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422 Mixing Flow and Items
Controlling flow with items and items with flow
Flow Controls Item model
This model is extends the one above, adding that the state of the Reception tank alters the movement of the item and interrupts the filling process.
As in the prior model, the Reception tank fills and empties based on the movement of an item and delays set in the two Activity blocks.
In this model, whenever the Reception
tank is full, it sends an indicator signal
to the Decision block (Value library).
This block in turn notifies the Activity
block labeled Filling Valve 1, pre-
empting the item whose presence
opened Valve 1 and allowed the tank
to fill. When the item is preempted, it
moves to the Activity block labeled
Emptying Valve 2. This causes Valve 1
to close, Valve 2 to open, and the
Reception tank to empty into the Sink for the duration specified in the second Activity block.
Flow controlling items and items controlling flow
The following model combines both of the previous concepts – flow controlling items and items controlling flow – into an even more complex system.
Step The Flow Process model
In this model the location of a “cycling item” triggers the opening and shutting of valves for the flow, while tank states control the opening and shutting of the gates for the item. The con- trol logic is circular in nature: the item's location defines the current stage; the current stage
Flow Controls Item model
Discrete Rate


































































































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