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RMS - Measure root mean square (RMS) value of signal

Library

Extras/Measurements

A discrete version of this block is available in the Extras/Discrete Measurements library.

Description

This block measures the root mean square value of an instantaneous current or voltage signal connected to the input of the block. The RMS value of the input signal is calculated over a running average window of one cycle of the specified fundamental frequency.

as this block uses a running average window, one cycle of simulation has to be completed before the output gives the correct value. The discrete version of this block allows you to specify the initial magnitude of inputs. For the first cycle of simulation the output is held to the RMS value of the specified initial input.

Dialog Box and Parameters

Fundamental frequency

The fundamental frequency, in hertz, of the input signal.

Example

In the power_controlvolt demo, you can add an RMS block as shown below to measure the RMS value of the capacitor voltage. The Controlled Voltage Source block introduces a third harmonic (180 Hz) in the voltage at t = 0.4 seconds.

At the beginning of the simulation, the RMS block needs one cycle of the fundamental frequency (60Hz) to calculate the RMS value of the voltage. At t = 0.4 seconds the RMS value slightly increases because of the addition of the third harmonic in the signal. Again, the RMS block needs one cycle of the fundamental signal to stabilize and give the correct result.

PWM Generator

Saturable Transformer

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