pH Instrument Control

Instrument control is one of the more important features of all systems. Some physical inadequacies can be reversed with good instrumentation. The four types of process control utilized for pH control, by order of complexity, are: On-Off, Proportional, Proportional- Integral (PI), and Proportional-Integral-Derivative (PID).
On-Off control activates the pump when a high or low set-point is exceeded. The pump is deactivated when the set point is reached. With proportional control, the pump is still activated when the set point is exceeded. However, proportional control also allows for reagent pump speed control.

pH Neutralization Control Panel

The pump speeds up when the process variable is far away from the set point value and slows down when the process variable is close to the set point. Proportional
control allows full use of the pump’s capacity and limits over additions of reagents.
Proportional-Integral and Proportional-Integral-Derivative Controllers allow more control than the simple proportional control. Typically, pH treatment systems are simple enough that PI or PID controls are not needed if all the other design criteria are met.
Systems that have steady influent flows and constant pH, either high or low, are controlled effectively with On-Off control systems. Systems that have varying influent flows and pH require proportional control systems.