Endress+Hauser Liquisys M CLM223 - Page 55

Liquisys M CLM223/253 Commissioning
Endress+Hauser 55
P(ID) controller
You can define various controller functions for the transmitter. On the basis of the PID
controller, P, PI, PD and PID controllers can be implemented. For an optimum control
system, use the controller that best suits your application.
• P controller
Used for simple linear control purposes with small system deviations. Where major
changes are to be controlled, overshooting may occur. In addition, a lasting control
deviation must be expected.
• PI controller
Is used for control systems where overshooting is to be avoided and no lasting control
deviation should occur.
• PD controller
Is used for processes that require quick changes and where peaks must be corrected.
• PID controller
Is used for processes where a P, PI or PD controller does not control sufficiently.
Configuration options of the P(ID) controller
The following configuration options are available for a PID controller:
• Change control gain K
p
(P influence)
• Set integral action time T
n
(I influence)
• Set derivative action time T
v
(D influence)
Basic load dosing (basic)
You can set a constant dosage amount (field R2311) with basic load dosing (field R231).
PID control plus basic load dosing
If you have selected this function (PID + Basic) in field R231, the PID-controlled dosage
amount does not drop below the basic load value entered in field R2311.
100 %
100 %
A
B
C
A0025221
 30 Control characteristic of PID controller with basic load dosing
A PID plus basic load
B Basic load
C PID
Commissioning
If you do not yet have any experience for setting the control parameters, set the values
that yield the greatest possible stability in the control circuit. Proceed as follows to
optimize the control circuit further:
• Increase the control gain K
p
until the controlled variable just starts to overshoot.
• Reduce K
p
slightly again and then reduce the integral action time T
n
so that the shortest
possible correction time without overshooting is achieved.
• To reduce the response time of the controller, also set the derivative action time T
v
.
Control and fine optimization of the set parameters with a recorder