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Tips and Techniques
Cycle timing
Solution #3: the Stop Message block
You can also use the Stop Message block (Utilities library) to prevent the Math and Holding Tank blocks from receiving two messages for every one item. This block stops messages from being passed through a value connection; it is designed to solve problems of this nature.
The Stop Message block is connected between the
value output of Get 1 and the value input on the
Math block. This will prevent the first message from reaching the Math block but will allow the value to be passed.
Cycle timing
The amount of time one block takes to process an item is known as the delay or processing time. Cycle time is the time an item takes to travel through a group of blocks. If there is no blocking in a model (that is, if all items leave their blocks exactly at the end of their delay time), the cycle time is the sum of the delay times for the section being measured. In most situ- ations, this would rarely occur, and cycle time is usually more than the sum of the processing times. For instance, it is common that an item cannot leave a block because the next block is still processing its item.
To track an item’s cycle time, use either the Timing attribute feature (if the item is being tracked from its origin) or a Set or Equation(I) block with an Information block (if the item is being tracked from some place other than its origin).
These methods are discussed below. In each
case, the Information block reads the attribute
and calculates the difference between when the
item started the cycle and when it ended. The
dialog of the Information block displays the
current, average, minimum, and maximum
cycle time for all items with the specified attri-
bute. Its output connectors report the count of
items, the time between items, their cycle time, and the throughput rate.
Using the Timing attribute feature
If you are tracking the item from its origin, use the Timing attribute feature in the Create block’s Options tab to create a new value attribute and assign it to all items that are generated by the Create block. Then place the Information block at the end of the section you want to observe and select the name of the attribute as the Timing attribute in its dialog.
In the example shown at
right, a value attribute
named CycleTime has
been created in the Cre-
ate block, and the
block’s Options tab is
set to Timing: Cycle-
Time. The Information
block is placed after the Primer activity and is set to Calculate TBI and Cycle Time statistics, and its Timing attribute: is also set to CycleTime. For this model, the Information block
Cycle time portion of Information dialog
Cycle Time 1
Discrete Event

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