An adaptive control system for use with non-linear processes, utilizing a non-linear controller with remotely adjustable deadband width, and an adaptive controller to perform said adjustment. The adaptive controller operates on the same deviation signal as the non-linear controller, but has a discriminator circuit in its input that reacts in opposite directions to high and low-frequency components in the deviation signal. Oscillations of the process at the natural period of the control loop are made to cause the non-linear deadband width to expand, while drift or offset causes it to contract. A 50 to 1 change in process gain can be accommodated with this system. The system is especially successful on non-linear processes such as the pH control of a chemical waste of randomly variable composition. By avoiding continuous cycling, the system can result in reduction in reagent usage of 50 percent, while still meeting effluent specifications.
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