A limit switch detects the physical motion of an object by direct contact with that object. An example of a…
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The simplest form of 4-20 mA current loop is the type used to represent the output of a process controller,…
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Although it seems each model of PLC has its own idiosyncratic standard for programming, there does exist an…
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The purpose of a control valve actuator is to provide the motive force to operate a valve mechanism. Both…
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Phasors are to AC circuit quantities as polarity is to DC circuit quantities: a way to express the…
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A simple control system drawn in block diagram form looks like this: Information from the measuring device…
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Negative feedback systems, in general, tend to cause confusion for those first learning their fundamental…
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Feedback Control System Components Before we begin our discussion on process control, we must define a few key…
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DC electric motors generate torque by a reaction between two magnetic fields: one field established by…
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The vast majority of PID controllers in service today are digital in nature. Microprocessors executing PID…
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The reason why a pneumatic control valve’s stem position corresponds linearly to the amount of air…
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In order for any PID controller to be practical, it must be able to do more than just implement the PID…
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Modern DC and AC motor drives provide features useful when using electric motors as final control elements.…
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Imagine a liquid-level control system for a vessel, where the position of a level-sensing float sets the…
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Virtually any mass above absolute zero temperature emits electromagnetic radiation (photons, or light) as a…
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Process measurements are often of an analog nature: the temperature of a furnace, the rate of fluid flow…
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Perhaps the most basic and necessary protective relay function is overcurrent: commanding a circuit breaker to…
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AC induction motors are based on the principle of a rotating magnetic field produced by a set of stationary…
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There are several different methods useful for causing an AC induction motor to brake, or slow down: DC…
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In addition to directly performing logic functions, electromechanical relays may also be used as interposing…
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A pneumatic controller receives a process variable (PV) signal as a variable air pressure, compares that…
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In order to provide an interface between the internal (digital) world of a computer and the external (analog)…
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An important type of “accessory” relay, especially for legacy electromechanical protective relays,…
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A very simple device used to measure pressure is the manometer: a fluid-filled tube where an applied gas…
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pH is the measurement of the hydrogen ion activity in a liquid solution. It is one of the most common forms of…
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A chemical reaction resulting in a net release of energy is called exothermic. Conversely, a chemical reaction…
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Two extremely important principles in electric circuits were codified by Gustav Robert Kirchhoff in the year…
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Three-phase AC is the dominant mode of electric power generation and distribution in modern societies.…
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Many traditional flowmeter technologies respond to the volumetric flow rate of the moving fluid.…
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A Safety Instrumented Function, or SIF, is one or more components designed to execute a specific…
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Take for instance the problem of measuring fluid flow through a pipe. To the layperson, this may seem to be a…
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In order for any PID controller to be practical, it must be able to do more than just implement the PID…
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Disturbances in the liquid tend to complicate liquid level measurement. These disturbances may result from…
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A technological advance introduced in the late 1980’s was HART, an acronym standing for Highway…
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A 4 to 20 mA current signal represents some signal along a 0 to 100 percent scale. Usually, this scale is…
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Phasors are to AC circuit quantities as polarity is to DC circuit quantities: a way to express the…
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Self-balancing pneumatic instrument mechanisms are very similar to negative-feedback operational amplifier…
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Perhaps the simplest form of solid or liquid level measurement is with a float: a device that rides on the…
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Like so many other industrial data networks, FOUNDATION Fieldbus is an “unswitched” or…
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A number of different sensors used in instrumentation generate DC voltage signals proportional to the process…
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