A Modified Relay-Based Technique for Improved Critical Point Estimation in Process Control

In this paper, we present a modified relay-based technique for estimating the critical point in process control systems with improved accuracy over existing relay-based methods. The proposed technique addresses the accuracy of the conventional approach by eliminating the errors introduced in the usual describing function analysis of nonlinear systems. The analytical basis of the technique is described in the paper, and it is also shown that it is theoretically possible to obtain an exact estimate of the process critical point under ideal conditions. The effectiveness of the proposed technique is verified by simulation results and also by real-time experimental results in the level control of a coupled-tanks system.