The flowchart below shows the control logic for a central heating system. (a) State the type of sensor needed to measure the temperature. [1] (b) Describe w...

(a) Sensor type: Thermocouple / thermistor / temperature sensor [1]

A thermistor changes its electrical resistance as temperature changes. A thermocouple generates a small voltage proportional to temperature. Both produce analogue signals that can be converted to digital readings.

(b) When the temperature reading is 16 degrees: [2]

The condition Temp < 18 is checked: 16 < 18 is TRUE. [1] The flowchart follows the "Yes" path and the heater is turned ON. The system then loops back to "Read temperature" and continues monitoring. The heater remains on as long as the temperature stays below 18 degrees. [1]

(c) When the temperature reading is 20 degrees: [2]

The condition Temp < 18 is checked: 20 < 18 is FALSE. [1] The flowchart follows the "No" path and the heater is turned OFF. The system then loops back to "Read temperature" and continues monitoring. [1]

(d) Why this is a closed-loop system: [1]

The system continuously reads the temperature (input), compares it to a threshold, and adjusts the heater (output) based on the reading. The heater's effect (warming the room) directly changes the temperature that the sensor reads next, creating a feedback loop. The output influences the input, and the system continuously adjusts itself without human intervention. This continuous monitoring and self-correction through feedback is the defining characteristic of a closed-loop system.