Mitsubishi Electronics MELSEC-F

/FX

3UC

PLC User's Manual - Analog Control Edition

Table of Contents

PID Instruction (FNC 88)

1. Outline M-3

1.1 Outline of function....................................................................................................................... M-3

1.2 Basic Operation Expressions in PID Instruction (Reference)......................................................M-4

2. How to Use PID Instruction M-5

2.1 Explanation of function and operation.........................................................................................M-5

2.2 Relationship Between Parameter Setting and Auto-Tuning........................................................M-6

3. Parameter M-7

3.1 Parameter List: (S3) to (S3) + 28................................................................................................M-7

3.2 Details of Parameters..................................................................................................................M-9

3.2.1 Sampling time (TS): (S3).............................................................................................................M-9

3.2.2 Operation setting (ACT):(S3)+1.................................................................................................M-10

3.2.3 Input filter (α): (S3)+2................................................................................................................M-12

3.2.4 Proportional gain (KP): (S3)+3...................................................................................................M-13

3.2.5 Integral time (TI): (S3)+4...........................................................................................................M-13

3.2.6 Differential gain (KD): (S3)+5.....................................................................................................M-15

3.2.7 Differential time (TD): (S3)+6.....................................................................................................M-15

3.2.8 Alarm output flag: (S3)+24........................................................................................................M-17

4. Auto-Tuning M-18

4.1 Limit Cycle Method....................................................................................................................M-18

4.1.1 Parameters set in auto-tuning (of limit cycle method)............................................................... M-18

4.1.2 Auto-tuning procedure...............................................................................................................M-19

4.1.3 Reference: How to obtain three constants in PID control (limit cycle method)..........................M-20

4.2 Step Response Method.............................................................................................................M-21

4.2.1 Parameters to be set by auto-tuning (step response method)..................................................M-21

4.2.2 Auto-tuning procedure...............................................................................................................M-21

4.2.3 Reference: How to obtain three constants in PID control (step response method)...................M-22

4.3 Cautions on Auto-Tuning Execution..........................................................................................M-22

5. Example of Practical Programs (for Step Response Method) M-23

5.1 Example: System and operation...............................................................................................M-23

5.2 Program example of auto-tuning (step response method) and PID control..............................M-24

5.3 Program example of auto-tuning (step response method)........................................................M-26

6. Troubleshooting M-28

6.1 Error Codes...............................................................................................................................M-28

Warranty......................................................................................................................................i

Revised History.........................................................................................................................ii