IR Compensation
IR compensation is factory adjusted and sealed
for 3% maximum speed change with a 95%
load change throughout the motor speed range.
Therefore, readjustment should not normally be
necessary. However, if the following facilities
are available, readjustment can be performed.
To adequately adjust IR compensation, an
adjustable load is required that can be applied
and removed while the motor is running. In
addition, a close reading tachometer is needed
to record speed changes. If these facilities are
unavailable, do not readjust IR compensation.
If, during this adjustment procedure, motor
speed becomes unstable or oscillates (hunts),
slowly turn IR COMP potentiometer (R9)
counterclockwise until the hunting stops.
1. Turn IR COMP potentiometer (R9) fully
counterclockwise.
2. Remove the load from the motor and
depress the RUN button.
3. Turn the MOTOR SPEED potentiometer until
the motor runs at the maximum speed of the
desired speed range, normally rated motor
base speed. Record motor speed.
4. Apply load to the motor until it draws rated
armature current. (See Table 1 for motor
current ratings.) Note the speed change.
5. Turn IR COMP potentiometer (R9) until the
motor returns to the speed recorded in
Step 3.
6. Remove the load and repeat Step 3.
7. Repeat Steps 4, 5 and 6 until desired speed
regulation is attained.
Current Limit
The current limit prevents excessive armature
current and resulting excessive line current by
limiting armature current at 150% of rated.
Since the current limit is factory adjusted and
sealed, readjustment should not be performed
unless an application requires a lower limit of
armature current, e.g., limiting torque or
accelerating high inertia loads.
1. Turn off the AC input power and connect a
DC ammeter, with a rating of at least twice
rated armature current, in series with the
armature. Observe correct polarity when
connecting the ammeter. (
See Table 1 for
motor current ratings
.)
2. Turn the CURRENT LIMIT potentiometer
(R12) fully counterclockwise.
3. Connect maximum load to the motor.
4. Turn on the AC input power and the AC
POWER ON/OFF switch.
5. Turn the MOTOR SPEED potentiometer fully
clockwise.
6. Depress the RUN button, and slowly turn
CURRENT LIMIT potentiometer clockwise
(R12) while the motor is accelerating until
the ammeter records the desired armature
current.
Do not turn potentiometer
(R12) past the factory setting in
the increase direction.
Resulting excessive current could damage the
controller and motor.
To obtain a particular percentage of rated
output torque, set the armature current at a
percentage of rated armature current; e.g., 50%
torque is obtained with 50% rated armature
current.
11
P-3026 • Doc. No. 60881 • Boston Gear
®
Ratiotrol
®
DC Motor Speed Control
Maintenance
Section IV
CAUTION