Nyquist plots are a graphical way of representing the frequency response of a system.

• Why learn about Nyquist plots?
• Nyquist plots are one way - of many ways - of representing frequency response data for a system.
• What should you know to learn about closed loop systems?
• You need to know about linear systems, transfer functions, and frequency response concepts.
• What do you need to know about Nyquist plots?
• Low frequency behavior of a Nyquist plot depends upon details of the transfer function - including DC gain.
• High frequency behavior of a Nyquist plot depends upon the excess of poles over zeroes.
• Low frequency behavior - when the system has one or more poles at the origin - is of interest in integral control systems.
• How do you use Nyquist plots?
• Nyquist developed a criterion for determining stability for a closed loop system - the "Nyquist Stability Criterion".  You use Nyquist plots when you are determining the stability of a closed loop system.
• Problems
• Additional Information
• Links to Frequency Response Calculators