Rockwell Automation 1771-PD PID MODULE (+DU) - Manual (Page 131)

Programming
Chapter 3
3Ć88
The same applies to outputs. The analog output of the PID module can be
read by the PC processor and written to another type of output module.
The PC processor can read analog inputs and set analog outputs. It can
perform its own sophisticated PID control of many interactive loops. PID
modules can function as analog I/O modules and be programmed for
back-up. In the event of a PC processor failure or a break in
communication with the PID module, PID modules can control their
respective loops. The soft fault mode selection bit, W19(W39) B15, B14,
B13 should be set to 1,0,0 respectively.
Adaptive gain control can be performed by the PC processor and PID
modules. The C processor can change PID gain constants based on PID
error values and external disturbances. Continuous processes can be fine
tuned. Batch processes can be sequenced.
The fine tuning of a PC processor interactive system can depend on the
remote scan time and length of user program. Tuning should be done in
the fully operating system. If another model PC processor is substituted,
the system may have to be returned.
When initializing an unprogrammed PID module, we recommend that you
program only the minimum required rungs (Figure B.2 and Figure B.6)
and load only the minimum data necessary. Then add PID control
parameters (Dynamic block and loop block data) using on-line data
change or the module’s soft fault mode.
Load only the following data, setting all other data words and bits to zero.
Word W01 Bit 17 = 1, Bit 16 = 1, Bit 07 = 1
Set Bit 15 to 1 if using one loop.
Set Bit 15 to 0 if using two loops.
Word W03 Load the dynamic block start address.
Word W04 Load the Loop 1 block start address.
Word W11 Load the Loop 2 block start address, if
using two loops.
Word W18 Bit 16 = 1
Programming
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