Week 2 System Modelling

Is a basic toaster an open- or closed-loop system?

• Closed-loop system

• Open-loop system

Answer explanation

A toaster is open-loop: it does not measure the toastiness of your bread and make adjustments. It just burns your toast if you set it too high!

Is the HVAC (heating, ventilation, air-conditioning) in our lecture theatre open-loop or closed-loop?

• Closed-loop

• Open-loop

Answer explanation

The HVAC is closed loop: the system measures the temperature in the room, and then adjusts the fuel input to the heating or air conditioning so as to achieve a desired temperature.

In a "bank run" (e.g. the collapse of Northern Rock), what are the inputs and outputs?

• Number of customers and amount of money they have.

• Weight (of gold) and it's price.

• Information: belief (that the bank will run out of money) and observable behaviour.

• Voltage and current.

Answer explanation

A bank run is a social positive feedback loop between beliefs and behavior: if enough people believe that something is true (e.g. the bank will collapse), their behavior can make it true, and observations of their behavior in turn increase belief.

Do all controlled systems have a feedback loop?

• Yes

• No

Answer explanation

Feedback loops generally work better, but are not always possible. You can adjust the input or output in an open loop system too (e.g. the temperature control on your toaster, or volume control on a speaker)

What is a Transfer Function?

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