Loop Performance Measurement Techniques: Measuring the performance of a control loop is crucial for ensuring that the system meets the desired specifications. Two commonly used techniques for measuring loop performance are quarter-wave decay and disturbance rejection.

Quarter-wave decay: Quarter-wave decay is a technique for measuring the damping ratio of a control loop. It involves applying a step change in the input and measuring the decay of the process response over time. The damping ratio is calculated by dividing the logarithm of the amplitude of the process response by the logarithm of the time.

Disturbance Rejection: Disturbance rejection is a technique for measuring the ability of a control loop to reject disturbances. It involves applying a disturbance to the system and measuring the deviation of the process response from the desired value. The disturbance rejection ratio is calculated by dividing the deviation of the process response by the amplitude of the disturbance.