SKEDSOFT

Transport lag in Bode Diagrams

Fig: Phase-angle characteristic of transport lag

Transport lag is of nonminimum-phase behavior and has an excessive phase lag with no attenuation at high frequencies. Such transport lags normally exist in thermal, hydraulic, and pneumatic systems.

Consider the transport lag given by

The magnitude is always equal to unity since

Therefore, the log magnitude of the transport lag e^-jωT is equal to 0 dB. The phase angle of the transport lag is

The phase angle varies linearly with the frequency ω. The phase-angle characteristic of transport lag is shown in Figure.