Instruction Manual
Manfred Weber
Metra Mess- und Frequenztechnik in Radebeul e.K.
Meissner Str. 58 - D-01445 Radebeul / Germany
Phone +49-351 849 21 04 Fax +49-351 849 21 69
Email: Info@MMF.de 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-01445 Radebeul / Germany
Tel. +49-351-836 2191
Fax +49-351-836 2940
Email Info@MMF.de
Internet www.MMF.de
Notice: The latest version of this manual can be found at
http://www.mmf.de/produktliteratur.htm
© 2017 Manfred Weber Metra Mess- und Frequenztechnik in Radebeul e.K.
May/ 17
Contents
1. The M12 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........................................................................10
AC Output.....................................................................................10
Overload Indication......................................................................10
Power Supply................................................................................10
Triple Insulation............................................................................10
4. Installation................................................................................................11
4.1. Preparing Measuring Points..........................................................................11
Sensor Location............................................................................11
ISO 10816-1................................................................................. 12
4.2. Installation and Adjustment..........................................................................13
4.2.1. Attachment............................................................................................13
Terminals......................................................................................14
4.2.2. Power Supply........................................................................................14
Power-on Alarm Delay..................................................................14
4.2.3. Sensor................................................................................................... 15
Sensor Input..................................................................................15
Sensitivity Adjustment..................................................................15
Sensor Status Indication................................................................15
Sensor Connection........................................................................17
Operation of Two M12 Modules with One Sensor........................17
4.2.4. Selecting a Vibration Quantity..............................................................18
Dynamic Range of the Integrators.................................................19
RMS / Peak-to-Peak.....................................................................19
Response time...............................................................................19
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..............................................................21
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
4.2.10. 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 M12DIS.................................................................29
Connection....................................................................................29
LED Backlighting.........................................................................29
Mounting...................................................................................... 30
Calibration....................................................................................30
5. Measuring Methods for Machine Vibration.............................................31
5.1. Vibration Severity Measurement for Unbalance...........................................31
ISO 10816-1................................................................................. 31
Measurement with the M12..........................................................32
5.2. Vibration Measurement on Reciprocating Engines.......................................33
DIN/ISO 10816-6.........................................................................33
Measurement with the M12..........................................................34
5.3. Bearing Monitoring......................................................................................34
General.........................................................................................34
Crest Factor...................................................................................34
Diagnostic Coefficient..................................................................35
Measurement with the M12..........................................................35
6. Technical Data..........................................................................................36
Appendix: Warranty
Declaration of CE Conformity
1.The M12 at a Glance
Front View:
AC O ut-I Out+I Out
COM
+UsPK-PKRMS
-UsGNDInp ut
relay outputs
4-20 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.
10
100
%
0 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 8 910
Function of the DIP switches
in their lower position:
1: Sensor supply on
2: Range 10
3: Range 50
4: Range 250
5: Double integration (displacement)
6: Single integration (velocity)
7: Integration off (acceleration)
8: RMS monitoring
9: Peak-to-peak monitoring
10: 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 machinery to ISO 10816 and bearing monitoring. The M12 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 M12 can
reduce cost caused by production loss and unnecessary repairs. The M12 can also be used for many tasks in process
and quality control.
Its flexible design makes it easy to adapt the M12 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 M12 provides standardized output signals for further processing. A relay output for shut-off functions or alarm messages is also available.
Measured
Vibration
Quantities
The M12 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, integrated 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 M12 particu larly versatile. High pass and low pass frequencies can be selected individually by means of an extensive range of available 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 1: Block diagram
Sensor Input
The M12 requires for operation a piezoelectric accelerometer
with integrated electronics to IEPE standard. The instrument
is factory calibrated for standard industrial accelerometers
with 100 mV/g sensitivity, for example Models KS80 or
KS81 of Metra with protection grade IP67 and insulated case.
The constant current for the integrated sensor electronics is
supplied by the M12 and can be activated by DIP switch 1.
Amplifier
The amplifier with variable gain has over 50 kHz bandwidth.
At the side wall of the instrument a potentiometer for transducer sensitivity fine tuning can be found. The adjustable
range is 10 to 100 mV/g. The M12 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 10 m/s² 10 mm/s 100 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
4-20 mA
Alarm
Threshold
Alar m
Delay
Ala rm
Hold
Alar m
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
10
Input
Stage
Lowpass
4 poles
Plug-in
module
Filters
The M12 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 attenuation.
Integrators
For measuring vibration acceleration the M12 is used without
integrators. When vibration velocity is measured, one integrator is in the signal path. Vibration displacement requires double 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 10 VDC output for external processing. The RMS refresh rate is approx. 1 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 100 ms are added. The peak-to-peak output is
available via a 0 to 10 VDC output for external processing.
The refresh rate is 100 ms.
DC Outputs
Both RMS and peak-to-peak values are available simultaneously at two separate outputs. Only one of these signals, however, 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 current 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 M12 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 M12 features a relay output 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. 10.
Figure 2 illustrates how the alarm management works.
8
t
Alarm
threshold
Alarm on
Alarm off
t
d
t
t
d
1
2
3
4
7
6
5
t
h
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 delay 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.
