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Delaying Flow 411
Controlling a Valve’s maximum rate
The following screenshot shows how the Changeover Gate’s duration goal has been configured on its Flow Control tab:
Flow Control tab, goal is duration
• Thegoaldurationisaconstant20minutes.Thedurationcouldbemadevariablebyinstead choosing Goal durations is: value at G connector.
• The20minuteblockingofflowallowsthechangeovertooccur.Themaximumrateonthe Changeover Gate’s Valve tab is 0. This would cause the flow to be blocked in the absence of any goal being set for this block. Consequently, if the block has a duration goal and it is On, that maximum rate of 0 will be observed and flow will be blocked from entering. When the goal turns Off after 20 minutes, the Changeover Gate doesn't apply any constraining rate on the flow because it is set to Off: ignore maximum rate.
• Anewdurationgoalisstartedonlywhenthestartinputconnectorreceivesavalueof3. Consequently, a new duration goal begins only when the upstream Production Gate's quan- tity goal has finished.
• WhenthechangeoverhascompletedandthedurationgoalswitchesfromOntoOff,asignal is sent from the Changeover Gate to the Production Gate. This results in a new quantity goal starting in the Production Gate.
Setting hysteresis in a Valve
Hysteresis is a property of systems that causes them to not react instantly to a change. The pur- pose of adding hysteresis in a model is to introduce a delay in the time it takes some part of the system to switch from one state to another.
Hysteresis allows you to insert a lag or delay in a Valve’s response to system requirements. It is used to avoid oscillations and to achieve better control over flow movement. This is accom-
Discrete Rate

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