SAF OP-STOP DCI - Manual (Page 8)

OP-STOP DC INJECTION BRAKE
Page 3
1.3 CONTROLS
The OP-STOP unit contains two major parts, the power circuit and the control card.
The power circuit is a 4 SCR single phase full wave controlled rectifier. This configuration
optimizes the DC current injected to the motor per input current.
The control is contained in a single PC board, CA398. This board is common to all OP-STOP
models.
1.3.1 CA398 LOGIC
DC injection will be applied to the motor when two conditions are met. The starter is
opened and the motor terminal voltage has decayed to 30% or 80%, jumper dependent, of
the line voltage. The starter can not be energized for a period of 1-2 seconds after the DC
injection cycle.
This design has the significant advantage that the braking module will remain off in the
case of having an open auxiliary contact from either a broken wire or faulty contact. The
braking action can be externally defeated at any time by applying 115 VAC to the
Disable Input.
The braking action is inhibited when an instantaneous over current is detected. The IOC
fault is detected and latched until the Reset switch is pressed. A form C relay contact is
available to interlock the brake unit from the motor starter. The starter cannot be
energized while DC current is being applied to the motor or during a fault condition.
1.3.2 CA398 REGULATION
The brake module operates in current control at all times. The current is adjusted via an
internal potentiometer and the current feedback signal is generated by a current
transformer mounted on the AC line. A unique circuitry reconstructs the free wheeling
current in the DC output for accurate current regulation.
The output of the current regulator is used in a comparator circuit that performs the phase
control on two SCR's. The other two SCR's are fully phased on to provide free wheeling
action, minimizing the ripple current.
Two opto-couplers are used to generate the line synchronization signal. Each opto output
is used to generate a ramp that is used in the comparator with the current regulator
output.
The motor voltage feedback is used to sense voltage levels for proper sequencing and not
to perform any regulation.