10 between 2 and 10 seconds. When this hold time is over at
point the relay switches back. The purpose of a pre-selected hold time is to ensure save switching of external components.
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 10 and 100 % 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
M12DIS (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 M12 is guaranteed by a two-stage self-test circuitry:
Monitoring of sensor bias voltage recognizes defective accelerometers and cables. When an open loop at the sensor input 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 M12 also provides a “raw”
vibration signal. By means of Jumper 1 a selection can be
made between the buffered and unfiltered sensor signal or the
amplified, filtered and, if selected, integrated signal (see Figure 1).
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 accordance with the selected vibration quantity and the inserted filters.
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
±10 V.
Power Supply
The M12 needs for operation a DC supply voltage of 12 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
4-20 mA
Output
Signal Path
Figure 3: Triple Insulation
10
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 condition 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 indispensable for precise vibration transmission from the machine
to the accelerometer. Measuring points that are uneven,
scratched or insufficiently sized may cause considerable errors, particularly at frequencies above 1 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).
11
ISO 10816-1
The standard ISO 10816-1 recommends that vibration measurements on machines be made at the housing of bearings or
nearby measuring points.
For routine monitoring it is sufficient in many cases to measure vibration either in vertical or in horizontal direction.
Rigidly mounted machines with horizontal shafts have their
highest vibration levels mostly in a horizontal direction. Flexibly mounted machines may have high vertical components of
vibration, too.
For inspections, vibration should be measured in all three directions (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 13373-1.
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
12
a
x
i
a
l
2
vertical 2
h
o
r
i
z
o
n
t
a
l
2
vertical 1
a
x
i
a
l
1
h
o
r
i
z
o
n
t
a
l
1
Figure 7: Measuring points on electric motors
4.2.Installation and Adjustment
4.2.1.Attachment
The M12 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
13
Make sure that there is at least 4 cm clearance above and under the case in order to allow ventilation. The power dissipation of each M12 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 0.14 to 4 mm² for single wire and 0.14 to 2.5 mm² for stranded wire.
Before attaching the case to the DIN rail, check that the following settings have been done:
Filter settings: Chapter 4.2.6, Page 20;
AC output settings: Chapter, 4.2.10, Page 25.
4.2.2.Power Supply
The M12 requires for operation a DC supply voltage between
12 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 M12 is protected against false polarization
and short overvoltage transients. The power supply is insulated from the signal path.
AC Out-I Out+I Out
COM
+UsPK-PKRMS
-UsGNDInput
N.C. N .O.
10
100
%
0 25
s %
10
100
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.
14
4.2.3.Sensor
Sensor Input
The M12 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 dynamic input range independent of the sensor bias voltage. The
constant current source is activated by pushing the DIP switch
no. 1 “IEPE Supply” towards the “ON” position (Figure 10).
Figure 10: Activation of sensor supply
Sensitivity
Adjustment
The M12 is suited for IEPE compatible accelerometers with
sensitivities between 10 and 100 mV/g or 1 to 10 mV/ms-2,
respectively. The instrument is supplied pre-calibrated for
transducers with a sensitivity of 100 mV/g. If sensors with
other sensitivities are used, the M12 must be re-calibrated
(see chapter 4.3, Page 28).
Please make sure that the constant current source (IEPE supply, DIP switch no. 1) 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 insulated base or with insulating flanges should be used. The
ground potentials of the machine and the M12 are thereby
separated.
Sensor Status
Indication
The M12 can detect sensor faults. This is achieved by monitoring 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 constant 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 reason might also be an extreme overload condition at the sensor
output.
Figure 11 illustrates the sensor bias voltage and the limits of
the dynamic range.
The “OK” LED flashes when the input is shorted.
15
1 2
3 4 5
6 7
8 9 10
IEPE supply on
1 2
3 4 5
6 7
8 9 10
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
0V
positive overload
threshold of sensor
monitoring: 20 V
Figure 11: Dynamic range and bias voltage of IEPE sensors
Sensor
Connection
The accelerometer is connected via coaxial cable or multiwire shielded cables. Cables of several hundred meters length
are permissible. Limitations are cable resistance and electromagnetic immunity.
The connection of the sensor is shown in Figure 12.
AC Out-I Out+I Out
COM
+UsPK-PKRMS
-UsGNDInput
N.C. N .O.
10
100
%
0 25
s %
10
100
Alarm OK OVL
rear terminals
front terminals
sensor ground
sensor signal
Figure 12: Sensor connection
Important: Make sure not to swap sensor ground and sensor
signal. This may destroy the electronic circuit inside the sensor. Please contact the sensor manufacturer if you are not sure
about the cable assignment.
16
Operation of Two
M12 Modules
with One Sensor
Two M12 modules can be operated with one mutual sensor. In
this way many useful applications are possible.
Figure 13 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 14 shows an example for monitoring vibration velocity
to ISO 10816 with 2 alarm levels. By 2 different alarm settings pre-alarm and main alarm can be triggered.
Figure 14: Monitoring system with 2 alarm levels
17
AC Out-I Out+I Out
COM
+UsPK-PKRMS
-UsGNDI nput
N.C. N.O.
