Microprocessors and sensor input in control systems

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Control[1]

The digital integrated circuit (IC) called a microprocessor has ushered in a whole new era for control systems electronics This revolution has occurred because the microprocessor brings the flexibility of program control and the computational power of a computer to bear on any problem. Automatic control applications are particularly well suited to take a of this technology and microprocessor-based control systems are rapidly replacing many older control systems based on analog circuits or electromechanical relays[2]

Having a microprocessor in a control system has several advantages:[3]

  • They can process data very quickly and much faster than a human could
  • Due to these fast speeds they can react very quickly to change in the control system
  • Control systems can run through out the year 24/7
  • They can work in places where it would be dangerous for a human to
  • Outputs are consistent and error free
  • Low level signals from sensors, once converted to digital, can be transmitted long distances virtually error-free.
  • A microprocessor can easily handle complex calculations and control strategies
  • Long-term memory is available to keep track of parameters in slow-moving systems
  • Changing the control strategy is easy by loading in a new program; no hardware changes are required
  • Changing control strategy is easy by loading in a new program; no hardware changes are required.
  • Microprocessor controllers are more easily connected to the computer networka group or system of interconnected people or things. within an organization. This allows designers to enter program changes and read current system status from their desk terminals

However there are several disadvantages

  • It may cost a lot of money to develop the software for a control system as they are specialized
  • The system will not be able to run in the case of a power shortage
  • The system will not be able to run in the case of a computer malfunction
  • A computer can't react to events that it has not been programmed for, unlike a human could
  • It can cause some concern if total control for a system and the decisions are handed over to a computer

Sensor types

The following are some sensors with explanation and example uses:

  • Heat: measures temperature, e.g. central heating, fire alarm
  • Humidity: measures water vapour in the air, e.g. greenhouses, swimming pool halls
  • Infra-red: measures radiation, e.g. security alarm systems
  • Light: brightness, e.g. security lights
  • pH: acidity levels, e.g. environmental monitoring
  • Pressure: 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

Actuator types

Actuators give a system an output form. A few examples include:

  • 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

Feedback loops

Control systems can be open loop or closed loop.

Open loop systems will just consider the input and then keep repeating the same task given the input, e.g. a microwave heats for a given time period without actually checking the temperature of the food.

Closed loop systems on the other hand will also take into account other factors, including the output itself. For example a water tank control system that keeps water levels constant will constantly adjust its output (opening or closing a valve) depending on the input it gets from water level sensors.[4]

Standards

  • OutlineGive a brief account. the uses of microprocessors and sensor input in control systems.

References