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PID and Fuzzy Logic Control Systems
John Limroth, Software Engineer
Yiannis Pavlou, Applications Engineer
Tues, 10:15a and 11:30a
Wed. 10:15a, 11:30a, 12:45p, 2:00p, 3:30p, and 4:45p
Exhibit Hall (3B)
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OverviewOverview
Control technology• PID control• Fuzzy logic
National Instruments products for control• LabVIEW RT• PID Control Toolset for LabVIEW
Control technology• PID control• Fuzzy logic
National Instruments products for control• LabVIEW RT• PID Control Toolset for LabVIEW
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Control Terminology
Terms: Process variable Setpoint Controller output Plant
Terms: Process variable Setpoint Controller output Plant
Examples: Temperature Desired temperature Heater voltage Furnace
Examples: Temperature Desired temperature Heater voltage Furnace
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PID Control
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PID Parameters Proportional gain – Kc
Integral gain – Kc/Ti
• Ti is the integral time constant or “reset time”
Derivative gain – Kc*Td
• Td is the derivative time constant or “rate time”
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PID Gains – PPID Gains – P
Proportional gain K c – “The Sledgehammer”
• Provides immediate controller response to setpoint change, but PV may not settle exactly on SP using proportional control alone
Proportional gain K c – “The Sledgehammer”
• Provides immediate controller response to setpoint change, but PV may not settle exactly on SP using proportional control alone
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PID Parameter Tuning – P only
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PID Gains – PIPID Gains – PI
Proportional gain Kc – “The Sledgehammer”
• Provides immediate controller response to setpoint change, but PV may not settle exactly on SP using proportional control alone
Integral gain Kc / Ti – Fine tuning
• Integrates the error over time to overcome the offset from Proportional alone such that PV = SP. However, integral action may cause overshoot, oscillation, and/or instability problems
Proportional gain Kc – “The Sledgehammer”
• Provides immediate controller response to setpoint change, but PV may not settle exactly on SP using proportional control alone
Integral gain Kc / Ti – Fine tuning
• Integrates the error over time to overcome the offset from Proportional alone such that PV = SP. However, integral action may cause overshoot, oscillation, and/or instability problems
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PID Parameter Tuning – PI only
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PID Gains – PIDPID Gains – PID
Proportional gain Kc – “The Sledgehammer”• Provides immediate controller response to setpoint change, but PV
may not settle exactly on SP using proportional control alone
Integral gain Kc / Ti – Fine tuning• Integrates the error over time to overcome the offset from
Proportional alone such that PV = SP. However, Integral action may cause overshoot, oscillation and/or instability problems
Derivative gain Kc* Td – Whoa…• Used to put the reigns on PI control to prevent overshoot and
oscillation and to add stability
Proportional gain Kc – “The Sledgehammer”• Provides immediate controller response to setpoint change, but PV
may not settle exactly on SP using proportional control alone
Integral gain Kc / Ti – Fine tuning• Integrates the error over time to overcome the offset from
Proportional alone such that PV = SP. However, Integral action may cause overshoot, oscillation and/or instability problems
Derivative gain Kc* Td – Whoa…• Used to put the reigns on PI control to prevent overshoot and
oscillation and to add stability
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PID Parameter Tuning – PID
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PID Autotuning
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Fuzzy Logic DataflowFuzzy Logic Dataflow
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Fuzzy Logic Control for LabVIEW
Why is fuzzy logic important? Easy to implement an intuitive control
strategy Better control of non-linear systems
• PID control is linear• Fuzzy control is non-linear
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Rule-Based ControlRule-Based Control
Example• “If temperature is high, then heater voltage output
should be low.”
Membership sets• What is meant by “high?”
Example• “If temperature is high, then heater voltage output
should be low.”
Membership sets• What is meant by “high?”
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Fuzzy Sets
Boolean (or two-valued) sets:• Members belong to a set – non-members do not• Traditional Boolean values (on/off, 1/0)
Fuzzy Sets:• Partial membership to set allowed• Values along continuum of 0 to 1
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Boolean Set – “High Body Temperature”
Temperature
Mem
ber
ship
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Fuzzy Set – “High Body Temperature”
Temperature
Mem
ber
ship
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Fuzzy Logic Control
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Fuzzy Logic and PID Combined
IF … AND … THEN …
IF … AND … THEN …
IF … AND … THEN …
Rule base
• • •
Fuzzification Fuzzy Inference Defuzzification
ProcessFuzzy ControllerSet Point Values
Measured Values
PID
Command Variable
P I D
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Fuzzy Logic Design Software
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OverviewOverview
Control technology• PID control• Fuzzy logic
National Instruments products for control• LabVIEW RT• PID Control Toolset for LabVIEW
Control technology• PID control• Fuzzy logic
National Instruments products for control• LabVIEW RT• PID Control Toolset for LabVIEW