The Yokogawa FLXA21® is the new generation of two-wire liquid transmitters with a new modular design for continuous on-line measurements in industrial installations. It provides the flexibility for either single or redundant measurement. The FLXA21 modular design offers the flexibly to assemble a variety of systems for applications measuring pH/ORP, Contacting Conductivity (SC), Inductive Conductivity (ISC) or Dissolved Oxygen (DO). For redundant measurement, the FLXA21 supports up to two sensors of the same type: pH/ORP and pH/ORP, SC and SC, and DO and DO, thereby reducing installation costs and saving panel space. In addition, this configuration provides a highly reliable backup system. By adding an HIM (HART Interface Module) device, the FLXA21 can be programmed for additional functionalities. These include a variety of calculated data from the two measurement inputs. When used as a redundant system, the main output parameter is automatically switched over to the second sensor output in case of the main sensor’s failure.