Microprocessor-based family of pH panel mounted controller are designed for a wide variety of environmental monitoring applications. The units features automatic or manual temperature compensation of pH, two 5 amp mechanical relays and a choice of a scalable 4 to 20 mA, or 0 to 20 mA control or recording output or a 0 to 10 V output. For ease of operation all calibration and parameter setpoints are selectable through the front keypad. The PHCN model can be interfaced with a variety of pH electrodes.