Omega PHCN-430/435/440/445 pH Controller is microprocessor-based and comes with two time-proportional relay contacts and a 3-digit LED display. All models have the capability of automatic temperature compensation. Along with the pH value, the PHCN-430 and PHCN-435 models simultaneously display temperature. It has two mechanical time delay SPDT mechanical relays. The PHCN-440 and PHCN-445 feature two time proportioning relay outputs for acid and base additions. PHCN-440 also includes a proportional 4-20 mA output for proportional control with metering pump interface.