1. A steady state distillation process is shown diagrammatically as FIGURE 1.

 

 

FIG. 1

      

   s u p p

l    i

e  d  t

 o  b o i l e

r

  

Assuming no heat losses to the atmosphere:  

(i)        Write four balanced equations for this system.

 

(ii)     Identify where any. constitutive equations may be required for the modelling processes

 

2.          A process can be represented by the first order equation

 

 

dyt   3u t  4  y t  dt



Assume the initial state is steady (y = 0 at t = –0).  

(a)      Determine the transfer function of this process in the s domain.

 

(b)      If the input is a ramp change in u(t) = 4t, determine the value of y(t) when t = 10 s.

3.          Using a simulator of your own choice, or the one used during the lessons at the website; http://newton.ex.ac.uk/teaching/CDHW/Feedback/OvSimForm–gen.html note the initial values used by the simulator and the output produced.

For BOTH ON-OFF and PID control,

 

(a)      sketch (or print copies) of the effect of changing the following parameters from their existing value (resetting them to the original after every change has been recorded):

(i)          Increasing the proportional control by a factor of 10. (ii) Decreasing proportional control by a factor of 10.

(iii)  Increasing the integral control by a factor of 10.

(iv)  Decreasing integral control by a factor of 10.

(v)     Increasing the derivative control by a factor of 10.

(vi)  Decreasing derivative control by a factor of 10.

(vii)                    Increasing the hysteresis by a factor of 10.

(viii)                  Decreasing hysteresis by a factor of 10.

(ix)  Increasing the system lag by a factor of 10. (x) Decreasing system lag by a factor of 10.  

(b)      Explain your results.

 

 

 

6

 

4.          The purpose of the arrangement shown in FIGURE 4 is to mix the two liquid products A and B in a fixed mass ratio. Product A, which is itself a mixture, is a ‘wild’ flow, whilst product B, a pure compound, is controlled. As the mixture leaves the tank the transmitter TX measures its density.

(a)      Complete the diagram to show how the arrangement could be controlled by the method of ‘variable ratio control’. (b) Identify which transmitter provides ‘feedforward’.

 

(c) Describe how the control system responds to a disturbance caused by a variation in the density of product A.

 

 

 

 

 

                                                    Fig 4            7

 

5.          FIGURE 5 shows a partially completed diagram of a flow control system. The flow controller is reverse acting and has a 0.2 to 1.0 bar pneumatic output signal which will supply both control valves V1 and V2.

The small range control valve, V2, only needs to operate on the first 25% output change of the controller output signal. For larger flow rates the small range valve will remain fully open and control will be achieved by operation of the large range valve. Note the differing air failure action of the two valves.

 

 

 

                                                             Fig 5

 

Design a system utilising valve positioners which will meet the prestated specifications.