PID Wizard (Closed Loop Control)

NOTE: The PID Wizard is only available in SIMATIC mode.

STEP

 

1

Select a Loop

2

Set Up Loop Parameters

3

Loop Input and Output Options

4

Loop Alarm Options

5

Specify Memory Area for Calculations

6

Specify Initialization Subroutine and Interrupt Routine

7

Generate Code

The PID Formula for the S7-200 Instruction Wizard can be used to simplify the configuration of PID operations. The wizard queries you for initialization options, and then generates program code and data block code for the specified configuration. After you choose PID from screen one, the wizard queries you for the following information:

STEP 1 Select a Loop

Which PID loop would you like to configure? Different PLCs support a different number of PID loops.

STEP 2 Set Loop Parameters

1.The PID instruction uses a 36 byte parameter table in V memory. You must specify the address for this table as a direct V memory byte address.

Note:

Do not create a symbolic name for the parameter table address. The code generated by the PID wizard uses the parameter table address to create operands as relative offsets into the parameter table. If you create a symbolic name for the parameter table address, and then change the address assigned to that symbol, the code generated by the PID wizard can no longer execute correctly.

2.Specify the normalized loop setpoint. For the loop setpoint, you can enter a double word address or a real constant between 0.0 and 1.0.

3.What should be the gain for the loop?

4.What is the loop sample time?

5.What is the loop integral time?

6.What is the loop derivative time?

For a description of how the loop parameters affect the performance of the PID calculation, see PID Calculation.

STEP 3 Set Loop Input and Output Options

Loop input options:

1.What is the loop process variable? This can be specified as a word address or a defined symbol.

2.What scaling should be performed on the process variable before the loop calculation?

Loop output options:

1.Is the output digital or analog?

2.What is the loop output variable? If the output is analog, this can be specified as a word address or a defined symbol. If the output is digital, then this can be specified as a bit address or a defined symbol.

3.What scaling should be performed on the output after the loop calculation?

STEP 4 Set Loop Alarm Options

1.Should a bit be set as a low value alarm? If so, you can enter a bit address or a defined symbol for the alarm address, and specify a value for the low alarm limit.

2.Should a bit be set as a high value alarm? If so, you can enter a bit address or a defined symbol for the alarm address, and specify a value for the high alarm limit.

3.Should a bit be set to indicate an error in the analog input module? If so, you can enter a bit address or a defined symbol for the error indicator, and you must specify where the input module is attached to the PLC.

STEP 5 Specify Memory Area for Calculations

1.The PID calculation requires a “scratchpad” space for temporary results. You need to specify the V memory byte address where this calculations area should begin.

2.Optional: Add manual control of the PID?

STEP 6 Specify Initialization Subroutine and Interrupt Routine

This screen allows you to assign names to the Initialization subroutine and execution interrupt routine that is generated by the Wizard.

STEP 7 Generate PID Code

This screen shows a list of the POUs generated by the PID Wizard, and gives a brief description of how these should be integrated into your program.

Once these queries have been answered and you have pressed "Finish", the S7-200 Instruction Wizard generates program code and data block code for the configuration you have specified.

See Also:

PID Instruction