HARDWARE MANUAL Document reference MAMPS-HW/E
VM600 machinery protection system (MPS) Edition 18 - March 2022
7-12
Smax measurement
PROCESSING MODES AND APPLICATIONS
7.7 S
max
measurement
(1) Description
S
max
is a vibration measurement used in machinery monitoring systems, defined in
ISO 7919-1 as the maximum vibratory displacement in the plane of measurement.
S
max
monitoring is a special case of shaft relative vibration monitoring that measures the
radial motion of the shaft. Like shaft relative vibration, it is typically measured using two
proximity transducers (X and Y) mounted on the machine bearing at approximately 90° to
each other (see Figure 7-8).
In general, the two proximity transducer (X and Y) values are added vectorially to provide the
S
max
(maximum displacement) value as defined in ISO 7919-1. However, there are different
methods of calculating S
max
, defined as methods A, B and C in ISO 7919-1 Annex B.
Method C – Measuring the real maximum displacement value (Smax) directly from
the orbit
According to ISO 7919-1 method C, the value of S
max(pk)
the maximum value of
displacement, can be calculated directly from the orbit using the following equation:
S
max(pk)
= Maximum { ( X(t)
2
+ Y(t)
2
)
0.5
}
This also allows the value of S
max(pp)
(that is, peak to peak) to be approximated from the
following equation:
S
max(pp)
= 2 ×S
max(pk)
NOTE: The S
max
processing on VM600 MPC4 cards, VM600 XMV16 cards and
VibroSmart VSV300 modules all use ISO 7919-1 method C to calculate the value
of S
max
.
However, since the actual signal processing implemented by VM600 MPC4 cards,
VM600 XMV16 cards and VibroSmart VSV300 modules is different, the calculated
S
max
values obtained from their respective S
max
processing functions can be
slightly different.
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