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MODEL 365A & E365A VIBRASWITCHES
Section 4 - OPERATION
4.1 OPERATION
The Vibraswitch (ref. Figure 4-1), is sensitive to
vibration
in
a
direction
perpendicular to its mounting base.
vibration detecting mechanism, which also functions
as a "mechanical amplifier", to activate a snap-action
switch when the selected level of vibration is exceeded
and the detecting mechanism "trips".
The detecting mechanism consists of an armature
suspended on a flexure pivot that is restrained from
motion by a permanent magnet (the holddown
magnet).
In the "armed" condition, the armature is
held against the stop pin by the holddown magnet.
The stop-pin maintains a precise air gap between the
armature and the holddown magnet. On the opposite
end of the armature, the compression spring provides
an adjustable force to oppose the force of the
holddown magnet.
Whenever the peak vibration
inertial force (mass x acceleration) plus the adjustable
compression spring force exceeds the force of the
holddown magnet, the armature is released and is
pulled into the latching magnet ("tripped position").
Simultaneously, it activates the snap-action switch.
This detecting mechanism has a uniform response
from 0 to 300 Hz over a range of 0 to 4.5 g's.
The mechanism may be reset to the "armed" position
manually (locally) or electrically (remotely). Manually,
depress the reset button to move the armature away
from the latching magnet ("tripped" position) until it is
held
against
the
stop
Electrically, the reset coil may be energized to pull the
armature into the "armed" position against the stop pin.
A reset and holding coil is provided, in the DC/AC
voltage as specified, so that accidental shutdowns on
starts can be prevented.
circuits are required to maintain voltage at the holding
coil during startup period and then release this voltage
when operation is normal. At full voltage the reset coil
should not be energized for more than four minutes to
prevent overheating. Then, the reset coil must be de-
energized for a period of ten minutes before re-
energizing. For longer hold-in requirements the reset
coil should be energized at full voltage and then held-
in at one-half the rated voltage.
The Vibraswitch may be used in conjunction with the
Vibraswitch Monitor, Model 563A. This monitor is a
solid-state electronic system designed to "sort-out"
false signals received by the Vibraswitch so that Alarm
and/or Shutdown of the operating machine will not
result from false, transient disturbances. Examples of
transient disturbances are the closing of pipeline check
valves on pumping applications, the start-up of
(the
sensitive
axis)
It contains a
pin
("armed"
position).
External time-delay relay
additional pumps on a line, and the initial start-up of
various operating machines. These disturbances may
cause the Vibraswitch to "trip-out" if the vibratory shock
level is in excess of its setpoint.
The purpose of the Vibraswitch Monitor is to
"supervise" and "sort-out" the transient disturbances so
that Alarm or Shutdown is not falsely imposed on the
machine being monitored, but any continuous vibration
level which exceeds the Setpoint of the Vibraswitch will
cause Alarm and/or Shutdown.
S E T P O I N T
A D J U S T M E N T S C R E W
C O M P R E S S I O N
S P R I N G
A R M A T U R E
L E A F S P R I N G
F L E X U R E P I V O T
Operating Principal for the
4.2 ADJUSTMENTS OF SETPOINT
The operating setpoint for the Vibraswitch varies with
the type of machine and its location (measurement
point) on the machine.
suggested in this manual are for machines which are
functioning in a "good" or "normal" condition.
method follows the concept of vibration tolerance for
the machine and in this case is dependent upon an
individual who is experienced in the operation of the
machine vibration as "normal", "fair", "slightly rough",
etc. These various degrees of machine vibration are
therefore, based on the individual's physical perception
between normal and abnormal roughness while the
machine is operating.
It is agreed that this method can lead to differences in
the classification of degree of vibration between
individual observers.
and experience bears out this conclusion, that if the
machine is operating satisfactorily as previously
defined and the acceleration as measured by the
Vibraswitch is within certain limits, the settings as
outlined in the instructions will offer protection to the
machine and prevent catastrophic failure.
For example, assume that a relatively new machine
which, in the experience of the operator, is operating
as "smooth" or "good" regarding vibration and the
Vibraswitch measures this acceleration level to be 0.25
g above its static condition (zero).
suggests that a reasonable level for
would be a minimum of twice this value or 0.5 g. It
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909GF294G
S E N S I T I V E A X I S
R E S E T B U T T O N
S W I T C H
L A T C H I N G M A G N E T
A I R G A P
H O L D O W N M A G N E T
S T O P P I N
R E S E T C O I L
Figure 4-1
Vibraswitch
The setpoint adjustments
It is Robertshaw's contention,
Experience
alarm conditions
This
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