Omron CP - PROGRAMMING MANUAL 05-2007 Programming Manual page 651

Data Control Instructions
Flags
Precautions
Example
618
Name Label
Error Flag ER
Greater Than >
Flag
Less Than Flag <
Carry Flag CY
PID(190) is executed as if the execution condition was a STOP-RUN signal.
PID calculations are executed when the execution condition remains ON for
the next cycle after C+9 to C+38 are initialized. Therefore, when using the
Always ON Flag (ON) as an execution condition for PID(190), provide a sepa-
rate process where C+9 to C+38 are initialized when operation is started.
If the C data is out of range, an error will occur and the Error Flag will turn ON.
If the actual sampling period is more than twice the designated sampling
period, an error will occur and the Error Flag will turn ON. PID control will still
be executed, however.
The Carry Flag turns ON while PID control is being executed.
The Greater Than Flag turns ON if the manipulated variable after the PID
action exceeds the upper limit. At this time, the results are output at the upper
limit.
The Less Than Flag turns ON if the manipulated variable after the PID action
is below the lower limit. At this time, the results are output at the lower limit.
Within the PID parameters (C to C+38), the only value that can be changed
while the input condition is ON is the set value for C. If any other value is
changed, be sure to turn the input condition from OFF to ON to enable the
new value.
At the rising edge of CIO 0.00 (OFF to ON), the work area in D209 to D238 is
initialized according to the parameters (shown below) set in D200 to D208.
After the work area has been initialized, PID control is executed and the
manipulated variable is output to CIO 2000.
When CIO 0.00 is turned ON, PID control is executed at the sampling period
intervals according to the parameters set in D200 to D208. The manipulated
variable is output to CIO 2000.
The PID constants used in PID calculations will not be changed if the propor-
tional band (P), integral constant (Tik), or derivative constant is changed after
CIO 0.00 turns ON.
Operation
ON if the C data is out of range.
ON if the actual sampling period is more than twice the
designated sampling period.
OFF in all other cases.
ON if the manipulated variable after the PID action
exceeds the upper limit.
OFF in all other cases.
ON if the manipulated variable after the PID action is
below the lower limit.
OFF in all other cases.
ON while PID control is being executed.
OFF in all other cases.
Section 3-17