How to derive or extract either an analog output or an analog error output from a CD_Feedback icon

[wer12]

May I know if there is any ways which can allow me to extract either the analog error value, which is found in the difference between the input value and the feedback while running a basic CD control system, or the analog feedback value of the CD control system, from this CD Feedback icon.

[Angela M]

Hello wer12,

This is an interesting question.  The point of this function is to return the closed loop model from two other specified models.  It is a mathematical transformation to find the value you are looking for, give me some time so that I can double check my math.  I am curious as to why you are interested in this value?

I will post back when I have more time to investigate the VI you posted.

Regards,

Angela M

Product Support Engineer

[Angela M]

Hello wer12,

I have been looking into this in more detail and I think you would be better off to not reduce your transfer functions using the CD Feedback.vi if you are interested in this error value.  This VI implements a model reduction and does not make available the information you are looking for.

If you have 2 transfer functions that you want in a feedback loop, you could easily implement a feedback loop in simulation.  In simulation you would have access to your input, your output and error values.  If you reduce the model using CD Feedback you would only have access to your input and output values.

I hope this helps, please let us know if you have further questions about this.

Regards,

Angela M
Product Support Engineer