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Delaying flow with the Shift block
The Shift block (Item library) is discussed fully in “The Shift block” on page 232. It is used to schedule capacity in certain blocks found in the Item and Rate libraries. Shifts come it two types: On/Off and Numeric.
Rate library blocks do not support a Number type of shift. The following Rate library blocks can be controlled using On/Off Shifts:
• ConveyFlow.WhentheshiftisOff,theeffectiveinflowrateissetto0,blockinganynew flow from entering. Depending on which option has been chosen in the Convey Flow’s dia- log, the block’s speed will either also be set to 0 or it will remain unchanged from what is set in the dialog. If the Empty when shift is off checkbox is checked, any flow already on the conveyor at the Off shift time will continue progress towards exiting the block.
• Tank. The effective inflow and outflow rates are set to 0 when the shift is Off, effectively shutting the block down.
• Interchange.SamelogicastheTank.
• Valve.SamelogicastheTank.
Adding a Shift to a model
The easiest way to add a Shift block to a discrete rate model is to click the Add Shift button found on the Options tab of a Convey Flow, Tank, Interchange, or Valve block. This automati- cally does the following:
• Places a Shift block on the model worksheet below the originating block • EnterstheShiftnameintheoriginatingblock'sUseShiftfield
• OpenstheShift’sdialogsosettingscanbeentered
To use the Shift, enter the required information in the block’s dialog. (The Shift controls the originating block remotely; it does not need to be connected in the model.) Each Shift block starts with a default name for its shift. If you subsequently change the name of the shift, the new name will be reflected in the block that uses that shift.
For more information about using the Shift block, see “The Shift block” on page 232.
Convey Flow block
Setting an initial contents and the capacity of a Convey Flow block is discussed in the chapter “Storage and Units”. The current chapter focuses on the behavior of the Convey Flow block and how to set parameters that affect how flow is delayed through the block.
Flow entering the Convey Flow block is available to leave only after a specified delay that has been defined as a function of length and speed. The flow that enters is required to move some distance at a certain rate of speed before arriving at the block's exit point. The Convey Flow, then, is a residence block with flow distributed across its length at varying densities. (Density is the amount of flow that has accumulated at any one point on the conveyor.)
This block is useful for representing a conveyor, industrial oven, refrigeration system, or other similar piece of equipment with a length component where the position of flow must be taken into consideration.
Delaying Flow 413
Delaying flow with the Shift block
Discrete Rate

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