MMF M12 User manual

Instruction Manual
Manfred Weber
Metra Mess- und Frequenztechnik in Radebeul e.K.
Meissner Str. 58 - D- 1445 Radebeul / Germany
Phone [phone] Fax [phone]
Email: [e-mail] Internet: www.MMF.de
Universal
Vibration
Monitor
M12
Version C

Published by:
Manfred Weber
Metra Mess- und Frequenztechnik in Radebeul e.K.
Meißner Str. 58
D-0 445 Radebeul / Germany
Tel. [phone]
Fax [phone]
Email [e-mail]
Internet www.MMF.de
Notice: The latest version of this manual can be found at
http://www.mmf.de/produktliteratur.htm
© 20 7 Manfred Weber Metra Mess- und Frequenztechnik in Radebeul e.K.
May/ 7

Contents
. The M 2 at a Glance..................................................................................5
2. Purpose.......................................................................................................6
Measured Vibration Quantities.......................................................6
Outputs...........................................................................................6
Filters..............................................................................................6
LED Indicators...............................................................................6
3. Function......................................................................................................7
Sensor Input....................................................................................7
Amplifier.........................................................................................7
Filters..............................................................................................8
Integrators.......................................................................................8
RMS Rectification..........................................................................8
Peak-to-Peak Rectification..............................................................8
DC Outputs.....................................................................................8
4-20 mA Loop Output.....................................................................8
Alarm Relay....................................................................................8
Level Display..................................................................................9
Response time.................................................................................9
Self Test Functions........................................................................ 0
AC Output..................................................................................... 0
Overload Indication...................................................................... 0
Power Supply................................................................................ 0
Triple Insulation............................................................................ 0
4. Installation................................................................................................
4. . Preparing Measuring Points..........................................................................
Sensor Location............................................................................
ISO 08 6- ................................................................................. 2
4.2. Installation and Adjustment.......................................................................... 3
4.2. . Attachment............................................................................................ 3
Terminals...................................................................................... 4
4.2.2. Power Supply........................................................................................ 4
Power-on Alarm Delay.................................................................. 4
4.2.3. Sensor................................................................................................... 5
Sensor Input.................................................................................. 5
Sensitivity Adjustment.................................................................. 5
Sensor Status Indication................................................................ 5
Sensor Connection........................................................................ 7
Operation of Two M 2 Modules with One Sensor........................ 7
4.2.4. Selecting a Vibration Quantity.............................................................. 8
Dynamic Range of the Integrators................................................. 9
RMS / Peak-to-Peak..................................................................... 9
Response time............................................................................... 9
4.2.5. Selecting the Measuring Range.............................................................20
Overload Indication......................................................................20
4.2.6. Plug-in Filters.......................................................................................20

Slope.............................................................................................20
Factory Configuration...................................................................20
Replacing Filter Modules..............................................................2
4.2.7. Relay Output.........................................................................................22
Adjustments..................................................................................22
Connection of the Relay Output....................................................22
Self Test Function.........................................................................23
Sensor Monitoring........................................................................23
Contact Rating..............................................................................23
4.2.8. Current Loop 4-20 mA Output.............................................................23
Connection....................................................................................24
Insulation......................................................................................24
False Polarization.........................................................................24
4.2.9. DC Outputs...........................................................................................25
4.2. 0. AC Output...........................................................................................25
Filtering and Integration...............................................................25
Settings.........................................................................................25
Output Level.................................................................................27
Bandwidth.....................................................................................27
Connection....................................................................................27
4.3. Calibration....................................................................................................28
Factory Calibration.......................................................................28
Calibration Point...........................................................................28
Vibration Calibrator......................................................................28
Electrical Calibration....................................................................28
4.4. Vibration Level Display M 2DIS.................................................................29
Connection....................................................................................29
LED Backlighting.........................................................................29
Mounting......................................................................................30
Calibration....................................................................................30
5. Measuring Methods for Machine Vibration.............................................3
5. . Vibration Severity Measurement for Unbalance...........................................3
ISO 08 6- .................................................................................3
Measurement with the M 2..........................................................32
5.2. Vibration Measurement on Reciprocating Engines.......................................33
DIN/ISO 08 6-6.........................................................................33
Measurement with the M 2..........................................................34
5.3. Bearing Monitoring......................................................................................34
General.........................................................................................34
Crest Factor...................................................................................34
Diagnostic Coefficient..................................................................35
Measurement with the M 2..........................................................35
6. Technical Data..........................................................................................36
Appendix: Warranty
Declaration of CE Conformity