10
100
%
0 25
s %
10 100
Alarm OK OVL
AC Out-I Out+I Out
COM
+UsPK-PKRMS
-UsGNDInp ut
N.C. N.O.
10
100
%
0 25
s %
10 100
Alarm OK OVL
accelerometer
1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10
IEPE supply on IEPE supply off
Unit 1:
vibration
velocity
10 .. 1000 Hz
pre-alarm
Unit 2:
vibration
velocity
10 .. 1000 Hz
main alarm
Figure 13: Monitoring vibration velocity and acceleration with one sensor
AC Out-I Out+I Out
COM
+UsPK-PKRMS
-UsGNDInput
N.C. N.O.
10
100
%
0 25
s %
10
100
AlarmOK OVL
AC Out-I Out+I Out
COM
+UsPK-PKRMS
-UsGNDInput
N.C. N.O.
10
100
%
0 25
s %
10
100
AlarmOK OVL
Unit 2:
vibration
acceleration
1 .. 10 kHz
accelerometer
1 2
3 4 5
6 7
8 9 10
1 2
3 4 5
6 7
8 9 10
IEPE supply on IEPE supply off
Unit 1:
vibration
velocity
10 .. 1000 Hz
Please note that only one constant current source (IEPE supply, DIP switch no. 1) must be switched on when operating
two M12 modules with the same sensor (compare Figure 13
and Figure 14).
Nevertheless the sensor status indication will work normally
in both M12 units.
4.2.4.Selecting a Vibration Quantity
The M12 is capable of monitoring vibration acceleration, velocity and displacement, corresponding to no integration, single 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 pushing down one of the DIP switches nos. 5 to 7 as shown in Figure 15.
Figure 15: 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 integrators are switched on, the dynamic range of the M12 will decrease rapidly at frequencies of a few hundred Hertz (Figure
16). If double integration is selected, for example, the dynamic range at 160 Hz will become only 10 % of full scale.
Instead of 2500 µm the maximum displacement to be measured 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 integrators. It is recommended therefore to insert a high pass fil ter of 3 Hz or more when the integrators are used.
18
5: Displacement (double integration)
1 2
3 4 5
6 7
8 9 10
6: Velocity (single integration)
1 2 3 4 5 6 7 8 910
7: Acceleration
123 4 5 678 9 10
%
Dynamic range
100
10
1
1 10 100
1000
Hz
Vel.
mm/s
Displ.
µm
2500
250
Acc.
m/s²
250
Vibration velocity
single integration
Vibration displacement
double integration
Vibration acceleration
no integration
2502525
252,52,5
16016
Dynamic range for vibration displacement
Dynamic range for vibration velocity
Dynamic range for vibration acceleration
Figure 16: 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 17: 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 selected 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 10 m/s² 10 mm/s 100 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 VM12 was calibrated with its accelerometer (compare chapter 4.3, page 28).
19
8: RMS detection
1 2
3 4 5
6 7
8 9 10
9: peak-to-peak detection
1 2
3 4 5
6 7
8 9 10
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 beyond 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 J1 is in position 1-2.
4.2.6.Plug-in Filters
The M12’s replaceable filters make it particularly versatile.
They can be configured on site depending on the vibration
signal.
The M12 has two 8 pin sockets for a high pass and a low pass
filter module. These filter modules are available as accessories. Metra offers the following versions:
Low pass plug-in filter Model FB2: 0,1 kHz; 0,3 kHz;
0,5 kHz; 1 kHz;
3 kHz; 5 kHz; 10 kHz;
30 kHz kHz
High pass plug-in filter Model FB3: 2 Hz; 3 Hz; 5 Hz; 10 Hz;
30 Hz; 50 Hz; 100 Hz;
300 Hz; 500 Hz; 1000 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 M12 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 M12 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 18, by opening 6 snap
tabs using a screw driver.
Figure 18: Opening the case
20
After removing the lid, the back of the PCB becomes visible.
Pull out the PCB carefully. The main PCB is connected via a
ribbon cable with the front PCB. Prevent the front PCB from
sliding out with your finger. Put the main PCB beside the case
with its components facing towards you.
Caution: Electrostatic discharge may damage the electronic
circuit. Carefully discharge your hands and any tools before
touching the PCB.
The location of the filter modules can be seen in Figure 19.
Please make sure that the marking “Pin 1” on the filter is in
the same position as the marking on the PCB.
Figure 19: Location of filters and jumper J2 on the PCB
The low pass filter is necessary for operation of the M12. The
high pass filter can be omitted when a lower frequency limit
of 1 Hz is desired. If no high pass filter module is plugged in,
jumper J2 has to be in position “Off” (1-2) as shown in Figure
19.
4.2.7.Relay Output
Adjustments
The M12 features a relay output with “Form C” contact. It
can be used for alarm tripping when a pre-adjusted limit is exceeded. The switch behavior of the relay is shown in Figure 2
in chapter 3. An alarm tripping is indicated at the front panel
by the LED “Alarm”.
Alarm threshold and delay time are adjusted by two knobs at
the front panel (Figure 20). The adjustable range for the delay
time is from 0 s (immediate tripping) to a maximum of 25 s.
