• Working with the units database.

  • Working with unit groups

  • Working with unit definitions

Working with the units database

Even though CSI comes with a multitude of predefined units for specifying component properties and computation output, the user may want to expand or modify the units’ database used by the Control Simulator. All of the unit definitions are saved in the Units.mdb database.

CSI provides a user-friendly interface for working with the units.mdb database. This interface can be accessed by selecting the Units editor option under the Tools menu.

Figure 28

The top portion of the dialog shows the unit groups. Selecting a row on this grid will cause the applicable conversion factors to show on the grid below. CSI uses the displayed scale and factor values to convert values to and from the MKS system (CSI uses the MKS system for internal computations) as per the formulae show below:

·         MKS Unit = Scale * (User unit + Offset)

·         User Unit = (MKS unit / Scale) – Offset

Working with unit groups

Although CSI does yet not allow users to specify which of types of units a component’s property can accept, CSI provides a way to create new unit groups as framework for future enhancements. Open the unit group editor by pressing the Create new button or by double-clicking a unit group line. The unit group definition window is shown below:

Figure 29

Simply enter a 4-character alphanumeric type identifier and a description and select the check mark. CSI will check for identifier uniqueness.  The description must begin with * and should identify the type of unit and the MKS unit that is used internally.

Note: Component property unit types are hard-coded in CSI, therefore, unit group identifiers (type) should never be modified. The mechanism for modifying identifiers is presented here for future compatibility only.

Working with unit definitions

This is likely to be the only portion of the units database interface to be normally used. To create or modify a unit definition, first select the unit group in the units groups list, then press new unit button or double-click an existing unit definition. The unit definition dialog box window appears:

Figure 30

Users must enter a scale factor, an offset and a unit identifier. The dialog also shows the formula that CSI uses to convert numeric values to and from the MKS unit system.  For example, the internal MKS unit for temperature is K (Kelvin).  If you input 40 F, it is converted as follows:

            K = scale * (40 + offset)

            277.594 = 0.55555555556 * (40 + 459.67)

 NOTE:  It is assumed that the existing unit conversions are correct.  If you find an error, please do not just correct it.  Please let us know about the error!  Also, if you think a conversion is wrong, check it out very carefully before changing it.  They have been checked repeatedly.