Honeywell EXCEL 5000 User Manual

EXCEL CARE CONTROL ICONS ALPHABETIC REFERENCE
203 74-5577–33 (US)
EN2B-0184 GE51 R0518 (Europe)
Variable
Description
Comments
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)
causes inherent reverse
action
E
n-1
Error last controller cycle
E
n
Current Error
∑
=
n
i 0
Error sum
The PID Plus algorithm is implemented in Excel 5000 controller operation based on
the following code:
;;; 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
≥
15)) Error_Sum = Error_Sum + E
n
ELSE Error_Sum = 0
;;; This limits the integral action to the range
±
50
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 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.

Honeywell EXCEL 5000 Specifications

General

Brand	Honeywell
Model	EXCEL 5000
Category	Control Systems
Language	English