User manual

IEC61131 User and Reference Manual
April 22, 2008
328
pidd
Discrete Output PID Function Block
Description
The pidd function block performs a PID algorithm and controls two discrete outputs. The
output is a duty cycle of a Boolean value. The duty cycle depends on the value of the output.
The increase output, iOut, is cycled when the outputPercent is greater than zero. The
decrease output, dOut, is cycled when the outputPercent is less than zero.
In automatic mode, the output is calculated using the PID algorithm. A new calculation is
done at the rate specified by cycleTime.
In manual mode (auto = FALSE), the outPercent is set to the value of the outManualPercent
input. The output is limited to the range set by fullPercent and zeroPercent.
If the cycleTime parameter is less than the cycle time of the ISaGRAF application program,
the sampling period is the period of the application.
The analog output function block pidd appears as follows.
pv
sp
gain
reset
rate
deadband
fullPercent
zeroPercent
cycleTime
auto
outManualPercent
dOut
pidd
motorOutput
iOut
outPercent
Arguments
Inputs
Type
Description
pv
Real
The process value is used to calculate the process
error in the PID algorithm. error = pv – sp
sp
Real
The setpoint value is used to calculate the process
error in the PID algorithm. error = pv – sp
gain
Real
The proportional gain. A positive value of gain
configures a forward-acting PID controller and a
negative value of gain configures a reverse acting
controller.