Information Technology (9626) | Monitoring and control

Welcome to Monitoring and Control (Topic 3)

Hey there! This chapter is where Information Technology gets really practical. We’re moving beyond just processing numbers on a screen and looking at how computers interact with the real physical world—whether it’s controlling the temperature in a greenhouse or keeping your home secure.

You will learn the crucial difference between merely observing the environment (Monitoring) and taking automatic action based on those observations (Control). Don't worry if this seems tricky at first; we will use simple, everyday examples to show you exactly how these systems work!

3.1 Monitoring and Measurement Technologies

Monitoring is essentially about collecting data about the physical environment. A monitoring system gathers data using sensors but does not usually take automatic action in response—it typically just alerts a human user.

Sensors: Our Digital Eyes and Ears

A Sensor is a device that detects and responds to some type of input from the physical environment. The input might be light, heat, motion, or pressure. The sensor converts this physical input into a digital signal that a computer can understand and process.

Here are the key sensors you need to know, and what they measure:

• Light/UV Sensor: Measures light intensity or ultraviolet radiation levels. (e.g., Used in weather stations to measure sunlight.)
• Temperature Sensor: Measures heat or cold. (e.g., Measuring ambient temperature in a room or a greenhouse.)
• Pressure Sensor: Measures force applied over an area. (e.g., Measuring atmospheric pressure at a weather station.)
• Humidity Sensor: Measures the amount of water vapour in the air. (e.g., Measuring absolute and relative humidity for weather or storage facilities.)
• pH Sensor: Measures acidity or alkalinity. (e.g., Monitoring water pollution or soil quality.)
• Gas Sensors: Detect the presence and concentration of specific gases. (Includes oxygen, carbon dioxide (CO2), carbon monoxide (CO), and oxides of nitrogen (NOx).)
• Sound Sensor: Measures noise level or detects specific frequencies. (e.g., Used in burglar alarm systems to detect glass breaking.)
• Infrared Sensor (IR): Detects infrared radiation (heat). (e.g., Used in burglar alarms to detect the movement of a human body which emits heat.)
• Touch Sensor: Responds to physical contact or proximity. (e.g., Measuring fluid levels inside a container.)
• (Electro)magnetic Field Sensor: Detects changes in magnetic fields. (e.g., Used in security applications.)
• Proximity Sensor: Detects the presence or absence of an object without physical contact. (e.g., In smartphones, switches off the screen when held close to the ear.)

Did you know? The array of sensors used in a modern weather station allows it to gather all the necessary input data (temp, pressure, humidity, light) required to create accurate environmental forecasts.

Uses of Monitoring and Measurement Technologies

These sensors are vital for gathering data in many applications:

Environmental Monitoring

• Monitoring Water Pollution: pH and dissolved oxygen sensors constantly check the water quality in rivers and reservoirs.
• Weather Stations: Combining temperature, pressure, and humidity sensors to collect data used for forecasting.

Monitoring Patients

• In hospitals, sensors constantly monitor a patient's vital signs (heart rate, temperature, blood oxygen levels). The system monitors the data and, if a reading is outside the safe range, it triggers an alarm to alert a human nurse or doctor.

Calibration: Keeping Sensors Accurate

Calibration is the process of adjusting a measuring instrument (sensor) to ensure it provides accurate readings compared to a known standard.

Why is Calibration Important?

If sensors drift over time or are installed incorrectly, they will provide inaccurate data. In a control system (like regulating temperature in a nuclear reactor), inaccurate data can lead to dangerous outcomes.

Methods of Calibration:

Think of calibrating a scale. You use known weights to ensure it reads correctly.

1. One-Point Calibration:

• You check the sensor against only one known standard value, usually the zero point or a central point.
• Example: Ensuring a temperature sensor reads exactly 0°C when placed in ice water. This confirms the baseline is correct.

2. Two-Point Calibration:

• You check the sensor against two known standard values, typically at the low end and the high end of the expected measurement range.
• Example: Checking the temperature sensor at 0°C (ice water) and again at 100°C (boiling water). This ensures the sensor is accurate across the whole scale, not just the starting point.

3. Multipoint Calibration:

• You check the sensor against three or more known standard values spread across the measurement range.
• This is used when very high precision is required, as it confirms the sensor is linear and accurate at intermediate points too.

Key Takeaway for Monitoring: Monitoring relies on sensors to gather data. This data must be accurate, which is achieved through regular calibration, often using two-point or multipoint checks to ensure the readings are reliable across the full operational range.

3.2 Control Technologies: Making Systems Work

A Control System doesn't just collect data; it uses that data to automatically adjust or control a physical process. This is the heart of automation. The system works in a continuous cycle:

Sensor (Input) -> Processor (Decision) -> Actuator (Output Action) -> Sensor (Input for next cycle)

Actuators: The System's Muscles

An Actuator is a component of a machine that is responsible for moving or controlling a mechanism or system. It takes energy (electrical, hydraulic, etc.) and converts it into motion or action.

