Microprocessors and sensor input in control systems

Control

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.

Standards

• Outline the uses of microprocessors and sensor input in control systems.

Give a brief account.