3.2 Input & Output Devices

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Automated Systems

Monitoring & Control Systems

Syllabus Topic 3.2.2: Automated Decision Making

1. The Need for Automated Systems

Automated systems use sensors and microprocessors to perform tasks without human intervention. They offer several advantages:

  • Safety: Can operate in dangerous environments (e.g., nuclear plants or chemical vats) where humans cannot go.
  • Consistency: Do not get tired or bored; they perform the same task exactly the same way 24/7.
  • Speed: Can react to changes (like a pressure spike) much faster than a human could.
  • Efficiency: Saves time and money by optimizing resource use (e.g., only heating a room when someone is in it).

2. Monitoring vs. Control

The fundamental difference lies in whether the system affects the environment or just reports on it.

Observation Only

Monitoring Systems

The system records data and alerts a human if values go outside a safe range. It does not take action to fix the problem.

Example: ICU Patient Monitor.

  • Sensors: Heart rate, Temperature, Oxygen.
  • Process: Microprocessor compares data to pre-set limits.
  • Outcome: Sound an alarm or display a warning on screen.
Action & Feedback

Control Systems

The system records data and takes direct action via actuators to maintain a specific state or "Set Point."

Example: Automated Greenhouse.

  • Sensors: Humidity, Light, Temperature.
  • Process: Microprocessor sends signals to actuators if values drift.
  • Outcome: Open windows (motors), Turn on fans, or start irrigation (valves).

3. System Components & Operation

Both systems follow a similar loop, but only Control systems complete the "Feedback Loop" via actuators.

SENSOR ➔ ADC ➔ MICROPROCESSOR ➔ [ALARM or ACTUATOR]
Component Role in the System
Sensor Continuously measures physical properties (Analogue).
ADC Converts analogue sensor data into digital for the processor.
Microprocessor Compares input to "Pre-set" or "Stored" values.
Actuator (Control only) Performs physical work (Valve, Motor, Heater).

4. Detailed Example: Street Lighting

This is a Control System because it changes the state of the light.

  • Sensor: Light Sensor (LDR) measures ambient light.
  • Pre-set Value: e.g., "If light level < 20%".
  • The Loop:
    1. Sensor sends analogue signal to ADC.
    2. Digital value sent to Microprocessor.
    3. Processor compares value to 20%.
    4. If Lower: Processor sends signal to switch on the lamp.
    5. If Higher: Processor sends signal to switch off the lamp.
⚠️ Exam Note: In a Monitoring system, the output is always an alert (Siren, Light, Message). In a Control system, the output is an actuator action (Opening a valve, starting a motor).
End of Monitoring & Control Notes • Ready for Primary and Secondary Storage?