Omron CJ - INSTRUCTIONS REFERENCE MANUAL 07-2009 Reference Manual page 682

• If the AT Command Bit is turned ON during PIDAT(191) execution, PIDAT(191) interrupts the PID
control being performed with the user-set PID constants, performs autotuning, and then resumes PID
control with the calculated PID constants.
The following flowchart shows the autotuning procedure:
Note 1 If autotuning is interrupted by turning OFF the AT Command Bit during autotuning, PID control will start
with the PID constants that were being used before autotuning began.
2 Also, if an AT execution error occurs, PID control will start with the PID constants that were being used
before autotuning began.
In both cases described in notes 1 and 2, the PID constants will be enabled if they were already
calculated when autotuning was interrupted.
PID Control
• 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 variable 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 designated.
• 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 PIDAT(191) instruction
execution (with each cycle).
• The timing of enabling changes made to PID constants can be set to either 1) the beginning of
PIDAT(191) instruction execution or 2) the beginning of PID instruction execution and each sampling
period. Only the proportional band (P), integral 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.
CS/CJ/NSJ Series Instructions Reference Manual (W474)
The AT Command Bit (bit 15 of C+9) is
ON at the start of PIDAT(191) execution
or it is turned ON during execution.
PID control is interrupted, the PV is
forcibly changed, and the PID constants
are calculated automatically.
The calculated P, I, and D constants are
set in C+1, C+2, and C+3 respectively.
The AT Command Bit is turned OFF.
PID control starts (or restarts) with the
new PID constants.
3. Instructions
3
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