If a PID VI receives an invalid input, such as NaN (Not a Number), the VI outputs NaN until you reinitialize the VI. However, you can use the Not A Number/Path/Refnum? function to check for invalid inputs and respond in a way that is appropriate to the application. The following block diagram uses the Not A Number/Path/Refnum? function with a Select function and a Feedback Node to reuse the last valid input when the VI receives an invalid input.
Refer to the General PID with Fault Protection VI in the labview\examples\control\PID directory for an example of a single-channel PID implementation that includes fault protection.
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