Sensitivity in sampled-data systems

The sensitivity of sampled-data systems to plant variations and load disturbance is examined with reference to two fundamental configurations. It is shown that the sensitivity function of a sampled-data system containing no continuous feedback is theoretically limited if the plant possesses low-pass response characteristics. Since the limitation imposed by sampling can be removed by continuous feedback, consideration is given to a sampled-data system containing a continuous minor-loop feedback path. A sensitivity function is derived which measures the individual effectiveness of the inner and outer loops in desensitizing the system, thereby providing the basis for a realistic design approach. This sensitivity function is applied to a design example.