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CONTROL SYSTEMS

V. Ryan 2003 - 2009

 

PDF FILE - CLICK HERE FOR PRINTABLE WORKSHEET BASED ON EXERCISE BELOW (CLOSED SYSTEMS)

CLOSED SYSTEMS:

When designing a control system it is good practice to consider it as a number of stages. For example;
A simple weather station can be looked upon as the following;

 
   

   

   

INPUT:
The heat from the sun causes the temperature sensor to produce data and this is sent to the computer.

 

PROCESS:
Data is received by the computer and it is processed. The processed data is displayed on the monitor as a graph.

 

OUTPUT:
The temperature levels are printed out. This is one form of output.

         
 

The temperature is constantly monitored and this is called feedback. As long as the sensor works, the computer processes and the printer prints out - feed back is taking place.

 
   

   

OPEN SYSTEMS

   

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A system that does not have feedback is an open system. An open system normally works once and then stops. A good example is seen below. A digital camera is used to take a photograph, it is transferred to the computer where processing of the picture takes place and finally a printout is produced. This is a closed system because there is no feedback and no attempt is made to improve the picture.
The person taking the picture decides to improve the final printout, using graphics software. He prints out the photograph several times and alters the photo with the software. Is the system still an open system or has it now changed to a closed system with feedback?

   

When drawing a systems diagram the boxes are labelled and there is no need to draw pictures representing each stage. However, when attempting course work, adding drawings helps present the diagram in a more graphical way. The open systems diagram shown below represents use of a digital camera which is shown graphically above.

   

   

QUESTION:

Draw a systems diagrams to represent a closed system of your choice and an open system.

     
     

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