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Tutorial for Discrete Rate Systems 335
A basic discrete rate model
To gather information about the amount of yogurt processed:
Connect from the Yogurt tank’s inflow connector to the top input on the plotter.
Connect from the Yogurt tank’s LE (level of contents) value output connector to the plot- ter’s second input.
Reposition the blocks as desired. Note that when you do this, ExtendSim will anticipate how you want the connection lines between Flow connectors to behave. For more information see “Auto route connection lines” on page 799. This feature can be disabled in the Edit > Options > Model tab.
When you are finished, the model should look like the one shown on page 333.
Entering dialog parameters and settings
To reflect the basic assumptions for this model, the flow units and the constraints need to be defined.
Each model must contain one or more blocks (typically a Valve with a non-blank maximum rate) to restrict flow. The ExtendSim discrete rate architecture attempts to move flow through the model as fast as possible. In the absence of any constraints, the flow rate would theoreti- cally approach infinity and flow would move from one part of a model to another instanta- neously. This condition would cause ExtendSim to stop the simulation and display an error message.
For the Liquid Supply tank:
In its Tank tab, check the  (infinite)checkbox for the field labeled Initial contents. This places the word “infinite” in the initial contents field, as seen at right.
Initial contents set to “infinite”
In the block’s Options tab, select
New Unit in the popup menu for Flow group unit: and enter gallons as the flow unit.
In the dialog of the Valve block, enter Maximum rate: 100 gallons/minute.
There are no entries to make for the Yogurt tank. Its default settings indicate that it has no
initial contents and its maximum capacity is infinite, which is what you want.
In this model, the plotter will display the Valve’s maximum rate on its top input and the num- ber of gallons of yogurt processed on the second input. Since the scaling for these numbers is so different, the plotter’s graph needs to be adjusted. To do this:
In the plotter dialog’s toolbar, open the Trace Properties dialog. Choose that the second input (Values) is plotted against the Y2 axis. Change the style of the line for that second input to interpolated.
(For information on how to change the properties of lines, see “Trace properties tool” on page 683.)
Save the model and run the simulation.
Discrete Rate

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