PIDINIT - Set PID Tuning Constants

Topic: DMD0139

Help File Version: 2.9.4.37

PIDINIT - Set PID Tuning Constants

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.

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.

Eliminating Proportional, Integral or Derivative Action

It 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.

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.