1.
GENERAL DESCRIPTION
When ordered, the OC2-500 open chassis control can be supplied in a NEMA 12
enclosure. When supplied in this manner, the basic OC2-500 control is furnished
with the following additional features, and is designated by model number OC2E-
500:
a)
Power “Off-On” switch with separate pilot light indication.
b)
“Run-Off-Jog” (momentary position ) mode selection switch.
c)
Speed Adjust Potentiometer.
The OC2-500 open chassis motor control has been designed as a basic building
block solid state regulated power unit. The OC2 open chassis, unit, which uses
state of the art control circuitry, can be used by itself, by wiring in the provided
speed potentiometer, as a straight forward speed regulated control, or can be
incorporated into much more sophisticated system designs utilizing contactor
operation, external speed programming, tach feedback, etc. (These applications
and others are discussed later in this manual.
The control circuitry incorporates a sophisticated regulator scheme that maintains
motor speed precisely at the set level within the advertised motor and control
speed rages. There are two control loops, speed and torque, that operate
simultaneously and independently of each other. In most cases the speed loop is in
control. (The speed loop can use either armature voltage or tachometer voltage
feedback. ) When in control, the speed loop maintains speed constant at the
desired value until the motor load (torque) requirements exceed a preset value,
normally 150% of rated motor torque. As this occurs, the torque regulator
assumes control of the SCR’s and allows speed to drop as is necessary in order to
maintain and not exceed the preset limit value. If the motor load continues to
increase, as would the case if a driven machine had jammed, the torque limit is
capable of holding this preset value of torque precisely without run out down to a
locked rotor or zero speed condition. Operation in both the speed and torque
modes is smooth and stable, and through the use of optimized networks transfer
between the two loops is smooth and bump less. Figure I is a block diagram of the
OC2-500 control system.
In the speed mode the control hold the motor speed constant at a valued
determined by the voltage present at the speed input. In a basic control this
voltage is set by a Speed Adjust potentiometer. In most controls armature voltage
is used as feedback in the speed (velocity) loop. When using armature
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