The threshold between 10 and 100 % of the measuring range
can be chosen. The bar graph display shows the adjusted
alarm threshold.
21
The M12 has a power-on alarm delay of 5 seconds (compare
section 4.2.2 on page 14).
AC Out-I Out+I Out
COM
+UsPK-PKRMS
-UsGNDInput
N.C. N.O.
10
100
%
0 25
s %
10
100
Alarm OK OVL
alarm threshold
delay time
Figure 20: Adjustment of alarm threshold and delay time
The alarm duration (hold time) can be chosen by DIP switch
no. 10 between 2 s (short) and 10 s (long) as shown in Figure
21.
1 2 3 4 5 6 7 8 9 10
DIP10:
2 s (Short)
8 s (Long)
Figure 21: Alarm duration
Connection of
the Relay Output
Figure 22 shows the relay terminals. In alarm condition terminals 1 and 2 are shorted. Under normal operation terminals 2
and 3 are shorted.
AC Out-I Out+I Out
COM
+UsPK-PKRMS
-UsGNDInput
N.C. N.O.
10
100
%
0 25
s %
10
100
Alarm OK OVL
front terminals
rear terminals
1 2 3
Figure 22: Relay output, contacts shown in alarm condition
Self Test
Function
If no alarm is tripped, the relay coil is current-carrying. In the
alarm condition the coil is without current. Therefore, a failure of the power supply voltage will cause the relay to switch
into alarm position. In this way the power supply of the M12
is monitored.
Sensor
Please note that a sensor failure will also cause the relay to
22
Monitoring
give an alarm message (compare chapter 4.2.3).
Contact Rating
The relay contacts are insulated from the circuit of the M12.
They can carry up to 2 A at 40 VAC. If several M12 modules
are in use, the relay outputs can be grouped by series connection (AND function) or parallel connection (OR function).
4.2.8. Current Loop 4-20 mA Output
In addition to the relay output the M12 features a 4-20 mA
current loop output. Current loop signals can be advantageous
for long distance transmission over several kilometers. The 420 mA output provides the vibration signal as selected by the
DIP switches (see chapter 4.2.4). It can represent the RMS or
peak-to-peak value depending on the positions of DIP
switches 8 and 9. The maximum current of 20 mA corresponds to 100 % of the measuring range or the upper LED of
the bar graph display.
The corresponding vibration level (V) of an output current
can be calculated by:
V =
MR (I - 4 mA)
16 mA
where MR is the selected measuring range.
For example a loop current of I
LOOP
= 8 mA and a measuring
range of 10 mm/s (peak-to-peak) come to a vibration velocity
of:
The 4-20 mA output acts as a current drain. Therefore, a voltage supply is required in the loop circuit. Figure 23 shows the
loop principle. The loop output of the M12 needs a minimum
voltage of 12 VDC over the terminals +I
OUT
and -I
OUT
. Hence
the voltage source (US) has to be designed as follows:
US > 12 V + UL.
UL is the voltage drop over all resistors in the loop including
cable resistance at 20 mA.
measuring resistors and cable resistance
supply voltage
M12
+I
-I
+
-
>12 V
U (20 mA)
L
U
S
OUT
OUT
23
V =
10 mm/s (8 mA-4 mA)
16 mA
= 2,5 mm/s
pk-pk
pk-pk
Figure 23: 4-20 mA loop circuit
Often the 24 VDC supply voltage of the M12 is also used as
loop supply.
The voltage at the terminals +I
OUT
and -I
OUT
must not exceed
30 VDC.
Connection
Figure 24 shows the terminals of the 4-20 mA output
AC Out-I Out+I Out
COM
+UsPK-PKRMS
-UsG NDInput
N.C. N.O.
10
100
%
0 25
s %
10
100
Alarm OK OVL
+ current loop
- current loop
Figure 24: 4-20 mA current loop connection
Insulation
Insulation of the current loop output is provided by an opto coupler. Thus potential differences, as they often occur in
large cable networks, will not affect the accuracy of the M12.
False
Polarization
The 4-20 mA output is protected against false polarization of
the loop supply voltage
24
4.2.9.DC Outputs
The M12 features two DC outputs for the RMS and the peakto-peak values of the selected vibration quantity (Figure 25).
Both outputs are referred to ground (GND). Their voltage
range is 0 to +10 V.
AC Out-I Out+I Out
COM
+UsPK-PKRMS
-UsG NDInput
N.C. N .O.
10
100
%
0 2 5
s %
10
100
Alarm OK OVL
peak-to-peak
RMS
GND
Figure 25: DC outputs
The RMS detection has an integration time constant of approximately 1 second.
The hold time of the peak-to-peak output is also 1 second.
Please note that the peak-to-peak output will already be overloaded when the RMS output voltage exceeds 10 V.
4.2.10.AC Output
In addition to the RMS and peak-to-peak outputs, it is often
desirable to measure the unrectified accelerometer signal. By
means of external equipment like analyzers or scopes an experienced maintenance engineer can acquire additional information about the source of vibrations. This analysis can be performed either on site, or, after storing the analog signal on a
data logger, at another place. For connecting such equipment
the M12 features an AC output.
