×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Answer to my question by skogsgurra

Answer to my question by skogsgurra

Answer to my question by skogsgurra

(OP)
Hi Skogsgurra

your answer does not really help. Of course I do know that impedances are normally  complex.

But assume I am calculating the complex impedance of an RC-circuit. The parameters of R and C will be real. If I then use the complex impedance of the RC-circuit thus obtained as "data" to be fitted, the mcd fitting procedure should find the parameters I originally used and they should be REAL. However, this is only the case if the guess values are already very close to the original values.

This causes problems if I want to apply the fitting procedure to actually measured data.

RE: Answer to my question by skogsgurra

Sorry. I couldnt resist the "complex real world" paradox.

I still do not see your problem. You can make up any complex impedance from real components - even negative impedances can be built.

I think that it is a bad idea to start a new thread. We should keep this discussion in the original thread.

RE: Answer to my question by skogsgurra

(OP)
Sorry, for opening a new thread. I am using this forum for the first time. Just after having submitted the new thread I realized that I did wrong.



I surely know that one can make complex impedances from real components. My only problem was to tell mathcad not to use complex fitting values instead of real ones for I always obtained complex solutions which might be correct from a mathematical point of view, but not from a physical.

I have solved this problem now.

RE: Answer to my question by skogsgurra

This should be posted either in the Mathcad forum here or the Mathcad collaboratory website: http://collab.mathsoft.com/~Mathcad2000

Numerical fitting, by its very nature, is imprecise.  However, if you apply the constraints that R and C >0, it should force the solver to dump any complex solutions.

TTFN

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources