Page 390 - ExtendSim User Guide
P. 390

Storage and Units
Units and unit groups
Block units
The Tank and Inter-
change blocks can have
an internal block unit
that is different than the
flow unit. This is an
internal representation
of volume that is spe-
cific to the Tank or
Interchange block, and
does not affect the flow
unit for the unit group. If you select a block unit that differs from the flow units that come into and out of a block, you must enter a conversion factor. The conversion factor represents the ratio of the block unit to the flow unit. Block units are discussed fully in “Defining block units” on page 365.
Flow and block units in the Tank
☞ Using block units is optional; the default block unit is the flow unit.
Time units
Time units can be generic, in which case the block will just say “time” or can be specific. Each model can define specific time units, which become the default for the model. You can change a discrete rate block’s time unit from the model default time unit to any local time unit using a popup menu in the block’s Options tab.
Default time unit
If a local time unit is selected in a discrete rate block, that local time applies to the entire block but only to that block. Changing to a local time unit does not change the global time unit for the flow group or for any blocks in the rest of the model. For complete information, see “Time units” on page 604.
Calendar dates are not available if months or years have been selected as the specific global time unit for a discrete rate model. Furthermore, if Calendar dates has been selected, Rate library blocks will not be able to select Months or Years as their local time unit.
Length units
For convenience, the Convey Flow block allows you to name a length unit. This is used inter- nally by the block with other settings to determine the block’s speed. You can use the default generic unit “length unit” or declare a specific unit of length such as feet or meters.
Unit groups
A unit group is two or more blocks connected together through flow connections and sharing one flow unit. Connecting the first block’s outflow connector to the second block’s inflow con- nector creates a unit group. Unless the unit group is explicitly changed, all the blocks that are connected through flow connectors use the same flow unit and are in the same unit group. If a flow unit is changed in one of the blocks in a unit group, the unit group does not change but all the other blocks in that group are updated automatically to the new flow unit.
To see the unit group, click the grey square to the right of a block’s flow units popup menu, shown above. All the blocks in that block’s unit group will be highlighted on the model worksheet.
Unit group selector to right of popup
Discrete Rate

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