67
•
Number of the Slave (address of communication of the Slave
device).
•
The type of data (word or bit).
•
The address ModBus relative to the datum (or data) to transfer.
•
The area of internal memory of the PL250A for reading or
writing the data.
•
The number of words (the instructions of reading and writing
can transfer up to consecutive 16 bits/words).
7.21 StartPID, PID and SetOutPID functions
The functions StartPID, PID and SetOutPID allow the regulation of
a size through an algorithm of action that is proportional, integral,
and derived.
The function
StartPID
activates the regulation. The function can
be activated a single time at startup or repeated at a later moment
permitting the modification “on the fly” of the parameters of
regulation. The integral action of the PID is zeroed only by calling
the functions and fixing the integral time to “0”. Otherwise, even in
case of shutdown, the system will initialize the regulation
maintaining as point of departure the same percentage of integral
action, thus limiting the time of transition.
Parameters of the function
StartPID
:
•
Proportional band
•
Integral time
•
Derived time
•
Dead band
The parameters can be inserted in numerical format, or can refer
to areas of memory. The integral time is expressed in the units of
time in which the function PID is called (for instance, function PID
called every 1 second, integral time expressed in seconds). The
derived time, however, is expressed with an additional decimal
digit with respect to the integral time. The proportional band and
the dead band are instead expressed in numeric values equal to
the setpoint and the process to regulate.
