RMS

Compute true root mean square (RMS) value of signal

• 

Libraries:
Simscape / Electrical / Specialized Power Systems / Sensors and Measurements

Description

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:

$$RMS(f(t))=\sqrt{\frac{1}{T}{\displaystyle \underset{t-T}{\overset{t}{\int }}f{\left(t\right)}^{2}dt}},$$

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.

Characteristics

Sample Time	Specified in the Sample Time parameter. Continuous if Sample Time = 0.
Scalar Expansion	Yes, of the parameters.
Dimensionalized	Yes.

Ports

Input

Port_1 — Input signal

scalar | vector

The input signal for which the block computes the RMS value, specified as a scalar or vector.

Output

Port_1 — RMS of input signal

scalar | vector

The RMS value of the input signal, returned as a scalar or vector.

Parameters

True RMS value — Compute true or fundamental RMS value

on (default) | off

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.

Examples

The power_RMS_THD example 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 fundamental frequency.

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.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Version History

Introduced in R2013a