1.The M12 at a Glance
Front View:
AC Out-I Out+I Out
COM
+UsPK-PKRMS
-UsGNDInput
relay outputs
4-2 mA loop / AC output
RMS / peak-to-peak outputs
positive supply terminal
sensor input, signal ground
negative supply terminal
rear terminals
front terminals
N.C. N.O.
1
1
%
25
s %
LED bargraph display
for monitored quantity
and alarm threshold
Alarm OK OVL
LEDs for alarm,
sensor condition and overload
potentiometers for alarm delay
and alarm threshold
rear terminals
front terminals
Side View:
5
Adjustment of
transducer sensitivity
1 2 3 4 5 6 7 8 91
Function of the DIP switches
in their lower position
1: Sensor supply on
2: Range 1
3: Range 5
4: Range 25
5: Double integration (displacement)
6: Single integration (velocity)
7: Integration off (acceleration)
8: RMS monitoring
9: Peak-to-peak monitoring
1 : Alarm duration short

2.Purpose
The Universal Vibration Monitor is suitable for applications
where vibrations need to be monitored or measured. Typical
applications include condition monitoring of rotating machin-
ery to ISO 08 6 and bearing monitoring. The M 2 provides
information about the running condition of a machine.
Thereby it helps the maintenance engineer to predict wear in
time and to avoid unexpected breakdown. Thus the M 2 can
reduce cost caused by production loss and unnecessary re-
pairs. The M 2 can also be used for many tasks in process
and quality control.
Its flexible design makes it easy to adapt the M 2 for any
monitoring application. This can be of particular advantage if
no information about the vibration signal and its frequency
components is available before installation.
The M 2 provides standardized output signals for further pro-
cessing. A relay output for shut-off functions or alarm mes-
sages is also available.
Measured
Vibration
Quantities
The M 2 is designed for operation with an IEPE compatible
piezoelectric accelerometer. It can be used for measuring the
following quantities
• Vibration acceleration (without integration)
• Vibration velocity (single integration)
• Vibration displacement (with double integration)
For each vibration quantity among 3 measuring ranges can be
chosen.
Outputs The vibration signal is available at the following outputs:
• AC wide band output of amplified but unfiltered sensor
signal
• AC output of amplified, filtered and, if necessary, inte-
grated sensor signal
• DC output of true RMS for selected vibration quantity
• DC output of peak-to-peak value for selected vibration
quantity
• 4-20 mA current loop output of RMS or peak-to-peak
value for selected vibration quantity
Filters The use of replaceable filter modules makes the M 2 particu-
larly versatile. High pass and low pass frequencies can be se-
lected individually by means of an extensive range of avail-
able filter modules.
LED Indicators The following LED indicators can be found at the front panel:
• Alarm LED
• Sensor status LED
• Overload LED
• LED bar graph for monitored vibration quantity and
alarm threshold
6

3.Function
Figure : Block diagram
Sensor Input The M 2 requires for operation a piezoelectric accelerometer
with integrated electronics to IEPE standard. The instrument
is factory calibrated for standard industrial accelerometers
with 00 mV/g sensitivity, for example Models KS80 or
KS8 of Metra with protection grade IP67 and insulated case.
The constant current for the integrated sensor electronics is
supplied by the M 2 and can be activated by DIP switch .
Amplifier The amplifier with variable gain has over 50 kHz bandwidth.
At the side wall of the instrument a potentiometer for trans-
ducer sensitivity fine tuning can be found. The adjustable
range is 0 to 00 mV/g. The M 2 has 3 gain ranges which
can be selected by the DIP switches nos. 2, 3 and 4 at the side
wall as shown in the following table:
Vibration
acceleration
Vibration
velocity
Vibration
displacement
DIP 2 0 m/s² 0 mm/s 00 µm
DIP 3 50 m/s² 50 mm/s 500 µm
DIP 4 250 m/s² 250 mm/s 2500 µm
7
IEPE
Supply
Integrator
1
Highpass
2 poles
Plug-in
module
~
~
pk-pk
rms
AC Output
Integrator
2
pk-pk
rms
Transducer
Monitoring
Opto
Coupler
U
I
Loop Output
4-2 mA
Alarm
Threshold
Alarm
Delay
Alarm
Hold
Alarm
Relay Relay
Output
Alarm Threshold
(Front)
Dalay
(Front)
2/8 s
DC Output
rms
Bar
graph
Level
Alarm Threshold
Sensor OK
Alarm
Transd.
Fault
Overload LED
Overload
Comparator
DC Output
pk-pk
V1
V2
V3
ICP
a
v
d
Transducer sensitivity
Output
Driver
Amplifier
J1
filtered
unfiltered
1
2
3
4
5
6
7
8
9
1
Input
Stage
Lowpass
4 poles
Plug-in
module

