Systems that have no sensor are often referred to as an open loop system.

This means there is no feedback

The systems operates via a set of commands and does not take it's environment into account

Anything that uses an open loop will carry on regardless of what is going on. For example. a toaster will continue to cook toast even if it is burning. it will continue to follow it's set program until it is finished.

Systems that have a sensor are known as closed loops. They use feedback to determine which command or action to follow next.

For example, a Kettle will stop boiling the water once it reaches a certain temperature. Systems with a closed loop can deviate from their main program depending on feedback

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