peak time waveform

8/12/2019 Peak Time Waveform

1/5

Use of Maximum Peak Time Waveform Trend ParameterWritten By

Nelson Baxter

ABM Technical Services

Plainfield, IN

Edited By

Todd Reeves

Computational Systems, Incorporated

Knoxville,TN

Introduction:

This paper presents some examples of the use of the Maximum Peak Time Waveform

Parameter. This feature, patented by CSI, is used exclusively in the route

based mode of CSIs 2120 Machinery Analyzer. ABM Technical Services has found

this parameter to be very useful in identifying bearing problems. In many cases,

this parameter will flag a problem that every other parameter misses.

Background:

Depending upon overall velocity readings or velocity spectra alone to detect

bearing problems can result in errors. The following are two reasons that can

explain why velocity readings need to be backed up with other analysis

parameters.

Most advanced analysts understand that the FFT is a batch process. For instance

to generate a 400 line spectrum, 1024 time samples are taken. All of these

samples are used in the calculation of the spectral components. Depending upon

the type of weighting window, some values may be attenuated and others

amplified, but they are nonetheless all used in the calculations. If the

signal is continuous as in the case of unbalance, vane-pass or electrical

problems, the FFT does a good job of calculating an accurate magnitude of eachspectral component. If, however, the signal is transient relative to the time

period of the analysis window, the amplitudes calculated by the FFT will be in

error. In the case of bearings with defects, that is exactly the situation that

exists. For instance, if a maximum frequency range of 2000 Hz is selected at a

setting of 400 lines, the time period to collect the data would be 400/2000

which equals 0.2 seconds. If a machine is running 20 Hz and has a bearing

defect frequency of 4.8 times its speed, the impact rate would be 96 times per

second. In the 0.2 second window, nineteen impacts could be expected. This

means that if the pulses are one sample wide that of the 1024 time samples only

nineteen would have energy associated with the bearing defect. When the FFT is

calculated, the bearing defect frequency will have a very low value. If there is

any noise present, it is likely that the bearing defect will be totally lost

below the noise floor. To make matters worse, when the maximum frequency is

increased, there are even fewer impacts in the time sample. For instance in the

above sample, if the maximum frequency is set to 5000 HZ, the time period would

then be 0.08 seconds and the number of defect impacts would be reduced to less

than eight. If a couple of those are attenuated by the Hanning window on each

end of the time block, there is nothing left to create a bearing defect spectral

component.

The second reason that velocity and velocity spectra can miss a bearing problem

is that velocity spectra by the very nature of the physics involved are produced

by integrating the acceleration signal. Defects are impactive pulse events. The


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sharper and narrower the impact, the more the integration process will attenuate

round-off and smear their characteristics.

As a result of these problems, other techniques have been developed that

reinforce the velocity readings. Envelope detection and CSIs PeakVueTM

technology are valuable techniques that help in the early detection of bearing

problems. However, not everyone takes enveloped or PeakVue data, because extra

data has to be taken and then interpreted.

The Value Of The Maximum Peak Time Waveform Parameter

ABM Technical Services has found that for the vast majority of bearings an

extremely valuable aid in calling out bearings is monitoring a trend of the

maximum peak value detected in the raw RMS acceleration time display. The

analyzer is set up for digital integration with the spectra then being displayed

in velocity. A time plot is obtained in then obtained in acceleration. A

Maximum Peak Time parameter is then setup. By monitoring the peak value seen in

the time display, impacts due to bearing defects can easily be detected. They

are neither FFTd nor integrated away. Every month we detect problems with this

technique that do not show up in velocity or even RMS Acceleration measurements.

The following are some plots of data showing a comparison between the Maximum

Peak Time parameter and velocity or RMS Acceleration trends.

