Topic: DMD0139 PIDINIT - Set PID Tuning Constants |
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The Set PID Tuning Constants (PIDINIT) instruction is used to initialize the runtime parameters of the specified PID loop.
Note: to use variables to set the tuning constants use the Move Value instruction referencing the individual PID structure members, for example MyPID.Gain, MyPID.SampleTime, etc..
Note: at the conclusion of a successful Auto-tune process the user can elect to automatically create a PIDINIT instruction.
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Parameters:Note: Use the F9 key to open the Default Element Selection Tool (the Element Picker or the Element Browser) or use the Down-Arrow key (Auto-Complete) on any parameter field to see a complete list of the memory locations that are valid for that parameter of the instruction.
PID Struct - specifies the PID Loop structure which will receive the tuning values. This can be any existing PID Loop structure.
Sample Time (ms) - specifies the Sample Time (in milliseconds). This can be any constant value greater than or equal to 1.
Gain (P) - specifies the Gain (Proportional) value. This can be any constant value.
Reset (I) - specifies the Reset (Integral) value. This can be any constant value.
Rate (D) - if enabled, specifies the Reset (Derivative) value. This can be any constant value.
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Eliminating Proportional, Integral or Derivative ActionIt is not always necessary to run a full three mode PID control loop. Many loops require only the PI terms or just the P term. Parts of the PID equation may be eliminated by choosing appropriate values for the gain, reset and rate, thereby yielding a P, PI, PD, I and even an ID and a D loop.
Eliminating Gain (Proportional) Action - Although rarely done, the effect of proportional term on the output
may be eliminated by setting the value to 0. Eliminating Reset (Integral) Action - The effect of integral action on the output may be eliminated
by setting the Reset value to 0. Eliminating Rate (Derivative) Action - The effect of derivative action on the output may be eliminated by setting the value to 0.
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Status Display:
When the ladder status is ON (Debug -> All Status On) the Set PID Tuning Constants instruction displays the referenced PID loop's most pertinent values.
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See Also:
DEADBAND - Set Outside Deadband
INTEGRAT - Integrate Over Time
PIDINIT - Set PID Tuning Constants
TIMEPROP - Time Proportional Control
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Rung Example:
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