarithmic scale so that you can accommodate enough of the high frequency variation in level on the same plot as the low frequency variation in level. Because of this averaging levels would have to be done before plotting the the decibel values, which would then mean that you wouldn't be able to change the number of bins used for the plot without first converting from log to linear and then un-averaging the values, or using a more complex transform function.

So, the Waveform Averaging of Resolution Enhancement wouldn't work in the same way in a Spectrum Mode plot as it does in a Scope Mode plot. In any case, there is a better way to achieve an even better effect in Scope Mode and that is by modifying the number of bins used. For instance, if you double the number of bins used you are pushing the noise floor down by 3dB using an effect known as Process Gain (for an explanation, and worked example, see here: topic25101.html?&p=86081&hilit=process+gain#p86081). Once again, as the signal starts out noisy (so you are losing vertical resolution to noise) by pushing the noise floor down by 6dB you are increasing the effective vertical resolution by 1-bit. However, in Spectrum Mode, when you increase the vertical resolution by increasing the number of bins, you are also increasing the horizontal resolution (as opposed to decreasing it when using Resolution Enhancement in Scope Mode) which is why this is a better method.

So, to put this another way, if you start with 6-bit effective resolution (because of 2 bits of noise) then, even if you stick to the default number of Spectrum bins (32,768), you will have a process gain of 42dB (or 7-bits). So, by default, you would start out with an effective resolution of 13-bits, and you can then increase the number of bins to see more vertical detail and more horizontal detail. The practical limit of how much vertical resolution you can have then becomes one of 3 factors, i.e.:
1/ The limit of the distortion level of the hardware PicoScope (if you get too close to this you won't have enough certainty that the signal values you are measuring are not distortion values).
2/ The limit of signal stability (if the signal levels you are trying to measure are so low in value that they keep jumping around in level, then the average level will be the absolute minimum that you can measure with enough certainty).
3/ The time to convert a Spectrum Plot (if the number of bins are high, and the bandwidth is small, then it may take an unacceptably long time to do one conversion, and a ridiculously long time to average values over many conversions). This time is known as the 'Time Gate' (which you can see if you enable the 'Properties View' Pane by going to the 'View' Menu and selecting 'View Properties').

Regards,

Gerry
Gerry
Technical Specialist

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