Asahi/America 94 Series, Installation, Operation And Maintenance Manual

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ASAHI/AMERICA, INC 655 ANDOVER STREET LAWRENCE, MA. 01843 TELEPHONE 800-343-3618
File: assembly/manuals/Series 94 Gen II A/C Modulating Svc Manual Rev. A 11/19/19
Page 20 of 27
stall. To avoid this condition, the limit switches must be set outside of the
operating range set by the CLOSE and OPEN functions.
Electronic Brake Feature
The
Electronic Brake feature of the DHC-100 provides highly reliable and
accurate braking of the motor, and it is a key element in achieving high resolution.
A mechanical brake can still be implemented without interfering with the DHC-100
operation. A mechanical brake can still be implemented without interfering with
the DHC-100 operation. Mechanical brakes can be useful for providing a holding
brake in the event power to the actuator is lost.
Since the
Electronic Brake feature provides the primary braking of the motor, the
life of a mechanical brake is dramatically extended. Additionally, the Adaptive
Control feature of the DHC-100 automatically compensates for changes in the
mechanical brake’s performance due to temperature or age.
Note that the actuators limit switches should be set outside of the operating range
set by CLOSE and OPEN functions. The
Electronic Brake feature degrades in
performance if a limit switch is engaged. Limit switches exhibit wide variations,
and the DHC-100 can position the actuator more precisely at
closed and open
than the limit switches. A limit switch serves better as a fail safe device to protect
against electrical failures in the actuator.
Duty Cycle Control
The
Duty Cycle Control feature of the DHC-100 allows actuators rated at 25%
duty or more to be safely used in automated valve applications. The DHC-100
accurately monitors the relative heating of the motor and automatically duty cycles
the unit at a safe level when a process becomes unstable, or if a control loop is
not properly set. While the thermal switch in the motor protects the motor from
overheating, thermal switches can shut down the actuator for ten minutes or
more. Further, typical thermal switches do not activate until temperatures inside
the actuator become too high for other components in the actuator.
The
Duty Cycle Control feature allows continuous operation of the motor until it
detects an excess heat buildup in the motor (usually well below the limit of the
thermal switch). At that time, duty cycle operation is automatically enabled and
continues until the motor cools enough to resume continuous operation. The duty
cycle period is approximately 2 seconds with an on time that automatically various
depending on the heating of the motor. While this operation slows down the
actuator's operation, it does not impact the resolution performance of the DHC-
100, and it prevents disruption of a process due to a thermal switch shutdown.