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Delaying Flow 409
Controlling a Valve’s maximum rate
☞ This examples uses the G (goal) connector to control the “when” and “how much” aspects of the goal. Alternately, the Control Flow tab allows you to choose to start a new goal when the start connector receives a message or when the previous goal finishes.
Setting a Valve’s duration goal
Like the quantity goal, the duration goal is used to modulate a Valve's maximum rate. How- ever, the duration goal cycles between the On and Off states as a function of time rather than the volume criteria used for the quantity goal.
A duration goal remains in the On state for some amount of simulation time before switching to the Off state:
• WhileadurationgoalisOn,thevalueintheValvetab’sMaximumratefield,orthevalueat the block’s R (maximum rate) input connector, is observed. The goal remains On until either the specified amount of time has passed, or the goal is interrupted. At that point the goal switches to the Off state.
• What happens when the goal switches to the Off state depends on the Off option selected in the block’s dialog: stop the flow, do not constrain flow, or observe maximum rate.
☞ To interrupt a goal, send a value to the Valve’s stop input connector.
Duration Goal model
The Duration Goal model is similar to the Quantity Goal model from above, except the goal allows the flow to move through the Valve for a certain period of time.
In this model, the Valve’s Flow Control tab is set to
observe its maximum rate of 20 gallons/minute for 45
minutes. When the goal is On, the block passes through
whatever amount of flow it can, at the maximum rate of
20 gallons/minute. When the 45 minutes passes, the
goal is set to Off and all flow through the block stops. The Pulse block (Value library) restarts the goal every 60 minutes. As the model runs, the block’s maximum rate cycles from 20 gal- lons/minute to 0, depending on whether the goal is On or Off. As a result, the block’s effective rate stays at 0 for the period of time (15 minutes) from when the previous goal ends until when a new goal starts.
Changeover With Only Goals model
The Changeover With Only Goals model is equivalent to the Changeover Quantity Goal model (discussed earlier) in terms of behavior. However, while the Production Gate valve still has a
Duration Goal model
Discrete Rate

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