Measurement noise filter design for unstable time delay processes in closed loop control

A second order measurement noise filter (SONF) is designed to eliminate the noise influence on first and second order unstable time delay processes controlled by PID controllers in closed loop configuration. Such a design doesn’t exit for unstable processes and is the objective of this research. The noise filter time constant is designed based on an iterative method and is a function of the cross over frequency of the loop gain (ω gc ) and design parameter (β). The design parameter (β) is selected to balance robustness, performance and noise reduction. Systematic procedure is developed to design the filter. Simulations investigates are conducted with different unstable processes to show the reduction of the noise measurement effect on controller and process outputs. The effect of the SONF is calculated by taking into consideration perfect and disturbing process parameters based on the Total variance (TV), Integral Absolute error (IAE) and Integral square error (ISE) criteria.