Page 391 - ExtendSim User Guide
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Storage and Units 365
Units and unit groups
You can define multiple unit groups, which use different flow units, in portions of a discrete rate model. For instance, one part of the model could be expressed in bottles and another could represent boxes of bottles. The Change Units block can create a different unit group.
Declaring and selecting flow units
As mentioned above, flow units indicate what is moving from one flow connector to another, and a unit group is a collection of connected blocks that share the same flow unit. This section focuses on defining, selecting, and changing flow units.
To convert from one unit group to another in a model, use the Change Units block discussed on page 366.
Where to declare a flow unit
Each block in the Rate library has the ability to select an existing flow unit or create a new one. This is done in the block’s Options tab, which has a popup menu for either selecting an existing flow unit or creating a new one. Specifying a flow unit in one block causes that unit to be used by every block within the same unit group, and automatically sets that flow unit for any blocks that are subsequently added to that unit group.
To see the unit group, click the unit group selector button to the right of a block's flow units popup menu. All the blocks in that block's unit group will be highlighted on the model worksheet.
Declaring a flow unit
Unit group selector to the right of the popup menu
To declare a flow unit, select an existing unit or create a new unit from the popup menu in the Options tab. The selected flow unit applies not only to the block but also to the entire flow unit group and it will automatically be set in new blocks that are connected within the unit group. For instance, page 335 of the discrete rate tutorial showed how to create a new flow unit named “gallons”. When the fruit processing section was added, the popup menu for the Fruit Supply Tank already included gallons selected as its flow unit.
Managing flow units in the Executive block
The Executive block’s Discrete Rate tab has a sec- tion for managing flow units in a model. The table displays all the units for a given model and pro- vides buttons for adding, deleting, and renaming the units.
To use this feature, select the flow unit you want to change in the table, then click the appropriate button. ExtendSim will warn you and give options if the unit is being used in the model.
Defining block units
Flow units for Yogurt Production model
As mentioned earlier, the Tank and Interchange blocks allow you to define a block unit that is different from flow units. This is an internal representation of volume only and is specific to the Tank or Interchange block. It does not change the flow units or the unit group for the flow that has entered or exited the block. If a block unit has been specified, a factor to convert the block unit into flow units must also be entered.
Discrete Rate

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