SPM Vibrameter VIB-11B Instruction Manual

Technical data are subject to change without notice.

© Copyright SPM 2003-10. 71679 Z

Instruction Manual

Vibrameter VIB-11B

SPM Instrument AB • Box 504 • SE-645 25 Strängnäs • Sweden

Tel [phone] • Fax [phone] • [e-mail] • www.spminstrument.com

1

Technical data are subject to change without notice.

ISO 9001 certified. © Copyright SPM 2003-10. 71679.Z

SPM Instrument AB • Box 4 • SE-645 21 Strängnäs • Sweden
Tel [phone] • Fax [phone] • [e-mail] • www.spminstrument.com

Vibration Monitoring

Instruction Manual for
Vibrameter VIB-11B

Contents

Introduction ........................................................................................ 2

Vibration ............................................................................................. 3

Measurement...................................................................................... 4

Measure Acceleration - Display Velocity ............................................ 5

Machine Classes ................................................................................. 6

Measuring Points ................................................................................ 7

Recording of Readings ....................................................................... 8

Follow-up Form .................................................................................. 9

Measuring Equipment ...................................................................... 10

Transducer Mounting ....................................................................... 10

Hand-held Probe .............................................................................. 11

Taking Readings ............................................................................... 11

Changing Batteries ........................................................................... 11

Maintenance Based on Vibration Records ....................................... 12

Fault Analysis Chart .......................................................................... 13

Technical Specifications, Part Numbers .......................................... 14

Definition of Machine Classes According to ISO 2372 .................... 15

2

Technical data are subject to change without notice.

ISO 9001 certified. © Copyright SPM 2003-10. 71679.Z

SPM Instrument AB • Box 4 • SE-645 21 Strängnäs • Sweden
Tel [phone] • Fax [phone] • [e-mail] • www.spminstrument.com

Condition Based Maintenance

Condition Based Maintenance is by now a widely accepted concept in industry. The idea is simple and not
exactly new: keep plant machinery in good working condition by locating and repairing minor faults
before they grow large enough to cause expensive breakdowns and production stops.

The problem is to assess machine condition and detect a slow deterioration long before a piece of plant
grinds to a shuddering halt. In the past, a skilled operator could do this largely without the help of
instruments, by listening, touching, smelling. Modern machinery is often unattended, soundproofed, out
of easy reach. It rotates faster and is less massively constructed, which means that even a minor
deterioration of its working condition can have very serious consequences. Therefore personal skill and
subjective judgement have to be supported by monitoring systems and instrument readings.

Vibration Monitoring

Vibration monitoring is a very useful method for an overall assessment of machine condition. Changes in
the vibration level always imply changes in the operating condition. Excessive vibration has basically three
causes: something is loose, misaligned or out of balance. These three causes cover virtually all possible
mechanical faults.

Moreover, the assessment of machine vibration has been much simplified by international standards which
define the acceptable vibration level for a given type of machine and recommend monitoring methods
suitable for industrial purposes.

A Maintenance Tool

Effective Condition Based Maintenance requires economical and simple monitoring methods which can be
applied by maintenance personnel without special training. Their primary task is to locate trouble spots
early and direct the efforts of the maintenance crews to the right place at the right time. Fault analysis and
repairs are a secondary step which may require expert knowledge and a different type of instrumentation.

SPM vibration monitoring equipment is designed as a maintenance aid. In accordance with the interna­tional standards, it measures vibration severity over a large frequency range. It allows a practical
classification of machine condition in relative terms: good, acceptable, just tolerable or bad. Regular
measurements will also show the development trend of the vibration level and thus the urgency of the
maintenance problem: stable condition, slow deterioration or fast deterioration.

Measurements can be carried out in various ways; either periodical readings with portable equipment
(Vibrameter VIB-11B), or continuous monitoring of preset limit values (Machine Guard MG4 or CMM
System). This manual gives an introduction to vibration monitoring and describes condition assessment
and basic fault analysis with SPM Vibrameter VIB-11B.

Measuring Units

ISO Recommendations use metric units (mm/s RMS) for measuring vibration severity. In this manual, all
metric units have been converted to inches /1 in = 2.54 mm / 1 mm = 0.03937 in). A metric version (VIB-10)
is available, together with an instruction manual (71678 B) and follow-up forms (VIC-11) with metric tables.

3

Technical data are subject to change without notice.

ISO 9001 certified. © Copyright SPM 2003-10. 71679.Z

SPM Instrument AB • Box 4 • SE-645 21 Strängnäs • Sweden
Tel [phone] • Fax [phone] • [e-mail] • www.spminstrument.com

Vibration

In every moving machine, part of the force that makes
it work acts on the machine itself. Since no structure
or machine is perfectly rigid, any force acting on it will
cause slight movements.

The forces causing movement are usually cyclic, that
is they operate regularly first in one direction and
then in another. They can act in two main directions,
like the up and down forces associated with piston
engines, or they can rotate with the shaft, like out of
balance forces on a fan. They move the machine back
and forth from its rest position: the machine vibrates.

