Simple Simulation Model with Algebraic Loop

[Ubiqvit91]

Good afternoon,

I have created a simple linear model of respiratory system which unfortunately incorporates algebraic loop. I have tried to eliminated the algebraic loop by adding either Feedback node, Transport delay, or Memory block. However, all my tries were unsuccessful - output is either zero or consists of divergent values.

Do you have any ideas how to eliminate the loop in the model so that the functionality is perserved?

As a first debugging step, I have visualised the input data outside the simulation loop in order to ensure that the input is correct and does not cause the error. Furthermore, I have realised the same model in Simulink, where it works fine. Simulink can cope with the algebraic loop. It just reports warning because it detect one.

Version used: LabVIEW 2017 64-bit running under Windows 10 64-bit.

Any ideas or comments are appreciated.

Thank you in advance.

Richard

[Bob_Schor]

Please attach a ZIP file with your VI and some data so we can "try this for ourselves", see what is happening, see if we can "find a fix" that works.  Working from pictures is not very pleasant.

Bob Schor

[Ubiqvit91]

Thank you for the prompt reply. Attached are some resources for testing.

[Bob_Schor]

A little bit of Web searching (which you could have done) found the following right here in the LabVIEW Forums:

https://forums.ni.com/t5/LabVIEW/Connecting-Simulink-Circuit-to-LABview-Controller/td-p/3313296.  This discusses both NI's Control Design & Simulation Module and also how to incorporate Simulink models into LabVIEW.

Bob Schor

[Ubiqvit91]

Solutions suggested in the post you are mentioning are one of the first ones I have explored (among many others I have found here and on MathWorks forums). 

It all boils down to difficulties caused by the algebraic loop. The model simply won't compile (build). All other resources and white paper assume compiled models.

Again, I have read resources dealing with the elimination of algebraic loops in both LabVIEW and Simulink. However, non of the suggested solutions (adding transport delays, unit delays, memory blocks, shifting registers.. etc.) worked for me.

This is most likely caused by my lack of experience and understanding of underlying simulation processes. That's why I started this post at the first place - seeking advice from more experience users. Coming back to my original question: How can I eliminated the algebraic loop if (in my understanding) it is essential for the model to run properly?