Estimation of the optimal sampling frequency for process analyzers

The sampling theorem states that the sampling frequency should be twice the highest frequency of the studied signal. This sets limits to the lowest allowable sampling frequency of a process analyzer. Economic criteria together with the instrument analysis time define the highest sampling frequency. The stability of the control loop requires that the roots of the characteristic equation of the control loop in the z plane should lie inside the unit circle. An example is discussed. In order to minimize the error in the estimation of parameters of a system using an impulse excitation signal, the sampling time should be equal to the dominant time constant of the system.