Analog computer techniques for plotting Bode and Nyquist diagrams

Two methods of plotting Bode and Nyquist diagrams with an analog computer are presented. Both methods have the advantage of being able to give the open loop response from a closed loop simulation on the computer, which makes them applicable to systems with open loop poles in the right hand plane. Neither method requires any adjustment by the operator, other than to change the frequency of the input signal.The first method makes use of some trigonometric identities, which yield functions which identically equal the real and imaginary parts of points in the Nyquist diagram. It makes rather extensive use of multiplying equipment, but no other non-linear equipment is required.The second method makes use of diode and relay switching techniques to measure phase, and peak value readers to measure amplitude. One divider and no multipliers are used, but diodes and relays are necessary.Nyquist and Bode plots are presented, as computed by both methods.