Numerical Question 11 12 and 13

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11. The time constant of a unity gain, first order plus time delay process is 5min. If the phase lag at a frequency of 0.2rad/min is 60. Then the dead time (in min ) is? Ans. 5/12 12. The characteristic equation of a closed loop control system is 0.25s3+0.8s2+5.6s+1+0.35K=0 Find the limiting value of K, above which the closed loop system will be unstable. (Write answer up to two decimal place) Ans. 48.34 13. A proportional controller is used for two non-interacting liquid level system. The time constant for tanks are 1 and 0.5. The value of the gain of controller is 5 . Assume unity feedback control system. The set point of the control system is given step change of magnitude of 0.4 . Determine the offset. (Write answer up to two decimal place)