MMF VM25 User manual

Instruction Manual
Manfred Weber
Metra Mess- und Frequenztechnik in Radebeul e.K.
Meissner Str. 58 - D- 1445 Radebeul
Tel. [phone] Fax [phone]
Email: [e-mail] Internet: www.MMF.de
Vibration Meter
VM25
Valid from Version 1. 9

Published by:
Manfred Weber
Metra Mess- und Frequenztechnik in Radebeul e.K.
Meißner Str. 58
D-0 445 Radebeul
Tel. [phone]
Fax [phone]
Email [e-mail]
Internet www.MMF.de
Note: The latest version of this manual can be found at
http://www.mmf.de/product_literature.htm
Specification subject to change.
© 20 2 Manfred Weber Metra Mess- und Frequenztechnik in Radebeul e.K.
Full or partial reproduction subject to prior written approval.
Feb/ 7

Contents
. Purpose..................................................................................................................3
2. Function.................................................................................................................3
2. . The Vibration Sensor......................................................................................3
2.2. The Measuring Instrument..............................................................................4
3. Measuring Ranges.................................................................................................4
3. . Measurable Vibration Quantities....................................................................4
3.2. Vibration Acceleration....................................................................................5
3.3. Vibration Velocity...........................................................................................5
3.4. Vibration Displacement..................................................................................7
3.5. Rolling Bearing Parameters K(t)....................................................................8
3.6. Rotational Speed............................................................................................9
3.7. Temperature....................................................................................................9
4. The Batteries..........................................................................................................9
4. . Inserting the Batteries.....................................................................................9
4.2. Switching On and Off................................................................................... 0
4.3. Battery Display and Battery Type.................................................................
4.4. Shut-off Timer.............................................................................................. 2
5. Preparation of Measuring Points.......................................................................... 2
5. . General Information on Measurement Point Choice..................................... 2
5.2. ISO 08 6- Recommendations................................................................... 2
5.3. VMID Measurement Point........................................................................... 4
5.3. . How the VMID Measurement Point Functions..................................... 4
5.3.2. Mounting the VMID Measurement Point.............................................. 4
6. Measurement....................................................................................................... 5
6. . Measurement Value Display......................................................................... 5
6.2. Selecting the Display Quantity..................................................................... 5
6.3. Measurement Point Detection....................................................................... 6
6.3. . Reading the VMID Data with the VM25.............................................. 6
6.3.2. Entering the Measurement Point Text................................................... 6
6.3.3. Editing and Deleting Measurement Point Data..................................... 8
6.4. Saving Measurands....................................................................................... 8
6.5. Graphical Trend Display............................................................................... 8
6.6. Viewing Saved Measurement Values............................................................ 9
6.7. Deleting Saved Measurement Data...............................................................20
6.8. K(t) Measurement.........................................................................................20
6.9. Frequency Analysis.......................................................................................23
6.9. . Settings.................................................................................................23
6.9.2. FFT Memory.........................................................................................24
6. 0. Rotation Speed Measurement.....................................................................25
6. . Temperature Measurement..........................................................................26
7. Measurement Evaluation with Standard Values...................................................27
8. Setting the Date and Time....................................................................................29
9. Calibration...........................................................................................................30
0. Sensor Check.....................................................................................................32
. Headphone Output.............................................................................................32
2. Reset Key...........................................................................................................33

3. Connection to a PC............................................................................................33
3. . Device Driver.............................................................................................33
3.2. VM2x Measurement Database....................................................................34
3.3. Export of FFT Data to a PC........................................................................35
3.4. Firmware Update........................................................................................36
4. Technical Data...................................................................................................38
Limited Warranty....................................................................................................40
2
Figure : VM25 with vibration sensor

