Page 217 - ExtendSim User Guide
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Processing 191
Interrupting processing
the quantity of the item at demand. For instance, each item with a quantity of 10 creates a demand for 10 items before the Gate will close.
Fixed period of time
You may want to keep the optional machine on for a particular length of time instead of for a certain number of items.
Fixed Time model
To do this, use the Create block, set to Create values by schedule, to output values to the demand connector on the Gate block.
Fixed Time model
In the table in the Create block’s dialog, the first line has 0 for the output time and a value of 1. The sec- ond line has the time you want to turn off the optional machine, and a 0 for the value. For example, to keep the optional machine on for five minutes, you enter the values as shown at right.
Once start is activated, the demand connector will receive a value of 1 (True). After 5 time units have passed, the value at demand will change to 0 (False). Because you are connecting a value output to demand, the Gate block will stay activated as long as the value the demand connector receives is greater than or equal to 0.5, which in this example is for 5 time units.
Interrupting processing
Activating “demand” with a value
In discrete processes, it is common for interruptions to occur. This could happen for any num- ber of reasons, such as the arrival of an item that has a higher priority for processing, random machine failures, planned shutdowns, the occurrence of a higher priority event, and so forth. Interruptions are of two kinds, preemption and shutdown.
• PreemptionoccurswhenanActivityblockistoldtoprematurelyendoneormoreitems’ processing. When this occurs, the Activity immediately sends the preempted items out of the block through an alternate item output connector.
Discrete Event

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