17             Edit Units

Cell Illustrator contains a units dictionary with a set of pre-defined physical properties and their units. The standard units are can be viewed in the Edit Units dialog box. Additionally, non standard units and non standard physical properties can be defined in the Edit Units dialog. These user defined units are specific to the active model and are stored in the model file. Therefore the units defined in this dialog are not system wide, i.e., they are not visible in other models.

Each physical property has one standard unit. All other units can be converted to the standard unit using the multiplier and offset properties. This means, that units defined for one and the same physical property are convertible between each other, while unit for two different physical properties are not convertible.

 

To add a new unit to your model:

-         Select the desired physical property in the upper table. In the lower table you should see the list of all units defined for this physical property.

-         Press the Add button and enter the Name of the unit and press OK. The new unit has been added to the lower table.

-         Define the conversion rule by specifying multiplier and offset parameters. These parameter allow for the conversion of the new unit to the standard unit.

-         The example below shows a new volume unit cm3 (cubic centimeter) that was defined by the user. The cubic centimeter is derived from the standard unit m3 (cubic meter) with the conversion parameters: multiplier equal to 1e-6 and offset equal to zero.

-         The units defined in this dialog box are then available in the Element Settings Dialog Box, in which the unit of each entity value can be selected.

Note: The simulation engine supports non-standard units, however it performs the calculation in standard units. The value of each entity expressed in standard units is the absolute value that is used by in the Petri Net model. This has the following consequences:

-         Process speed should be always defined in standard units

-         Entities representing two different physical properties, e.g. mass and volume can be connected by a process or used in one mathematical formula (script). The process or formula will operates on the absolute entity values expressed in standard units of each physical property.

-         Non-standard units are converted to standard ones during initialization of the entity value, e.g. during the file open operation.

-         You may view the absolute entity values by un-checking the menu item View | Show User Units. Checking this item will display the entity values in user defined units.