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Page 389 - ExtendSim User Guide
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``````Storage and Units 363
Units and unit groups
1) Theblock’slengthandmaximumdensitydeter-
mine the maximized capacity. By default,
ExtendSim calculates a maximized capacity for
the Convey Flow block by multiplying its
length by its maximum density. This is indi-
cated in the Capacity field by the “maximized”
capacity checkbox shown above. In this case, the block’s maximum capacity will equal its maximized capacity.
2) AnumberintheCapacityfieldintheOptionstabcanreducethecapacitybelowthemaxi- mized amount. In some cases, it may be necessary to define a capacity smaller than the maximized capacity determined by the length*density calculation. For instance, the Con- vey Flow block could have structural properties limiting how much weight it can safely support. To do this, uncheck the checkbox in the Capacity field of the Options tab and enter the desired number. In this case, the block’s maximum capacity will be less than or equal to its maximized capacity.
☞ A Convey Flow block’s maximum capacity can never exceed its maximized capacity, no mat- ter what number is entered in the Capacity field.
For example, if the Convey Flow block’s length is 100 and maximum density is 10, the block’s maximized capacity will be 1,000. To reduce the capacity to something less than 1,000, enter a number (for instance 300), in the Capacity field. The block will then only be able to contain 300 units of flow, even though its calculated maximized capacity was 1,000.
Units and unit groups
This section focuses on defining, selecting, and changing flow units, discusses the effect of changing time units, and shows how to use the Change Units block to change the unit group.
Definitions
The following sections discuss flow, block, time, and length units. A unit group is two or more blocks connected together through flow connections and sharing one flow unit.
Units and unit groups were introduced on page 329; they are described fully below.
Flow units
The flow unit indicates what is flow-
ing from one Rate library block to
another. As is true for ExtendSim
time units, flow units can be unspeci-
fied generic units (in which case the
block dialog will just display the
word “units”) or they can be specifi-
cally defined in the model. For instance, a defined flow unit could be a packet, gallon, transac- tion, box, liter, and so forth. Existing flow units can be selected, and new units can be defined, in the Options tabs of Rate library blocks. In addition, the Discrete Rate tab of an Executive block (Item library) has a section for managing flow units. This provides a central location where units can be added, deleted, or renamed.
☞ This chapter will be mostly concerned with flow units.
Maximized capacity
Generic flow and time units in a Valve
Discrete Rate

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