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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Perhaps the most basic and necessary protective relay function is overcurrent: commanding a circuit breaker to…
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In addition to directly performing logic functions, electromechanical relays may also be used as interposing…
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A bridge circuit is basically a pair of voltage dividers where the circuit output is taken as the difference…
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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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AC induction motors are based on the principle of a rotating magnetic field produced by a set of stationary…
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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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In the United States, the most common language used to program PLCs is Ladder Diagram (LD), also known as…
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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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DC electric motors generate torque by a reaction between two magnetic fields: one field established by…
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Virtually any mass above absolute zero temperature emits electromagnetic radiation (photons, or light) as a…
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Non-dispersive analysis, while newer in discovery than dispersive analysis (Isaac Newton’s 17th-century…
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A limit switch detects the physical motion of an object by direct contact with that object. An example of 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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Negative feedback systems, in general, tend to cause confusion for those first learning their fundamental…
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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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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 important rule of controller tuning is to know the process before attempting to adjust the…
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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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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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An engineer named Bob Metcalfe conceived the idea of Ethernet in 1973, while working for the Xerox research…
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The final element of PID control is the “D” term, which stands for derivative. This is a calculus…
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Some analyzers measure the composition of a process stream by directly immersing the sensing element in that…
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So far we have just looked at instruments that sense, control, and influence process variables. Transmitters,…
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A limit switch detects the physical motion of an object by direct contact with that object. An example of a…
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Like many other mathematical operations, the derivative and the integral perform inverse operations from each…
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By definition, a source is a device delivering energy into a system, while a load is a device extracting…
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Disconnect Switches Disconnects are switches designed to isolate sections of a power system in case of damage…
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As defined previously, calibration means the comparison and adjustment (if necessary) of an instrument’s…
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To show a practical process example, let’s examine three diagrams for a compressor control system,…
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The following animation shows the calculus concepts of differentiation and integration (with respect to time)…
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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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In order to provide an interface between the internal (digital) world of a computer and the external (analog)…
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Light is known to interact with matter in very specific ways, which may be exploited as a means of measuring…
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The vast majority of modern process transmitters (both analog and digital) come equipped with a feature known…
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At the root of successful system diagnosis is a rigorous adherence to scientific reasoning. There exists no…
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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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Temperature measurement devices may be classified into two broad types: contact and non-contact. Contact-type…
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There are multiple motives for compromising the security of an industrial control system, some of which…
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