Filters The M 2 contains separate high pass and low pass filters.
These filters are designed as plug-in modules. Thus they can
be replaced on site if necessary. The high pass filter has two
poles with an attenuation of about 40 dB/decade. The low
pass filter has four poles with about 70 dB/decade attenua-
tion.
Integrators For measuring vibration acceleration the M 2 is used without
integrators. When vibration velocity is measured, one integra-
tor is in the signal path. Vibration displacement requires dou-
ble integration. The integrators are switched on or off by the
DIP switches nos. 5 to 7.
RMS
Rectification
The instrument measures the true RMS value which ensures
high accuracy independently of the signal shape. The RMS
output is available via a 0 to 0 VDC output for external pro-
cessing. The RMS refresh rate is approx. value / second.
Peak-to-Peak
Rectification
Additionally, the peak-to-peak value of the selected vibration
quantity is measured. True peak-to-peak rectification ensures
high accuracy independently of the signal shape. The absolute
values of the highest positive and the lowest negative sample
of the last 00 ms are added. The peak-to-peak output is
available via a 0 to 0 VDC output for external processing.
The refresh rate is 00 ms.
DC Outputs Both RMS and peak-to-peak values are available simultane-
ously at two separate outputs. Only one of these signals, how-
ever, can be used for controlling the relay and the 4-20 mA
output. The monitoring mode is selected by the DIP switches
no. 8 (RMS) and 9 (Peak-to-peak).
4-20 mA Loop
Output
The RMS or peak-to-peak value of the selected vibration
quantity is available as 4-20 mA current loop signal. This cur-
rent loop output allows the transmission of analog signals
over long distances with inexpensive cables. At the destina-
tion the pre-processed vibration signal can be fed into PLCs,
panel meters, recorders or other 4-20 mA equipment.
A side effect of long distance signal transmission can be
ground loops. The accuracy of the M 2 will not be affected
by this phenomenon since the current loop output is optically
insulated from the rest of the circuit.
Alarm Relay In addition to its analog outputs, the M 2 features a relay out-
put which can be used to trigger external events when the ad-
justed threshold is exceeded. Possible devices to be connected
are, for instance, contactors, alarm signals or binary inputs of
a PLC. The relay output has a potential-free “Form C” con-
tact. An “Alarm” LED indicates that the relay has responded.
Both alarm threshold and delay (td) can be adjusted at the
front panel. The adjustable delay range is 0 to 25 seconds.
The relay hold time can be selected between two and eight
seconds by means of DIP switch no. 0.
Figure 2 illustrates how the alarm management works.
8

t
Alarm
threshold
Alarm on
Alarm off
tdt
td
12
3
4
7
6
5
th
on
Figure 2: Alarm management
The upper curve of the diagram represents a typical vibration
signal over time. It can be RMS or peak-to-peak signals. The
lower curve shows the relay response.
At point  the adjusted threshold was exceeded. Now the de-
lay time td starts. It can be adjusted at the front panel between
0 and 25 s. Since the signal drops below the threshold at point
 before the delay time was over, no alarm will be tripped at
point . By selecting an appropriate delay time is guaranteed
that no alarm will be tripped by short signal transients. They
may occur during machine start up or under the influence of a
short mechanical shock pulse. At point  the alarm threshold
is exceeded again and the delay time starts for the second
time. Now an alarm will be tripped since after td at point 
the alarm threshold is still exceeded. The relay remains active
until the vibration level drops below the limit at . Now the
alarm hold time th begins. It can be selected by DIP switch no.
0 between 2 and 0 seconds. When this hold time is over at
point  the relay switches back. The purpose of a pre-se-
lected hold time is to ensure save switching of external com-
ponents.
Level Display The bar graph display at the front panel has two functions. On
one hand, it shows the current RMS or peak-to-peak value of
the selected vibration quantity between 0 and 00 % of the
full-scale value. On the other, it shows the relay threshold
which can be adjusted by the potentiometer below.
The LED display gives comprehensible information about the
current status of the vibration monitor.
Please note also the optionally available display module
M 2DIS (see section 4.4).
Response time For time-critical monitoring applications the peak-to-peak
value is recommended because of its higher refresh rate at the
analog outputs and the relay output.
9

