Please take a minute to review and accept our Terms of Use.
Welcome to the PLECS User Forum, where you can ask questions and receive answers from other members of the community.

Many technical questions regarding PLECS are answered on the Technical Solutions page of our website. Tutorial videos, specific application examples, and pre-recorded webinars are available on our YouTube page. Please follow us on LinkedIn for the latest Plexim news.

RMS Function , how i can set the parameters?

+1 vote
46 views
the RMS function of a pure sine wave must be like a strait line >>> and when you get the di/dt for the RMS it must be = zero ...

but when i am useing the RMS block funtion the program ask about (sampling time , Number of sample) and i dont know what is the reight parameter must be set to get the right output ... So any one please help me and explain if i have something wrong .
asked Mar 26 by Ahmed Raafat (20 points)

1 Answer

+3 votes

The RMS value of a periodic signal is the DC (straight line) value which would transfer the same power per period.  The Nyquist-Shannon sampling theorem states that in order to properly resolve a sampled signal, the sampling rate must be at least twice the frequency of the highest frequency component you want to measure.

For a pure sine wave at 10 kHz, for example, you would need to sample at 20 kHz or greater in order to properly distinguish the waveform from a similar waveform of lower frequency (see this figure).  Since the period is the reciprocal of the frequency, you should select a sampling time and number of samples such that their product is less than or equal to 1/(2*f), where f is the frequency of your generated sine wave; in other words:

2f <= 1/(Ns*Ts)

A description of the block, including these parameters, is available in the PLECS manual, page 354, and can also be seen by right-clicking on the RMS block and selecting "Help".

answered Mar 28 by angrmgmt (43 points)
...