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Filters and Enveloping - A Practical Discussion -
Filters and Enveloping - A Practical Discussion -
Agenda Sample
Agenda Sample
Consider This Simple Vibration Signal in the Time Domain
Consider This Simple Vibration Signal in the Time Domain
Or in the Frequency Domain
Or in the Frequency Domain
Basic Filter Terminology  High Pass Filter
Basic Filter Terminology High Pass Filter
Basic Filter Terminology  Low Pass Filter
Basic Filter Terminology Low Pass Filter
Basic Filter Terminology  Band Pass Filter
Basic Filter Terminology Band Pass Filter
Basic Filter Theory  When Does the Filtering Occur
Basic Filter Theory When Does the Filtering Occur
Basic Filter Theory  Analog Filter
Basic Filter Theory Analog Filter
Basic Filter Theory  Analog Filter
Basic Filter Theory Analog Filter
Basic Filter Theory  Analog Filter is a Roll Off Filter
Basic Filter Theory Analog Filter is a Roll Off Filter
Basic Filter Theory  Analog Filter is a Roll Off Filter
Basic Filter Theory Analog Filter is a Roll Off Filter
Basic Filter Theory  Digital Filter
Basic Filter Theory Digital Filter
Basic Filter Theory  Digital Filter
Basic Filter Theory Digital Filter
Basic Filter Theory  Software Filter
Basic Filter Theory Software Filter
A Word About Bearings
A Word About Bearings
Rolling Element Bearing Faults
Rolling Element Bearing Faults
Rolling Element Bearing Faults
Rolling Element Bearing Faults
Remember our Band Pass Filter or Envelope
Remember our Band Pass Filter or Envelope
Enveloping and High Pass Filtered Signal
Enveloping and High Pass Filtered Signal
What Envelope or High Pass Filter Should We Use
What Envelope or High Pass Filter Should We Use
What Envelope or High Pass Filter Should We Use
What Envelope or High Pass Filter Should We Use
Bearing System Natural Frequencies
Bearing System Natural Frequencies
What High Pass or Envelope Filters are Available in the Hardware
What High Pass or Envelope Filters are Available in the Hardware
What Does the Spectrum Look Like
What Does the Spectrum Look Like
Where Do the Sidebands come from
Where Do the Sidebands come from
Theres more to Enveloping
Theres more to Enveloping
Bearing Fault Frequencies
Bearing Fault Frequencies
Any Questions
Any Questions

: Filters and Enveloping - A Practical Discussion. : Denise Bruneau. : Filters and Enveloping - A Practical Discussion.ppt. zip-: 501 .

Filters and Enveloping - A Practical Discussion

Filters and Enveloping - A Practical Discussion.ppt
1 Filters and Enveloping - A Practical Discussion -

Filters and Enveloping - A Practical Discussion -

William Tudoroff Condition Monitoring Services Product Manager Rockwell Automation

1

Copyright 2005 Rockwell Automation, Inc. All rights reserved.

2 Agenda Sample

Agenda Sample

1. Basic Filter Terminology

2. Basic Filter Theory

3. Rolling Element Bearing Faults

4. Applying Envelopes

2

Copyright 2005 Rockwell Automation, Inc. All rights reserved.

3 Consider This Simple Vibration Signal in the Time Domain

Consider This Simple Vibration Signal in the Time Domain

3

Copyright 2005 Rockwell Automation, Inc. All rights reserved.

4 Or in the Frequency Domain

Or in the Frequency Domain

Amplitude

Frequency

40 Hz

4

Copyright 2005 Rockwell Automation, Inc. All rights reserved.

5 Basic Filter Terminology  High Pass Filter

Basic Filter Terminology High Pass Filter

High Pass Filter Allows Frequencies Higher than the filter value to be retained in the signal also known as the Low Corner Frequency*

40 Hz High Pass Filter

*Remember If its an important concept in the world of Vibration, there must be more than one name for it

Amplitude

Frequency

40 Hz

5

Copyright 2005 Rockwell Automation, Inc. All rights reserved.

6 Basic Filter Terminology  Low Pass Filter

Basic Filter Terminology Low Pass Filter

Low Pass Filter Allows Frequencies Lower than the filter value to be retained in the signal also known as the High Corner Frequency or Frequency Maximum

40 Hz Low Pass Filter

Amplitude

Frequency

40 Hz

6

Copyright 2005 Rockwell Automation, Inc. All rights reserved.

