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Mixing Flow and Items
Using the Interchange block to mix items with flow
The scheduled release conditions can
be superseded at any time by using the
preempt connector. Whenever the pre- Preemption options for Interchange block
empt connector receives a value that
corresponds to the preemption options selected in the Item/Flow dialog, seen above, it will trigger a preempt.
☞ To immediately dispose of an item after it releases flow, connect an Exit block (Item library) to the Interchange block’s item output connector. To instead have an item present all the time, connect a Create block set to Create items infinitely to the block’s item input connector.
Interchange modes
The Interchange block has two modes: • Tank only exists while item is in it
• Tank is separate from item These are illustrated below.
Tank only exists while item is in it
In this mode, the Interchange's capacity to handle flow is completely dependent upon the pres- ence of an item. The arriving item can be thought of as a “tank” with a capacity to hold flow. This item/tank can move through the item-based blocks just like any other item would. How- ever, once it enters an Interchange block, the item/tank can release flow directly into the block’s outflow connection and/or accept flow directly from its inflow connection. In the absence of the item/tank, the Interchange block has no flow capacity.
Two very important behaviors result from an item exiting the block when it is set to this mode:
• Oncetheconditionsforitemreleasehavebeenmet,theexitingitemwillalwaystakewithit any flow currently residing in the block.
• Until a successor item arrives, the Interchange’s inflow and outflow will be blocked.
In this mode, the absence of an item eliminates not only the Interchange's capacity to hold flow but also its capacity to pass flow from an upstream source to a downstream sink. (This differs from the behavior of a Tank block, which passes flow through even if its capacity has been set to zero.)
Shipping model
A typical exam- ple of how the Interchange block could be used in this mode is illustrated by the Shipping model. In this example, an empty ship (an item) arriving at a loading port (an
Shipping model
Discrete Rate

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