Self Test
Functions
It is expected that monitoring equipment should have a very
high reliability. Unnoticed faults need to be avoided and false
alarms as well. Maximum reliability of the M 2 is guaran-
teed by a two-stage self-test circuitry:
Monitoring of sensor bias voltage recognizes defective ac-
celerometers and cables. When an open loop at the sensor in-
put is detected, the “OK” LED is switched off. A short circuit
at the input is indicated by a flashing “OK” LED. In both
cases the relay will switch to alarm position whereas the
“Alarm” LED remains dark.
Power supply failure also causes the relay contact to switch
into the alarm position.
AC Output In addition to the DC outputs, the M 2 also provides a “raw”
vibration signal. By means of Jumper a selection can be
made between the buffered and unfiltered sensor signal or the
amplified, filtered and, if selected, integrated signal (see Fig-
ure ).
In the first case, the AC output provides the sensor signal with
a bandwidth of over 50 kHz. Please note that most standard
accelerometers have their resonance at 20 to 30 kHz.
In the second case, the AC signal is pre-processed in accor-
dance with the selected vibration quantity and the inserted fil-
ters.
Overload
Indication
An LED “OVL” is located at the front panel. It signals an
overload condition before the filters, after the amplifier and
after the integrators. If the LED starts flashing, the measuring
signal will still be undistorted but it reaches its limits at
± 0 V.
Power Supply The M 2 needs for operation a DC supply voltage of 2 to
28 V. Its current consumption is between 80 and 200 mA. The
lower the supply voltage, the higher the supply current.
Triple Insulation Optimum protection against grounding problems is achieved
by triple insulation between supply voltage, signal path and
current loop output.
Power
Supply
4-2 mA
Output
Signal Path
Figure 3: Triple Insulation
0

4.Installation
4.1.Preparing Measuring Points
Sensor Location Before making measurements, suitable measuring points on
the machine need to be found. Experience in machine condi-
tion maintenance is advantageous for selecting optimum
spots.
Dynamic forces are normally transmitted via bearings and
their housings into the machine frame. Therefore, bearing
housings or points close to bearings are recommended as
measuring points. Less suitable are light or flexible machine
parts (Figure 4).
Uneven surface
Rough surface
Flexible part
F
Sensor coupling with best
transmission properties:
Stud bolt
smooth
surface
Stainless steel disk
Epoxy glued
or welded
A thin layer of grease improves
high frequency transmission.
Figure 4: Recommendations for sensor mounting
An even and smooth surface at the mounting point is indis-
pensable for precise vibration transmission from the machine
to the accelerometer. Measuring points that are uneven,
scratched or insufficiently sized may cause considerable er-
rors, particularly at frequencies above kHz.
For best coupling conditions, we recommend a stainless steel
disk with mounting thread (for instance Metra Model 229)
which can be epoxy glued or welded onto the machine.
The accelerometer is usually mounted by stud bolts. A thin
layer of grease will improve high frequency transmission. For
temporary installations a magnetic base can also be useful (for
instance Metra Model 008).

