HA_CS31_PID_FIXCYCLE - HA PID Controller with Fix Cycle¶
Function block HA_CS31_PID_FIXCYCLE
| Available as of PLC runtime system | V1.3 and above |
| Included in library | HA_CS31_AC500_V13.lib (V1.3) and above |
| Type | Function Block with historical values. |
This function block is a standard PID controller with automatic data synchronization in a High Availability application.
Note
Only internal variables and outputs are synchronized. Input variables and parameters are not synchronized. If needed, use HA_CS31_DATA_SYNC to achieve the same.
Parameter Description
The parameters Y_OFFSET, Y_MIN and Y_MAX serve for transformation of the manipulated variable within a prescribed range.
MANUAL parameter can be used to switch to manual operation.
CYCLE ia an input to to the function block and is to be set by the user (in ms).
RESET parameter can be used to re-initialize the controller.
The cycle time is not measured automatically. It is set by the input CYCLE (in seconds).
In normal operation (MANUAL = RESET = LIMITS_ACTIVE = FALSE) the controller calculates the controller error as difference from SET_POINT parameter – ACTUAL parameter, generates the derivation with respect to time de/dt and stores these values internally.
The output, i.e. the manipulated variable Y unlike the PD controller contains an additional integral part and is calculated as follows: Y = KP × (D + 1/TN ∫edt + TV dD/dt) + Y_OFFSET. So besides the P-part also the current change of the controller error (D-part) and the history of the controller error (I-part) influence the manipulated variable. The PID controller can be easily converted to a PI controller by setting TV=0. Because of the additional integral part, an overflow can come about by incorrect parametrization of the controller if the integral of error D becomes too great. Therefore for the sake of safety a boolean output called OVERFLOW is present, which in this case would have the value TRUE. This only will happen if the control system is instable due to incorrect parametrization. At the same time, the controller will be suspended and will only be activated again by re-initialization.