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A2. A process can be represented by the following transfer functions: 2 y*(s) = 551 1 55+1U*(S) 55+ 7d' (s) = ) ) 1 where y is a process variable, u is a manipulated variable and d is a disturbance to the process. An integral-only controller is to be used to regulate this process. a) Explain whether a direct-acting or reverse acting controller is required. It should be assumed that both the instrument and the control-valve have a transfer function of 1. [2 marks] b) Derive an expression for the closed-loop response of the process when under integral-only control. [8 marks] c) (i) Use the expression from part b) to determine the maximum integral gain, K, K that can be used before the control response tends to oscillate? = [3 marks] (ii) Calculate the value of K, that will result in a response with a damping coefficient of Y = 0.25. [3 marks] d) Explain whether you would recommend the integral-only scheme described above as being a favourable choice for most chemical process applications. Explaining your choice and any advantages or disadvantages, briefly describe an alternative scheme. (maximum 100 words). [4 marks]