Time Interval For The Pid Function - GE VersaMax PLC User Manual

PID Built-in Function Block
For public disclosure

14.3.3 Time Interval for the PID Function

The start time of each PLC sweep is used as the current time when calculating the time
interval between solutions of the PID function. The times and time intervals have a
resolution of 100 microseconds. When an application uses multiple PID functions, all of
them use the same time value.
The PID algorithm is solved when the current time is equal to or greater than the time of
the last PID solution plus the Sample Period or 10 milliseconds; whichever is larger. If the
Sample Period is set for execution on every sweep (value = 0), the PID function is
restricted to a minimum of 10 milliseconds between solutions. If the sweep time is
less than 10 milliseconds, the PID function waits until enough sweeps have
occurred to accumulate an elapsed time of 10 milliseconds. For example, if the
sweep time is 9 milliseconds, the PID function executes every other sweep, and the time
interval between solutions is 18 milliseconds. If a specific PID function is executed more
than once per sweep (by referencing the same reference array location in multiple PID
function blocks), the algorithm is solved only on the first call.
The longest possible interval between executions is 65,535 times 10 milliseconds, or 10
minutes, 55.35 seconds.
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