VELOCITY TREND OF BAD BEARING MAX PEAK IN TIME TRENDNLB - PA 1ST GRIND PUMP

402-1-971P-MOH MOTOR OUTBOARD HORZ

Trend Displayof

OVERALL VALUE

-- Baseline --

Value: .169Date: 08-DEC-98

0 20 40 60 80 100

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Days: 13-SEP-99 To 07-DEC-99

PK

VelocityinIn/Sec

FAULT

Date:Time:Ampl:

07-DEC-9909:52:44 .110

NLB - PA 1ST GRIND PUMP402-1-971P-MOH MOTOR OUTBOARD HORZ

Trend Display

ofPEAK TIME

-- Baseline --Value: 3.188

Date: 08-DEC-98

0 20 40 60 80 100

0

2

4

6

8

10

12

14

Days: 13-SEP-99 To 07-DEC-99

RMSAccelerationinG-s

FAULT

Date:

Time:Ampl:

07-DEC-99

09:52:44 12.00

VELOCITY SPECTRA TIME WAVEFORM

NOT MUCH IS SEEN THE CHANGE IS OBVIOUS

PK

VelocityinIn/Sec

Frequency in kCPM


0 20 40 60 80 100 120

0

0.06

0.12

0.18

0.24

0.30Max Amp.0343

05-OCT-99

02-NOV-99

07-DEC-99

RPM= 1785.09:52:4307-DEC-99

Freq:Ordr:Sp 3:

71.40 40.00 .00729


Revolution Number

AccelerationinG-s

0 1 2 3 4 5 6

Plot

Span

-8

8

05-OCT-99 10:06

02-NOV-99 05:55

07-DEC-99 09:52

Time:

Ampl:

2.185

.09461

The above plots show what is occurring. In terms of the velocity level, there

was not much of an increase. This is also reflected in the velocity spectra.

There is an increase in the broad base band energy. However, as can be seen from

the Maximum Peak trend, which records the highest acceleration level in the time

block, there was a very significant increase. As would be expected, the time

TMPeakVue is a registered trademark of Computational Systems, Incorporated.

The increase in

the Maximum Peak

value is obvious.

It says, go look

at time plot


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based plot has much higher levels. It after all is where the maximum peak in

measured.

A Case Of Another Motor Bearing:

VELOCITY TREND RMS ACCELERATION TREND

NEW - VETTER PRESS #1SP0143 -MOH MOTOR OUTBOARD HORZ

Trend Displayof

OVERALL VALUE

-- Baseline --

Value: .189Date: 12-APR-99

0 60 120 180 240 300

0

0.06

0.12

0.18

0.24

0.30

0.36

Days: 12-APR-99 To 09-DEC-99

PKVelocityinIn/Sec

Date:Time:Ampl:

09-DEC-9905:27:24 .140

N E W - V E T T E R P R E S S # 1

S P 0 1 4 3 - M O H M O T O R OU T B O A R D H O R Z

Trend Display

of

Acceleration

-- Baseline --

Value: .08301

Date: 12-APR-99

0 60 120 180 240 300

0

0.3

0.6

0.9

1.2

1.5

1.8

2.1

2.4

2.7

3.0



Date:

Time:

Ampl:

09-DEC-99

05:27:24

.684

VELOCITY SPECTRA MAXIMUM PEAK IN WAVEFORM TREND

Not much here

PK

VelocityinIn/Sec

Frequency in kCPM

NEW - VETTER PRESS #1SP0143 -MOH MOTOR OUTBOARD HORZ

0 20 40 60 80 100 120

0

0.050.10

0.15

0.20

0.25

0.30

0.35Max Amp.0880

09-SEP-99

07-OCT-99

03-NOV-99

09-DEC-99

NEW - VETTER PRESS #1

SP0143 -MOH MOTOR OUTBOARD HORZ

Trend Display

of

PEAK TIME

--Baseline--

Value: .676

Date: 12-APR-99

0 60 120 180 240 300

0

1

2

3

4

5

6



Date:

Time:Ampl:

09-DEC-99

05:27:24 4.750

TIME PLOTS IN GS SHOWS CHANGENEW - VETTER PRESS #1

SP0143 -MOH MOTOROUTBOARDHORZ

RevolutionNumber

Acceleratio

ninG-s

0 1 2 3 4 5 6

Plot

Span

-4

4

07-OCT-99 05:24

03-NOV-99 09:13

09-DEC-99 05:27

Time:Ampl:

.583 4.740

In this case, there was virtually no increase in the overall velocity. There is

some broad band energy in the velocity spectra that if recognized could have

Note that the peak

recorded in the

maximum peak trend

(4.7 gs)only

occurred once out of

1024 samples, but

was detected and put

on trend.

