{"id":1608,"date":"2021-02-11T03:26:15","date_gmt":"2021-02-11T03:26:15","guid":{"rendered":"http:\/\/learnlearn.uk\/alevelcs\/?page_id=1608"},"modified":"2021-03-08T06:00:42","modified_gmt":"2021-03-08T06:00:42","slug":"open-vs-closed-loop-systems","status":"publish","type":"page","link":"https:\/\/learnlearn.uk\/alevelcs\/open-vs-closed-loop-systems\/","title":{"rendered":"Open vs Closed Loop Control Systems"},"content":{"rendered":"
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Open Loop<\/h2>\n
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Open Loop Control Systems<\/h3>\n

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An open loop system is a control system where the output has no effect on the controlling action of the input system.<\/p>\n

Example – Automatic Room Heating System<\/strong><\/p>\n

A simple example of an open look system is a central heating system based on a timer. It is generally colder at night so the central heating system is programmed to turn on at 6pm and turn off a 6am.<\/p>\n

Advantages<\/strong><\/p>\n

This system has a number of advantages:<\/p>\n

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  • It requires very few components and is quick to program so I will be cheaper than other systems to build.<\/li>\n
  • Due to its simplicity it will likely have few, if any bugs.<\/li>\n
  • It is very predictable as it does the same thing over and over.<\/li>\n<\/ul>\n

    Disadvantages<\/strong><\/p>\n

    This simple system has a problem though, when the conditions of the environment<\/em> are unpredictable then it doesn’t perform as well:<\/p>\n

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    • If it is a very cold day outside then the system won’t adapt to the temperature change.<\/li>\n
    • If the central heating system turns on an heats up the room beyond the desired temperature then the system won’t turn off.<\/li>\n<\/ul>\n

      <\/h3>\n\n<\/div>

      Discrete Closed Loop<\/h2>\n
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      Discrete Closed Loop Control System<\/h3>\n

      \"\"<\/p>\n

      A simple improvement to this system would be the use of a temperature sensor into the system that has a trigger event – such as the temperature exceeding\/dropping below a certain value. When the temperature drops below a threshold set value the system power is turn on to full power and the room is heated up. When the room reaches the desired temperature the heating system turns off. The output of the system is fed back as a input to the system, creating a feedback loop. This simple type of closed loop system is known as a discrete closed loop system.<\/p>\n

      This improved\u00a0 system has a bit of a problem though – it tends to over compensate for the temperature changes as the system is either on full power or no power and only changes when the threshold set value is reached. Take a look at the model below as see for yourself.<\/p>\n