Pid Loop Definition Table - Siemens SIMATIC S7 System Manual

PID loops and tuning

11.1 PID loop definition table

11.1 PID loop definition table
Eighty (80) bytes are allocated for the loop table from the starting address you enter for
Table (TBL) in the PID instruction box. The PID instruction for the S7-200 SMART CPU
references this loop table that contains the loop parameters.
If you use the PID Tune control panel, all interaction with the PID loop table is handled for
you by the control panel. If you need to provide auto-tuning capability from an operator
panel, your program must provide the interaction between the operator and the PID loop
table to initiate and monitor the auto-tuning process, and then apply the suggested tuning
values.
Table 11- 1 Loop table
Offset Field
0 Process variable (PV
4 Setpoint (SP )
n
8 Output (M )
n
12 Gain (K )
C
16 Sample time (T
20 Integral time or reset (T
24 Derivative time or rate
(T )
D
28 Bias (MX)
32 Previous process varia-
ble (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) REAL
60 Suggested Gain (AT_K
582
Format
) REAL
n
REAL
REAL
REAL
) REAL
S
) REAL
I
REAL
REAL
REAL
ASCII
BYTE
BYTE
BYTE
BYTE
REAL
REAL
REAL
) REAL
C
Type Description
In Contains the process variable, which must be scaled
between 0.0 and 1.0.
In Contains the setpoint, which must be scaled between
0.0 and 1.0.
In/Out Contains the calculated output, scaled between 0.0 and
1.0.
In Contains the gain, which is a proportional constant. Can
be a positive or negative number.
In Contains the sample time, in seconds. Must be a posi-
tive number.
In Contains the integral time or reset, in minutes.
In Contains the derivative time or rate, in minutes.
In/Out Contains the bias or integral sum value between 0.0 and
1.0.
In/Out Contains the value of the process variable stored from
the last execution of the PID instruction.
Constant 'PIDA' (PID Extended Table, Version A): ASCII constant
In See the following table
Out See the following table
In/Out See the following table
In See the following table
In Normalized value of the maximum PV oscillation ampli-
tude (range: 0.025 to 0.25).
In Normalized value of the PV hysteresis used to deter-
mine 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.
In Normalized size of the step change in the output value
used to induce oscillations in the PV (range: 0.05 to
0.4).
In Maximum time allowed between zero crossings in sec-
onds (range: 60 to 7200).
Out Suggested loop gain as determined by the auto-tune
process.
System Manual, V2.3, 07/2017, A5E03822230-AF
S7-200 SMART