ISO 10816-1
The standard ISO 08 6- recommends that vibration mea-
surements on machines be made at the housing of bearings or
nearby measuring points.
For routine monitoring it is sufficient in many cases to mea-
sure vibration either in vertical or in horizontal direction.
Rigidly mounted machines with horizontal shafts have their
highest vibration levels mostly in a horizontal direction. Flex-
ibly mounted machines may have high vertical components of
vibration, too.
For inspections, vibration should be measured in all three di-
rections (vertical, horizontal and axial) at all bearings.
The following illustrations show some examples for suitable
measuring points.
You will also find recommendations for measuring points at
different types of machines in ISO 3373- .
vertical
horizontal
axial
vertical
horizontal
axial
Figure 5: Measuring points on pillow block bearings
horizontal
axial
vertical
axial horizontal
vertical
Figure 6: Measuring points on end shield bearings
2

axial 2
vertical 2
horizontal 2
vertical 1
axial 1
horizontal 1
Figure 7: Measuring points on electric motors
4.2.Installation and Adjustment
4.2.1.Attachment
The M 2 is designed for 35 mm DIN rails which are mounted
horizontally. It should be installed in a dry and dust protected
environment, preferably in switch cabinets.
To attach or release a module pull out the black lever on the
top of the enclosure using a screw driver as shown in Figure
8.
1. Pull out lever
2. Insert notch
3. Snap into position
Figure 8: DIN rail attachment
3

Make sure that there is at least 4 cm clearance above and un-
der the case in order to allow ventilation. The power dissipa-
tion of each M 2 is approx. 2.5 W.
The ambient temperature must not exceed 55 °C. In some
cases artificial ventilation may be necessary.
Terminals All inputs and outputs are connected via terminal blocks.
They are suited for cable diameters of 0. 4 to 4 mm² for sin-
gle wire and 0. 4 to 2.5 mm² for stranded wire.
Before attaching the case to the DIN rail, check that the fol-
lowing settings have been done:
Filter settings: Chapter 4.2.6, Page 20;
AC output settings: Chapter, 4.2. 0, Page 25.
4.2.2.Power Supply
The M 2 requires for operation a DC supply voltage between
2 and 28 V which is usually available in switch cabinets.
Well suited are industrial 24 VDC power supplies for DIN
rail attachment. The current consumption is between 80 and
200 mA, depending on the supply voltage. Figure 9 shows the
connections. The M 2 is protected against false polarization
and short overvoltage transients. The power supply is insu-
lated from the signal path.
AC Out-I Out+I Out
COM
+UsPK-PKRMS
-UsGNDInput
N.C. N.O.
1
1
%
25
s %
1 1
Alarm OK OVL
rear terminals
front terminals positive supply (+)
negative supply (-)
Figure 9: Power supply connection
Power-on Alarm
Delay
After connecting the power supply 5 seconds will pass before
monitoring starts. During this time the relay is held in “OK”
position. This avoids false alarms during settling.
4

4.2.3.Sensor
Sensor Input The M 2 is suitable for all kinds of IEPE accelerometers.
The built-in constant current supply provides 4 mA supply
current. A compliance voltage of 24VDC ensures full dy-
namic input range independent of the sensor bias voltage. The
constant current source is activated by pushing the DIP switch
no. “IEPE Supply” towards the “ON” position (Figure 0).
Figure 0: Activation of sensor supply
Sensitivity
Adjustment
The M 2 is suited for IEPE compatible accelerometers with
sensitivities between 0 and 00 mV/g or to 0 mV/ms-2,
respectively. The instrument is supplied pre-calibrated for
transducers with a sensitivity of 00 mV/g. If sensors with
other sensitivities are used, the M 2 must be re-calibrated
(see chapter 4.3, Page 28).
Please make sure that the constant current source (IEPE sup-
ply, DIP switch no. ) is switched on.
The input is protected against overvoltage transients which
may occur when the sensor is exposed to mechanical shock.
Ground loops may cause considerable measuring errors. To
avoid these problems, preferably accelerometers with insu-
lated base or with insulating flanges should be used. The
ground potentials of the machine and the M 2 are thereby
separated.
Sensor Status
Indication
The M 2 can detect sensor faults. This is achieved by moni-
toring the bias voltage at the sensor output. Normal sensor
operation is indicated by the LED “OK”. The LED is
switched off and the relay switches to the alarm position
when the bias voltage exceeds 20 VDC. In this case the con-
stant current source is not able to drive sufficient current
through the sensor circuit. Possible reasons may be a broken
sensor cable, a loose plug or a defective sensor. Another rea-
son might also be an extreme overload condition at the sensor
output.
Figure illustrates the sensor bias voltage and the limits of
the dynamic range.
The “OK” LED flashes when the input is shorted.
5
1 2 3456 7 8 9 1
IEPE supply on
1 2 3 4 5 6 7 8 9 1
IEPE supply off

