Abstract: A sensor system for measuring the pH level in a process flow pipe, such system utilizing a sensing electrode that fits within, and is protected by, a rugged cylindrical metallic sheath. The sensing electrode is slid by an insertion tube through a ball valve into the process flow pipe. Two spaced collars with two pairs of restraint cables cooperate to retain the sensor system in alignment during the insertion procedure. After insertion, the sensor system is held in position by the pair of shorter restraint cables extending between the collars, while a compression nut is advanced onto a tube fitting to mechanically join the insertion shaft to the sensor system.