Page 211 - ExtendSim User Guide
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Processing 185
Setting the processing time
☞ Although items with a CheckTime value of 0 will not be processed by the Activity block, they may be delayed in the Queue (which is set to FIFO order) while a preceding item undergoes checking.
Implied processing time
Some ExtendSim blocks allow you to specify distance, speed, or other factors that indirectly result in a processing time. For example, the Convey Item block allows you to enter an item length and the length (in feet or meters) and speed (in feet or meters per time unit) for an accu- mulating or non-accumulating conveyor.
These settings in Convey Item and Transport blocks result in delay times for items. For exam- ple, if you set the Transport to be 10 feet long with a speed of 1 foot per time unit, it will take 10 time units for an item to travel to the next block.
For more information about using the Convey Item and Transport blocks, see “Transportation and material handling” on page 200.
☞ If the Metric distance units preference is selected in the Edit > Options dialog, length units in these blocks are set by default to meters. Otherwise, their length units are in feet.
Cumulative processing time: time sharing
The prior section discussed setting an item’s attribute to the time required by a specific activity. You can also set its attribute value to the total processing time required, then route the item to a series of activities, each of which performs one part of the processing, until the attribute value is reduced to zero and the item is fully processed. This is common when there are several sta- tions with different processing times, any of which can process the item. Or when there is one machine that processes each item for a specified time, then passes the item to another section for further processing, and the item must be returned to the original machine for finishing.
You can do this using an activity block, building the model such that the attribute value is decreased by the amount of processing time. In this situation, each activity subtracts its pro- cessing time from the attribute value, so that the value represents the remaining processing time. Use a Get block after each activity to determine if the item was fully processed or not, and therefore whether it should proceed to the next activity or be routed out of the line.
Time sharing occurs when an activity processes an item, sends it back to a queue for a short period, then processes it again until the required processing time is completed. This is common for computer networks and telephone communication systems. In these systems, time is speci- fied in small fractions of a second, there are a lot of jobs that must be processed at the same time, and there are only a limited number of processors to do the work. In time sharing, instead of each job being processed sequentially, all jobs are processed at what appears to be the same time. However, each job is processed a small bit at a time, and a given job may have periods in between where nothing is happening to it. Since the time units are so small, the periods when there is no processing of a specific job are typically not noticed, and each job appears to be processed continuously.
Discrete Event


































































































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