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Participant

Join Date: Oct 2009
Location: India
Posts: 4

# Phase Lags in a Loop

10/16/2009 1:58 AM

phase lags in a control loop are expressed with reference to sinusoidal signals only but in practical the signals are not of that kind then why phaselags

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Guru

Join Date: Jan 2009
Posts: 1012
#1

### Re: Phase Lags in a Loop

10/17/2009 12:19 AM

Meenakshi,

"with reference to sinusoidal signals"

Periodic waveforms are made of sine waves of different frequencies and amplitudes so the cause of phase shifting applies to each of them.

Anything that causes one or more of the frequencies to be amplified, attenuated or phase shifted changes the form of the overal waveform.

The process of decomposing a periodic function into its constituent sine or cosine waves is called Fourier analysis. You can characterize the wave in terms of the amplitudes of the constituent sine waves which make it up.

Simple geometric waves have a rich complement of harmonics.

A simple way of looking at it is:

The square wave contains only odd harmonics with the amplitudes.

The sawtooth wave is useful for synthesis since it contains all harmonics in the geometric ratio.

The triangle wave contains only odd harmonics with the amplitudes.

Jon

Participant

Join Date: Oct 2009
Location: India
Posts: 4
#2

### Re: Phase Lags in a Loop

10/17/2009 12:38 AM

Thank you sir

2
Power-User

Join Date: Dec 2008
Location: Anthem, AZ
Posts: 367
#3

### Re: Phase Lags in a Loop

10/17/2009 11:15 AM

The responses of a servo system are best described in terms of poles and zeros (it is the Laplace Transform). This is the domain used to develop a servo amp using software. Each pole has frequency, phase, damping, and magnitude. If you test it with an impulse and use the normalized cross spectrum to describe it (a Bode plot), you will see the Magnitude and Phase of each pole clearly. The damping is the relative "sharpness" of each pole.

If you display the Cross Spectrum response with the Nyquist diagram, you will see circles for each pole. The direction of each circle shows whether the pole is in phase (up)or out of phase with the forcing function.

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