# Documentation

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# Total Harmonic Distortion

Measure total harmonic distortion (THD) of signal

## Library

powerlib_extras/Measurements

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

 Note:   The Measurements section of the Control and Measurements library contains the THD block. This is an improved version of the Total Harmonic Distortion block. The new block features a mechanism that eliminates duplicate continuous and discrete versions of the same block by basing the block configuration on the simulation mode. If your legacy models contain the Total Harmonic Distortion block, they continue to work. However, for best performance, use the THD block in your new models.

## Description

The Total Harmonic Distortion block measures the total harmonic distortion (THD) of a periodic distorted signal. The signal can be a measured voltage or current.

The THD is defined as the root mean square (RMS) value of the total harmonics of the signal, divided by the RMS value of its fundamental signal. For example, for currents, the THD is defined as

total harmonic distortion (THD) = IH/IF,

where

`${I}_{H}=\sqrt{{I}_{2}^{2}+{I}_{3}^{2}+\dots +{I}_{n}^{2}},$`

where

In = RMS value of the harmonic n
IF = RMS value of the fundamental current.

The THD has a null value for a pure sinusoidal voltage or current.

## Parameters

Fundamental frequency

The frequency, in hertz, of the fundamental signal.

## Inputs and Outputs

`signal`

Connect this input to the voltage or current you want to measure the total harmonic distortion.

`THD`

The output returns the THD of the input signal.