saturation voltage
of the sensor:
typically <1 V
sensor bias voltage:
typically 8 .. 12 V
negative overload
dynamic range of the sensor
V
positive overload
threshold of sensor
monitoring: 2 V
Figure : Dynamic range and bias voltage of IEPE sensors
Sensor
Connection
The accelerometer is connected via coaxial cable or multi-
wire shielded cables. Cables of several hundred meters length
are permissible. Limitations are cable resistance and electro-
magnetic immunity.
The connection of the sensor is shown in Figure 2.
AC Out-I Out+I Out
COM
+UsPK-PKRMS
-UsGNDInput
N.C. N.O.
1
1
%
25
s %
1 1
Alarm OK OVL
rear terminals
front terminals
sensor ground
sensor signal
Figure 2: Sensor connection
Important: Make sure not to swap sensor ground and sensor
signal. This may destroy the electronic circuit inside the sen-
sor. Please contact the sensor manufacturer if you are not sure
about the cable assignment.
6

Operation of Two
M12 Modules
with One Sensor
Two M 2 modules can be operated with one mutual sensor. In
this way many useful applications are possible.
Figure 3 shows, for example, a combination for monitoring
vibration velocity and acceleration with one sensor. It can be
used to measure unbalance and bearing noise simultaneously.
Figure 4 shows an example for monitoring vibration velocity
to ISO 08 6 with 2 alarm levels. By 2 different alarm set-
tings pre-alarm and main alarm can be triggered.
Figure 4: Monitoring system with 2 alarm levels
7
AC Out-I Out+I Out
COM
+UsPK-PKRMS
-UsG NDInput
N.C. N.O.
1
1
%
25
s %
1 1
Alarm OK OVL
AC Out-I Out+I Out
COM
+UsPK-PKRMS
-UsGNDInput
N.C. N.O.
1
1
%
25
s %
1 1
Alarm OK OVL
accelerometer
1 2 3 4 5 6 7 8 91 1 2 3 4 5 6 7 8 91
IEPE supply on IEPE supply off
Unit 1:
vibration
velocity
1 .. 1 Hz
pre-alarm
Unit 2:
vibration
velocity
1 .. 1 Hz
main alarm
Figure 3: Monitoring vibration velocity and acceleration with one sensor
AC Out-I Out+I Out
COM
+UsPK-PKRMS
-UsGNDInput
N.C. N.O.
1
1
%
25
s %
1 1
Alarm OK OVL
AC Out-I Out+I Out
COM
+UsPK-PKRMS
-UsGNDInput
N.C. N.O.
1
1
%
25
s %
1 1
Alarm OK OVL
Unit 2:
vibration
acceleration
1 .. 1 kHz
accelerometer
1 2 3456 7 8 9 1 1 2 3 4 5 678 91
IEPE supply on IEPE supply off
Unit 1:
vibration
velocity
1 .. 1 Hz

Please note that only one constant current source (IEPE sup-
ply, DIP switch no. ) must be switched on when operating
two M 2 modules with the same sensor (compare Figure 3
and Figure 4).
Nevertheless the sensor status indication will work normally
in both M 2 units.
4.2.4.Selecting a Vibration Quantity
The M 2 is capable of monitoring vibration acceleration, ve-
locity and displacement, corresponding to no integration, sin-
gle integration and double integration. RMS and peak-to-peak
rectification are available for each vibration quantity. During
installation the required quantity must be selected by the DIP
switches at the side wall of the case. These adjustments have
effect on the relay output, the 4-20 mA output and the bar
graph display.
The vibration quantities (or integrators) are selected by push-
ing down one of the DIP switches nos. 5 to 7 as shown in Fig-
ure 5.
Figure 5: Selecting the vibration quantity
Dynamic Range
of the Integrators
A typical property of integrators is that the output voltage de -
creases with increasing frequency. When one or both integra-
tors are switched on, the dynamic range of the M 2 will de-
crease rapidly at frequencies of a few hundred Hertz (Figure
6). If double integration is selected, for example, the dy-
namic range at 60 Hz will become only 0 % of full scale.
Instead of 2500 µm the maximum displacement to be mea-
sured will be only 250 µm, consequently. Therefore, the use
of integrators usually makes sense only at lower frequencies.
Vibration signals with frequencies in the Kilohertz range
should always be measured as acceleration.
For very low frequencies the integrators provide high output
levels. Low frequency noise, which may originate from the
sensor or the amplifier circuit, will be amplified by the inte-
grators. It is recommended therefore to insert a high pass fil-
ter of 3 Hz or more when the integrators are used.
8
5: Displacement (double integration)
1 2 3 4 5 6 7 8 91
6: Velocity (single integration)
1 2 3 4 5 6 7 8 9 1
7: Acceleration
123 4 5 6 78 91

