Flow control

Replies

• 

  Voltaire

  I am not looking to be told the answer ...I want to understand it myself rather than just been told.

  Good man! That is the way it should be asked!!!
  Ok, please explain your question just a bit more - I'm old and forgetful 😀
• 

  O'Fithcheallaigh

  Hello 😀
  
  The question involves having a tank which has to be kept at a specified level of water ...so water can flow out, and in to the tank. The level is determined by a sensor, if it gets low, water flows in when a motor opens the required valve ...if the level is too high, the motor opens a different valve and water flows out, allowing the tank to reach the required and correct level.
  
  I have the model for the motor and the valve, but not for the tank ...the lecturer said the input (water flowing in) to the tank and the output (water flowing out) are related by the level in the tank ...but I just don't know how to model this ...I don't know where to start getting the TF for it.
  
  Thanks in advance.
  
  Seán
• 

  Voltaire

  Ok
  Let's make a start somewhere then we take it from there
  Assuming dr for the tank is zero we can say that dV = rdh (since dV = d(rh) = rdh + hdr)
  The inflow rate dV/dt = rdh/dt = Q*. The same goes for outflow
  Am I on the right track here? Is this where you wanted to go?
• 

  O'Fithcheallaigh

  Hey,
  
  Thanks for the reply ...I am not sure ...in a way I think it is ...generally, our Transfer Functions involve Laplace operators etc, so I think what I need to do is use your information to move forward.
  
  I'm in class at the minute, so won't really have time to think about this until I get home! But thanks again ...I actually think this might set me on the right road 😁
  
  Seán
• 

  Voltaire

  Great! 😀
  Try linearity with one-to-one proportionality so that
  1. L(ah) = aH and L(h + k) = H + K
  2. L(h) = L(k) i.e. h = k
• 

  O'Fithcheallaigh

  Thanks 😀
  
  I will go from here ...and if I have any issues, I will be back.
  
  Cheers
  Seán
• 

  O'Fithcheallaigh

  Hey,
  
  Just wanted to let know you, you were right ...I had to use the flow out and flow in, but also a function to represent the tank itself ...but we got there in the end.
  
  So, again, thanks for your help! 😎
  
  Seán
• 

  icehari

  so, you are going to create a closed loop control system... am i right?.
  
  you can use a float as a level sensor and the level of the water will be proportional to the resistance output in the float and that resistance output can change the speed of the motor proportionally....
  
  got any starting idea now.....