Efficient Plant November 2017 - 33

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scheduled manual inspection."
Continuous monitoring, he continued,
can detect those situations when the
vibration curve begins to climb toward
a failure point, informing maintenance
technicians while there is still time to
respond before a failure and outage. Software can spot those kinds of movements,
and then sound alarms appropriate to the
urgency of the situation and criticality of
the equipment.
According to Yamamoto, economical
vibration sensors have made permanent
installations more practical for more pieces of equipment, but the costs of wiring a
sensor haven't decreased. In fact, in many
situations, those costs have gone up. One
of the biggest technological advances of
the past decade has been the emergence
of effective and practical wireless-instrumentation protocols, including ISA100
Wireless (see sidebar), and sensors able to
communicate using these protocols.

LAUNCHING A PROGRAM
"Vibration-monitoring program implementations are usually incremental,"
Yamamoto said, "and involve working
down a list of installations, beginning
with the most critical. In this context, the
term 'critical' takes different forms, the

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HOW IT WORKS
The complete system is selfpowered using a battery module
in the communication module.
With a one-minute data update
rate, one set of batteries can
run for as long as 10 years. The
data is sent through the wireless
network to the system gateway.
If other ISA100 wireless field
devices are already in use in the
facility, the vibration monitors can
become part of the same network,
communicating with the gateway
just like any other communication
module or sensor.
The wireless vibrationmonitoring system has all the
specifications necessary to
perform the functions required
for condition monitoring (see
"Main Specifications for Condition
Monitoring" table). Data from
the units installed throughout
the plant can be directed to a
control or monitoring system to
inform operators and maintenance
personnel as conditions change
with the equipment being
monitored.
METHODOLOGY

The piezo-electric vibration sensor
from Yokogawa Electric (Tokyo)

Table: Main Specifications for Condition Monitoring
Measurement frequency band

10 Hz to 10 kHz

Measurable range velocity:
0 to 160 mm/s

Acceleration: 0 to 300 m/s2

Data update time

10 to 3, 600 seconds

Cable length

10 m (between the acceleration
sensor and the field wireless
multifunction module)

Explosion-proof approval
(intrinsically safe)

FM, CSA (cFM), ATEX, IECEx

NOVEMBER 2017	

is capable of measuring velocity
and acceleration. The nature of
the vibration and the type of
equipment helps determine which
analytical method is best when the
primary objective is determining
equipment condition. The ruleof-thumb suggests that where
frequencies are low, velocity is
the preferred measure, but when
frequency increases, it's better to
measure acceleration.
Plant personnel determine
reading frequency and what
analytical techniques should be
used for each installation. Ranges
of what is considered tolerable
vibration versus dangerous have
been published by various sources,
but the ultimate guidelines for a
given piece of equipment in each
plant may need to be established
in cooperation with the equipment
OEM.
"While the sensor can send a
new reading as often as every
10 seconds," Yokogawa's Shuji
Yamamoto said, "the need for
such rapid refreshment is rare,
and it comes at the cost of battery
life. Switching to an update rate
of once per minute can extend
battery life significantly, while still
providing more than enough data
for most applications."
If more sophisticated analysis
is required, software packages
are available from third-party
vendors to look for patterns and
identify sources of abnormal
vibration. This type of work is done
in the host system rather than
the individual devices, and often
combines signals from multiple
sensors deployed around the
equipment to pinpoint sources of
trouble.

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Table of Contents for the Digital Edition of Efficient Plant November 2017
