Instrumentation Controls Lab (EE2327L) Practice Exam

In this tuning method, you determine the point where the closed-loop system just starts to sustain oscillations and measure those two values from that condition. The gain at that point is the ultimate gain, and the period of the sustained oscillation is the ultimate period. These two numbers are then fed into the Ziegler–Nichols rules to set the PID gains (for example, Kp ≈ 0.6 Ku, Ki ≈ 2Kp/Pu, Kd ≈ Kp Pu/8 for the full PID version). That’s why the two measured values used to compute the PID gains are the ultimate gain and the ultimate period. The other options refer to different stability metrics or analysis methods (open-loop gain and phase margin, system delay and dead time, or gain/phase margins) that aren’t the measurements used in the classic Ziegler–Nichols PID tuning.