This example shows how to find the root mean
square (RMS) value of a sine wave, a square wave, and a rectangular
pulse train using
rms. The waveforms in this
example are discrete-time versions of their continuous-time counterparts.
Create a sine wave with a frequency of π/4 radians/sample. The length of the sine wave is 16 samples, which equals two periods of the sine wave.
n = 0:15; x = cos(pi/4*n);
Compute the RMS value of the sine wave.
rmsval = rms(x)
The RMS value is equal to 0.7071 as expected.
Create a periodic square wave with a period of 0.1 seconds. The square wave values oscillate between –2 and 2
t = 0:0.01:1; x = 2*square(2*pi*10*t); stem(t,x,'markerfacecolor',[0 0 1]); axis([0 1 -2.5 2.5]);
Find the RMS value.
rmsval = rms(x)
The RMS value agrees with the theoretical value of 2.
Create a rectangular pulse train sampled at 1 kHz with
the following parameters: the pulse is on, or equal to 1, for 0.025
seconds and off, or equal to 0, for 0.075 seconds in each 0.1 second
interval. This means the pulse period is 0.1 seconds and the pulse
is on for 1/4 of that interval. This is referred to as the duty
pulstran to create the
rectangular pulse train.
t = 0:0.001:(10*0.1); pulsewidth = 0.025; pulseperiods = [0:10]*0.1; x = pulstran(t,pulseperiods,@rectpuls,pulsewidth); plot(t,x); axis([0 1 -0.5 1.5]); xlabel('Seconds'); ylabel('Amplitude');
Find the RMS value and compare it to the RMS of a continuous-time rectangular pulse waveform with duty cycle 1/4 and peak amplitude 1.
rmsval = rms(x) thrms = sqrt(1/4)
The observed RMS value and the RMS value for a continuous-time rectangular pulse waveform are in good agreement.