Having a two CSTR cascade with a concentration ACS (Fig. 11.23), using Nyquist criterion, determine the maximum controller gain for which the loop is stable. The data are the following: the reaction...

Having a two CSTR cascade with a concentration ACS (Fig. 11.23), using Nyquist criterion, determine the maximum controller gain for which the loop is stable.

The data are the following:

the reaction is isothermal with first order kinetics and the rate constant is k = 2 h⁻¹
. The concentration transducer has the measurement range
 and the output

signal in the range 4–20 mA; the delay of the transducer is given by the time constant T_T
= 2 min. The control valve is linear and works with unified signal 4–20 mA and controls a flow between 0 and