Page 388 - ExtendSim User Guide
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Storage and Units
• IfaTank'scapacityissettozero,flowcanstillmovethroughtheblockbuttheflowwillnot stay in the block for any length of time. In this case, the Tank is neither full nor not-full, and the effective inflow rate will equal the effective outflow rate.
☞ If a Tank has no outflow connection, by definition it is being used as a sink. If at some point the sink reaches the full state, its effective inflow rate will be set to zero for the remainder of the simulation run.
Interchange block’s capacity
The Interchange block has two options that affect how the block’s initial contents and maxi- mum capacity are set. These options are discussed in “Interchange block modes” on page 350.
Capacity when “Tank only exists while item is in it”
This is the default behavior. With this setting the Interchange block has a capacity to hold flow only while an item resides in the block. With an item present, the block acts like a tank and therefore has a definable capacity, either finite or infinite. If the capacity is finite, as along as an item is present in the block, the block can alternate between the full and not-full states.
The block’s capacity is fixed at the moment the item enters the block; it remains fixed until the item leaves. When the item leaves, the Interchange's capacity automatically goes back to zero. Therefore, at the time of item departure any flow currently in the block is loaded onto the item. The timing of when the item leaves the Interchange depends on logic set in the Interchange block. For more information, see “Item release conditions” on page 425.
To define the capacity for an Interchange block when it is set to this behavior, choose one of the options from the dialog’s popup menu, shown at right.
Maximum capacity; default behavior
• Aconstant.Enteranumberinthefield;thedefaultisinfinite.
• ValueatIC.Thevalueatthisinputconnectorwillcontroltheblock’scapacity.
• Valueofattribute.Selectanattributeinthedialog.Whenanitemarrives,thetank’scapacity will equal the item’s attribute value.
In the Yogurt Production model of the Discrete Rate Tutorial, the Interchange blocks are set to Tank only exists when item is in it and their capacity is set to the constant value 24.
Capacity when “Tank is separate from item”
With this option, the Interchange block’s behavior is similar to a Tank block – it receives flow from its inflow connector, it holds flow, and it releases flow from its outflow connector. The difference is that an item’s arrival can contribute flow to the existing contents and an item’s departure can remove flow from the existing contents. The item’s impact on the block’s con- tents is entered in the Define Item behavior section of the block’s Item/Flow tab.
To set the capacity for the block when this behavior has been selected, enter a number in the Maximum capacity field or leave it set to the default value of infinite.
Convey Flow block’s capacity
Maximum capacity; alternate behavior
The maximum capacity for a Convey Flow block is a combination of two factors:
Discrete Rate

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