Honeywell EXCEL 5000 User Manual page 201

EXCEL CARE CONTROL ICONS
;;; Reverse Acting PID Controller
;;; Integral action is enabled if the integral time is greater than or equal to 15 seconds and the integral
;;; action flag Xd is true.
IF (Xd=True) AND (Tn
ELSE Error_Sum = 0
;;; This limits the integral action to the range
Error_Limit = Xp * Tn / ( to * 2 )
Error_Sum = MIN ( Error_Limit, Error_Sum )
Error_Sum = MAX ( -Error_Limit, Error_Sum )
;;; Integral Term
IF (Tn < 15)
Int_Term = 0
ELSE
Int_Term = to * Error_Sum / Tn
;;; Derivative Term
Derv_Term = (Tv *(E n - E n-1 ) / to)
Y = 50 + (100/Xp) * (E n + Int_Term + Derv_Term)
Y = MIN(Y,max_out)
Y = MAX(Y,min_out)
PID Plus Example
Variable Description
Xp throttling range or proportional band
Tv derivative time
Tn integral action time
min_out minimum output
max_out maximum output
X controlled Variable
W set point or reference variable
Xd integral action control digital point
Y controller output
to Cycle Time (sec)
E Error (W - X)
E n-1 Error last controller cycle
E n Current Error
n
∑
Error sum
=
i 0
The PID Plus algorithm is implemented in Excel 5000 controller operation based on
the following code:
≥
15)) Error_Sum = Error_Sum + E n
±
50
This example implements automatic switchover from P to PI control. The PID Plus
derivative parameter must be set to zero to establish PI control. The following
diagram shows how PID Plus operates in a CARE setup.
203
ALPHABETIC REFERENCE
Comments
causes inherent reverse
action
74-5577–33 (US)
EN2B-0184 GE51 R0518 (Europe)