What are the main process variables that are controlled in chemical processes?

Main process variables include: Flow - most common, fast response, affects material balance; Level - inventory control, can be integrating; Pressure - affects equilibrium, safety critical, often fast; Temperature - most common for product quality, usually slow; Composition/Quality - direct quality indicator, often slow measurement (analyzer), expensive sensors. Other variables: pH, conductivity, density, viscosity. Selection of controlled and manipulated variables based on process requirements and dynamic characteristics.