Look for a few more regulated mechanisms !

Think about how they work and which phenomenon they produce.

Our environment is full of vending machines. And only very rarely do we think about how all this works; mostly only when they don't work.

Examples:
 
The epitome of a regulated mechanism is the computer (-processor), the so-called chip, which we find in the computer, in the clock, in the refrigerator, in the mobile phone, in the camera, in the car, in the ... simply everywhere.
 
In the household, however, there are often still relatively primitive devices that are a little more illustrative. A typical example is the toilet flush, where the cistern "automatically" fills up again, but does not overflow. Or the cooking clock, which starts to ring after a certain time.

The mode of operation is always based on the fact that a kind of switch opens or closes the device power. An automatic heater, for example, could be designed in such a way that the pointer on the thermometer is energized. When the pointer reaches the 18 degree mark, it makes contact with a contact that may reach 23 degrees, so that the current flows and opens a solenoid valve in the oil supply, which causes the burner to get more oil, i.e. burn more and therefore heat more. When the pointer moves beyond 23 degrees, the circuit is broken again and the valve in the oil line is closed again.

There are many different designs conceivable (and actually available on the market), but the principle always remains the same: one energy circuit (the secondary) controls another energy circuit (the primary). In the example the current in the thermometer controls the oil flow in the burner. So there are two separate energy circuits. We call the oil circuit primary because it supplies the energy with which heating is done, while the current represents energy which is not used for heating, but only for controlling - or only "indirectly" heating.