PID Structure

Each PID instruction has a Proportional Integral Derivative (PID) structure that contains status information about the instruction.
Mnemonic
Byte Offset
Data Type
Description
.CTL
00
DINT
The flags word stores these status bits in one, 16-bit word.
You can set and clear these status bits.
Bit
Number
Data Type
Description
.EN
31
BOOL
.CT
30
BOOL
cascade type (0=slave; 1=master)
.CL
29
BOOL
cascade loop (0=no; 1=yes)
.PVT
28
BOOL
process variable tracking (0=no; 1=yes)
.DOE
27
BOOL
derivative of (0=PV; 1=error)
.SWM
26
BOOL
software mode (0=no-auto); 1=yes- sw manual)
.CA
25
BOOL
control action (0=direct (SP-PV); 1=reverse (PV-SP))
.MO
24
BOOL
station mode (0=automatic; 1=manual)
.PE
23
BOOL
PID equation (0=independent; 1=dependent)
.NDF
22
BOOL
derivative smoothing (0=no; 1=yes)
.NOBC
21
BOOL
bias calculation (0=no; 1=yes)
.NOZC
20
BOOL
zero crossing (0=no; 1=for deadband)
02
You can set and clear these status bits.
Bit
Number
Data Type
Description
.INI
15
BOOL
PID initialized (0=no; 1=yes)
The PID instructions sets these status bits. You can clear these status bits.
Bit
Number
Data Type
Description
.SPOR
14
BOOL
setpoint out of range (0=no; 1=yes)
.OLL
13
BOOL
CV is below minimum output value (0=no; 1=yes)
.OLH
12
BOOL
CV is above maximum output value (0=no; 1=yes)
.EWD
11
BOOL
error is within deadband (0=no; 1=yes)
.DVNA
10
BOOL
error is alarmed low (0=no; 1=yes)
.DVPA
09
BOOL
error is alarmed high (0=no; 1=yes)
.PVLA
08
BOOL
PV is alarmed low (0=no; 1=yes)
.PVHA
07
BOOL
PV is alarmed high (0=no; 1=yes)
.SP
04
REAL
setpoint
.KP
08
REAL
independent proportional gain (unitless)
ISA controller gain (unitless)
.KI
12
REAL
independent integral gain (1/sec)
ISA reset term (minutes per repeat)
.KD
16
REAL
independent derivative gain (seconds)
ISA rate term (minutes)
.BIAS
20
REAL
feedforward or bias
.MAXS
24
REAL
maximum scaling
.MINS
28
REAL
minimum scaling
.DB
32
REAL
deadband
.SO
36
REAL
set output %
.MAXO
40
REAL
maximum output limit (% of output)
.MINO
44
REAL
minimum output limit (% of output)
.UPD
48
REAL
loop update time (seconds)
.PV
52
REAL
scaled PV value
.ERR
56
REAL
scaled error value
.OUT
60
REAL
output (% of 4095)
.PVH
64
REAL
process variable high alarm value
.PVL
68
REAL
process variable low alarm value
.DVP
72
REAL
positive deviation alarm
.DVN
76
REAL
negative deviation alarm
.PVDB
80
REAL
process variable alarm deadband
.DVDB
84
REAL
error alarm deadband
.MAXI
88
REAL
maximum PV value
.MINI
92
REAL
minimum PV value
.TIE
96
REAL
tieback value for manual control (0-4095)
.MAXCV
100
REAL
maximum CV value
.MINCV
104
REAL
minimum CV value
.MINTIE
108
REAL
minimum tieback value
.MAXTIE
112
REAL
maximum tieback value
.DATA[17]
116
REAL
The .DATA[17] member stores:
Element Description
.DATA[0] integral accumulation
.DATA[1] derivative smoothing temporary value
.DATA[2] previous .PV value
.DATA[3] previous .ERR value
.DATA[4] previous valid .SP value
.DATA[5] percent scaling constant
.DATA[6] .PV scaling constant
.DATA[7] derivative scaling constant
.DATA[8] previous .KP value
.DATA[9] previous .KI value
.DATA[10] previous .KD value
.DATA[11] dependent gain .KP
.DATA[12] dependent gain .KI
.DATA[13] dependent gain .KD
.DATA[14] previous .CV value
.DATA[15] .CV descaling constant
.DATA[16] tieback descaling constant
total memory per structure
120 bytes
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