User Actions to Affect the Fitting Process

See HELP for the EOS Control Center for descriptions of the actions listed here.

The fitting process consists of fitting and data rejection operations until convergence is achieved.

User actions affecting this process are:

• Selection/De-selection of properties and constraints using check boxes. It is not recommended to select additional properties for the Peng-Robinson or PC-SAFT equation.
• Change of relative weights for properties and constraints by right-clicking and increasing or decreasing the relative weight.
• Editing data.
• Adding data.

Fitting technique

The user can simply click the Fit button and wait for the result. If the default procedure does not produce a satisfactory result, (which may happen for the Span-Wagner equation), the reason may be inconsistent raw data or a local minimum in the error function. It is recommended that properties with inadequate representation (high adequacy criterion values) be reviewed, and to reject or correct erroneous experimental values, if any.

As a remedy against achieving a local minimum, the user can try the following:

• Select additional fitting constraints.
• Increase/decrease relative weight of different properties by right-clicking.
• Temporarily exclude, then again include some properties.
• Try another fitting method.
• Start from a different approximation. For that purpose Open EOS (for Fitting) a previously saved successful EOS for a similar compound and try fitting it.