FUNCTION_BLOCK PID_FIXCYCLE
Represents a PID controller for which the cycle time can be set manually
A PID controller continuously calculates an error value e(t) as the difference between a desired set point and a measured process variable. The PID contoller applies a correction based on proportional, integral, and derivative terms (sometimes denoted P, I, and D respectively) which give their name to the controller type.
Note
For fast and fix tasks it is recommended to use PID_FIXCYCLE instead of PID, because the cycle time is defined accurately, whereas PID only can measure the cycle time with a maximum accuracy of milliseconds. In case of very short cycles (1ms) this might lead to a rough run (see PID).
Note
It is not necessary to readjust the controller parameters (KP, TN, TV) if the cycle time changes.
For more information see: PID.
InOut:
|
Scope |
Name |
Type |
Initial |
Comment |
|
Input |
ACTUAL |
REAL |
Actual value, process variable |
|
|
SET_POINT |
REAL |
Desired value, set point |
||
|
KP |
REAL |
Proportionality const. P |
||
|
TN |
REAL |
Reset time I in sec |
||
|
TV |
REAL |
Rate time, derivative time D in sec |
||
|
Y_MANUAL |
REAL |
Y is set to this value as long as MANUAL = TRUE |
||
|
Y_OFFSET |
REAL |
Offset for manipulated variable |
||
|
Y_MIN |
REAL |
Minimum value for manipulated variable |
||
|
Y_MAX |
REAL |
Maximum value for manipulated variable |
||
|
MANUAL |
BOOL |
TRUE: Manual: Y is not influenced by controller FALSE: Controller determines Y |
||
|
RESET |
BOOL |
TRUE: Sets Y output to Y_OFFSET and reset integral part |
||
|
CYCLE |
REAL |
Time in s between two calls |
||
|
Output |
Y |
REAL |
Manipulated variable, set value |
|
|
LIMITS_ACTIVE |
BOOL |
FALSE |
TRUE: Set value would exceed limits Y_MIN, Y_MAX |
|
|
OVERFLOW |
BOOL |
FALSE |
Overflow in integral part |
