PID control of FOPDT plants with dominant dead time - The frequency domain approach

We present an application of the well-known frequency-domain modulus optimum criterion for obtaining settings of PID controller for the first order systems with dead time. The settings are obtained analytically for any value of the dead time parameter. Although the method usually gives very favourable closed-loop behaviour, in the case of large dead time the stability margin gets reduced and even non-stable behaviour can be observed. We propose a simple correction that preserves the stability margin, keeping maximum of the performance.