Phase of the Frequency Response Function - FRF - Vibration

• Dec 12, 2019

• #2

GregLocock

Automotive

Apr 10, 2001

23,891

Orbiting a small yellow star

It might be correct, nobody can tell from a screenshot. The phase is just telling you the amount of sin and cos in each frequency line. Usually I would not look at the phase from a single channel, it's the phase difference between 2 channels that is important.

It is 'noisy' around 20 hz because there's no signal there.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

Upvote 0 Downvote

• Dec 12, 2019

• #3

Strong

Mechanical

Jul 20, 2003

854

US

I assume you are doing two channel measurements with accelerometer and hammer/shaker with load cell. Your Phase plot look Okay, since you are only interested in Phase at Natural Frequencies. There is a lot of tutorial information on Web. Here is a quick reference:

https://community.sw.siemens.com/s/article/what-is-a-frequency-response-function-frf

Walt

 

Upvote 0 Downvote

• Dec 18, 2019

• #4

hacksaw

Mechanical

Dec 7, 2002

2,587

US

1. the FFT is performed over a specific time interval and characterizes that data including, that of the time window which introduces its own contribution.

2. by the way there is a danger in equating "amplitude" with FFT magnitude.

 

Upvote 0 Downvote

• Dec 20, 2019

• #5

Sofistioelevib

Industrial

Jun 24, 2015

100

IT

Amin,
look at higest peak, where you have enough energy to calulate correctly phase.
Seems #2 resonance 12 and 37 Hz aprox. In 12Hz it is clear the change phase shift with 90degrees at resonant frequency.

In order to well understand if your measurement is correct it is usefull to use choerence function.

 

Upvote 0 Downvote