Endress+Hauser Liquiline CA80SI, Руководство по эксплуатации

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Liquiline System CA80SI Operation
Hauser 99
10.7.3 Controller
Controller structure in Laplace representation
A B
A0015007
 72 Block diagram of the controller structure
A Neutral zone I Integral value
B Output limiting D Derivative value
K
p
Gain (P ‐ value) αT
V
Damping time constant with α = 0 to 1
T
n
Integral action time (I ‐ value) e Control deviation
T
v
Derivative action time (D ‐ value) w Set point
T
w
Time constant for set point damping x Controlled variable
T
wu
Time constant for anti ‐ windup feedback y Manipulated variable
P Proportional value
The controller structure of the device comprises set point damping at the input to prevent
erratic changes in the manipulated variable if the set point changes. The difference
between the set point w and the controlled variable (measured value) X results in the
control deviation which is filtered by a neutral zone.
The neutral zone is used to suppress control deviations (e) that are too small. The control
deviation thus filtered is now fed to the actual PID controller which divides into 3 parts
based on the P (proportional), I (integral) and D (derivative) values (top-down). The
integral section (middle) also comprises an anti ‐ windup mechanism for limiting the
integrator. A low-pass filter is added to the D ‐ section to damp hard D ‐ terms in the
manipulated variable. The sum of the 3 sections results in the internal controller
manipulated variable which is limited according to the settings (for PID ‐ 2s to ‐ 100% to
+100%).
The graphic does not illustrate a downstream filter for limiting the rate of change of the
manipulated variable (can be configured in the menu in Max y change rate ).
In the menu do not configure the gain K
p
. Instead configure the reciprocal value, the
proportional band X
p
(K
p
=1/X
p
).
Configuration
Make the following decisions to configure a controller:
• (1) What type of process can your process be assigned to? → Process type
• (2) Should it be possible to influence the measured variable (controlled variable) in one
direction or in both directions? One-sided or two-sided controller, → Controller type
• (3) What should be the controlled variable (sensor, measured value)? → Controlled
variable
• (4) Do you have a disturbance variable that should be active at the controller output? →
Disturbance variable