Filtering and
Integration
The AC output can deliver two kinds of signals:
• Raw signal of the transducer: In this mode the AC output
provides the unfiltered but amplified acceleration signal.
• Filtered / integrated: In this mode the AC output signal is
pre-processed depending on the selected monitoring
quantity. Hence the AC signal can be filtered and, if vibration velocity or displacement are selected, integrated.
Settings
The AC output mode is selected by jumper J1. You will find it
after removing the lid from the case. This can be done by
opening six snap tabs using a screw driver as shown in Figure
26.
25
Figure 26: Opening the case
After removing the lid the back of the PCB becomes visible.
Pull out the PCB carefully. The main PCB is connected via a
ribbon cable with the front PCB. Prevent the front PCB from
sliding out with your finger. Put the main PCB beside the case
with its components facing towards you.
Caution: Electrostatic discharge may damage the electronic
circuit. Carefully discharge your hands and any tools before
touching the PCB.
Figure 27: Setting the AC output mode by jumper J1
Figure 27 shows the position of jumper J1. In its left position
(1-2 closed) the AC output provides the unfiltered sensor signal. In the right position (2-3 closed) the AC output provides
the filtered and integrated signal.
26
Output Level
The AC output voltage depends on the selected measuring
range (compare chapter 4.2.5) and the calibrated transducer
sensitivity. The following table shows the output sensitivity
for all measuring ranges and integrator options provided the
M12 has been calibrated with its accelerometer (compare
chapter 4.3, page 28).
Measuring range AC Output
10 m/s² (no integrator)
10 mm/s (single integration)
100 µm (double integration)
500 mV/ms-²
500 mV/mms
-1
50 mV/µm
50 m/s² (no integrator)
50 mm/s (single integration)
500 µm (double integration)
100 mV/ms-²
100 mV/mms
-1
10 mV/µm
250 m/s² (no integrator)
250 mm/s (single integration)
2500 µm (double integration)
20 mV/ms-²
20 mV/mms
-1
2 mV/µm
The sensitivity at the AC output is half the sensitivity of the
DC outputs (RMS and peak-to-peak). For example, 10 VDC
at the RMS output correspond to 5 V
RMS
at the AC output or
10 VDC at the peak-to-peak output correspond to 5 V
PK-PK
at
the AC output.
The dynamic range of the AC output is ±10 V.
Bandwidth
The AC output is DC coupled with a serial resistance of
100 . In the unfiltered mode (J1 in position 1-2) its bandwidth is 1 Hz to > 30 kHz. Please note that most industrial accelerometers have their natural resonance at 20 to 30 kHz.
In the filtered mode (J1 in position 2-3) the bandwidth depends on the used filters and the integrators.
Connection
Figure 28 shows how the AC output is connected. The output
signal is referred to GND. The cable length at the AC output
must not exceed 5 to 10 m.
AC Out-I Out+I Out
COM
+UsPK-PKRMS
-UsG NDInput
N.C. N.O.
10
100
%
0 25
s %
10
100
Alarm OK OVL
GND
AC output
Figure 28: AC output
27
4.3.Calibration
Factory
Calibration
Metra supplies the M12 calibrated with its sensor if the instrument is ordered together with a Metra accelerometer. If
the M12 is ordered without transducer its default sensitivity
calibration will be 100 mV/g.
Factory calibration is only valid with unaltered transducer
sensitivity adjustment.
Calibration Point
The calibration potentiometer for transducer sensitivity can be
found next to the DIP switches. At the left stop the sensitivity
is about 100 mV/g (10 mV/ms-2), at the right stop it is about
10 mV/g (1 mV/ms-2). The potentiometer has 25 turns.
1 2 3 4 5 6 7 8 9 10
Calibration point
Figure 29: Calibration of transducer sensitivity
Vibration
Calibrator
If the plugged-in filter modules are linear at 160 Hz calibration can be performed using a Vibration Calibrator of Metra’s
VC series. It provides a stabilized vibration signal of 10 m/s²,
10 mm/s and 10 µm at a frequency of 160 Hz. This signal can
be used to excite the accelerometer and to calibrate the M12
in mechanical units.
Electrical
Calibration
Otherwise the M12 may be calibrated by feeding in an electric signal instead of the accelerometer signal. The generator
signal to be fed in depends on the sensitivity of the accelerometer. If the sensitivity given in the accelerometer data
sheet is, for example, 2.53 mV/ms-2, a generator magnitude of
253 mV is necessary to simulate an acceleration of 100 m/s².
Choose the calibration frequency in the middle of the filter
pass band.
If the M12 is used for monitoring vibration velocity or displacement, it can be calibrated in the acceleration range and
afterwards the integrators can be switched on.
28
4.4.Vibration Level Display M12DIS
A useful option for the M12 is the display module M12DIS. It
turns the M12 monitor into a vibration meter. Depending on
the M12 settings it will display RMS or peak-to-peak values
of vibration acceleration, velocity or displacement. Model
M12DIS is a 3½ digit LCD for connection to the M12 current
loop output. The unit is loop powered. No additional power
supply is required except for the LED backlighting.
