3a. (15 points) You have been called to the New Kensington Municipal Sewage Trea

Question

3a. (15 points) You have been called to the New Kensington Municipal Sewage Treatment Plant to install a new West model 6100 PID controller. You meet with the plant superintendent, Lee Keyrear, who you suspect has been smelling the plant odors a little too long because he agrees to let you make the chlorine control system become marginal stable in order for you to get the data you need to tune the new controller. You install the new controller and disable the integral and derivative control. You then adjust the gain and find that when Kp is 4.5 the chlorine control looks like it is marginally stable. You go to the data collection computer and print out the following plot. From the plot you notice that the process is pretty slow and so you decide to use PID control. Calculate the necessary values for Kp. Ki, and Kd for this control. What will be the West controller settings for this control? EMET 410 Test 2 Problem 83 10 8 0 10 Time (minutes) 5 15

Explanation / Answer

From the graph it is looking like period of oscillations

tp= 2minitues

And critical value of k = 4.5

From z n pid tuning rules when pid controller was used pid settings given by formula

Kp =0.6×k = 0.6×4.5 = 2.7

Ki = (2kp)/tp = (2×2.7)/(2×60sec) = 0.045

Kd = kp * tp/ 8 = 2.7×2×60/8 = 40.5

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