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Topic 7 (HL)

Control Systems

IB Computer Science

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Control Systems

  • a device, or set of devices that controls, manages, commands, directs or regulates the behavior of other devices or systems
  • In the context of IBCS, some sensor or electrical input is processed to generate some output
  • Examples include refrigerators, air conditioners, traffic lights (current time is input)

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Control System Components

  • microprocessor
  • sensor
  • actuator

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Microprocessor

  • an integrated circuit (chip) that contains all the functions of a computer’s CPU (arithmetic, logical, and control operations)
  • accepts electrical signal, processes, and outputs different signal
  • Performs calculations and data processing

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Transducers

  • Confirms one form of energy into another
  • Sensors and actuators are both transducers

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Sensor

  • a device which detects or measures a physical property and records, indicates, or otherwise responds to it

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Types of Sensors

  • Heat: measures temperature, e.g. central heating, fire alarm
  • Humidity: measures water vapour in the air, e.g. greenhouses, swimming pool halls
  • Infrared: measures radiation, e.g. security alarm systems
  • Light (photodiode/phototransistor): brightness, e.g. security lights
  • pH: acidity levels, e.g. environmental monitoring
  • Pressure (piezoresistive pressure sensor): force applied on the sensor, e.g. automatic doors, alarm systems
  • Smoke: particles in the air, e.g. fire alarm
  • Sound: sound pressure level, e.g. noise pollution monitoring, voice controlled systems, alarm systems
  • Tilt: angle of tilt, e.g. aircrafts, alarm systems installed in windows
  • Touch: more sensitive than pressure/detects contact, e.g. robots

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Actuator

  • converts input energy of one form to another
  • In IBCS, input energy is usually an electrical signal that is converted to physical motion
  • requires a control device (which emits a control signal) and a source of energy

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Types of Actuators

  • LED/light bulb: creates light, e.g. display of information
  • Heater: increases temperature, e.g. central heating
  • Cooling unit: decreases temperature, e.g. central heating, AC
  • Motor: spins things around, e.g. robots, washing machines, elevator
  • Pump: pushes air/water through pipes, e.g water cleaning system, process control
  • Buzzer/bell/siren: creates (loud) noises, e.g. fire alarm

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Analog-to-Digital (ADC) Converters

  • Converts analog data from sensors into digital data, which can be read by computers

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IPO (Input-Process-Output) Model

  1. Sensors take in analog input and convert them to digital data.
  2. Digital data is processed by the microprocessor, to output different digital data.
  3. Transducers turns this digital data into some sort of physical motion.

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Feedback

  • If either the output or some form of the output is utilized as part of the system input, then it is known as feedback.

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Open Loop System [Feedback Loops]

  • Doesn’t take feedback into account, repeats same action based on input
  • Examples: TV Remote Control, Light Bulb, Coffee Machine, Toaster

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Closed Loop System [Feedback Loops]

  • Takes feedback into account, including output and possibly other factors external to the system
  • Correct Errors in output by using feedback loop to alter subsequent input
  • Example: Home Thermostat, Airplane Autopilot

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Negative Feedback Loop

  • A system in which feedback is given in order to reduce fluctuation in subsequent output
  • Try to move output closer to some equilibrium, or target value

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Positive Feedback Loop

  • Enhances or amplified changes in output to move a system further away from equilibrium or a given value.

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Control Systems: Pros & Cons

Pros

Computer can respond much more quickly than humans

Control systems can run without a break (24/365)

Control systems are less error prone than humans

Control systems can be placed in environments hazardous to humans

Cons

Technical malfunctions can occur

Cannot react to unexpected events

Relies on consistent supply of electricity

Could be more expensive than a human solution

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Centralized vs. Distributed Control Systems

  • Centralized system - All components are controlled by a centralized processing unit

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  • Distributed system - Different components are controlled by a number of different processing units located throughout the system - all work towards common goal

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Centralized System Pros & Cons

Pros

Cons

Easier to maintain and troubleshoot

If main sensor/controller/actuator fails, the whole system fails

More control

Less power

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Less flexibility

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Distributed System Pros & Cons

Pros

Cons

Shared processing load

Harder to maintain

More reliability

More complex software

Flexibility

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Autonomous Agents

  • “Autonomous agents are software programs which respond to states and events in their environment independent from direct instruction by the user or owner of the agent, but acting on behalf and in the interest of the owner.”
  • Examples
    • recommendation systems
    • drone swarms
    • search engine crawlers

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Autonomous Agents (4 Characteristics)

  1. Autonomy - Can selected independently select tasks in order to achieve overarching goal
  2. Reactive - Senses environment and reacts based on this input
  3. Concurrency/Sociality - Can interact with other agents cooperatively, competitively, or in coordination
  4. Persistence - an agent consistently acts in pursuit of its goal

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IB Questions

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Home Surveillance system

Cam-1

Cam-2

Cam-3

Central Computer

Motion/ Presence Sensor

Motion/ Presence Sensor

Motion/ Presence Sensor

Process

Transducer/ ADC

If(motion detected)

Warning Notification

Sound

Notification

true

false

Feedback

Playback/ Video database

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