7 Basic Filter Terminology  Band Pass Filter

Basic Filter Terminology Band Pass Filter

Band Pass Filter Allows Frequencies in the Band defined by the filter value to be retained in the signal also known as Enveloping

30 - 50 Hz Band Pass Filter

Amplitude

Frequency

40 Hz

7

Copyright 2005 Rockwell Automation, Inc. All rights reserved.

8 Basic Filter Theory  When Does the Filtering Occur

Basic Filter Theory When Does the Filtering Occur

Although we have visualized the filter in the Frequency Domain the actual signal processing can occur in either the Frequency or Time Domain. Also, when filtering in the Frequency Domain, this can occur in the hardware as the data is being processed, or in the Software, after the data has been processed

8

Copyright 2005 Rockwell Automation, Inc. All rights reserved.

9 Basic Filter Theory  Analog Filter

Basic Filter Theory Analog Filter

Filtering in the Time Domain is also called an Analog Hardware Filter because the filtering occurs during the actual capture of the Time Waveform.

Analog Input

Analog to Digital Converter

Analog Filter

Digital Output

Digital Signal Processor

9

Copyright 2005 Rockwell Automation, Inc. All rights reserved.

10 Basic Filter Theory  Analog Filter

Basic Filter Theory Analog Filter

If the Raw Time Waveform was made up of the 20 Hz and 60 Hz Signals Below

40 Hz Analog High Pass Filter

This becomes the Analog Signal Sent to the Analog to Digital Converter

10

Copyright 2005 Rockwell Automation, Inc. All rights reserved.

11 Basic Filter Theory  Analog Filter is a Roll Off Filter

Basic Filter Theory Analog Filter is a Roll Off Filter

An Analog Filter is considered a Roll-Off Filter in other words the filter is not a brick wall but allows some of the signal beyond the filter value to pass through The Filter Attenuates or reduces the amplitudes of the frequencies below the filter value The filter values will be defined by the hardware manufacturer as they are an actual Analog Chip Lets visualize it in the Frequency Domain even though the filtering is occurring in the Time Domain

11

Copyright 2005 Rockwell Automation, Inc. All rights reserved.

12 Basic Filter Theory  Analog Filter is a Roll Off Filter

Basic Filter Theory Analog Filter is a Roll Off Filter

40 Hz High Pass Filter

Roll-Off

Amplitude

Frequency

40 Hz

60 Hz

12

Copyright 2005 Rockwell Automation, Inc. All rights reserved.

13 Basic Filter Theory  Digital Filter

Basic Filter Theory Digital Filter

Filtering in the Frequency Domain is often called a Digital Hardware Filter because the filtering occurs during the actual Digital Signal Processing of the Time Waveform into a Frequency Spectrum

Analog Input

Analog to Digital Converter

Analog Filter

Digital Output

Digital Signal Processor

Fast Fourier Transform, Integration and Digital Filtering Occur Here

13

Copyright 2005 Rockwell Automation, Inc. All rights reserved.

14 Basic Filter Theory  Digital Filter

Basic Filter Theory Digital Filter

A Digital Filter is considered an Absolute Filter in other words the filter is essentially a brick wall, allowing none of the signal beyond the filter value to pass through The filters available are dependent on the hardware being used Most common example is the Frequency Maximum (FMAX) setting we are all familiar with

40 Hz FMAX

Amplitude

Frequency

40 Hz

60 Hz

14

Copyright 2005 Rockwell Automation, Inc. All rights reserved.

15 Basic Filter Theory  Software Filter

Basic Filter Theory Software Filter

Filtering in the Frequency Domain after the data has been processed in the hardware is called a Software Filter because many vendors just display Zero amplitude in any bins (lines of resolution) that are being filtered out Thus, an infinite number of filters is available using this method

40 Hz High Pass Filter

Amplitude

Frequency

40 Hz

60 Hz

15

Copyright 2005 Rockwell Automation, Inc. All rights reserved.

16 A Word About Bearings

A Word About Bearings

The vast majority of bearings are one of two types: Rolling Element, or Anti-Friction Bearings and Fluid Film Bearings

Rolling Element: Low cost, simple to apply. But are capable of only moderate speeds and relatively light loads. Rotor dynamics arent bad but diagnostics can be complex due to all those spinning balls!

Fluid Film: Capable of supporting very high loads, high temperatures, high speed. Expensive and associated rotor dynamics are very complex.

Accelerometer

Eddy Current Probe

bearing

bearing

bearing housing

bearing housing

Oil Wedge (load zone)

Soft Metal (Babbitt)

16

Copyright 2005 Rockwell Automation, Inc. All rights reserved.

17 Rolling Element Bearing Faults

Rolling Element Bearing Faults

What happens when there is a fault or defect on the inner or outer race of the bearing?

