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3.6 Algorithm Set Up Group
Function
Selections or
Prompt
Range of Setting
Lower Display
Upper Display
CONT ALG
ON-OFF
PID A
ATTENTION
PID A should not
be used for
Proportional only
action; i.e., no
integral (reset)
action. Instead,
use PD+MR with
rate set to 0.
PID B
04/08
The CONTROL ALGORITHM lets you select the type of control
that is best for your process.
ON/OFF is the simplest control type. The output can be either ON
(100 %) or OFF (0 %). The Process Variable (PV) is compared with
the setpoint (SP) to determine the sign of the error (ERROR = PV–
SP). The ON/OFF algorithm operates on the sign of the error
signal.
In Direct Acting Control, when the error signal is positive, the
output is 100 %; and when the error signal is negative, the output is
0 %. If the control action is reverse, the opposite is true. An
adjustable overlap (Hysteresis Band) is provided between the on
and off states.
ATTENTION Other prompts affected: OUT HYST
DUPLEX ON/OFF is an extension of this algorithm when the output
is configured for a Duplex control algorithm. It allows the operation
of a second ON/OFF output. There is a deadband between the
operating ranges of the two inputs and an adjustable overlap
(hysteresis) of the on and off states of each output. Both Deadband
and Hysteresis are separately adjustable. With no relay action the
controller will read 50 %.
ATTENTION Other prompts affected: OUT HYST and
DEADBAND
PID A is normally used for three-mode control. This means that the
output can be adjusted somewhere between 100 % and 0 %. It
applies all three control actions—Proportional (P), Integral (I), and
Derivative (D)—to the error signal.
Proportional (Gain)—Regulates the controller's output in
proportion to the error signal (the difference between Process
Variable and Setpoint).
Integral (Reset)—Regulates the controller's output to the size of
the error and the time the error has existed. (The amount of
corrective action depends on the value of proportional Gain.)
Derivative (Rate)—Regulates the controller's output in proportion
to the rate of change of the error. (The amount of corrective action
depends on the value of proportional Gain.)
PID B—Unlike the PID A equation, the controller gives only an
integral response to a setpoint change, with no effect on the output
due to the gain or rate action, and it gives full response to PV
changes. Otherwise controller action is as described for the PID A
equation. See note on PID A.
UDC3200 Universal Digital Controller Operator Manual
Parameter Definition
33
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