Peaktronics DHC-100 Instruction Manual

01-22-04 PRELIMINARY INFORMATION
DHC-100
PEAKTRONICS
U.S. Patent 4,803,481 applies to this product; other patents pending
7
only manual operation or a mechanical override can clear
the fault. Alternatively, the DHC-100 can be powered off
and then on to temporarily clear the fault; however, this
practice should be avoided without permanently correcting
the cause of such a fault.
STALL DETECTION FEATURE
The Stall Detection feature of the DHC-100 (see
FAULT INDICATOR) essentially performs a similar
function as commonly used torque switches; however, the
differences should be considered before eliminating the
torque switches. The DHC-100 feature does not measure
torque, but rather motion; if the load is sensitive to exces-
sive torque, the torque switches may be desirable. Since
common torque switches are mechanical devices, they can
provide a fail safe feature in the event of electrical failures
(such as shorted wires or damage to the DHC-100).
The Stall Detection feature is useful for detecting
when any of the motor wires become disconnected. How-
ever, limit switches employed in actuators essentially dis-
connect one of the motor windings. The DHC-100 will
detect this as a motor 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 inter-
fering 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. Additonally, the Adap-
tive Control feature of the DHC-100 automatically com-
pensates for changes in a mechanical brake's performance
due to temperature or age.
Note that the actuator's limit switches should be
set outside of the operating range set by the 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 FEATURE
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 acu-
rately 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 prop-
erly 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, typi-
cal 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 continu-
ous operation of the motor until it detects an excess heat
build up 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 mo-
tor. While this operation slows down the actuator's opera-
tion, it does not impact the resolution performance of the
DHC-100, and it prevents disruption of a process due to a
thermal switch shutdown.

Peaktronics DHC-100 Specifications

General

Brand	Peaktronics
Model	DHC-100
Category	Controller
Language	English