Control systems: heating, alarms, smart meters and sensors

Topic 5: Control Systems

1. Types of Control Systems

   • Central Heating Systems
     • A central heating system is controlled by a microprocessor that er of sensors attached to it.
     • The process follows a continuing cycle.
       • Regular readings of temperature are input.
         • The microprocessor analyses the reading.
           • If the temperature is too hot, it switches off the heater. If the temperature is too cold it on the heater.
   • Burglar Alarms
     • Often very complex and use many sensors.
     • Passive infrared (PIR) sensors can detect movement in a room.
     • Proximity sensors can be used on windows and doors to detect when they are opened.
     • Pressure pads can be placed under mats to sense when someone stands on them.
     • If any sensor is activated a signal will be sent to an alarm, bell or sometimes directly to a police station or security guard.
   • Smart Meters
     • Measure the amount of electricity, gas or water that is being used in a home.
     • Take readings at regular time intervals.
       • Send the readings back to the head office, so there is no need for human meter readers.
         • Monitor when the greatest consumption of the resource is taking place.
           • Help customers become more efficient in their use of the resource.
   • Security Systems
     • Many buildings including houses, have smoke detectors and fire detection systems.
     • They can activate a siren or bell.
     • They can set off an automatic sprinkler system.
     • They can send a message automatically to the fire station.

2. Greenhouse Control System

   • Start.
     • Sensors dectect humidity, light, temperature.
       • Control program examines inputs and sends signals to actuators.
         • Actuators switch on/off heat/sprinklers, open/close blind/windows.
           • Back to start.

3. Computer Control Systems

   • Advantages
     • Changing circumstances are monitored more frequently than a human can manage.
     • Computers do not get tired or take holidays.
     • They will never go on strike.
     • Every job is done with exactly the same precision.
     • The computer will only do what it is programmed to do, so there are no surprises.
   • Disadvantages
     • The computer can only do what it was programmed to do so cannot adapt to changes easily.
     • If there is a mistake in the programming this will be repeated endlessly until stopped.