“Wire: is a member of a cycle” Errors with the Simulation Module Primary Software: LabVIEW Toolkits>>Control Design ToolkitPrimary Software Version: 2.1.2 Primary Software Fixed Version: N/A Secondary Software: N/A
Problem: I am trying to use the LabVIEW simulation module to simulate a PID controller that was designed using the Control Design toolkit. When I load the controller and the plant transfer functions to the "transfer function" block in the simulation module and close the loop, thus creating a feedback controller, the simulation VI shows a broken arrow and gives the error "Wire: is a member of a cycle". I also noticed that if I change the controller transfer function so that the zeros are less than the poles, then the broken arrow disappears. Why does this occur and what possible method can I use to resolve this error using the existing controller and plant models? Solution: The relationship between a function input and output defines the feed through behavior of that I/O pair. An I/O pair can have Indirect, Direct, or Parameter-Dependent feed through behavior. If an I/O pair has Indirect feed through behavior, you can create a feedback cycle between that input and output. An I/O pair with Direct feed through behavior does not allow a feedback cycle. Most likely you have two functions with a Direct feed through behavior and you are also trying to loop the values back. If you change one of your Transfer functions to have more poles than zeros, or more zeros than poles, then that Transfer function becomes Indirect instead of Direct automatically. At least one of the Transfer functions must be Indirect in order to remove this error. Basically you will need to change the functions that you are using in order to get it to work properly. You can find more detailed information in the help documentation in the LabVIEW help that is attached as a screenshot below. You can use one or more Simulation functions and other LabVIEW functions in a feedback cycle as long as at least one Simulation function in the feedback cycle has Indirect feed through behavior. The Indirect feed through function can start the data flow by executing the function output at the current step before receiving an input from the cycle at the current step. Therefore, the input at the current step and the output at the current step must not depend on each other directly in at least one function in the cycle. Related Links: Products & Services: NI LabVIEW Control Design Toolkit Analysis: LabVIEW add-on: PID Control Attachments: 
Report Date: 02/08/2007 Last Updated: 02/09/2007 Document ID: 467JGDHB |
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