Advanced Topics - Emerson PACSystems RX3i User Manual

User Manual
GFK-2409B
5.1

Advanced Topics

PID Function Blocks
The PID function block uses a data structure consisting of 40 registers. These registers
contain not only configuration parameters, but also intermediate and final terms used in the
internal calculations. Some of the internal calculations are based upon values from the PLC's
system clock. Because the internal clocks in the two CPUs are not synchronized precisely to
each other, it is necessary to include a small amount of logic to compensate for the
difference.
Also, it will be necessary to include the PID registers in one or more of the %R Synchronized
Data Groups. This ensures that the PID in the Backup CPU tracks the Master.
The ladder logic is straightforward:
Figure 64:
Programming Considerations
Chapter 5
Oct 2019
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