[Scilab-users] calculate TRMS value in Xcos

[Michael J McCann]

RMS Value:
In a dynamic system simulation you can readily generate an instantaneous 
power value that can be recorded  simply by using a volts*current 
product or any other dimensionally equivalent product.
If however you want to do some averaging of the power level then you 
must have a record of that instantaneous  value and do the averaging 
over the length of the record,  which your request implies you have and 
therefore implies a post processing operation. You can partition the 
record into whatever shorter lengths you want and generate true RMS 
values over those time segments. But beware, if the model is  simulating 
a fixed frequency  (e.g.50Hz) power system then the periods must be 
integer multiples of the cycle time.

If you want a value that appears like a metered  value might appear then 
you can put the product term through a 1st order lag (exponentially 
weighted effect)
   G(s)=1/(1+sT)       // xdot=(1/T)*(Input- x);
and imitate the behaviour of a meter. All you have to do is chose the 
"time constant",T, of the meter. e.g several cycles.

The MATLAB (2017a)  Moving RMS includes the exponential weighting option 
and the true moving window version as well. I expect it could be 
replicated in XCOS with a SciLab function.

Mike.
==================

On 19/05/2017 05:51, Sachverständigenbüro Niedermaier Holger wrote:
> Dear all,
> by simulating an electrical power circuit I’d like to plot the voltage and the current over time, which is easy to perform by using the scope block.
> In addition to the signal recorded I’d like to calculate the TRMS value of the plotted current and voltage signal.
> Unfortunately Xcos does not include a TRMS block like e.g. Simulink do.
> Because I’m so far not so familiar with Xcos and Scilab I’d like to ask the community for support.
> Does anybody have a good idea or advise how to get the TRMS value of the recorded signal?
> Thanks and nice weekend
> Holger
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-- 
Dr.M.J.McCann,MJMcCann-Consulting

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