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Oscilloscope Mistakes, Part 3

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Steve.Picotest
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Re: When to use averaging
Steve.Picotest   9/26/2013 1:59:49 PM
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This is a great question, though not a particularly simple one.  Some applications that would seem obvious to use averaging can be problematic, for example looking at the switch node in a power supply or a step load would seem like a suitable time to use averaging, but in many cases this isn't so. Another example is the step load of a POL, which often has large signal effects, so each cycle can be different than the one before or after it.  The switch node often has jitter in switching frequency and/or pulse width as well as amplitude modulation.  These artifacts would all be averaged distorting the the result or failing to let you see them. 

 

One time that you would want to use averaging  is to isolate a signal that is mixed with other signals.  Say you want to isolate the switching ripple from load induced noise (such as a step load).  If the scope is triggered on the switching frequency averaging will keep the switching ripple result and average out all other signals so long as the other signals are not synchronized to the switching frequency.

One way to tell if averaging is resaonable is to switch on persistance mode.  If the resulting waveform envelope is very small averaging is probably ok, but if the envelope is significant don't use averaging. 

If there is any doubt, skip the averaging.

The impact of averaging on the measurement can be substantial and a picture is worth a thousand words, so maybe I will do a blog on the subject. to appear after part 4 of this one.

 

Thanks for the great question.

 

Steve

 

Steve.Picotest
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Re: When to use averaging
Steve.Picotest   9/26/2013 1:59:46 PM
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This is a great question, though not a particularly simple one.  Some applications that would seem obvious to use averaging can be problematic, for example looking at the switch node in a power supply or a step load would seem like a suitable time to use averaging, but in many cases this isn't so. Another example is the step load of a POL, which often has large signal effects, so each cycle can be different than the one before or after it.  The switch node often has jitter in switching frequency and/or pulse width as well as amplitude modulation.  These artifacts would all be averaged distorting the the result or failing to let you see them. 

 

One time that you would want to use averaging  is to isolate a signal that is mixed with other signals.  Say you want to isolate the switching ripple from load induced noise (such as a step load).  If the scope is triggered on the switching frequency averaging will keep the switching ripple result and average out all other signals so long as the other signals are not synchronized to the switching frequency.

One way to tell if averaging is resaonable is to switch on persistance mode.  If the resulting waveform envelope is very small averaging is probably ok, but if the envelope is significant don't use averaging. 

If there is any doubt, skip the averaging.

The impact of averaging on the measurement can be substantial and a picture is worth a thousand words, so maybe I will do a blog on the subject. to appear after part 4 of this one.

 

Thanks for the great question.

 

Steve

 

MeasurementBlues
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When to use averaging
MeasurementBlues   9/26/2013 8:01:00 AM
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>The averaging function is useful in cases where the measurement is very consistent and the noise you wish to eliminate is not time correlated with the measurement.

Steve, can you give an example of when to use avaraging?

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