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Creating Flow 353
Flow attributes
its I (indicator) output connector. However, if the level of the Tank instead decreases from 230,000 to 175,000 containers, the block will compare that value to its High Limit and output the value 2.
☞ The value that is output at the I (indicator) connector depends on whether the level of flow is increasing or decreasing, and where in the range the new indicator level falls. The Tank block has a S (status direction) output connector that reports if the level is going up or down when the event occurs.
Tank Flow Units model
The Yogurt tank in the Tank Flow Units model (Examples\Discrete Rate\Sources and Storage) outputs values that indicate the level of flow in the Tank; those values are displayed on the third line on the plotter.
☞ For more information about the Convey Flow block, including the use of sensors, see the dis- crete rate chapter on “Delaying Flow”.
Flow attributes
A flow attribute is a quality or characteristic of flow that stays with it as it moves through the model. Flow attributes provide information about the flow and allow you to organize quantities or volumes of flow into layers.
The entire set of attribute values assigned to a particular layer is what distinguishes it from other layers. In other words, all the units of flow in a layer possess the same set of flow attri- bute values.
While not all Rate models require the use of flow attributes, some uses for flow attributes include:
1) TheflowheldinaTankcanbeorganizedintoindividual,distinctlayers.Thisallowsyouto control where incoming flow is deposited and which type of outgoing flow next exits.
2) FlowratesthroughtheValveblockcanbecalculatedbasedonflowattributevalues.
3) FlowcanberoutedthroughtheMergeandDivergeblocksbasedonflowattributevalues.
Attributes are assigned to the flow by the model builder. They become linked to sections of flow that pass through the blocks, according to settings in the blocks’ dialogs.
Names and values of flow attributes
As with item attributes (discussed on page 125), each flow attribute is composed of a name and a value.
• Aflowattribute'snameidentifiessomegeneralcharacteristicoftheflowsuchas“Product”, “Flavor”, or “Color”. Attribute names are limited to 15 characters.
• Aflowattribute'svalueindicatesonedimensionofthenamedcharacteristic.Forinstance,a flow attribute named Product could have a value of 1 or a value of 5, while a flow attribute named Flavor could have a value of 1 (for Vanilla), 2 (for Berries), or 3 (for Caramel).
Attributes are meant to be unique;. If you attempt to add a new flow attribute with exactly the same name as an existing one, ExtendSim warns you that the name already exists. While attri- bute names are not case sensitive (Type is equal to type), spaces are significant and should be avoided.
Discrete rate models can have many flow attributes and each attribute can have multiple val- ues.
Discrete Rate

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