FAQ for OMDI Add-Ins

(updated 97.3.27)

General

Q: How can I call the functions from Visual Basic?
A: Look at the interpolation example for ideas.

Q: Can I license your code or libraries for use or distribution with our products?
A: Yes! Contact us.

Q: All units [for Element and Pure Component] are in base SI. Can I change this?
A: No. For standard interfaces, we chose base SI as our delivery. If you want some other unit, use OMDI Unit Tools conversion utilities. Examples:
--- for unified atomic mass units, from kilograms
=UnitConvertFromSI( cellRef, "u")
--- for temperature celcius, from kelvin
=UnitConvertFromSI( cellRef, "°C" ) { or "1C" }
--- for dipole momement, from coulomb meter
=UnitConvertFromSI( cellRef, "debye" )

OMDI Unit Tools

Q: I enter "amu" for atomic mass units and I get an error.
A: That is because "u" is the accepted symbol for unified atomic mass units.

Q: Why don't you use deg for degrees, ohm for ohms, etc.?
A: This was a design decision; various standards recommend that symbols be used in technical documents. Since we believe the end use of our software will be technical documents, we wanted an input/output mechanism that reflected this. If you have an opinion on this, please contact us.

Q: Why don't you support plane or solid angle?
A: Units relating to angles end up being dimensionless. We supported them in the original engine, but since they are "exceptions," we commented out the code since it impacted 1) readability and 2) performace.

Q: Why don't you support monetary units?
A: Money markets are always changing. Measures for physical quantities are fixed. Our engine can support any units, and "dynamic units" and/or "user defined units" are on the table for future releases of the engine. However, we won't support these in the Excel projects.

OMDI Element Tools


Q: I'd like to calculate the mass of Magnesium Hydroxide; how do I?
A: The MassCalc function does not currently support our formula script. This means if you enter the formula "Mg(OH)2" it won't be valid. In the short term, try "MgO2H2". Expect this in the 1.1 release (along with capability to calculate mass of specific isotopes and ionic compounds.)

Q: I'd like the Mass Calculator to remember the last information I entered.
A: No problem! Expect this in the 1.1 release. (We have quarterly release cycles.)

Q: How come the Mass Calculator doesn't let me just calculate atomic mass?
A: To calculate atomic mass, use the "ElemMassCalc" function.

=ElemMassCalc( "H2O" )

Q: How can I calculate isotopes with the Mass Calculator?
A: We have a prototype for a "molecular formula script" that lets you specify ions and mass numbers. We will update the mass calculator when this script goes mainstream. Until then, remember the mass calculator calls the other element functions to do its work. If you have D2O (which the mass calculator will recognize), and you wanted to find out the D2 fraction,

=(2*ElemIsotopeMass(1,2))/((2*ElemIsotopeMass(1,2))+ElemMass(8))

OMDI Pure Component Tools


Q: The TBS EOS abnormally terminates my copy of Windows Excel.
A: Yes (it was the compiler's fault.) This is fixed in the 1.11 release.

Q: Your Wagner vapor pressure calculation is wrong.
A: Yes (I forgot to divide by Tr.) This is fixed in the 1.1 release.

Q: You can have multiple spurious roots; why does PureZSpurious returns only one?
A: The vapor, liquid, and spurious fraction calculations are a quick and dirty way of examining the three roots returned by PureZFactors. When in doubt, use PureZFactors and make the determination yourself about multiple phases.

Q: Do you do mixtures?
A: No. We might support mixing rules in the future. No promises.



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