WDS Series differential pH and ORP sensors are designed for long lasting and reliable industrial applications. This series has a replaceable salt bridge for long life and transmits signals up to 3000 feet. It is also resistant to ground loop problems. Sensors are easily replaced if the reference solution becomes contaminated or the salt bridge becomes clogged. Differential measurement technique uses two electrodes, one for process measurement and the other for reference measurement. Each electrode is measured differentially with respect to a third metal electrode. The reference electrode is constructed from pH glass and is embedded in pH 7 buffer within the sensor behind a porous, replaceable salt bridge. Walchem Corporation 5 Boynton Road, Hopping Brook Pk. Holliston, MA, 01746