Peaktronics DHC Series User Manual

8
AVERAGE % DUTY CYCLE
00BE DOUB
Duty cycle is a measure of the amount of time an
actuator is turned on versus the amount of time it is turned
off. The measurement is expressed as a percentage of time
the actuator is turned on. For example, if over a 50 second
period, the actuator was turned on for a total of 10 seconds,
it is said that the percent duty cycle is 20% (10 seconds
divided by 50 seconds).
In a typical PID control application, the average
duty cycle will range from 10% to 20%. Persistent readings
above 20% duty can indicate that PID settings are changing
too fast for the process being controlled. It can also
indicate that the actuator/valve combination is not suitably
sized for the application.
To protect an electric actuator motor from
overheating, the DHC-100, 300, and 400 Series controllers
incorporate a duty control feature that intentionally reduces
the duty cycle to a safe level when they detect excessive
heating of the motor. This has the effect of slowing down
the actuator, which offsets PID signals that are changing too
fast. In this case, the reduced duty cycle is reflected in the
Average % Duty Cycle parameter.
The Average % Duty Cycle parameter represents
the duty cycle measured during the past 80 to 100 seconds.
This parameter is assigned to a DOUB byte value that
ranges from 0 to 100, representing 0% to 100% duty.
In the following example, $000D (13 decimal) represents a
duty cycle of 13%.
PACS
®
Command (RD#BE):
51 00 BE
Returned Data (example):
00 0D
Since the Average % Duty Cycle parameter is
limited to a value of 100 ($64 hexadecimal), the most
significant byte of the returned data is always zero. This
parameter can also be read as a SING byte value as shown
below:
PACS
®
Command (RS#BF):
50 00 BF
Returned Data (example):
0D
MAXIMUM DEVIATION
00C0 DOUB
While the command input signal provides the
desired position, the actual achievable position will most
often be somewhat less or more. The difference between
the actual position achieved and the desired position is
called deviation. The DHC controller automatically
determines the best performance that can be attained based
on the actuator being controlled.
The Maximum Deviation parameter provides a
measure of this performance. The parameter is a DOUB
byte value ranging from 0 to 10000 that represents 0% to
100%. In the example below, $000F (15 decimal) indicates
a maximum deviation of 0.15%. If the command input
signal is 40.00%, then the position the DHC controller can
achieve will be from 39.85% to 40.15%.
PACS
®
Command (RD#C0):
51 00 C0
Returned Data (example):
00 0F
In a typical PID application, the Maximum
Deviation parameter will be 0.50% or less, and quite
commonly will vary between 0.10% and 0.20%. When this
parameter exceeds 0.50%, the PID control algorithm will
tend to move the actuator more often which will be
reflected in the Average % Duty Cycle parameter.
HOURS OF OPERATION
00C2 QUAD
The DHC controller maintains an internal "hour
meter" which can be read as the Hours of Operation
parameter. The parameter is a QUAD byte value that
ranges from 0 to 4,294,967,295 representing the number of
hours that power has been applied to the DHC since its time
of manufacture. The parameter is set to zero at the time of
manufacture and cannot be changed or reset by the user.
The Hours of Operation parameter can be useful in
automating preventative maintenance schedules. In the
following example, $0000131C (4892 decimal) indicates
that the DHC controller has been powered for 4,892 hours.
PACS
®
Command (RQ#C2):
52 00 C2
Returned Data (example):
00 00 13 1C

Peaktronics DHC Series Specifications

General

Brand	Peaktronics
Model	DHC Series
Category	Controller
Language	English