Contact US

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!

*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

Arrhenius data curve fitting in Mathcad 13

Arrhenius data curve fitting in Mathcad 13

Arrhenius data curve fitting in Mathcad 13

I have been attempting to use a solve block to fit my kinetics data using the Arrhenius equation predicted value, subtracting |predicted - actual|, and finding the best fit through minimizing the sum of the differences.  In Excel this is tedious but achievable; in Mathcad I am stumped.

My process logic is roughly:
1.  import data into array: time, weight, weight change, temp; determine rows in file
2.  start solve block with given
3.  assign guess values for A, E, m, and n
4.  use loop to calculate 2D vector of weight and weight change based on guess values for A, E, m, and n.
5.  calculate 1D vector of |predicted - actual|
6.  sum the 1D vector as "S"
7.  Use Minerr(S,A,E,m,n) to minimize S.
8.  Plot two graphs - dW/dt actual and dW/dt predicted

What actually happens is there are no iterations of A, E, m, or n occurring, and therefore no curve fitting.  I am confident my equations are correct; if I use the proper guess values I get the proper plots.  It is abundantly clear I am clueless about the logic in solve blocks.  The examples provided in Mathcad are understandable but not obviously applicable to my particular problem.

For those unfamiliar with the Arrhenius equation, it has the general form:

dW/dt = -A*exp(-E/RT)*(W)^(n)*(1-W)^(m)

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! Already a Member? Login


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close