5-1
VIBXPERT 11.2010
Measurement tasks
Chapter 5: Measurement tasks
This chapter contains information on the individual measurement
tasks and tips for carrying out a measurement.
The '2-Channel Measurements' module must be registered if you
want to measure on both channels (see P. 2-23, P. 6-22).
Characteristic overall vibration values
Characteristic overall vibration values are used for assessing ma-
chine, bearing and gear conditions. A good indicator of the vibration
forces acting on a machine is the effective value (RMS) of the
vibration velocity in the frequency range 10 - 1000 Hz or 2 - 1000 Hz.
Yardsticks for the assessment of the permissible vibration levels are
specified in the ISO 10816-3 norm (see below). These ranges are
preprogrammed in VIBXPERT in the form of threshold values and can
be called as the Assessment Setup.
As well as the effective value of the vibration, VIBXPERT records the
highest signal amplitudes as peak values (0-peak, peak-peak) and
calculates the crest factor from these.
What is the crest factor?
The 'Crest Factor' is the ratio of the highest amplitude to the effective
value (RMS) of a vibration and is a measure of the intensity of the
impacts in the form of a vibration. Among other things, the crest
factor is deployed for wear diagnosis in roller bearings and gearing
mechanisms as well as for cavitation. A harmonic vibration of
amplitude '1' has 0.707 as its effective value and a crest factor of 1.41.
If the crest factor is higher than 1.41, impacts with higher amplitudes
are occurring.
ISO 10816-3 for the assessment of
machine vibrations
To assess the machine condition, the
machine is first assigned a machine
class with the aid of the lower axis. The
range in which the measured effective
value falls can be read from the axis at
the side.
What you need to do:
Range A: Continue to measure at
regular intervals.
Ranges B,C: Look for the cause of the
vibration. Observe the machine closely.
Schedule a power down.
Range D: Take immediate measures:
Localize the cause, switch the machine
off and remedy the problem.
Note
Overall vibration values
acceleration
velocity
displacement
V
ibration velocity (r
.m.s.)
(10 - 1000 Hz n > 600 min
-1
)
(2 - 1000 Hz n > 120 min
-1
)
Foundation
Machine type
Group
rigid
soft
rigid
soft
med. sized mach.
15 kW<P<300 kW
large machines
300 kW<P<50 MW
Motors
160<H<315 mm
Motors
315 mm < H
Group 2
Group 1
mm/s
0,71
1,4
2,3
2,8
3,5
4,5
7,1
11
inch/s
0,03
0,06
0,09
0,11
0,14
0,18
0,28
0,43
D
C
B
A
Summary of Contents for VIB 5.300 EX Series
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