Nyquist Plot generator

Description| How it works

This app will generate the Nyquist Plot for a transfer function of the form (a + bs) e-ts / (g + hs). In process control, Nyquist plots are used for analyzing the stability of controllers.


.xls file (142 KB) or .zip file (21 KB)

How to use

The use of this app is quite straightforward, simply key in the values of a, b, g, h and t into the cells B6 through B10. Key in the frequency range into the cells B13 and B14. Note that the units of frequency is rad/time. The Nyquist plot is generated.

Lets say we wish to obtain the Nyquist plot of e-4s/(1 + 2s), from 0.01 rad/s to 100 rad/s. We have

a = 1,
b = 0,
g =1,
h = 2 and
t = 4.

Key in these values and the range, the Nyquist plot is shown below.The following couple of images were obtained by running 1000 iterations. The first has a center at (0,0) and span of 4 while the center of the second at (-1,0) and span of 2.

Nyquist Plot

Also See:

PID Loop Simulator

Bode Plot Generator

Bode Plot using Complex Functions

PI Control of Integrating Process