4.17. THE CONCEPT OF FEEDBACK
A simulation model with Vensim
In every house there is an automatic mechanism that fills the water deposit in the bathroom every time we empty it. This mechanism doesn't need our intervention to fulfil its function. There is a buoy that acts as a measurer of the level of water. And a mechanism that automatically regulates the amount of the water that enters so that the deposit is filled. Once full, the flow of water is retained. This process functions correctly if one condition is met: that there is gravity.
Now we will analyse a similar subject as we are going to make a simulation model in which a person fills a glass of water. We suppose that one condition is met: that the person acts with logic.
To create this model we will make a Causal Diagram. We know that:
- The more water that enters, the higher the level of water in the glass.
- The higher the lever of water in the glass, the lower the empty volume will be.
- The more empty volume, the more water will enter.
To make a flow diagram, we will:
- Make a mental photo of the system. What appears in the photo is a Level.
- Define as Flows the elements that vary the Level.
- The rest of the elements of the system are Auxiliary variables.
Simulate different behaviours modifying the table that can be found in Entry of Water.Remember that the points signal how much water enters per second (output) depending on the quantity of water there is in the glass (input).
To visualise all the simulations together, respond No when the following screen appears an signal a name for the simulation (fast, slow, etc.)
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