Cambridge O Level Computer Science · Syllabus 2210 · Automated and Emerging Technologies
Preset Value
What is Preset Value?
A target value, limit or range stored in the microprocessor against which each sensor reading is compared, so that the system can decide whether an action is required.
This definition is part of the Automated and Emerging Technologies chapter in Cambridge O Level Computer Science.
Preset Value in context
A sensor is an input device: it detects or measures a physical property and sends the measurement to the microprocessor as input data. A microprocessor is the processing component: it processes that data, compares it with a stored preset value or range, and decides according to its stored program whether an action is needed. An actuator is an output component: it receives an output signal and converts it into a physical action. The sensor never decides, the microprocessor never measures or moves anything itself, and the actuator never reports a measurement back. Keeping those three sentences separate is what every process description in this topic is built from.
The syllabus asks how the three components are used in collaboration, and that single word decides the marks. A list of three definitions describes the parts; it does not describe the system. What earns credit is the ordered chain: a physical condition exists → the sensor measures it → the reading is sent to the microprocessor as input data → the microprocessor compares it with the stored preset value → it decides, following its program, whether action is needed → an output signal is sent to the actuator → the actuator carries out a physical action → the condition changes → the sensor measures again. The last step is what makes it a loop rather than a line.
The syllabus names seven scenario areas — industry, transport, agriculture, weather, gaming, lighting and science — and expects you to describe automated systems drawn from them. The trap is to learn seven vague sentences. What actually earns marks is one concrete system per area, held in memory with its sensor, its measured property, its preset value and its actuator, so that when an unfamiliar variant appears you have a working template rather than a slogan. This section covers the first three areas; section 6.1 E covers the remaining four.
Common mistakes with Preset Value
- M1. “Every automated system is artificially intelligent.” Why wrong Almost every automated system in this syllabus compares one measurement with one preset value and switches something. That is rule-based control, and no reasoning across a body of knowledge takes place. Say instead “The microprocessor compares the reading with the stored preset value and, following its stored program, sends an output signal to the actuator.”
- M3. “The sensor controls the actuator directly.” Why wrong This removes the comparison and the decision, which is where most of the marks in a process question sit. A sensor measures and reports; it has no route to the actuator. Say instead “The sensor sends the reading to the microprocessor, which compares it with the preset value and then sends the output signal to the actuator.”
- M7. “Automated systems never need human supervision.” Why wrong Someone sets the preset values, calibrates and maintains the sensors, and must be able to override the system when something happens that its rules do not cover. Say instead “Automation removes the need for continuous supervision, not the need for people.”
Questions students ask about Preset Value
What is the difference between a sensor and a microprocessor?
A sensor is an input device that measures a physical property and sends the reading onward. A microprocessor is the processing component that receives that reading, compares it with a stored preset value and decides what to do. The sensor never decides; the microprocessor never measures.
How much should I write for a “describe how this automated system works” question?
Roughly one linked step per mark. Three marks: sensor measures, microprocessor compares with the preset value, actuator acts. Six marks: add the input data, the decision, the output signal as a separate step from the action, and the fact that the sensor measures again so the cycle repeats.