Instruments and Systems: Monitoring, Control, and Diagnostics Annotation << Back Selection of Robust Settings of Industrial Controllers based on the Condition of the Ultimate Degree of Stability for Objects With Delay A.M. TSIRLIN The problems of robust tuning of industrial controllers (proportional, integral, PI, and PID controllers) for a typical process plant with delay under the condition of the maximum degree of stability are considered. The typical plant is a series connection of a pure delay element and a fi rst-order aperiodic element. This expression can be used to approximate the transfer functions of a wide class of processes in which temperatures, pressures, levels, concentrations, fl ow rates, etc., are subject to stabilization. The conditions for the maximum degree of stability boil down to the fact that the roots of the characteristic equation of the control system closest to the imaginary axis must be real and multiple. Moreover, their multiplicity exceeds the number of sought-after controller parameters by one. This property made it possible to derive analytical expressions for the sought-after parameters. It is shown that for systems with an open-loop AFC modulus monotonically decreasing with frequency, robust tunings correspond to critical values of the plant parameter vector in the zone of possible deviations. This is the vector with the maximum gain and the minimum ratio of the time constant to the pure delay. A method for calculating controller parameters in dualloop systems with variable selection of the intermediate pulse sampling point, as well as for a cascade control system, is proposed. Keywords: Limit stability, calculation of controller parameters, two-loop systems, pure delay, robustness, critical values of parameters. DOI: 10.25791/pribor.2.2026.1652 Pp. 44-56.