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The coupled tank liquid level control system approximated by the second order plus time delay (SOPTD) model was considered and the proposed improved relay tuning method was applied to calculate the corrected ultimate gain (Ku). It was found that the error in calculation of ultimate gain by proposed methods has been reduced considerably than that of conventional method. The corrected Ku was used to estimate optimum PID parameters by Ziegler Nichols method. The closed loop response was obtained using optimum values of PID parameters and compared with that of conventional method. It was found that the Integral Time Absolute Error (ITAE) has been decreased and robustness has been increased by proposed method I & II as compared to that of conventional method. Hence the proposed improved relay tuning method gives better performance.