Siemens SIMATIC S7 - Page 321

Program instructions
7.9 PID
S7-200 SMART
System Manual, V2.3, 07/2017, A5E03822230-AF
321
Loop table
The loop table is 80 bytes long and has the format shown in the following table.
Offset
Field
Format
Type
Description
0 Process variable (PV
n
) REAL In Contains the process variable, which must be scaled
between 0.0 and 1.0.
4 Setpoint (SP
n
) REAL In Contains the setpoint, which must be scaled be-
tween 0.0 and 1.0.
8 Output (M
n
) REAL In/Out Contains the calculated output, scaled between 0.0
and 1.0.
12 Gain (K
C
) REAL In Contains the gain, which is a proportional constant.
Can be a positive or negative number.
16 Sample time (T
S
) REAL In Contains the sample time, in seconds. Must be a
positive number.
20 Integral time or reset (T
I
) REAL In Contains the integral time or reset, in minutes. Must
be a positive number.
24 Derivative time or rate (T
D
) REAL In Cont
ains the derivative time or rate, in minutes. Must
be a positive number.
28 Bias (MX) REAL In/Out Contains the bias or integral sum value between 0.0
and 1.0.
32 Previous process variable
(PV
n-1
)
REAL In/Out Contains the value of the process variable stored
from the last execution of the PID instruction.
36 to 79
Reserved for auto-tuning variables. Refer to PID loop definition table (Page 582) for details.