Mitsubishi FX3U-4AD - Page 21

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FX 3G /FX 3U /FX 3UC PLC User's Manual - Analog Control Edition
Table of Contents
PID Instruction (FNC 88)
1. Outline L-3
1.1 Outline of function ........................................................................................................................L-3
1.2 Basic Operation Expressions in PID Instruction (Reference).......................................................L-4
2. How to Use PID Instruction L-5
2.1 Explanation of function and operation..........................................................................................L-5
2.2 Relationship Between Parameter Setting and Auto-Tuning.........................................................L-6
3. Parameter L-7
3.1 Parameter List: (S3) to (S3) + 28 .................................................................................................L-7
3.2 Details of Parameters...................................................................................................................L-9
3.2.1 Sampling time (TS): (S3) ..............................................................................................................L-9
3.2.2 Operation setting (ACT):(S3)+1..................................................................................................L-10
3.2.3 Input filter (α): (S3)+2 .................................................................................................................L-12
3.2.4 Proportional gain (K
P): (S3)+3....................................................................................................L-13
3.2.5 Integral time (T
I): (S3)+4 ............................................................................................................ L-13
3.2.6 Differential gain (K
D): (S3)+5...................................................................................................... L-15
3.2.7 Differential time (T
D): (S3)+6......................................................................................................L-15
3.2.8 Alarm output flag: (S3)+24 .........................................................................................................L-17
4. Auto-Tuning L-18
4.1 Limit Cycle Method.....................................................................................................................L-18
4.1.1 Parameters set in auto-tuning (of limit cycle method) ................................................................L-18
4.1.2 Auto-tuning procedure................................................................................................................L-19
4.1.3 Reference: How to obtain three constants in PID control (limit cycle method)...........................L-20
4.2 Step Response Method..............................................................................................................L-21
4.2.1 Parameters to be set by auto-tuning (step response method) ...................................................L-21
4.2.2 Auto-tuning procedure................................................................................................................L-21
4.2.3 Reference: How to obtain three constants in PID control (step response method)....................L-22
4.3 Cautions on Auto-Tuning Execution...........................................................................................L-22
5. Example of Practical Programs (for Step Response Method) L-23
5.1 Example: System and operation ................................................................................................L-23
5.2 Program example of auto-tuning (step response method) and PID control ...............................L-24
5.3 Program example of auto-tuning (step response method).........................................................L-26
6. Troubleshooting L-28
6.1 Error Codes................................................................................................................................L-28
Warranty...................................................................................................................................... i
Revised History ......................................................................................................................... ii