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Owning Palette: PID VIs

Installed With: PID Control Toolkit

Implements a PID controller using a PID algorithm with advanced optional features. The PID algorithm includes the features of the algorithm the PID VI uses, as well as manual mode control with bumpless manual-to-automatic transitions, non-linear integral action, two degree-of-freedom control, and error-squared control. Use the DBL instance of this VI to implement a single control loop. Use the DBL Array instance to implement parallel multi-loop control.

Details  Example

Use the pull-down menu to select an instance of this VI.

Select an instance PID Advanced (DBL)PID Advanced (DBL Array)

PID Advanced (DBL)

	manual control specifies the value of the control output when auto? is FALSE.
	auto? specifies whether to use automatic or manual control. When auto? is TRUE, this VI uses automatic control. When auto? is FALSE, this VI uses manual control. This VI uses bumpless transfer from manual control to automatic control. The default is TRUE.
	output range specifies the range to which to coerce the control output. The default range is –100 to 100. output high specifies the maximum value of the controller output. The default is 100. output low specifies the minimum value of the controller output. The default is –100.
	setpoint specifies the setpoint value, or desired value, of the process variable being controlled.
	process variable specifies the measured value of the process variable being controlled. This value is equal to the feedback value of the feedback control loop.
	setpoint range specifies the maximum and minimum values for the setpoint/process variable range. This VI uses the setpoint range to calculate non-linear integral action. The default range is 0 to 100. setpoint low specifies the minimum value of the setpoint/process variable range. setpoint high specifies the maximum value of the setpoint/process variable range.
	PID gains specifies the proportional gain, integral time, and derivative time parameters of the controller. proportional gain (Kc) specifies the proportional gain of the controller. The default is 1. In the equation that defines the PID controller, KC represents the proportional gain. integral time (Ti, min) specifies the integral time in minutes. The default is 0.01. derivative time (Td, min) specifies the derivative time in minutes. The default is 0.
	dt (s) specifies the interval, in seconds, at which this VI is called. If dt (s) is less than or equal to zero, this VI uses an internal timer with a one millisecond resolution. The default is –1.
	reinitialize? specifies whether to reinitialize the internal parameters, such as the integrated error, of the controller. The default is FALSE.
	beta specifies the relative emphasis of disturbance rejection to setpoint tracking. The default value of 1 is appropriate for most applications. You can use a smaller value between 0 and 1 to specify emphasis on disturbance rejection, such as process load changes.
	linearity specifies the linearity of the error response. The valid range for linearity is 0 to 1. A value of 1 provides a normal linear response, while a value of 0.1 provides an approximately parabolic response.
	output returns the control output of the PID algorithm that is applied to the controlled process.
	dt out (s) returns the actual time interval in seconds. dt out (s) returns either the value of dt (s) or the computed interval if you set dt (s) to –1.

PID Advanced (DBL Array)

	manual control specifies the value of the control output when auto? is FALSE. This VI resizes the manual control input array to match the size of the process variable input array.
	auto? specifies whether to use automatic or manual control When auto? is TRUE, this VI uses automatic control. When auto? is FALSE, this VI uses manual control. This VI uses bumpless transfer from manual control to automatic control. The default is TRUE.This VI resizes the auto? input array to match the size of the process variable input array.
	output range specifies the range to which to coerce the control output. The default range is –100 to 100. output high specifies the maximum value of the controller output. The default is 100. output low specifies the minimum value of the controller output. The default is –100.
	setpoint specifies the setpoint value, or desired value, of the process variable being controlled. This VI resizes the setpoint input array to match the size of the process variable input array.
	process variable specifies the measured value of the process variable being controlled. This value is equal to the feedback value of the feedback control loop.
	setpoint range specifies the maximum and minimum values for the setpoint/process variable range. This VI uses the setpoint range to calculate non-linear integral action. The default range is 0 to 100. setpoint low specifies the minimum value of the setpoint/process variable range. setpoint high specifies the maximum value of the setpoint/process variable range.
	PID gains specifies the proportional gain, integral time, and derivative time parameters of the controller. proportional gain (Kc) specifies the proportional gain of the controller. The default is 1. In the equation that defines the PID controller, KC represents the proportional gain. integral time (Ti, min) specifies the integral time in minutes. The default is 0.01. derivative time (Td, min) specifies the derivative time in minutes. The default is 0.
	dt (s) specifies the interval, in seconds, at which this VI is called. If dt (s) is less than or equal to zero, this VI uses an internal timer with a one millisecond resolution. The default is –1.
	reinitialize? specifies whether to reinitialize the internal parameters, such as the integrated error, of the controller. The default is FALSE.
	beta specifies the relative emphasis of disturbance rejection to setpoint tracking. The default value of 1 is appropriate for most applications. You can use a smaller value between 0 and 1 to specify emphasis on disturbance rejection, such as process load changes. This VI resizes the beta input array to match the size of the process variable input array.
	linearity specifies the linearity of the error response. The valid range for linearity is 0 to 1. A value of 1 provides a normal linear response, while a value of 0.1 provides an approximately parabolic response.
	output returns the control output of the PID algorithm that is applied to the controlled process. This VI determines the length of the output array from the size of the process variable input array.
	dt out (s) returns the actual time interval in seconds. dt out (s) returns either the value of dt (s) or the computed interval if you set dt (s) to –1.

PID Advanced Details

You can use the DBL Array instance of this polymorphic VI in multi-loop PID control applications. In this case, the length of the primary input array determines the length of the output array. Other input arrays do not necessarily need to be the same length as the primary input array. This VI resizes other input arrays to the same length as the primary input array as follows:

• If the input array is longer than the primary input array, the input array is truncated to the length of the primary input array. Additional values in the array are not used.
• If the input array is shorter than the primary input array, the last value of the input array is repeated until the size matches that of the primary input array.

In this manner, an input value that must be used for each output calculation does not need to be specified repeatedly in the array passed into this VI. Instead, the array can consist of a single value that is used for each output calculation.

Example

Refer to the Manual-Automatic Control VI in the labview\examples\control\pid\prctrlex.llb for an example of using the PID Advanced VI.