Shock Pulses
Resonance Frequency
Peaks around the
resonant frequency
Unbalance
0.05
0
0
5000
4
1 .10
4
1.5 .10
4
2 .10
Hz
4
2.5 .10
4
3 .10
4
3.5 .10
4
4 .10
Shock Pulse Transducer
Trancients
Resonance
2
0
Bearing
damage
2
0
0.005
0.01
0.015
Unbalance
0.02
0.025
0.03
Unbalance
0.035
n
0.6
0.4
Bearing damage
0.2
0
0
100
200
300
400
500
Hz
600
700
800
900
1000
Enveloping at a Resonance Frequency
2
0
2
0
0.005
0.01
0.015
0.02
0.025
0.03
Peaks
the the
Peaksaround
around
resonans
frequency
resonant
frequency
Unbalance
0.05
0
0
5000
Band pass filter
0.035
4
1 10
4
1.5 10
4
2 10
Hz
4
2.5 10
4
3 10
4
3.5 10
4
4 10
0.1
0
0.1
Signal after
band pass filter
0.1
After rectifying
.01
After enveloping
Peak detection
0
2
0
Bearing damage
2
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
Bearing damage
0.1
0
0.1
0
I. Time domain (SPM)
II. Frequency domain
dBm
0.1
dBc
0
Hz
dBc
dBc
The dBc value is effected by the lubrication condition in a
bearing. It is commonly referred to as the background noise or
the carpet noise of a bearing.
The dBc value is calculated by sampling the incoming signal
about a 1000/sec an average of all the lower Shock Pulses.
Full film lubrication
Partial lubrication
Boundary lubrication
Static and
dynamic load
Preload
Lubricant
type
Lubricant
supply
Alignment
Properly sized shaft
and housing fits
Geometric quality
of bearing
Temperature
Viscosity
Total load
Rolling velocity
Things that effect
the Lubricant film
thickness
Surface finish
Contaminants in
Lubricant film
Cleanliness
dBm
dBc
The dBm value is
calculated by sampling
the incoming signal
approximately 50/ sec
an average of all the
stronger Shock Pulses.
The dBm value indicates the bearing operating
condition once a measurement is completed. The
dBm is commonly referred to as the Max value
On the Infinity, the LED s and the color coded
dots to the left of the measuring results indicate
the operating condition.
dBm
dBc
SPM Evaluation Scale
dBsv 100
dBn 60
51 dbm
33 dbc
dbi 15
-9
Normalized measuring scale: dBsv = dBn + dBi
36 dbm
18 dbc
0
Time
This becomes
the starting
point for the 0
60 Green Yellow - Red
scale.
The dBi value is
calculated once
the RPM and
Shaft Diameter
have been
input into the
instrument or
software.
Bearing Operating Condition:
Red
Yellow
Green
- Bad (dBm 35 and more)
- Caution (dBm 21 to 34)
- Good (dBm up to 20)
SPM recommends changing the
bearing when dBm reaches 55
1
2
3
Low dBm/dBc readings with
small delta indicates a good
bearing
Small delta with elevated
dBm/dBc readings typically
indicate lubrication problems
Large delta (15 or >) with
elevated dBm/dBc readings
indicate possible bearing
damage or other mechanical
problems
SPM dbm/ dbc trend graph
Bearing replaced
Bearing Lubricated
because dbc reading
increased it also
drove up the dbm.
Signal Source?
Is the Red or Yellow SPM Reading
from the bearing or outside source?
SPM Spectrum used to confirm
bearing and lubrication concerns
Add bearing
coefficients in
software to
utilize Bearing
Symptom
feature
SPM Spectrum with Bearing
Symptom in software
Bearing
Symptom
matches up
with FTF in
this
example
confirming
bearing
damage.