Pixsys PL260, Руководство пользователя

Страница: 67 / 72

67
2.2.23 Functions StartPID , PID , SetOutPID
Functions StartPID, PID and SetOutPID enables control of a process by
means of PID algorithm (proportional, integral, derivative).
Function StartPID starts the relevant control block and sets parameters as
required. Function can be activated once at the starting or it may be
recalled later to modify quickly control parameters. PID integral action is
initialized only calling this function and setting integral time to 0, otherwise
even in case of switch-off the system will start control action keeping the
same percentage of integral action and consequently limiting the transient
times. Parameters required by function StartPID are the following:
•
Proportional band
•
Integral time
•
Derivative time
•
Dead band
Parameters can be entered with numeric format or referring to internal
variables. Integral time is expressed in time unit used for PID function (ex.
PID function recalled every 1 sec., integral time expressed in seconds).
Derivative time is expressed with one decimal digit more than integral time.
Proportional band and dead band are expressed with a numeric value as
setpoint and process.
PID function requires following parameters:
•
Setpoint
•
Process
•
Output value
•
Type of control action
•
Type of output
After acquisition of necessary parameters values, PID function will enter
the value obtained by control algorithm in the variable “Output value”. This
value will have been obtained rescheduling the percentage value 0 – 10000
(0.00%
÷
100.00%) between minimum and maximum value of PID output as
entered using the function RANGE.
For optimal results, PID function should be recalled at regular intervals. A
timer can be used or even an internal Interrupt, to get shorter intervals.
Function SetOutPID is used for control actions which foresee both
automatical and manual functions. The function allows to avoid process
oscillations when changing from manual to automatical PID control.
Following parameters are required:
•
Output value