digital computers and networks for management, data logging, monitoring, automatic and manual control of industrial process variables, namely, flow of materials, temperature, pressure and liquid level, comprised in whole or in part of 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, namely, automatically operated fluid flow control valves, liquid and gas analyzing apparatus and instruments, namely, [liquid and gas chromatographs, octane analyzers, gas analyzers using infrared techniques and data recording and indicating apparatus and instruments for the aforementioned goods;] apparatus and analytical instruments for measuring, indicating and recording chemical properties, pH and conductive properties of solutions, namely, pH electrodes, reference electrodes, electrode holders and mechanical electrode cleaners; particle size analyzing apparatus and instruments, namely, instruments for detecting very small particles in liquids 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 and semiconductor sensors and parts for the aforementioned goods