Siemens SIMATIC S7-200 System Manual page 397

Table 15-1 Loop Table
Offset Field
0 Process variable
(PV )
n
4 Setpoint
(SP )
n
8 Output
(M )
n
12 Gain
(K )
C
16 Sample time
(T )
S
20 Integral time or reset
(T )
I
24 Derivative time or rate
(T )
D
28 Bias
(MX)
32 Previous process
variable (PV )
n- -1
36 PID Extended Table ID
40 AT Control (ACNTL)
41 AT Status (ASTAT)
42 AT Result (ARES)
43 AT Config (ACNFG)
44 Deviation (DEV)
48 Hysteresis (HYS)
52 Initial Output Step
(STEP)
56 Watchdog Time
(WDOG)
60 Suggested Gain
(AT_K )
C
64 Suggested Integral Time
(AT_T )
I
68 Suggested Derivative
Time (AT_T )
D
72 Actual Step size
(ASTEP)
76 Actual Hysteresis
(AHYS)
PID Auto-Tune and the PID Tuning Control Panel
Format Type
REAL In
REAL In
REAL In/Out
REAL In
REAL In
REAL In
REAL In
REAL In/Out
REAL In/Out
ASCII Constant 'PIDA' (PID Extended Table, Version A):
BYTE In
BYTE Out
BYTE In/Out
BYTE In
REAL In
REAL In
REAL In
REAL In
REAL Out
REAL Out
REAL Out
REAL Out
REAL Out
Description
Contains the process variable, which must
be scaled between 0.0 and 1.0.
Contains the setpoint, which must be scaled
between 0.0 and 1.0.
Contains the calculated output, scaled
between 0.0 and 1.0.
Contains the gain, which is a proportional
constant. Can be a positive or negative
number.
Contains the sample time, in seconds. Must
be a positive number.
Contains the integral time or reset, in
minutes.
Contains the derivative time or rate, in
minutes.
Contains the bias or integral sum value
between 0.0 and 1.0.
Contains the value of the process variable
stored from the last execution of the PID
instruction.
ASCII constant
See Table 15-2
See Table 15-2
See Table 15-2
See Table 15-2
Normalized value of the maximum PV
oscillation amplitude (range: 0.025 to 0.25).
Normalized value of the PV hysteresis used
to determine zero crossings (range: 0.005 to
0.1). If the ratio of DEV to HYS is less than
4, a warning will be indicated during
auto-tune.
Normalized size of the step change in the
output value used to induce oscillations in
the PV (range: 0.05 to 0.4)
Maximum time allowed between zero
crossings in seconds (range: 60 to 7200)
Suggested loop gain as determined by the
auto-tune process.
Suggested integral time as determined by
the auto-tune process.
Suggested derivative time as determined by
the auto-tune process.
Normalized output step size value as
determined by the auto-tune process.
Normalized PV hysteresis value as
determined by the auto-tune process.
Chapter 15
383