Siemens SIMATIC 505 - Profibus Operations and I;O Finding

Selected Functions
5-6
PID Algorithms (continued)
5.2.3
The dynamic PID algorithm is a variation of the implementation suggested
for use with the DSP chip applications. As is suggested by its name, this
algorithm is faster -reacting and consequently does not require that the
setpoint be forced into the output upon change.
The basic equation for the dynamic PID algorithm is as follows:
k
c
 + gain
t
d
 + rate
t
i
 + reset
t
s
 + scantime
vsf + velocity scaling factor
setpoint + setpoint from table
prevpos + previous position
currpos + current position
input from V memory table
″
″
″
″
″
inputfromańd
″
Calculate integral constant term:
k
i
 +
  gainscantime
reset
Calculate derivative constant term:
k
d
 +
gainrate
scantime
Calculate process variable:
PVnew +
[prev pos - curr pos]  
vsf
Calculate new error term:
curr err + setpoint * PVnew
Calculate new bias term:
trialm
x
 + k
i
currerr ) prevoutput
Calculate new output value:
trialm
n
 +
k
c
currerr

 * k
d
PVnew * PVold ) trialm
x
newoutput + trialm
n
Dynamic PID
Algorithm