Thank you for choosing a Metra Vibration Measurement Instrument!
1. Purpose
The VM25 has been developed, particularly, for the measurement and monitoring of
vibrations on rotating machines. The purpose of such measurements is to monitor
the condition of the machine in order to avoid unscheduled shut-down. Furthermore
vibration measurement is carried out prior to the distribution of new machinery and
subsequently to repair with a view to quality control and the issuing of product guar-
antees.
The basis for successful machine condition monitoring is the measurement of the vi-
bration severity over a longer period of time. Measurements are taken at regular in-
tervals of time and recorded.
The VM25 measures and records vibration acceleration, vibration velocity or vibra-
tion displacement. The VM25 specification complies with the ISO 2954 regulations
for machines that measure vibration velocity and is therefore suitable for measuring,
among other things, machine vibrations in accordance with ISO 08 6.
In addition to vibration quantities the VM25 also measures the temperature and the
rotation speed with contactless sensors.
An external piezoelectric accelerometer is used as the sensor, and is provided to-
gether with the instrument. The VM25 is fitted with an electronic measurement
point detector (VMID) which enables it to take routine measurements of a large
number of measurement points very effectively. A software package for transferring
the measurement data to a PC is also available from Metra.
In the common hierarchy of condition monitoring the VM25 is equivalent to 'Level
'. This represents the long term monitoring of parameters with low technical and
personnel requirements.
For fault detection ('Level 2'), as a further step, spectral diagnostic measurements are
taken, which require a large degree of expertise and sophisticated measurement tech-
nology.
In the development of the VM25 value was placed on simple operation and mainte-
nance requirements, which enable trained personnel to operate the instrument with-
out the need of being specially qualified.
2. Function
2.1. The Vibration Sensor
The VM25 operates with a piezo ceramic shear accelerometer. Piezoelectric vibra-
tion transducers are characterized by high precision and resolution with great robust-
ness. The accelerometer of the VM25 has an integrated electronic circuit for imped-
ance conversion in accordance with the IEPE standard. At the base of the sensor a
magnet has been integrated for mounting to the measurement point. In the center of
the magnet there is a contact point from which the identification number can be
read. The measurement point ID is saved in the available VMID measurement
points.
The coupling surface is protected by a metal cap which attaches to the sensors mag-
netic base.
3

2.2. The Measuring Instrument
Figure 2 shows the block diagram. The VM25 supplies the IEPE Sensor with 2 mA
constant current. At the sensor output, a vibration acceleration proportional AC volt-
age arises, which is amplified in the instrument to produce an optimum level. The
gain switch-over takes place automatically. The subsequent analogue/digital con-
verter is a Sigma-Delta converter with 24 bit resolution.
Further signal processing, such as filtering, integration (for calculating velocity and
displacement from acceleration) as well as the RMS and peak value rectification is
carried out in the micro controller. The micro controller also controls the graphic
display, the infrared thermometer, the rotation speed sensor, the USB communica-
tion and storing of measurements.
3. Measuring Ranges
3.1. Measurable Vibration uantities
The VM25 can display the vibration quantities acceleration, velocity and displace-
ment. Velocity and displacement are generated by single or double integration of the
sensor acceleration signal.
Furthermore, various frequency ranges can be selected.
The display rate adjusts itself according to the selected quantity in order to ensure
that the RMS does not fluctuate even at lower frequencies. The following table
shows the display rates.
4
Figure 2: Block Diagram
IEPE
supply
Progr.
amplifier
A
D
Display
Memory
Keys
Sensor
ID
Power
supply
USB
RPM
sensor
Infrared
thermometer
Micro
controller

Measurand Frequency Range Display Rate Sample Rate
Vibration acceleration 0,2 Hz – 0 kHz 5.6 s 23.438 kHz
Vibration acceleration 3 Hz – kHz .4 s 2.930 kHz
Vibration acceleration kHz – 0 kHz .4 s 23.438 kHz
Vibration velocity 2 Hz – kHz .4 s 2.930 kHz
Vibration velocity 0 Hz – kHz .4 s .7 9 kHz
Vibration displacement 5 Hz – 200 Hz 2.8 s 2.930 kHz
3.2. Vibration Acceleration
The VM25 has the following frequency ranges for vibration acceleration:
•0.2 Hz to 0 kHz: full frequency bandwidth of the accelerometer
•3 Hz to kHz: lower frequency acceleration
• kHz to 0 kHz: high frequency vibration only
In this way specific signal components can be measured whilst others are attenuated.
For example, when taking measurements on machines, at a frequency of kHz to
0 kHz predominantly the running noise of rolling bearings can be monitored,
whilst vibrational unbalances are attenuated.
3.3. Vibration Velocity
Measuring vibration velocity is a common procedure for assessing the running smooth-
ness of rotating machines. Vibration velocity, commonly known as vibration severity,
represents the energy expenditure of occurring vibrations. Vibrations are caused by rota-
tional unbalances, for example as a result of loose screws, bent parts, worn or slack bear-
ings or dirt residues on the fan blades. Often several factors have a mutually reinforcing
effect. Besides rotating machines, the measurement procedure is also suitable for recipro-
cating machines.
The specifications of vibration velocity measuring instruments are described in
ISO 2954. In the ISO 2954 a band filter for the vibration velocity of 0 to 000 Hz is de-
fined. The displayed value of the vibration severity is the true RMS.
5
Figure 3: Frequency response curves for acceleration
,1 1 1 1 1 1 1
, 1
, 1
,1
1
1 a: ,2Hz-1 kHz
a: 3Hz-1kHz
a: 1kHz-1 kHz
Hz
m /s ²

