ABSTRACT
The pH measuring system is expressly designed to report the activity of hydrogen ions in an aqueous solution. The pH measuring electrode in most common use is the glass electrode. It consists of a glass bulb containing a solution buffered to pH 7, with an internal reference cell identical to that in the reference electrode. The extreme gain changes presented by most titration curves, and their variability, pose special problems for the pH control system. The typically very high gain of the titration curve in the region about set point is its most demanding feature, causing most pH loops to cycle about the set point. Feedforward systems have been implemented using the pH of the feed as an indication of its composition, but with very limited success. This measurement is only representative of composition if the titration curve is fixed, which is never true for wastewater.
