Disturbances in the liquid tend to complicate liquid level measurement. These disturbances may result from…
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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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Thermodynamics is the study of heat, temperature, and their related effects in physical systems. As a subject,…
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Virtually any mass above absolute zero temperature emits electromagnetic radiation (photons, or light) as a…
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An important type of “accessory” relay, especially for legacy electromechanical protective relays,…
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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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A machine in the broad sense of the word is any device designed to translate some form of energy into useful…
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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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The disadvantages of pneumatic instruments are painfully evident to anyone familiar with both pneumatic and…
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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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The majority of flowmeter technologies operate on the principle of interpreting fluid flow based on the…
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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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Feedback Control System Components Before we begin our discussion on process control, we must define a few key…
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A number of different sensors used in instrumentation generate DC voltage signals proportional to the process…
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Many years ago, when I was first learning about electricity, I happened to discover a length of coaxial…
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Sensors used to measure vibration come in three basic types: displacement, velocity, and acceleration.…
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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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Mechanical pressure-sensing elements include the bellows, the diaphragm, and the bourdon tube. Each of these…
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Displacer level instruments exploit Archimedes’ Principle to detect liquid level by continuously…
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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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So far we have just looked at instruments that sense, control, and influence process variables. Transmitters,…
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A different strategy for controlling the flow of fluid is to insert a rotary element into the flow path.…
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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 addition to Ohm’s Law, we have a set of rules describing how voltages, currents, and resistances…
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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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A very simple device used to measure pressure is the manometer: a fluid-filled tube where an applied gas…
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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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In addition to directly performing logic functions, electromechanical relays may also be used as interposing…
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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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Diagnostic ability is arguably the most difficult skill to develop within a student, and also the most…
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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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Capacitors store energy in electric fields, proportional to the square of voltage. Inductors store energy in…
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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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Every programmable logic controller must have some means of receiving and interpreting signals from real-world…
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The electrical conductivity of liquids is an important analytical measurement in many industrial processes.…
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Virtually any mass above absolute zero temperature emits electromagnetic radiation (photons, or light) as a…
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Multiple accessories exist for pressure-sensing devices to function optimally in challenging process…
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An electromechanical relay is an electrical switch actuated by an electromagnet coil. As switching devices,…
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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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As described earlier in this chapter, calibration refers to the adjustment of an instrument so its output…
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Temperature measurement devices may be classified into two broad types: contact and non-contact. Contact-type…
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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 exciting development in industrial instrumentation is the WirelessHART radio communication standard,…
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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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A fundamental limitation of proportional control has to do with its response to changes in setpoint and…
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Shown here is a partial listing of principles applied in the subject matter of this chapter, given for the…
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Control valves are supposed to deliver reliable, repeatable control of process fluid flow rate over a wide…
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An interesting parallel to the “unity fraction” unit conversion technique is something referred to…
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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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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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As we have seen, the concept of differentiation is finding the rate-of-change of one variable compared to…
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A technological advance introduced in the late 1980’s was HART, an acronym standing for Highway…
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Two extremely important principles in electric circuits were codified by Gustav Robert Kirchhoff in the year…
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The following photograph shows a large air blower in a wastewater treatment facility equipped with a…
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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 4 to 20 mA current signal represents some signal along a 0 to 100 percent scale. Usually, this scale is…
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An electromechanical relay is an electrical switch actuated by an electromagnet coil. As switching devices,…
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The following animation shows the calculus concepts of differentiation and integration (with respect to time)…
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First, let us review some of the properties of differentials and derivatives, referencing the expression and…
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