Temperature difference quantities in Modelica not functioning as expected

Question

I'm trying to get temperature differences quantities to report the correct result when displayed in non-absolute temperature scales. See the following example:

model tempDiffTest
  Modelica.Blocks.Interfaces.RealOutput test1(quantity="ThermodynamicTemperature", unit="K") = 1 annotation(absoluteValue=false);
  Real test2(quantity="ThermodynamicTemperature", unit="K") = 2 annotation(absoluteValue=false);
  Modelica.SIunits.TemperatureDifference test3 = 3;
end tempDiffTest;

Note that

type TemperatureDifference = Real (
    final quantity="ThermodynamicTemperature",
    final unit="K") annotation(absoluteValue=false);

which is what drove the modifications I made to the test1 and test2 variables.

Now, the expectation is that when I display my results in degrees celsius they should be 1, 2, and 3 for test1, test2, and test3, respectively. The actual results are shown below from Dymola:

Therefore, only test3 was apparently successful (note that none of the results were successful in OpenModelica). Now, my question is how do I achieve what I'm after for test1 and test2?

Answer 1

Dymola does not support the usage of the absoluteValue annotation in the declaration of test1 and test2.

If you enable the annotation check in Dymola with

Advanced.EnableAnnotationCheck=true

Dymola reports during check

In class tempDiffTest component test1, the annotation 'absoluteValue' is unknown.

Looking at the Modelica spec, we note that it tells

A simple type or component of a simple type may have: annotation(absoluteValue=false);

In my opinion, this is a bit vague and your code should work (as test2 is a component of the predefined type Real). But Dymola accepts the annotation only in class definitions.

So to solve your problem, you simply have to declare a connector and a type to be able to use this annotation.

package tempDiffTest
  connector Test1 = Modelica.Blocks.Interfaces.RealOutput (quantity="ThermodynamicTemperature", unit="K") annotation(absoluteValue=false);
  type Test2 = Real(quantity="ThermodynamicTemperature", unit="K") annotation(absoluteValue=false);

  model Example
    Test1 test1 = 1;
    Test2 test2 = 2;
    Modelica.SIunits.TemperatureDifference test3 = 3;
  end Example;
end tempDiffTest;