Actuators carry out an action or movement. They can be classified by the type of motion they create:

• Linear: Movement in a straight line (e.g., a piston pushing a car park barrier up or down).
• Rotary: Movement in a circular path (e.g., turning a valve or motor).
• Soft: Flexible and adaptable movements, often inspired by biological systems.
• Hydraulic: Uses pressurised liquid to create force (very powerful, slow movement).
• Pneumatic: Uses compressed air or gas to create force (fast, used in factory robotics).
• Electric: Uses electric motors (most common, highly controllable).
• Thermal: Uses heat or temperature change to expand/contract (e.g., simple thermostats).
• Magnetic: Uses electromagnetic force (e.g., opening a magnetic lock).
• Mechanic: Converts simple input into mechanical work.

Microprocessor-Controlled Systems (The Brains)

These systems operate using a feedback loop, meaning the action taken by the actuator affects the next reading taken by the sensor—this is known as real-time processing.

Let’s look at key real-time control examples:

1. The Automated Greenhouse System

• Goal: Maintain optimal temperature and humidity for plants.
• Sensors Used: Temperature, Humidity, Light.
• Actuators Used: Heating system (electric/thermal), Ventilation fans (electric/rotary), Watering system (electric pump/valve).
• Process:
  1. Sensor measures temperature (Input).
  2. Microprocessor compares temperature to the desired set point (Decision).
  3. If temperature is too low, the microprocessor signals the heating actuator (Output).
  4. Heating turns on, raising the temperature.
  5. Sensor detects the new temperature, completing the feedback loop.

2. Central Heating and Air Conditioning Systems

These work exactly like a greenhouse system, using temperature sensors and electric/thermal actuators to maintain a set room temperature.

3. Burglar Alarms

• Sensors Used: Infrared (detects human body heat/movement), Sound (detects loud noises like breaking glass).
• Actuators Used: Siren/Bell (sound actuator), Lighting (electric actuator), Auto-dialler (communication actuator).

4. Traffic Control (Traffic Lights and Smart Motorways)

• Sensors Used: Induction loops (metal coil buried under the road that detects a change in the magnetic field when a car passes over it).
• Actuators Used: Traffic light lamps (electric actuators).
• Control: The system monitors traffic flow using induction loops. If many cars are detected on one road, the system automatically extends the green light time for that road.

5. Car Park Barriers

• Sensors Used: Induction loops, Light sensors (to ensure the vehicle is clear of the barrier), Proximity sensors.
• Actuators Used: Linear motor (to raise/lower the barrier arm).

Wireless Sensor and Actuator Networks (WSANs)

WSANs are modern, complex control systems where many small sensor nodes and actuator nodes communicate wirelessly over a large area. This allows for greater flexibility and scalability.

• Smart Homes: A network of temperature sensors, door sensors, and light sensors communicating with central hubs to control lighting, heating, and security (actuators).
• Autonomous Vehicles (Self-Driving Cars/Drones): These rely on complex WSANs, using ultrasonic sensors, electromagnetic field sensors, and radar sensors to map the environment, which then feed into guidance systems that control the steering, braking, and acceleration actuators.
• Guidance Systems (Space Rockets): Highly precise systems use a multitude of sensors to calculate position and velocity in real-time, instantly adjusting the thrust and direction actuators to keep the rocket on course.

Algorithms and Control

A control system must follow logical rules to make decisions. These rules are defined in the system’s algorithm, usually represented using pseudocode or flowcharts (covered in depth in Topic 4).

The core of a control algorithm is always a decision based on input data. For example:

IF (Temperature < SetPoint) THEN
    Activate Heater (Actuator)
ELSE
    Deactivate Heater
ENDIF

Advantages and Disadvantages of Control Technologies

When considering using an automated control system, we must weigh the pros and cons compared to human control.

Advantages:

• Speed and Consistency: Computers respond much faster than humans and perform actions consistently without fatigue or error. This is vital in real-time systems like traffic control.
• Accuracy: Digital sensors provide precise, quantifiable data, leading to greater accuracy in control adjustments (especially when properly calibrated).
• Operation in Hostile Environments: Control systems can operate 24/7 in dangerous, toxic, or high-temperature areas (e.g., nuclear power plants, deep-sea research).
• Cost Saving (Long Term): While installation is expensive, automation reduces ongoing labour costs.

Disadvantages:

• High Initial Cost: Setting up the infrastructure (sensors, actuators, microprocessors) can be very expensive.
• Maintenance: If sensors or actuators fail, specialised engineers are required for repair and recalibration.
• Lack of Flexibility: Control systems are programmed for specific tasks (following the algorithm). They cannot easily adapt to unexpected or novel situations the way a human operator can.
• Single Point of Failure: If the central microprocessor or a critical sensor fails, the entire control system can stop working, potentially leading to catastrophic results.

Key Takeaway for Control: Control systems use sensors for input, a microprocessor for decision-making (using algorithms), and actuators to generate physical output, forming a critical, closed-loop feedback cycle.