Q9Control System
Question
2 marks
Q.9. Draw electrical lag network and its pole zero plot.
Answer
An electrical lag network is an RC circuit (series R1 with parallel R2-C across the output) whose transfer function has a pole closer to the origin than its zero, producing phase lag; its pole-zero plot shows the zero to the right of the pole on the negative real axis.
A lag network is realized using resistors R1, R2 and capacitor C, giving a transfer function of the form:
since β > 1, the pole (at -1/(βτ)) lies closer to the origin (jω-axis) than the zero (at -1/τ), so on the pole-zero plot the pole is to the right of the zero on the negative real axis, and this network introduces a negative (lagging) phase angle over its useful frequency band.