HARDWARE MANUAL Document reference MAMPS-HW/E
VM600 machinery protection system (MPS) Edition 18 - March 2022
7-10
Shaft absolute vibration
PROCESSING MODES AND APPLICATIONS
NOTE: If different low-pass (LP) filter cutoff frequencies are defined for the Broad-band
absolute bearing vibration (BBAB) and Relative shaft vibration (RS) processing
functions, the lowest frequency will be used for both processes.
However, it is recommended to configure the same cutoff frequency for the
low-pass (LP) filters used by both processing functions.
NOTE: The high-pass (HP) filter cutoff frequency defined for the Broad-band absolute
bearing vibration (BBAB) processing function is also used by the Absolute shaft
vibration (AS) processing function.
As a result, frequencies present in the output from the Relative shaft vibration (RS)
processing can be absent from the final absolute shaft displacement output,
depending on the configuration of the high-pass (HP) filter used by the BBAB
processing function.
NOTE: The synchronisation of signals necessary for Absolute shaft vibration (AS)
processing requires that only digital integration is used (since analogue integration
using electronic circuitry introduces phase distortion).
When Broad-band absolute bearing vibration (BBAB) processing using an accelerometer is
used to provide the absolute shaft displacement:
• One BBAB processed output must be configured in acceleration units (g, m/s**2 or
inch/s**2).
• The other BBAB processed output must be configured in displacement units (µm, mm or
mils) – for use by the Absolute shaft vibration (AS) processing.
When Broad-band absolute bearing vibration (BBAB) processing using a velocity sensor (or
a velocity signal) is used to provide the absolute shaft displacement:
• One BBAB processed output must be configured in velocity units (mm/s or inch/s).
• The other BBAB processed output must be configured in displacement units (µm, mm or
mils) – for use by the Absolute shaft vibration (AS) processing.
For either way of obtaining the absolute shaft displacement (that is, from an accelerometer
or velocity sensor), both BBAB processed outputs must be configured and used as described
above. In this way, the MPC4 card is automatically configured to use digital integration as
required by the Absolute shaft vibration (AS) processing function (instead of using the
analogue integrator which is also available on the card for other processing functions).
NOTE: The MPC4 card performs shaft absolute vibration processing using digital
integration only – necessary for signal synchronisation – which results in slightly
more noise in the integrated output.
With respect to Figure 7-4, it is important to note that if the sensors are installed and measure
in the same direction and have the same polarity ( ), then:
• AS = BBAB + RS (that is, the signals must be added).
• So in the Absolute shaft vibration (AS) processing function, the angle between the two
sensors must be configured as 0°.
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