1.3.3 (l): describe how sensors are used in real-life scenarios

This is sort of how you will want to structure your answer in the exam. Another example is a burglar alarm system: 

There are lots of marks to attain here, but you get about 1 mark per point. 1 mark for mentioning ADC (analouge to digital converter), 1 mark for including sensors, 1 mark for comparing. etc ...

A controlling system example would be a street lighting system:

The number of minutes pass before another reading is a sort of confirmation that it could be dark or light. This is to prevent the light turning on and of repeatedly if say a cloud went over the lamp.

(Note this is also a cycle)

Exam Question:

(The valve is the actuator)

(a) Name the two sensors used in this application?

(b)Describe how the sensors and the microprocessor are used to maintain the correct condition in the fish tank

Answers:

a = Heat sensor and gas sensor ( oxygen sensor)

b = The temperature sensor and the O^2 sensor send data to the microprocessor through an analogue to digital converter. This data is checked against stored values. E.g checks the 25° and 20 ppm every 30 seconds. If this data is out of range, the microprocessor will send signals to the heater/oxygen supply through an digital to analogue converter (DAC) to correct the error. After this for example, if the temperature is 30° then the microprocessor will send a message to the heater through (DAC) to tell it to turn of for a while. Wait another 30 seconds and say if the temp is 23° then the microprocessor will tell it to turn on for a bit.