WDP and WPH Series Controllers are a perfect match with Walchem's WEL pH/ORP electrodes - offering an extremely reliable differential measurement technique immune to any possible ground loop problems.tible with GLI and Aquametrix (Lisle Metrix) controllers. Together they provide a true NEMA 4X system with no BNC connectors exposed to wet or corrosive conditions. Walchem's pH/ORP controllers and sensors are engineered to give you the most reliable measurement and control available.