National Instruments NI DIDS-2103, User Manual

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NI DIDS-2100 Series User Manual | © National Instruments | 153
4.10 Auxiliary PID Controller Setup Window
The purpose of the Auxiliary PID Controller Setup window is for configuring up to four general purpose Proportional-
Integral-Derivative (PID) controller functions for commanding a variety of Flex Control Parameters. The purpose of
a PID controller is to manipulate a final output parameter in such a way that the error between the PID setpoint and
the process variable is zero. The process variable for each PID controller can be sourced from a variety of inputs
to the system. The setpoint for each PID controller can be entered manually or overwritten by lookup table outputs
or operating points . Each PID controller has proportional gain, integral time, and derivative time for specifying PID
output behavior. The PID controller function output is added to a Feed-Forward parameter to produce a final output
value to be mapped to a Flex Control Parameter. The Feed-Forward can be entered manually or overwritten by
lookup table outputs or operating points. While PID operation is enabled, the final output value can be overridden
by a manual entry for debug purposes. Each PID controller can be monitored within a dedicated plot window to
assist with PID tuning. This document does not discuss the detailed theory of PID control. However, the general PID
equation used for PID control within this system is according to:
Where:
PV = Process Variable
e(t) = Error (Setpoint – Process Variable) as a function of time
Kc = Proportional gain
Ti = Integral time constant
Td = Derivative time constant
= Integral of error as a function of time
There are many internet articles and books available covering PID control theory. One recommended internet
resource for PID control theory is at http://www.ni.com/white-paper/3782/en . The core of the DI Driver System PID
control function is very similar to the LabVIEW code described in the above recommended article. This document
assumes that the reader understands the purpose of PID setpoints, process variables, and gains.