Besides the frequency range of 0 to 000 Hz, the VM25 has a further frequency
range for vibration severity measurements from 2 to 000 Hz. This is suitable for
measurements on slow running machines with a nominal speed of less than
20 min- and on reciprocating engines according to ISO 08 6-6.
The corresponding VM25 frequency response graph can be viewed in Figure 4.
Vibration velocity is formed through integration of the acceleration measured by the sen-
sor. The following formula applies to sinusoidal signals:
v=a
2Πf
It is evident that in the case of constant acceleration (a) the value of velocity (v) drops at
higher frequencies (f). As a consequence the measuring range limits of the velocity mea-
surements are frequency dependent. (Figure 5).The maximum velocity measurable
with the VM25 is around 000 mm/s (RMS). It yields a frequency independent
6
Figure 4: Frequency response curves for velocity
Figure 5: Amplitude range for velocity (RMS)
1 1 1 1 1
1
1
1
1
1
v: 2Hz – 3 Hz
v: 1 Hz – 1kHz
Integrator
Hz
mm/s
1 1 1 1 1
, 1
, 1
,1
1
1 v: 1 Hz – 1kHz
v: 2Hz – 1kHz
Hz
mm/s

modulation range of up to 40 Hz. At higher frequencies (RMS) the measuring range
limits for acceleration of around 240 m/s² take effect. In the attenuation range of the
low pass filter the modulation is further restricted.
3.4. Vibration Displacement
The vibration quantity most easily observed is displacement, also known as the de-
flection of the vibration. It is formed by double integration of the acceleration. In
comparison to velocity, the practically usable frequency range is even more re-
stricted. On the one hand it requires a high pass filter in order to attenuate low frequency
noise signals, which would otherwise appear amplified in the measurement values be-
cause of the double integration. On the other hand, frequencies in the range of less than
one hundred Hertz are so strongly dampened that an evaluable display value is no longer
recognizable.
Due to these restrictions, displacement measurements should only be applied where ac-
celeration or velocity is not capable of delivering the desired assessment.
The VM25 measures the vibration displacement from 5 to 200 Hz. The frequency re-
sponse diagram is shown in Figure 6. The curve ends at 200 Hz because even in the case
of a fully modulated sensor only single digit measurement values still occur.
The following formula applies to sinusoidal signals which have been formed through
double integration:
d=a
(2Πf)2
7
Figure 6: Frequency response curves for displacement
1 1 1 1
, 1
, 1
,1
1,
1 , d: 5Hz-2 Hz
Hz
mm

In the case of constant acceleration (a) it is visible that the displacement value (d) de-
creases quadratically with increasing frequency (f). As a consequence the measuring
range limits of displacement measurements are strongly frequency dependent. Figure 7
shows the measurement range limits depending on frequency.
The maximum displacement of the VM25 that can be measured is around 60 mm
(RMS). It yields a frequency independent modulation range of up to 0 Hz. At higher
frequencies the measuring range limits for acceleration of around 240 m/s² take effect.
3.5. Rolling Bearing Parameters K(t)
The rolling bearing parameter, also known as the diagnosis coefficient of Sturm
K(t), is an approved parameter for the condition analysis of rolling bearings, as de-
fined in the VDI 3832 (and other guidelines). It is formed by the RMS and peak
value of acceleration at a frequency range of to 0 kHz. The kHz high pass filter
ensures that the rolling bearing signal is not overlapped by the vibration of foreign
mechanical parts, such as imbalances.
The K(t) value relates the currently measured RMS and peak values to the RMS and
peak values at a starting point in time as follows:
K(t)= arms (0)⋅apk (0)
arms(t)⋅apk (t)
within this:
arms(0) RMS for the start point in time (reference point in time)
apk(0) maximum value (peak value) for start / reference point
arms(t) current RMS
apk(t) current maximum value (peak value)
The start or reference measurement is subsequent to first-time operation of the bear-
ing. Ideally after the elapse of a certain running-in time. At this point in time the
K(t) value is . Following ongoing wear and tear of the machine i.e. running dam-
8
Figure 7: Frequency response curves for displacement (RMS)
1 1 1 1
,1
1
1
1
1
Integratorkennlinie
d: 5Hz-2 Hz
Hz
mm