Connection
The display unit is connected to the 4-20 mA output of the
M12 and the loop power supply according to chapter 4.2.8.
The terminals I+ and I- of the display are used for connection.
The maximum voltage drop across these display terminals is
6 V. Further 4-20 mA instruments can be switched in series
with the display provided the loop supply voltage is high
enough to produce a voltage drop of 12 V across the M12
loop terminals. The 24 VDC supply voltage of the M12 may
also be used as loop supply.
Figure 30: Connection of the display
LED
Backlighting
If desired, an LED backlighting can be activated by means of
an additional DC supply voltage. It must be connected to the
terminals BL+ and BL- via a current limiting resistor RBL as
shown in Figure 30. The current consumption of the backlighting is 30 mA.
The resistor is calculated as follows:
R
BL
=
U - 5 V
BL
30 mA
The resistor RBL is not necessary if the supply voltage UBL is 5
V 0.25 V.
29
Other 4-20 mA
instruments
Loop supply
> 24 VDC
M12
+I
-I
+
>12 V
OUT
OUT
+
-
U
BL
R
BL
R
BL
=
U - 5 V
BL
30 mA
Supply voltage for
LED backlighting
< 6 V
Mounting
The display module is suitable for the attachment at front panels, switch boards, switch cabinet doors and other flat objects.
For this purpose a mounting bezel is supplied with the
M12DIS. The following pictures show the dimensions of the
cut out and how the display is mounted.
Figure 31: Panel cut out
1. 2. 3.
Figure 32: Display mounting
Calibration
If not ordered otherwise, the M12DIS is supplied factory calibrated to display “0” at 4 mA and “1000” at 20 mA.
For recalibration the potentiometers “Offset” (Zero) and
“Span” (full scale) are used.
Figure 33: Calibration points
30
Panel thickness
1 to 3 mm
Panel cut out
62 mm x 32 mm
Mounting bezel
Bracket
Insulating
washers
Shake-proof
washers
Full scale
Zero
Decimal point:
199.9
19.99
1.999
Not to be changed
Calibration of the M12DIS is carried out either directly by an
adjustable 4-20-mA constant current source or together with
the M12. For calibration with the M12 a vibration reference
signal is fed into the accelerometer or a generator signal is applied to the M12 input as explained in chapter 4.3. Preferably
a vibration calibrator should be used to eliminate errors by
calibration of the entire measuring chain.
The M12 must be calibrated before calibrating the display.
The measuring range of the M12 must be selected so that the
calibration signal provides at least 50 % of the full-scale
level, for instance, use the range “10” if the calibration level
is 10 mm/s.
After applying the calibration signal, adjust the display to the
reference level, for instance “1000” for 10 mm/s, using the
potentiometer “Span”.
Switch off the calibration signal and adjust the zero display
using the potentiometer “Offset”.
Repeat the calibration of span and offset alternately a few
times until both settings are correct.
Finally the position of the decimal point is set by means of
jumper DP1, DP2 and DP3.
5.Measuring Methods for Machine Vibration
Permanent vibration monitoring as part of a predictive maintenance program allows for the prediction of breakdown of
machines and will thereby save maintenance cost.
The assessment of machine vibrations requires a high degree
of experience. This chapter introduces briefly some proven
methods.
5.1.Vibration Severity Measurement for Unbalance
A widespread procedure for monitoring the unbalance of rotating machines is to measure vibration velocity (sometimes
also called vibration severity). Vibration severity is a measure
of energy of the emitted vibration. Reasons for unbalance may
be, for instance, loose screws, bent components, worn out
bearings with too much clearance or dirt on blower fans. Often several of these effects can influence one another.
ISO 10816-1
If no reference values of vibration severity are available on
the relevant machine, you may refer to the recommendations
of ISO 10816-1 (see table below). Here you will find permissible values of the vibration severity of different machine
types. The basis of the assessment is the maximum value of
all measured points on the machine.
31
Machine
Type
Power Rating
or
Shaft Height
Speed
min
-1
Foundation
Max.
Continuous value
mm/s
Steam
Turbines
300 kW – 50 MW rigid 7.1
300 kW – 50 MW flexible 11
> 50 MW < 1500 rigid 7.1
> 50 MW < 1500 flexible 11
> 50 MW 1500 – 1800 8.5
> 50 MW 3000 – 3600 11.8
> 50 MW > 3600 rigid 7.1
> 50 MW >3600 flexible 11
Electrical
Engines
< 160 mm rigid 2.8
< 160 mm flexible 4.5
160 – 315 mm rigid 4.5
160 – 315 mm flexible 7.1
> 315 mm 120 – 15000 rigid 7.1
> 315 mm 120 – 15000 flexible 11
Gas Turbines
< 3 MW rigid 7.1
< 3 MW flexible 11
> 3 MW 3000 – 20000 14.7
Generators
> 50 MW 1500 – 1800 8.5
> 50 MW 3000 – 3600 11.8
Blowers,
Compressors
< 15 kW rigid 2.8
< 15 kW flexible 4.5
15 – 300 kW rigid 4.5
15 – 300 kW flexible 7.1
> 300 kW rigid 7.1
> 300 kW flexible 11
Pumps with
separate drive
< 15 kW rigid 4.5
< 15 kW flexible 7.1
> 15 kW rigid 7.1
> 15 kW flexible 11
Pumps with
integrated
drive
< 15 kW rigid 2.8
< 15 kW flexible 4.5
> 15 kW rigid 4.5
> 15 kW flexible 7.1
Measurement
with the M12
Vibration severity to DIN/ISO 10816 can be measured with
the M12 in a simple way. A 10 Hz high pass filter and a 1 kHz
low pass filter are required. Vibration velocity is selected by
DIP switch no. 6. RMS monitoring is activated by DIP switch
no 8. The appropriate measuring range can be chosen by the
DIP switches nos. 2, 3 and 4.
