Omron CP - PROGRAMMING MANUAL 05-2007 Programming Manual page 650

Data Control Instructions
If the settings are within the permissible range, PID processing will be exe-
cuted using the initial values. Bumpless operation is not performed at this
time. It will be used for manipulated variables in subsequent PID processing
execution. (Bumpless operation is processing that gradually and continuously
changes the manipulated variable in order to avoid the adverse effects of sud-
den changes.)
When the execution condition turns ON, the PV for the specified sampling
period is entered and processing is performed.
Parameters (C to C+8)
PID control
PV input (S)
Manipulated variable (D)
The number of valid input data bits within the 16 bits of the PV input (S) is
designated by the input range setting in C+6, bits 08 to 11. For example, if 12
bits (4 hex) is designated for the input range, the range from 0000 hex to 0FFF
hex will be enabled as the PV. (Values greater than 0FFF hex will be regarded
as 0FFF hex.)
The set value range also depends on the input range.
Measured values (PV) and set values (SV) are in binary without sign, from
0000 hex to the maximum value of the input range.
The number of valid output data bits within the 16 bits of the manipulated vari-
able output is designated by the output range setting in C+6, bits 00 to 03. For
example, if 12 bits (4 hex) is designated for the output range, the range from
0000 hex to 0FFF hex will be output as the manipulated variable.
For proportional operation only, the manipulated variable output when the PV
equals the SV can be designated as follows:
0: Output 0%
1: Output 50%.
The direction of proportional operation can be designated as either forward or
reverse.
The upper and lower limits of the manipulated variable output can be desig-
nated.
The sampling period can be designated in units of 10 ms (0.01 to 99.99 s), but
the actual PID action is determined by a combination of the sampling period
and the time of PID(190) instruction execution (with each cycle).
The timing of enabling changes made to PID constants can be set to either 1)
the beginning of PID instruction execution or 2) the beginning of PID instruc-
tion execution and each sampling period. Only the proportional band (P), inte-
gral constant (Tik), and derivative constant (Tdk) can be changed each
sampling cycle (i.e., during PID instruction execution). The timing is set in bit 1
of C+5.
Of the PID parameters (C to C+38), only the set value (SV) can be changed
when the execution condition is ON. When changing other values, be sure to
change the execution condition from OFF to ON.
Section 3-17
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