[ Digital Computer Systems for Management, Data Logging, Monitoring, ] Automatic and Manual Control of Industrial Process Variables Such as Flow of Materials, Temperature, Pressure and Liquid Level [ and Including Elements Such as Central Processors, Microprocessors, Memory Units, Multiplexers, Teletypewriters, CRT Terminals, Paper Tape Readers and Punchers, Analog/Digital Converters, and Operator Interface Consoles; Industrial Process Control Operators Such as Automatically Operated Fluid Flow Control Valves; Liquid and Gas Analyzing Apparatus and Instruments Such as Liquid and Gas Chromatographs, Octane Analyzers, Gas Analyzers Using Infrared Techniques and Data Recording and Indicating Apparatus Associated with the Above Mentioned Apparatus and Instruments, ] Apparatus and Instruments for Measuring, Indicating and Recording the pH and Conductive Properties of Solutions Including Elements and Accessories Such as pH Electrodes, Reference Electrodes, Electrode Holders and Electrode Cleaners; Particle Size Analyzing Apparatus and Instruments Such as Instruments for Detecting Very Small Particles in Liquid and Large Particles in Mixtures; Apparatus and Instruments for Sensing and Indicating the Interface Between Different Fluids; Fluid Density Measuring and Indicating Apparatus and Instruments; Instruments and Apparatus for Measuring Pressure Using Pressure Sensitive Semiconductor Materials; Parts Fittings (Not Included in Other Classes) for the Aforementioned Goods