Velocity Trend

is flat RMS

ACCELERATION

IS UP

Maximum Peak in

time is up

significantly


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been analyzed. The RMS Acceleration went up some and the Maximum Peak in Time

went up the most.

Use of Maximum Peak in Time with PeakVue

NEW - DRY GLUTN CROSS CONV 4-1550

CD10702 -CIP CONVEYOR INSIDE BEARING PEAK VUE

Trend Display

of

OVERALL VALUE

--Baseline--

Value: .03038

Date: 23-NOV-98

0 50 100 150 200 250 300 350 400

0

0.3

0.6

0.9

1.2

1.5

1.8

2.1

2.4

2.7

3.0

Days: 23-NOV-98 To 07-DEC-99


Date:

Time:Ampl:

13-SEP-99

13:42:18 .316

RMSAcceleration

inG-s

Frequency in CPM

NEW - DRY GLUTN CROSS CONV 4-1550

CD10702 -CIP CONVEYOR INSIDE BEARING PEAK VUE

0 600 1200 1800 2400 3000

0

0.1

0.2

0.3

0.4

0.5

0.6Max Amp.0776

08-JUL-99

05-AUG-99

13-SEP-99

RPM= 36.00

13:42:1813-SEP-99

Freq:

Ordr:

Sp 3:

187.50

5.208

.06445

NEW - DRY GLUTN CROSS CONV 4-1550CD10702 -CIP CONVEYOR INSIDE BEARING PEAK VUE

Trend Displayof

P E A K W A V E

-- Baseline --Value: .303Date: 23-NOV-98

0 50 100 150 200 250 300 350 400

0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

Days: 23-NOV-98 To 07-DEC-99

RMS

AccelerationinG-s

Date:Time:Ampl:

13-SEP-9913:42:18 3.594

N E W - D R Y G L U T N C R O S S C O N V 4 - 1 5 5 0

C D 1 0 7 0 2 - C I P C O N V E Y O R I N S I D E B E A R I N G P E A K V U E

Revolution Number

AccelerationinG-s

0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

Plot

Span

-4

4

08-JUL-99 06:15

05-AUG-99 14:28

13-SEP-99 13:42

The above case shows how the Maximum Peak in Time Parameter can be used in

conjunction with PeakVue data to make it an even more effective tool in

recognizing short duration transients that may signal a problem. This was a very

low speed piece of equipment. The time based data was taken over an 8 second

time period. The PeakVue time plot clearly shows the presence of impacts as

high as 3.6 Gs (Lower right display). This was easily picked up in the Maximum

Peak in time plot(Lower left plot). However, as can be seen, the trend in the

overall PeakVue value only shows a maximum of 0.316 Gs (Upper left display) and

the maximum spectral component was only 0.06 G (Upper right display). This is a

good example of the problem discussed at the beginning of this paper. As stated

in the beginning, the FFT is a batch process and as such it does not produce a

good representation of the severity of transient events such as impacts from

bearings or chipped gear teeth.

The method ABM Technical Services has found most effective is to monitor, trend

and then alarm on the following parameters:

1.Velocity: Works best on unbalance, looseness, misalignment, vane-pass,electrical and other continuous signals.

2. RMSAcceleration: Works well when broad band signals such as cavitation

3.6 Gs

Detected in

time plot

Maximum peak in

spectrum display

is .06 G.

Overall

PeakVue value.316G

PeakVue Max

Peak in time


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or bearings with multiple defects are present.

3.Maximum Peak In Acceleration Time Plot: Works very well when there aretransient impacts that the integrated FFT and/or RMS do not pickup.

4. PeakVue: Is vital in low speed applications5.Maximum Time in PeakVue: Is helpful in very low speed applications

where the impacts dont occur very often.

Note the above parameters are only flags. AN analysis then has to be performedto determine if there is actually a problem and how severe it is. However, it is

very important to have as good a radar system as possible. If you collect, for

instance 3000 points, it is imperative that there be a reliable method of

screening the data to determine which points to analyze. The above combination

of parameters catches a very high percentage of all problems that occur. Due to

the reasons stated in the first part of this paper, theMaximum Peak in Time

parameter is a vital part of that detection system because it catches what other

parameters sometimes miss.

peak time waveform

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