MMF VM24 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: [email protected] Internet: www.MMF.de
Vibration Meter
VM24
Valid from Version xxx. 21

Published by:
Manfred Weber
Metra Mess- und Frequenztechnik in Radebeul e.K.
Meißner Str. 58
D-0 445 Radebeul
Tel. [phone]
Fax [phone]
Email [email protected]e
Internet www.MMF.de
Note: The latest version of this manual can be found at http://www.mmf.de/prod-
uct_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.
Aug/ 20

Contents
. Purpose.................................................................................................................3
2. Function................................................................................................................3
2. . The 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
4. The Batteries.........................................................................................................8
4. . Inserting the Batteries....................................................................................8
4.2. Switching On and Off....................................................................................9
4.3. Battery Display and Battery Type............................................................... 0
4.4. Shut-off Timer.............................................................................................
5. Preparation of Measuring Points.........................................................................
5. . General Information on Measurement Point Choice....................................
5.2. ISO 08 6- Recommendations..................................................................
5.3. VMID Measurement Point.......................................................................... 3
5.3. . How the VMID Measurement Point Functions.................................... 3
5.3.2. Mounting the VMID Measurement Point............................................. 3
6. Measurement...................................................................................................... 4
6. . Measurement Value Display........................................................................ 4
6.2. Selecting the Display Quantity.................................................................... 4
6.3. Measurement Point Detection...................................................................... 5
6.3. . Reading the VMID Data with the VM24............................................. 5
6.3.2. Entering the Measurement Point Text.................................................. 5
6.3.3. Editing and Deleting Measurement Point Data.................................... 7
6.4. Saving Measurands...................................................................................... 7
6.5. Graphical Trend Display............................................................................. 7
6.6. Viewing Saved Measurement Values.......................................................... 8
6.7. Deleting Saved Measurement Data.............................................................. 9
7. Measurement Evaluation with Standard Values.................................................. 9
8. Setting the Date and Time..................................................................................22
9. Calibration..........................................................................................................23
0. Sensor Check....................................................................................................25
. Reset Key..........................................................................................................25
2. Connection to a PC...........................................................................................26
2. . Device Driver............................................................................................26
2.2. VM2x Measurement Database...................................................................26
2.3. Firmware Update.......................................................................................27
3. Technical Data..................................................................................................30
Appendix: Warranty
Declaration of CE Conformity

2
Figure : VM24 with Sensor

Thank you for choosing a Metra Vibration Measurement Instrument!
1. Purpose
The VM24 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
guarantees.
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 VM24 measures and records vibration acceleration, vibration velocity or vibra-
tion displacement. The VM24 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.
An external piezoelectric accelerometer is used as the sensor, and is provided to -
gether with the instrument. The VM24 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 VM24 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
technology.
In the development of the VM24 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 Sensor
The VM24 operates with a piezo ceramic shear accelerometer. Piezoelectric vibra-
tion transducers are characterized by high precision and resolution with great ro-
bustness. The accelerometer of the VM24 has an integrated electronic circuit for im-
pedance 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
2 shows the block diagram. The VM24 supplies the IEPE Sensor with 2 mA con-
stant current. At the sensor output, a vibration acceleration proportional AC voltage
arises, which is amplified in the instrument to produce an optimum level. The gain
switch-over takes place automatically. The subsequent analogue/digital converter 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 USB communication and the storing of measurements.
3. Measuring Ranges
3.1. Measurable Vibration uantities
The VM24 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
Micro
controller
Display
Memory
Keys
Sensor
ID
USB
Power
supply

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 VM24 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 attenu -
ated. 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 VM24 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 VM24 frequency response graph can be viewed in 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. (5).
The maximum velocity measurable with the VM24 is around 000 mm/s (RMS). It
yields a frequency independent modulation range of up to 40 Hz. At higher frequen-
cies (RMS) the measuring range limits for acceleration of around 240 m/s² take ef-
6
Figure 4: Frequency response curves for velocity
Figure 5: Amplitude range for velocity (RMS)
1 10 100 1000
10
100
1000
10000
v: 2Hz – 1kHz
v: 10Hz – 1kHz
Integrator
Hz
mm/s
1 10 100 1000 10000
0,001
0,010
0,100
1,000
10,000 v: 2Hz – 1kHz
v: 10Hz – 1kHz
Hz
mm/s

fect. In the attenuation range of the low pass filter the modulation is further re -
stricted.
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 VM24 measures the vibration displacement from 5 to 200 Hz. The frequency re-
sponse diagram is shown in 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. 7 Dis-
plays the measurement range limits depending on frequency.
The maximum displacement of the VM24 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.
4. The Batteries
4.1. Inserting the Batteries
The VM24 is supplied by three alkaline standard cell type AAA (LR03) batteries.
NiMH batteries (HR03) may also be used. The minimum energy requirement of the
VM24 enables maximum utilization of the batteries.
Attention: Please switch the instrument off before changing the batteries. When
switched off, the contents of the memory are stored for a few minutes, without need
of the batteries, and the internal clock continues to run. If the batteries are removed
when the instrument is switched on or if they remain in the instrument until the bat-
teries have been completely discharged, the date and time will need to be reset. Fur-
ther settings as well as the saved measurands, are stored without need of the batter-
ies.
To insert the batteries, remove the two screws from the back cover of the device and
open the battery compartment (8). When inserting the batteries, please ensure that
their polarity is correct, (see the engraved markings inside the compartment).
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