Up to a degree, vibration is tolerated because it sim­ply cannot be avoided. Machines are designed to
withstand a “normal“ amount of vibration for a long
period of time. To assess the condition of any particu­lar piece of plant, one has to determine its “normal“
vibration level, then measure the actual amount and
type of vibration and compare the two values.

To decide what is normal one has to consider

· the function of the machine and the forces
involved

· the rigidity of the machine structure

A large diesel engine vibrates more than a small elec­tric motor - the forces involved are very different.

More force is needed to vibrate a machine on a stiff
concrete foundation than it takes to shake the same
machine on a flexible metal frame. The machine struc­tures are different and so are their normal vibration
levels.

Due to changes in the operating conditions and the
mechanical state of machines, vibration levels are sub­ject to gradual or sudden changes. Loose fixing bolts
or excessive bearing play will make the structure less
rigid - vibration will increase. A growing soot layer on
the impeller blades of an exhaust fan adds to the out
of balance forces. Vibration will increase above the
normal level and show that the machine is getting
worse. Usually the deterioration accelerates: heavier
vibration will further weaken the structure which in
turn will raise the vibration level.

4

Technical data are subject to change without notice.

ISO 9001 certified. © Copyright SPM 2003-10. 71679.Z

SPM Instrument AB • Box 4 • SE-645 21 Strängnäs • Sweden
Tel [phone] • Fax [phone] • [e-mail] • www.spminstrument.com

Measurement

If a fan is out of balance, it will shake at its speed of
rotation, i.e. move backwards and forwards once per
revolution. The number of vibrations per time unit is
the vibration frequency, measured in Hz (Hertz =
cycles per second).

The rotational speed of any piece of plant is known as
its fundamental frequency. For a fan with a speed of
1 500 r.p.m. the fundamental frequency is 25 Hz (1
500 r.p.m. ÷ 60).

In practice, machine vibration usually consists of many
different frequency components. For a general as­sessment of machine condition one uses wide fre-
quency band measurements, that is all vibrations
within a large frequency range are measured simulta­neously.

Cyclic movement can be measured and described in
three different ways, as

· displacement

· acceleration

· velocity

Displacement means the actual distance the object
moves, measured either from its rest position in one
direction (peak) or as the total movement in both
directions (peak to peak). Displacement is usually meas­ured in mils.

A part that is moving from rest, speeding up, slowing
down and stopping twice per cycle is obviously accel­erating and decelerating continuously. Acceleration is
measured in g (1 g = 32.17 ft/sec2).

The third measuring parameter is the speed at which
the object moves, the vibration velocity. Velocity is
expressed in in/sec.

Both acceleration and speed are constantly changing.
One can measure a peak value of either, but a mean
value often gives a better indication of the forces
involved in the movement. Most instruments measure
the RMS value (root mean square value) of the move­ment and use a scaling factor to indicate the peak
levels if they are given at all.

Frequency

Hz

Displacement

mil

Acceleration

g

Velocity

in/s

5

Technical data are subject to change without notice.

ISO 9001 certified. © Copyright SPM 2003-10. 71679.Z

SPM Instrument AB • Box 4 • SE-645 21 Strängnäs • Sweden
Tel [phone] • Fax [phone] • [e-mail] • www.spminstrument.com

Measure Acceleration - Display Velocity

All three vibration parameters - displacement, accel­eration, velocity - are mathematically related. One
can, for example, place an accelerometer on a vibrat­ing surface and convert its signal, via integrating cir­cuitry in the measuring instrument, into a reading of
vibration velocity or displacement.

The choice of displayed parameter (the instrument
reading) and measured parameter (the transducer type
used) depends on the problem to be solved and on
the cost, the complexity and the reliability of the
measuring equipment.

Experience has shown, that the RMS level of vibration
velocity, measured over a frequency range of 10 to
1000 Hz, is most useful for general assessment of
machine condition. The technical term used is vibra-

tion severity, defined as above and displayed in in/s
RMS on the instrument. Vibration severity is directly

related to the energy level of machine vibration, and
thus a good indicator of the destructive forces acting
on the machine.

There are transducers which measure velocity directly,
i.e. seismic probes with either moving coils or moving
magnets. These transducers are normally bulky, easily
damaged and expensive to manufacture. They are
therefore gradually being replaced by accelerometers.

An accelerometer is basically a piezo electric crystal (a
crystal that develops an electric charge when it is
compressed or stretched) with a small reference mass
attached. As the transducer is moved back and forth,
the reference mass compresses and stretches the crys­tal and the transducer gives an output directly related
to acceleration.

Piezo electric accelerometers are small, very robust
and relatively cheap to produce. They can work over a
very large frequency range. They can be mounted on
machines, held by hand against a vibrating surface or
be temporarily attached by wax or magnets. That is
why most practical measuring systems now use an
accelerometer as the transducer and an integrator
within the instrument to give a display in terms of
velocity.

in/s

RMS

Piezo electric
crystal

Housing

Mass

Base

Output

Integrator

Accelerometer

Piezo electric accelerometer