Control strategies such as cascade, ratio, feedforward, and those containing limit and selector functions can…
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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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Suppose we wished to measure the rate of propane gas flow through a hose to a torch: Flowmeters appropriate…
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Programmable logic controllers are essentially nothing more than special-purpose, industrial computers. As…
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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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In a manually-controlled process, a human operator directly actuates some form of final control element…
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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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Calculus has a reputation for being difficult to learn, and with good reason. The traditional approach to…
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Sensors used to measure vibration come in three basic types: displacement, velocity, and acceleration.…
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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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In addition to Ohm’s Law, we have a set of rules describing how voltages, currents, and resistances…
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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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Human-machine interfaces, or HMIs, are a critical part of nearly all control systems, complementing the…
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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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In some process applications, it is important that the control valve be able to completely stop fluid flow…
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A pressure switch is one detecting the presence of fluid pressure. Pressure switches often use diaphragms or…
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A proximity switch is one detecting the proximity (closeness) of some object. By definition, these switches…
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Weight-based level instruments sense process level in a vessel by directly measuring the weight of the vessel.…
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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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A unique form of differential pressure-based flow measurement deserves its own section in this flow…
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A limitation inherent to pneumatic valve actuators is the amount of air flow required to or from the actuator…
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An important design parameter of a control valve is the position it will “fail” to if it loses…
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In addition to Ohm’s Law, we have a set of rules describing how voltages, currents, and resistances…
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Human-machine interfaces, or HMIs, are a critical part of nearly all control systems, complementing the…
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A sliding-stem valve body is one where the moving parts slide with a linear motion. Some examples of…
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So far we have just looked at instruments that sense, control, and influence process variables. Transmitters,…
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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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While 50 and 51 (instantaneous and time overcurrent) relay functions monitor line current magnitude and guard…
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As defined previously, calibration means the comparison and adjustment (if necessary) of an instrument’s…
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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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Most people reading this book have likely had the experience of adjusting water temperature using two hand…
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An electromechanical relay is an electrical switch actuated by an electromagnet coil. As switching devices,…
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Every programmable logic controller must have some means of receiving and interpreting signals from real-world…
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A laser is a light source emitting waves of light that not only share the exact same frequency (color)…
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Filled-bulb systems exploit the principle of fluid expansion to measure temperature. If a fluid is enclosed in…
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Circuit breakers used in residential, commercial, and light industrial service are self-tripping devices: they…
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The fundamental principle of electromagnetism is that an electric current will create a magnetic field at…
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Tube, like pipe, is a hollow structure designed to provide an enclosed pathway for fluids to flow. In the case…
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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 reason why a pneumatic control valve’s stem position corresponds linearly to the amount of air…
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Layer 1 of the OSI Reference Model is where we define the “physical” elements of a digital data…
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An variable-area flowmeter is one where the fluid must pass through a restriction whose area increases with…
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An important type of “accessory” relay, especially for legacy electromechanical protective relays,…
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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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The following animation shows a rotating phasor in three-dimensional form. The phasor rotates in a complex…
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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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A great many precision instruments use the principle of balance to measure some quantity. Perhaps the simplest…
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Any power grid large enough to meet the demand of an entire nation must have multiple generators drawing from…
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A temperature switch is one detecting the temperature of some substance. Temperature switches often use…
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These fortifications focus on human behavior rather than system design or component selection. In some ways…
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All masses require force to accelerate (we can also think of this in terms of the mass generating a reaction…
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Suppose we wished to measure the consumption of propane over time for a large propane storage tank supplying a…
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In addition to Ohm’s Law, we have a set of rules describing how voltages, currents, and resistances…
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Three-phase AC is the dominant mode of electric power generation and distribution in modern societies.…
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There are multiple motives for compromising the security of an industrial control system, some of which…
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Constructing PID control systems using discrete components is a fairly simple method involving operational…
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So far we have just looked at instruments that sense, control, and influence process variables. Transmitters,…
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RTDs are completely passive sensing elements, requiring the application of an externally-sourced electric…
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While the term “probability” may evoke images of imprecision, probability is in fact an exact…
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One of the simplest classes of temperature sensor is one where temperature effects a change in electrical…
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