We feel an impact anytime a ball or roller passes over the defect This impact energy is typically very low amplitude

Fault or Defect on Outer Race

Accelerometer

bearing

bearing housing

17

Copyright 2005 Rockwell Automation, Inc. All rights reserved.

18 Rolling Element Bearing Faults

Rolling Element Bearing Faults

In fact, the vibration energy from a bearing fault is so small sometimes that it gets hidden by all the other machine vibration going on: Unbalance, Looseness, Misalignment, etc

18

Copyright 2005 Rockwell Automation, Inc. All rights reserved.

19 Remember our Band Pass Filter or Envelope

Remember our Band Pass Filter or Envelope

If we pass the signal through the right Envelope or High Pass Filter, we could theoretically leave only the vibration generated by our bearing fault

Band Pass Filter

Amplitude

Frequency

19

Copyright 2005 Rockwell Automation, Inc. All rights reserved.

20 Enveloping and High Pass Filtered Signal

Enveloping and High Pass Filtered Signal

Our Enveloped or High Pass Filtered Signal would look like this:

Amplitude

20

Copyright 2005 Rockwell Automation, Inc. All rights reserved.

21 What Envelope or High Pass Filter Should We Use

What Envelope or High Pass Filter Should We Use

We need to know what frequency or frequencies we are trying to isolate The frequencies are generated by the impact of the ball or roller as it passes over the defect on the race So what frequency is this?

21

Copyright 2005 Rockwell Automation, Inc. All rights reserved.

22 What Envelope or High Pass Filter Should We Use

What Envelope or High Pass Filter Should We Use

If we envelope properly, we should be able to eliminate all the higher amplitude, low frequencies that are present in the signal: Unbalance Frequency (1X) Misalignment Frequencies (1X and 2X) Looseness Frequencies (1X and 2X and possibly more running speed harmonics) Fundamental Bearing Defect Frequencies (Non-harmonics from around 3X to around 40X) So what frequency is this?

Amplitude

22

Copyright 2005 Rockwell Automation, Inc. All rights reserved.

23 Bearing System Natural Frequencies

Bearing System Natural Frequencies

If we envelope properly, all we should have left is the bearing natural frequency response to the impacts that are occurring as the balls or rollers pass over the defect(s) Why? Because this gives us a measure of the energy generated by any impacts or impulses on the system Since we are measuring the amount of resonance occurring in the system, it will be very sensitive to the severity of the impacts and hence, the severity of the fault If measured properly, we should see almost all bearing related energy

23

Copyright 2005 Rockwell Automation, Inc. All rights reserved.

24 What High Pass or Envelope Filters are Available in the Hardware

What High Pass or Envelope Filters are Available in the Hardware

Rockwell Automation (Entek and IRD Brands) Use Analog High Pass Filters 100 Hz, 200 Hz, 500 Hz, 1 KHz, 2 KHz and 5 KHz SKF Use Analog Envelope Filters 5 to 100 Hz, 50 to 1000 Hz, 0.5 to 10 kHz, 5 to 40 kHz and 250 to 350 kHz CSI Use Analog High Pass Filters 500 Hz, 1 KHz, 2 KHz and 5 KHz Both CSI and Rockwell Automation then apply a digital low pass filter to the signal to create the Envelope

24

Copyright 2005 Rockwell Automation, Inc. All rights reserved.

25 What Does the Spectrum Look Like

What Does the Spectrum Look Like

What are These?

Amplitude

Amplitude

Frequency

25

Copyright 2005 Rockwell Automation, Inc. All rights reserved.

26 Where Do the Sidebands come from

Where Do the Sidebands come from

Carrier Frequency

Sideband or Modulating Frequencies

Amplitude

Amplitude

Frequency

26

Copyright 2005 Rockwell Automation, Inc. All rights reserved.

27 Theres more to Enveloping

Theres more to Enveloping

If we apply a Digital Low Pass Filter as the upper end of the Envelope, we can then extract the modulating frequencies from the impact waveform

Digital Low Pass Filter (FMAX)

The Key Question: What frequencies are left?

Amplitude

Frequency

27

Copyright 2005 Rockwell Automation, Inc. All rights reserved.

28 Bearing Fault Frequencies

Bearing Fault Frequencies

Ball Pass of the Inner Race (BPIR) Ball Pass of the Outer Race (BPOR) Ball Spin Frequency (BSF)

28

Copyright 2005 Rockwell Automation, Inc. All rights reserved.

29 Any Questions

Any Questions

Remember, this was a practical overview!

29

Copyright 2005 Rockwell Automation, Inc. All rights reserved.

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