So far we have just looked at instruments that sense, control, and influence process variables. Transmitters,…
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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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Process measurements are often of an analog nature: the temperature of a furnace, the rate of fluid flow…
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Regardless of valve type, all stem-actuated control valves require some form of seal allowing motion of the…
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It is often useful to express the amplitude of an alternating quantity such as voltage or current in terms…
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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 laser is a light source emitting waves of light that not only share the exact same frequency (color)…
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A variety of technologies exist to measure the quantity of stored material in a vessel. For liquid…
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Capacitors store energy in electric fields, proportional to the square of voltage. Inductors store energy in…
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Light has long been used as a long-range signaling medium. While communication by light through open air is…
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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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When a high-energy photon strikes an atom, it may eject one of the lower-level electrons from its shell,…
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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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Virtually any mass above absolute zero temperature emits electromagnetic radiation (photons, or light) as a…
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Electromechanical relays may be connected together to perform logic and control functions, acting as logic…
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A wise PLC programmer once told me that the first thing any aspiring programmer should learn about the PLC…
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Another category of control strategies involves the use of signal relays or function blocks with the ability…
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As we have seen, feedforward control is a way to improve the stability of a feedback control system in the…
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Any conductor possesses a characteristic called inductance: the ability to store energy in the form of a…
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A great many chemical composition measurements may be made indirectly by means of electricity, if those…
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Those familiar with industrial instrumentation will find much within the electric power industry remarkably…
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Measuring the flow rate of liquid through an open channel is not unlike measuring the flow rate of a liquid…
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In November of 2007 a new computer virus was submitted to a virus scanning service. The purpose of this new…
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Finally, we arrive at the loop diagram (sometimes called a loop sheet) for the compressor surge control system…
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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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Like many other mathematical operations, the derivative and the integral perform inverse operations from each…
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In the United States, the ANSI and IEEE organizations have standardized a set of numerical codes referring to…
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A control strategy similar to ratio control is relation control. This is similar to ratio control in that a…
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Sometimes we encounter a diversity of instrument signal standards in one control system. Such is the case with…
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Using filter cells to eliminate wavelengths associated with interfering gases is called positive filtering in…
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“Polyphase” means “many phases,” describing a form of AC electrical system where…
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A Safety Instrumented Function, or SIF, is one or more components designed to execute a specific…
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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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An electromechanical relay is an electrical switch actuated by an electromagnet coil. As switching devices,…
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Capacitors store energy in electric fields, proportional to the square of voltage. Inductors store energy in…
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Modern analog-to-digital converters are phenomenally accurate, dependable, repeatable, and surprisingly…
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A unique form of technical diagram for describing the abstract functions comprising a control system (e.g. PID…
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A variety of technologies exist to measure the quantity of stored material in a vessel. For liquid…
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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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One of the fundamental laws of electric circuits is Kirchhoff’s Current Law, which states the algebraic…
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The following animation shows how the “rotating” magnetic field of a three-phase AC induction…
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The next level of detail is the Process and Instrument Diagram, or P&ID. Here, we see a “zooming…
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Many traditional flowmeter technologies respond to the volumetric flow rate of the moving fluid.…
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Hydrogen ion activity in aqueous (water-solvent) solutions is a very important parameter for a wide variety of…
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A hand switch is exactly what the name implies: an electrical switch actuated by a person’s hand motion.…
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An interesting parallel to the “unity fraction” unit conversion technique is something referred to…
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(Will be addressed in future versions of this book)
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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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Recall that an exothermic chemical reaction is one that releases a net sum of energy, as opposed to an…
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The key to understanding how three-phase electric motors work is to have an accurate mental picture of 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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Perhaps the most basic and necessary protective relay function is overcurrent: commanding a circuit breaker to…
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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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A special type flowmeter suited for powdered or granular solids is the weighfeeder. One of the most common…
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Control strategies such as cascade, ratio, feedforward, and those containing limit and selector functions can…
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Some problem-solving techniques are unique to quantitative problems, involving mathematical calculations. In…
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A control strategy similar to ratio control is relation control. This is similar to ratio control in that a…
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This section shows some of the many instrument symbols found in different types of technical diagrams used to…
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Up until this point, we have explored various types of instrumentation diagram, each one making reference to…
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Most pneumatic instruments use a simple but highly sensitive mechanism for converting mechanical motion into…
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