Library of Function Blocks
4.27
OPENS THE VALVE
CLOSES THE VALVE
100%
0%
0
C
If the actuated valve is "Air-to-open", MV=100% must be equivalent to 20 mA. Valves type Air-to-
close will require 100% being equivalent to 4 mA. This may be selected in Function 02 - Current
Output.
Tuning by the Front Panel
Parameter CACT also defines if the block allows changes on the tuning parameters through the
front panel push buttons or not (see "PID Constants" ahead).
Front panel adjustment is selected when CACT=0, 1, 4 or 5.
Control Algorithm
The CD600 offers two control algorithms:
Parallel or Ideal algorithm
dt
) de(t
T
D
+ )dt e(t.
T
R
1
+ ) e(t
K
p
= ) MV(t ∫
Noninteractive or ISA algorithm
]
dt
) de(t
T
D
+ )dt e(t.
T
R
1
+ ) [e(t
K
p
= ) MV(t ∫
Parameters 0, 1, 2 or 3 select the parallel or ideal.
Parameters 4, 5, 6 or 7 select the noninteractive or ISA.
For the noninteractive option, when K
p
=0 the controller is automatically set as ID.
ANTIRESET-WINDUP (CARL AND CARU)
The control algorithm automatically stops the contribution of the integral mode when the output
signal reaches the limits of 0 or 100%. Contributions of the Proportional and Derivative modes are
not affected.
The CD600 has a unique feature: the adjustment of the limits for the integral mode saturation.
It is normally fixed at 0% (CARL) and 100% (CARU), but can be narrowed, allowing quicker
responses and avoiding overshoot in heating processes, for example.
PID CONSTANTS (AKp, ATr, ATd)
The table is self-explanatory. It is good to remember that the Proportional action is in terms of Gain
and not of Proportional Band. Bigger gain means more action. PID constants may be adjusted by
means of the Hand Held Programmer or the controller's front panel (see tuning procedures). In order
to inhibit front panel tuning, simply configure parameter CACT with 2 or 3 instead of 0 or 1.
BIAS (ABIA)
With this parameter it is possible to assign an initial
bias value to the output signal when the control is transferred from Manual to Automatic. This may
be done only if input Feedback is not connected (LIC=0).
For bumpless Manual to Automatic transfer, the input C must be connected to the output of the A/M
block and the input D (track FB) must be connected to the status indication of the A/M block. In this
case, parameter ABIA is used to change the block output during automatic operation. The output
signal is subjected to a step type variation whenever the ABIA value is modified. Amplitude and
direction of this step are equivalent to the difference between the previous and the new ABIA value.
The connection diagram for both cases are shown on the following figures:
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