Code associated with "How to Write a PID Algorithm" by Garth Gaddy, p. 62, May 1997

listing 1
Screw servo motion program.

01		While (True)
02		       If (Auto_Mode = 1 )
03			If (First_PID_Execution = 0 OR First_PID_Execution = 1)
04				Error = (SP - PV) * (CV_Span / PV_Span)
05				Sum_Error = Sum_Error + Error
06				If (First_PID_Execution = 0)
07					Sum_Error = Manual_Command / KI 
08					First_PID_Execution = 1
09					Initial_Error = Error
10				Endif
11				Pterm = 0
12				Iterm = KI * Sum_Error
13				Dterm = 0
14				If (Initial_Error > 0 and Error < 0)
15                   				First_PID_Execution = 2
16                    				Last_PV = PV
17                			Endif
18                			If (Initial_Error < 0 and Error > 0)
19                    				First_PID_Execution = 2
20                    				Last_PV = PV
21                			Endif
22                			Last_SP = SP
23			Else
24				If (SP = Last_SP) 
25					Error = (SP - PV) * (CV_Span / PV_Span)
26					Pterm = KP * Error
27					Sum_Error = Sum_Error + Error
28					Iterm = KI * Sum_Error
29					d_PV = (Last_PV - PV) * (CV_Span / PV_Span)
30					Last_PV = PV
31					Dterm = KD * d_PV
32				Else
33					Error = (SP - PV) * (CV_Span / PV_Span)
34					Sum_Error = Sum_Error + Error
35					Pterm = 0
36                				Iterm = KI * Sum_Error
37                				Dterm = 0
38                             		If (SP > Last_SP and PV > SP)
39                    					Last_SP = SP
40                    					Last_PV = PV
41                				Endif
42                				If (SP < Last_SP and PV < SP)
43                    					Last_SP = SP
44                    					Last_PV = PV
45                				Endif
46              			Endif
47			Endif
48			CV = Pterm + Iterm + Dterm
49		      Else
50			CV = Manual_Command
51			First_PID_Execution = 0
52		      Endif
53		EndWhile