%
Dynamic range
1
1
1
1 1 1 1
Hz
Vel.
mm/s
Displ.
µm
25
25
Acc.
m/s²
25
Vibration velocity
single integration
Vibration displacement
double integration
Vibration acceleration
no integration
252525
252,52,5
1616
Dynamic range for vibration displacement
Dynamic range for vibration velocity
Dynamic range for vibration acceleration
Figure 6: Dynamic range of the integrators
RMS /
Peak-to-Peak
By means of the DIP switches nos. 8 and 9 a selection can be
made between RMS and peak-to-peak rectification.
Figure 7: Selecting the rectification mode
Only one of the DIP switches 8 and 9 must be switched on.
Response time For time-critical monitoring applications the peak-to-peak
value is recommended because of its higher refresh rate at the
analog outputs and the relay output.
4.2.5.Selecting the Measuring Range
The instrument features three measuring ranges. They are se-
lected by the DIP switches nos. 2, 3 and 4. Push the switch
lever for the desired range downwards. The following table
shows the measuring ranges for each vibration quantity.
DIP
Switch
Vibration
Acceleration
(no integration)
Vibration
Velocity
(single integration)
Vibration
Displacement
(double integration)
2 0 m/s² 0 mm/s 00 µm
3 50 m/s² 50 mm/s 500 µm
4 250 m/s² 250 mm/s 2500 µm
Only one of the DIP switches 2, 3 and 4 must be switched on.
The full-scale values in the above table are reached with both
RMS and peak-to-peak rectification. The measuring ranges
are only valid under the condition that the VM 2 was cali-
brated with its accelerometer (compare chapter 4.3, page 28).
9
8: RMS detection
1 2 3 4 5 6 7 8 9 1
9: peak-to-peak detection
1 2 3 4 5 678 9 1

Overload
Indication
If the LED “OVL” lights up the measuring range should be
increased. An overload indication does not necessarily mean
that the RMS or peak-to-peak outputs are overloaded. In some
cases the reason may be a dominant frequency component be-
yond the filter pass band which does not appear at the output
but which overloads the amplifier. This can be checked at the
AC output provided jumper J is in position -2.
4.2.6.Plug-in Filters
The M 2’s replaceable filters make it particularly versatile.
They can be configured on site depending on the vibration
signal.
The M 2 has two 8 pin sockets for a high pass and a low pass
filter module. These filter modules are available as acces-
sories. Metra offers the following versions:
Low pass plug-in filter Model FB2: 0, kHz; 0,3 kHz;
0,5 kHz; kHz;
3 kHz; 5 kHz; 0 kHz;
30 kHz kHz
High pass plug-in filter Model FB3: 2 Hz; 3 Hz; 5 Hz; 0 Hz;
30 Hz; 50 Hz; 00 Hz;
300 Hz; 500 Hz; 000 Hz
Filters with other frequencies can be supplied on demand.
Slope The low pass filters of FB2 series have 4th order Butterworth
characteristics with a slope of about 70 dB/decade.
The high pass filters of FB2 series are 2nd order filters with
about 40 dB/decade attenuation.
Factory
Configuration
The M 2 is supplied with the filter modules as desired by the
customer. The cut-off frequencies of the built in filters can be
found on the M 2 label.
Replacing Filter
Modules
To insert or replace a filter module the case has to be opened.
The lid is removed, as shown in Figure 8, by opening 6 snap
tabs using a screw driver.
Figure 8: Opening the case
20