32
5.2.Vibration Measurement on Reciprocating Engines
DIN/ISO 10816-6
Reciprocating engines, like combustion engines and compressors, are characterized by backward and forward going
masses. The vibration generated by this motion, is higher
than the vibration of rotating machinery. Standard ISO
10816-6 contains recommendations for the assessment of vibrations of reciprocating machines. The measured quantities
are the RMS values of acceleration, velocity and displacement. They are picked up at the machine block in all three
axes of the room. The recommended frequency range
reaches from 2 Hz up to 1000 Hz.
By means of the measured values of all three vibration quantities, the reciprocating engine may be classified as belonging to a particular class of assessment. The following table
allows this classification. At first read the relevant vibration
severity level for all three measured vibration quantities. The
decisive class is the highest of these three determined severity classes. In the right part of the table you find the degree
of machine condition in dependence on the machine class
(depending on size, construction, assembly and speed of the
machine).
Maximum Vibration Machine Class
Vibration
Severity
Level
Vibration
Displacem.
µm RMS
Vibration
Velocity
mm/s RMS
Vibration
Accelerat.
m/s² RMS
1 2 3 4 5 6 7
1.1 < 17.8 < 1.12 <1.76
1.8 < 28.3 < 1.78 < 2.79
2.8 < 44.8 < 2.82 < 4.42 A/B A/B A/B
4.5 < 71.0 < 4.46 < 7.01 A/B A/B
7.1 < 113 < 7.07 < 11.1 C A/B A/B
11 < 178 < 11.1 < 17.6 C
18 < 283 < 17.8 < 27.9 C
28 < 448 < 28.2 < 44.2 C
45 < 710 < 44.6 < 70.1 D D C
71 < 1125 < 70.7 < 111 D D C
112 < 1784 < 112 < 176 D D C
180 > 1784 > 112 > 176 D
The assessment classes have the following meanings:
A New machines
B Continuous running without restriction possible
C Not suitable for continuous running, reduced operabil-
ity until the next scheduled maintenance
D Too high vibration, damage to the machine cannot be
excluded
33
Measurement
with the M12
Monitoring reciprocating machines to DIN/ISO 10816-6 can
be performed by 3 M12 modules and a mutual accelerometer. For each unit a 2 Hz high pass filter and a 1 kHz low
pass filter are required. One M12 has to be adjusted for acceleration, the second one for velocity and the third for displacement. Select RMS rectification (DIP switch no. 8). The
appropriate measuring range is chosen by the DIP switches
nos. 2, 3 and 4. The measuring values can be processed as 420 mA or DC voltage signals.
5.3.Bearing Monitoring
General
The two methods to ISO 10816 described above are concerned with vibration caused by unbalanced masses. This section deals with vibration generated by roller bearings.
Typical reasons for damage to roller bearings are fatigue, corrosion, cage damage, insufficient lubrication or fatigue caused
by excess strain. The results are damages of the ball race (creation of pittings), rising temperature, increasing noise, rising
bearing clearance, flutter up to the breakage of the cage and
total breakdown of the machine.
The movement of rolling elements along such damage, such
as pittings, generates mechanical pulses which initiate vibrations of the whole bearing. These vibrations can be measured,
for instance, at the housing of the bearing.
As a rule, the vibrations of roller bearings have frequencies
above 1 kHz. Usually acceleration is measured.
Damage to roller bearings may be diagnosed either by frequency analysis or in the time domain by RMS and peak
value measurements.
The diagnosis of the frequency spectrum provides the most
detailed information about a bearing, but requires a high degree of experience.
Vibration measurement in time domain (measurement of RMS
and peak value of acceleration) is much easier to perform but
yields less specific results. In many cases, however, it is sufficient to evaluate the condition of a roller bearing.
Crest Factor
An established method in time domain is the measurement of
the crest factor. The crest factor is the quotient of the peak
value and the RMS of acceleration (â/a
rms
). This method is
based on the experience that in the early pre-damage stage of
the bearing the RMS of acceleration shows only small
changes, whereas the peak value increases significantly (see
Figure 34).
34
a
~3:1
>3:1
>>3:1
no damage
small solitary
damages
considerable
damage
â
a
eff
Time
Figure 34: Typical development of roller bearing damages
The following table shows the crest factor and, alternatively,
the product of peak and RMS values in dependence on the de gree of bearing damage.
