User manual

IEC61131 User and Reference Manual
April 22, 2008
329
Inputs
Type
Description
reset
Real
The reset time, in seconds. This controls the reset
gain (or magnitude of integral action) in a PI or PID
controller. Valid range is any value greater than 0. A
value of 0 disables the reset action.
rate
Real
The rate time, in seconds. This controls the rate
gain (or magnitude of derivative action) in a PD or
PID controller. Valid range is any value greater than
0. A value of 0 disables the rate action.
deadband
Real
The setpoint deadband is used by the PID algorithm
to determine if the process requires control outputs.
If the absolute value of the error is less than the
deadband, then the function block skips execution
of the control algorithm. This permits faster
execution when the error is within a certain
acceptable range or deadband. Valid range is any
value greater than 0.
fullPercent
Real
The full scale output limit in percent of cycleTime.
zeroPercent
Real
The zero scale output limit in percent of cycleTime.
cycleTime
Time
The value of the PID algorithm execution period
measured in seconds. Any value greater than or
equal to 0.001 seconds (1 ms) may be specified. If
the cycleTime specified is less than the scan time of
the ISaGRAF application program, the scan time of
the application becomes the PID cycleTime.
auto
Boolean
When set to TRUE to the output value is calculated
using the PID algorithm. When set to FALSE the
output value is set to the value of
outManualPercent.
outManualPercent
Real
The value that the output is set to when the pida
function block is in the manual mode.
motorOutput
Boolean
When set to TRUE iOut and dOut are off when
error is within the deadband. When set to FALSE
iOut and dOut act normally.
Outputs
Type
Description
iOut
Boolean
The increase output. This output cycles when
outPercent is greater than zero.
dOut
Boolean
The decrease output. This output cycles when
outPercent is less than zero.
outPercent
Real
PID algorithm output.
PID Velocity Algorithm
The PIDD function uses the velocity form of the PID algorithm. The velocity form calculates
the change in the output and adds it to the previous output.