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CONTROL SYSTEMS - AN EXAMPLE

V. Ryan © 2003

 

An Automatic Sprinkler System

An automatic water sprinkler system has been ordered by a farmer. The system must have sensors that detect dry weather and turn on water sprinklers to water valuable crops.
The company manufacturing the system have decided that a starting point is to think in terms of INPUT - PROCESS - OUTPUT and also include FEEDBACK. The basic plan is set out below.

  
   

INPUT
How will the dryness of the soil be sensed? Perhaps an electrode can be used.

  

PROCESS
What device(s) will be needed to control the output? A computer could monitor incoming data and control the output, a simple program will be required.

  

OUTPUT
This may be a sprinkler device which is turned on when the computer detects the need for water.
         
   

FEEDBACK
Feedback is constant as the computer continually checks the moisture level of the soil.

    
   

This is the layout to the systems diagram for the automatic sprinkler system.
   

One Possible Answer:    

 
   

The moisture sensor detects when the soil is dry. The darlington pair is a simple electronic device that amplifies the signal sent by the sensors so that the computer can read it. Without the darlington pair it is possible that the signal from the sensor could be too weak to be read by the computer. This would mean that the sprinkler system would not be turned on.
When the sensor determines that the soil is moist/damp the signal to the computer ends and the computer turns off the sprinkler. This is called FEED BACK.
   

   

QUESTION:
Draw a systems diagram for a domestic alarm system. Show clearly input, process and output. Explain the need for feedback.

  
     

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