Compute true root mean square (RMS) value of signal
Simscape / Electrical / Specialized Power Systems / Sensors and Measurements
The RMS block computes the true root mean square (RMS) value of the input signal. The true RMS value of the input signal is calculated over a running average window of one cycle of the specified fundamental frequency:
where f(t) is the input signal and T is 1/(fundamental frequency).
As this block uses a running average window, one cycle of simulation must complete before the output gives the correct value. For the first cycle of simulation, the output is held to this specified initial RMS value.
|Sample Time||Specified in the Sample Time parameter. Continuous if Sample Time = 0.|
|Scalar Expansion||Yes, of the parameters.|
Port_1 — Input signal
scalar | vector
The input signal for which the block computes the RMS value, specified as a scalar or vector.
Port_1 — RMS of input signal
scalar | vector
The RMS value of the input signal, returned as a scalar or vector.
True RMS value — Compute true or fundamental RMS value
on (default) |
Select this check box to have the block compute the true RMS value of the input signal.
Clear this check box to have the block compute the fundamental value of the input signal divided by sqrt(2).
Fundamental frequency (Hz) — Fundamental frequency
60 (default) | positive scalar
Specify the fundamental frequency, in hertz, of the input signal.
Initial RMS value — Initial RMS value
120 (default) | nonnegative scalar
Specify the initial RMS value of the output signal.
Sample time — Sample time of block
0 (default) | nonnegative scalar
Specify the sample time of the block, in seconds. Set to
0 to implement a continuous block.
shows two applications of the RMS Measurement block. One
RMS block calculates the true RMS value of a signal with harmonics,
and another RMS calculates the RMS value of the same signal at the
The model sample time is parameterized by the Ts variable set to a default value of
50e-6 s. Set Ts to
0 in the command window to
simulate the model in continuous mode.