control with smooth acceleration and deceleration,
precise regulated speed control, and fine minimum
speed capability.
7. Alternating current Magnetic Hoist Control
Selection:
a. An ac wound rotor motor with ac magnetic
control, reversing, with mechanical load brake.
This type of control is the least expensive control.
Good positioning and landing speeds are inherently
available for only a fraction of the loads, and
jogging must be heavily relied on. This type of
control should be used only for rough (nonprecision)
handling situations.
b. An ac wound rotor motor with ac magnetic
control, reversing, with automatically controlled
eddy-current brake. The eddy-current brake provides
a load on the motor permitting unregulated speed
control. This control is suitable for applications
that do not require accurate positioning of loads,
and where there are no requirements for precision
handling.
c. An ac wound rotor motor with ac magnetic
control, reversing, countertorque control braking
means. This control system is commonly used for
bracket and magnet handling cranes. The control is
only suited to those applications where at least 50
percent rated load is on the ropes at all times. If
the hoist is operated in lower mode without a
substantial load, the load may actually go up.
8. Alternating current Magnetic Travel Control
Selection: An ac wound rotor motor with ac magnetic
control, 5 speed, reversing, plugging type. This
type of control provides rough acceleration under
rated load. The [bridge] [gantry] or trolley will
accelerate almost to full speed regardless of
control point selected.
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Main hoist [and auxiliary hoist] motion control system shall be [[single]
[two] speed, with ac magnetic control of ac squirrel cage motor] [[single]
[two] speed, with ac magnetic control of ac wound rotor motor]. Control
shall provide for reversing, and for [a mechanical load brake] [an
automatically controlled eddy-current brake] [a countertorque control
brake] [ac stepless secondary saturable reactor control of an ac wound
rotor type motor] [ac adjustable frequency control of an ac squirrel cage
motor] [dc magnetic control of a dc series wound motor] [dc variable
voltage control of a dc shunt wound motor].
2.4.2.2
Travel Motion Control System
Bridge and trolley motion control system shall be [[single] [two] speed
with ac magnetic control of squirrel cage motors] [five-speed with dc
magnetic control of ac wound rotor motors] [ac static stepless secondary
saturable reactor control] [ac adjustable frequency control] [five-speed dc
SECTION 14630A
Page 28
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