The controller measures the acidity (pH) of the solution and opens the valves to add acid or base as needed. For this purpose, the controller is equipped with two control relay outputs that operate in “pulsed mode.” In this “pulsed mode” operation of the relay outputs, the acid and base valves release portions of the respective liquids. These portions can be adjusted by setting the pulse duration and the pause time. The following control laws are possible: three-position control, P (Proportional), PI (Proportional-Integral), or bidirectional PID (Proportional-Integral-Derivative).

Systems with Time-Varying Setpoints (Program-Based Control)
In many technological processes (such as drying, sterilization, ceramic firing, metal heat treatment, dyeing, etc.), it is necessary to control
