Page 355 - ExtendSim User Guide
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Introduction 329
Terminology and architecture
• The item connectors on the Interchange block provide an interface between portions of the model that are discrete rate and portions that are discrete event.
When combining discrete rate blocks with blocks from other libraries, you will only be able to connect compatible connectors. To represent the flow from one block to another, an outflow connector has to be connected to an inflow connector. Each flow connector can have one and only one flow connection. However, it is possible to connect an outflow connector to both an inflow and a value input connector. In this case the value connector reads the effective rate from the connection. A flow connection cannot be made with an item connector. For more information, see “Connector types” on page 574.
Units and unit groups
There are four types of units in the Rate library:
• Flowunitsindicatewhatisflow-
ing from one flow connector to
another. For instance, gallons,
bottles, and transactions are all
types of flow units. Each discrete
rate block in a discrete rate model
has a flow unit. The flow units are identical for all the blocks within a unit group (defined below).
• Timeunitsdefinehowtimeismeasuredasthemodelrunprogresses.LikeotherExtendSim blocks, blocks in the Rate library can use the default global time unit or a local time unit. Hours, minutes, and seconds are all examples of time units.
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.
• Lengthunitsspecifyhowlongsomethingis;theyareusuallyenteredasfeet,meters,andso forth. The Convey Flow block has a length unit.
• BlockunitsareaninternalunitofvolumespecifictotheTankandInterchangeblocks.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.
A unit group is a collection of blocks connected together through flow connections and sharing one flow unit. To
see the unit group, click the grey square 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.
For more information, see “Units and unit groups” on page 363.
One of the most important aspects of a discrete rate model is the rate of flow. A rate is the ratio of the flow units to the model’s time units. This is displayed in block dialogs as units/time, gal- lons/minute, transactions/second, boxes/hour, and so forth.
Several different types of rates are considered during the model building process:
Flow units
Unit group selector to right of popup
Discrete Rate

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