Monitoring & Control (Cambridge (CIE) A Level Computer Science) : Revision Note
Monitoring vs control
Monitoring systems
A monitoring system is used to collect data continuously through observation
It works by passively gathering data
It does not interact with or change the environment
The system does not take action based on the data collected
Designed for high accuracy using precise sensors and measurements
Examples of monitoring systems include:
Weather stations
Patient monitoring in hospitals
Weather stations
Collect data like temperature, wind speed, humidity, and rainfall
Used by meteorologists to observe and predict weather patterns
Data is collected 24/7 but the system does not react or change anything
Patient monitoring
Tracks heart rate, oxygen levels, and blood pressure in real-time
Alerts medical staff if readings go outside safe ranges
The system itself just records and displays data, it doesn’t directly treat the patient
Control systems
A control system is used to automatically manage or adjust a process based on data collected from sensors
It works by monitoring input, then taking action if certain conditions are met
Unlike monitoring systems, control systems do interact with the environment
They are designed to keep systems stable, safe, or working efficiently without human input
Examples of control systems include:
Central heating system
Automatic irrigation system
Central heating system
Monitors room temperature using a thermostat
If the temperature drops below the set level, the boiler is switched on
Once the target temperature is reached, the system turns the heating off automatically
The system constantly checks and adjusts to maintain the desired temperature
Automatic irrigation system
Monitors soil moisture levels in farmland or gardens
If moisture drops too low, it activates sprinklers to water the plants
Once the soil reaches the correct level, the system turns off the water supply
Ensures plants are watered efficiently without wasting resources
Use of sensors
What are sensors?
Sensors are input devices
They measure a physical property of their environment such as light levels, temperature or movement
Sensors can be used for both monitoring and control systems
A process where outputs are recycled and used as inputs, creating a continuous cycle is called a feedback loop
Sensor type | What it measures | Typical use |
|---|---|---|
Acoustic | Sound levels | To detect changes in sound levels of industrial machinery To monitor noise pollution In security system to detect suspicious sounds |
Accelerometer | Acceleration rate, tilt, vibration | Detecting sudden changes in vehicle movement and deploy safety features if needed In mobile phones to detect orientation of the device |
Flow | Rate of gas, liquid or powder flow | Detect changes in the flow through pipes in water system |
Gas | Presence of a gas e.g. carbon monoxide | Detect levels of gas in confined spaces Detect gas levels when fixing gas leaks |
Humidity | Levels of water vapour | Monitor humidity in greenhouses |
Infra-red | Detecting motion or a heat source | Security systems detecting intruders who break the beam Measures heat radiation of objects - used by emergency services to detect people |
Level | Liquid levels | Detects levels of petrol in a car tank Detect levels of water in a water tank Detect a drop in water levels due to a leak |
Light | Light levels | Automatically switching on lights when it gets dark (street lights, headlights) |
Magnetic field | Presence and strength | Anti-lock braking system Monitoring rotating machinery such as turbines |
Moisture | Presence and levels of moisture | Monitoring moisture in the soil Monitoring dampness in buildings |
pH | Acidity or alkaline | Monitoring soil to ensure optimum growing conditions Monitor ph levels in chemical processes |
Pressure | Gas, liquid or physical pressure | Monitoring tyre pressure Monitoring pressure in pipes during the manufacturing process |
Proximity | Distance | Monitoring the position of objects in robotics Used in safety systems to prevent objects from colliding |
Temperature | Temperature in Celsius, Fahrenheit or Kelvin | Used to maintain temperature in swimming pools Used to control temperature in chemical processes |
Feedback loops
What is a feedback loop?
A feedback loop is when a control system uses its output to influence its next input
Allows the system to automatically adjust and stay within set conditions
Feedback allows the system to check if it’s working as expected
The output affects the next input, helping the system make adjustments
This means the system can automatically respond to changes in its environment
Helps the system stay within set limits or target values (e.g. temperature, moisture)
Makes the system more accurate and efficient without needing human control
Example: Central heating system
The system uses a thermostat to monitor the room temperature
If the room gets too cold, the system turns the heating on
Once the room reaches the set temperature, the system turns the heating off
This process uses feedback:
The output (room temperature) affects the input (whether heating is needed)
Feedback ensures the system automatically adjusts to keep the room at the right temperature
No need for manual control as the system self-corrects using feedback
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