V. K. Singh and  P. K. Padhy,  The System Identification and PID Lead-lag Control for Two Poles Unstable SOPDT Process by Improved Relay Method.   journal   = {International Journal of Electrical and Computer Engineering}, [online]. World Academy of Science, Engineering and Technology.
    July 2011, vol. 55(7). 770 - 774
    [viewed 21 February 2020]. Available from: https://publications.waset.org/pdf/15669.