industrial instrumentation basics

Every process plant runs on valves — isolating equipment for maintenance, throttling flow, preventing backflow, and protecting against overpressure. While our Control Valve Basics post covers automated, actuated control valves specifically, this post covers the broader family of valve types you'll find throughout a plant — on/off, isolation, and specialty designs — and where each one fits. On/Off (Isolation) vs. Control Valves Before getting into specific types, it's worth separating valves into two broad functional categories: On/off (isolation) valves — designed to be either fully open or fully closed, used to isolate a section of pipe or equipment, typically for maintenance. Most aren't designed for throttling and will wear prematurely or perform poorly if used that way. Control valves — designed to modulate to any position between fully open and fully closed, precisely regulating flow, pressure, or level in response to a continuous control signal. Common V...

Pressure is one of the four process variables — alongside temperature, flow, and level — that shows up in nearly every industrial process. Understanding how it's measured, what instrument to pick for a given job, and how to calibrate that instrument correctly is core knowledge for any instrumentation technician. This article walks through the fundamentals: what pressure actually is, the scales used to express it, the sensing technologies behind pressure gauges and transmitters, and a practical calibration procedure you can use in the field. What Is Pressure? Pressure is force applied per unit area. In a process plant, pressure shows up almost everywhere — fluid flowing through a pipe, gas in a vessel, differential pressure across an orifice plate used for flow measurement, and so on. Pressure readings are affected by more than just the process itself. Altitude, weather, and atmospheric conditions all influence a pressure measurement, which is why pressure is expressed using a...