Condition a
eff
â â/a
eff
â a
eff
no damage small small
3
small
small individual damage small increased >3 slightly increased
several individual damages increased increased >3 medium increased
severe individual damage increased high >>3 increased
many severe individual damages high high >3 high
Diagnostic
Coefficient
Another method of monitoring roller bearings in time domain
is the diagnostic coefficient DK(t) according to Sturm. This
coefficient is calculated from the RMS and the peak values of
the acceleration at good operating condition of the bearing
(initial values with the index 0) and at the present condition
(index t):
D t
a
a t
K
eff
eff
0 â(0)
â(t)
According to Sturm the following values represent the indi cated conditions:
DK(t) Bearing Condition
> 1 Improvement
1 - 0.5 Good operating condition
0.5 - 0.2 Accelerating influence to the damaging process
0.2 - 0.02 Progressive damaging process
< 0.02 Damage
Measurement
with the M12
The two described methods of bearing monitoring can be applied using one M12 module. A 1 kHz high pass and a 10 kHz
low pass filter are required. The high pass filter suppresses
unbalance vibrations and lets only bearing noise pass. The 10
kHz low pass is recommended for suppressing the resonance
peak of the accelerometer. The M12 must be in the acceleration range. The DC outputs for RMS and peak-to-peak values
35
provide the relevant quantities. Multiplication and division
have to be performed externally.
Please note that the M12 measures the peak-to-peak value. It
has to be divided by 2 to obtain the peak value â.
6.Technical Data
Measuring ranges
Vibration acceleration
Vibration velocity
Vibration displacement
10 / 50 / 250 m/s²
10 / 50 / 250 mm/s
100 / 500 / 2500 µm
Accuracy (referred to full scale)
Vibration acceleration
Vibration velocity
Vibration displacement
RMS
5 %
5 %
8 %
peak-to-peak
5 %
8 %
15 %
Input
voltage input, R
I
= 1 M
AC coupled, IEPE compatible
Sensor supply
3.2 – 4.8 mA constant current
compliance voltage > 24 V
selectable by DIP switch
Suitable sensors
IEPE compatible accelerometers
sensitivity: 1 - 10 mV/ms
-2
Frequency ranges
Wide band signal at AC output
Vibration acceleration
Vibration velocity
Vibration displacement
1 Hz - > 50 kHz (-3 dB) without Filter
1 Hz - 50 kHz (without high pass / 50 kHz low pass)
3 Hz - 1 kHz (with high pass)
3 Hz - 200 Hz (with high pass)
Band filter
High pass
Low pass
plug-in high pass and low pass modules
Butterworth, 2nd order, 40 dB/decade
Butterworth, 4th order, 70 dB/decade
Rectification
true RMS, refresh rate approx. 1 s
true peak-to-peak value, refresh rate approx. 0.1 s
Relay output
Form C contact, 40 VAC / 2A
Adjustable relay threshold
10 - 100 % of measuring range, potentiometer
Adjustable relay delay
0 - 25 s 20 %, potentiometer
Relay hold time
selectable by DIP switch
short: approximately 2 s
long: approximately 10 s
4-20 mA current loop output
passive, optically insulated
terminal voltage: 12 - 30 V
36
Wide band output
acceleration signal, ûa = ± 10 V
1 Hz - > 50 kHz, impedance: 500
DC outputs
0 - 10 V RMS
0 - 10 V peak-to-peak
Sensor status indication
LED (“OK”) and alarm relay
thresholds: <1 V and >20 V bias voltage
Overload indication
LED (“OVL”)
at ± 10 V amplifier output voltage
Level display
10 step LED bar graph
10 - 100 % of measuring range and
display of alarm threshold
Power supply
12 - 28 VDC / 80 - 200 mA
insulated from signal path
protection against false polarization
Operating temperature range
-20 - 55 °C
rel. humidity < 95 %, no condensation
Dimensions (W x H x D)
22 x 76 x 111 mm³
Weight
140 g
37
Limited Warranty
Metra warrants for a period of
24 months
that its products will be free from defects in material or workmanship
and shall conform to the specifications current at the time of shipment.
The warranty period starts with the date of invoice.
The customer must provide the dated bill of sale as evidence.
The warranty period ends after 24 months.
Repairs do not extend the warranty period.
This limited warranty covers only defects which arise as a result
of normal use according to the instruction manual.
Metra’s responsibility under this warranty does not apply to any
improper or inadequate maintenance or modification
and operation outside the product’s specifications.
Shipment to Metra will be paid by the customer.
The repaired or replaced product will be sent back at Metra’s expense.
Declaration of Conformity
According to EMC Directive 2014/30/EC
Product: Vibration Monitor
Type: M12 Ver. C
It is hereby certified that the above mentioned product complies
with the demands pursuant to the following standards:
DIN EN 61326-1: 2013
DIN EN 61010-1: 2011
DIN 45669-1: 2010
The producer is responsible for this declaration
Metra Mess- und Frequenztechnik
in Radebeul e.K.
Meißner Str. 58, D-01445 Radebeul
declared by
Michael Weber
Radebeul, May 9, 2017
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