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True RMS isn't the same as "True RMS"

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True RMS isn't the same as "True RMS"

Postby ChristianScherer » Tue Mar 20, 2012 5:59 am

Hello Everybody

I have a BIG BIG problem to meassure some currents. I think the Picscope-Software has a bug in the True-RMS meassurements! When i export the waves and i calculate the RMS in excel, i have different results.
See attached files.
Is it possible to edit the meassurings in the Software?
Has anybody a usefull tip or idea?

Kind regards

Christian
Attachments
DC.zip
(173.72 KiB) Downloaded 157 times
MF-Upslope.zip
(225.03 KiB) Downloaded 160 times
Test1-Edited.psdata
(31.1 KiB) Downloaded 149 times
MF 10kA Upslope 125 Edited.psdata
(16.24 KiB) Downloaded 146 times
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Re: True RMS isn't the same as "True RMS"

Postby Martyn » Tue Mar 27, 2012 12:57 pm

We are currently looking at the Picoscope 6 measurements as there may be a few inaccuracies with these.
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Re: True RMS isn't the same as "True RMS"

Postby ChristianScherer » Tue Apr 03, 2012 8:50 am

is there any timebase to give me a solution for this problem?
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Re: True RMS isn't the same as "True RMS"

Postby Martyn » Tue Apr 03, 2012 12:38 pm

I have no time frame for this at present,I am waiting on a response from the development team
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Re: True RMS isn't the same as "True RMS"

Postby ChristianScherer » Mon May 14, 2012 8:40 am

Martyn wrote:I have no time frame for this at present,I am waiting on a response from the development team


Any new informations?
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Re: True RMS isn't the same as "True RMS"

Postby Martyn » Thu May 17, 2012 6:40 am

Not at present, although it is being raised by the support team on a regular basis
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Re: True RMS isn't the same as "True RMS"

Postby Martyn » Thu May 24, 2012 8:48 am

Sorry for the delay in this but I now have a response from the team


RMS and TRUE RMS both require an integer number of cycles to perform the measurement. Each time the waveform rises past, falls and rises back to the median value is a considered cycle.

With that in mind consider channel A of the psdata file:

The PicoScope rulers are set at 0.4-116.7ms. The nearest integer number of cycles to this is 9.99-110.0ms. Using excel this gives us 196.587 (cells B1231:B5320) which is pretty close to PicoScope 196.6.

You have chosen cells B782:B5622 (-0.984-117.4ms) which gives the wrong result.

Even if we were to use PicoScope ruler values of 0.4-116.7ms (cells B839:B5596) we get 195.0 which is still a lot closer than the customers result.


Hope this clears things up
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