A limit switch detects the physical motion of an object by direct contact with that object. An example of a…
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Virtually any mass above absolute zero temperature emits electromagnetic radiation (photons, or light) as a…
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An electric motor is often used as a discrete control element in a control system if driving a pump, conveyor…
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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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Although it seems each model of PLC has its own idiosyncratic standard for programming, there does exist an…
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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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In addition to directly performing logic functions, electromechanical relays may also be used as interposing…
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Negative feedback systems, in general, tend to cause confusion for those first learning their fundamental…
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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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Process measurements are often of an analog nature: the temperature of a furnace, the rate of fluid flow…
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Non-dispersive analysis, while newer in discovery than dispersive analysis (Isaac Newton’s 17th-century…
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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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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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The simple PLC ladder diagram (LD) commands consist of contacts and coils, arranged in sequences that mimic…
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Perhaps the most basic and necessary protective relay function is overcurrent: commanding a circuit breaker to…
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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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Regulating the electric power sent to an electric motor is a task performed by high-speed switching…
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The vast majority of PID controllers in service today are digital in nature. Microprocessors executing PID…
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DC electric motors generate torque by a reaction between two magnetic fields: one field established by…
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As discussed at the beginning of this chapter, instrumentation safety may be broadly divided into two…
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Imagine a liquid-level control system for a vessel, where the position of a level-sensing float directly sets…
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Valve actuators provide force to move control valve trim. For precise positioning of a control valve, there…
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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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Control strategies such as cascade, ratio, feedforward, and those containing limit and selector functions can…
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Linearity of Measurement Instruments The purpose of calibration is to ensure the input and output of an…
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Most of these formulae appear in molecular chemical form rather than structural form. For example, ethanol…
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In our first signal characterization example, we tackle the problem of measuring fluid flow through a pipe. To…
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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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Stoichiometry is the accounting of atoms before and after a chemical reaction. It is an expression of the Law…
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An interesting parallel to the “unity fraction” unit conversion technique is something referred to…
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Mechanical pressure-sensing elements include the bellows, the diaphragm, and the bourdon tube. Each of these…
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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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While the term “probability” may evoke images of imprecision, probability is in fact an exact…
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Thermodynamics is the study of heat, temperature, and their related effects in physical systems. As a subject,…
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The disadvantages of pneumatic instruments are painfully evident to anyone familiar with both pneumatic and…
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Perhaps the most basic and necessary protective relay function is overcurrent: commanding a circuit breaker to…
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A fluid is any substance having the ability to flow: to freely change shape and move under the influence of a…
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The following animation shows a rotating phasor in three-dimensional form. The phasor rotates in a complex…
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The Law of Mass Conservation states that matter can neither be created nor destroyed. The Law of Energy…
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When control valves operate between fully open and fully shut, they serve much the same purpose in process…
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