Proportional/Integral/Derivative (Pid) Loop Instruction - Siemens Simatic S7-200 System Manual

Proportional/Integral/Derivative (PID) Loop Instruction

The PID Loop instruction (PID) executes a PID loop calculation on
the referenced LOOP based on the input and configuration
information in Table (TBL).
Error conditions that set ENO = 0:
H SM1.1 (overflow)
H 0006 (indirect address)
Special Memory bits affected:
H SM1.1 (overflow)
The PID loop instruction (Proportional, Integral, Derivative Loop) is
provided to perform the PID calculation. The top of the logic stack
(TOS) must be ON (power flow) to enable the PID calculation. The
instruction has two operands: a TABLE address which is the starting
address of the loop table and a LOOP number which is a constant
from 0 to 7.
Eight PID instructions can be used in a program. If two or more PID instructions are used with the same
loop number (even if they have different table addresses), the PID calculations will interfere with one
another and the output will be unpredictable.
The loop table stores nine parameters used for controlling and monitoring the loop operation and includes
the current and previous value of the process variable, the setpoint, output, gain, sample time, integral
time (reset), derivative time (rate), and the integral sum (bias).
To perform the PID calculation at the desired sample rate, the PID instruction must be executed either
from within a timed interrupt routine or from within the main program at a rate controlled by a timer. The
sample time must be supplied as an input to the PID instruction via the loop table.
Table 6-41 Valid Operands for the PID Loop Instruction
Inputs/Outputs
TBL
LOOP
STEP 7-Micro/WIN offers the PID Wizard to guide you in defining a PID algorithm for a closed-loop control
process. Select the Tools > Instruction Wizard menu command and then select PID from the Instruction
Wizard window.
Instruction
Wizard
Data Types Operands
BYTE VB
BYTE Constant (0 to 7)
S7-200 Instruction Set Chapter 6
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