A much simpler alternative to continuous vibration sensors (displacement or acceleration) and monitoring…
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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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Self-balancing pneumatic instrument mechanisms are very similar to negative-feedback operational amplifier…
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While 50 and 51 (instantaneous and time overcurrent) relay functions monitor line current magnitude and guard…
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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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A proximity switch is one detecting the proximity (closeness) of some object. By definition, these switches…
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Capacitors store energy in electric fields, proportional to the square of voltage. Inductors store energy in…
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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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Another category of control strategies involves the use of signal relays or function blocks with the ability…
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Perhaps the most confusing aspect of discrete sensors is the definition of a sensor’s normal status.…
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“Polyphase” means “many phases,” describing a form of AC electrical system where…
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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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The electrical conductivity of liquids is an important analytical measurement in many industrial processes.…
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In this section I will show screenshots from a process loop simulation program illustrating the effectiveness…
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Circuit breakers used in residential, commercial, and light industrial service are self-tripping devices: they…
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Electromechanical relays may be connected together to perform logic and control functions, acting as logic…
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A vertical column of fluid generates a pressure at the bottom of the column owing to the action of gravity on…
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A fundamental principle in instrumentation system troubleshooting is that every instrument has at least one…
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A pneumatic controller receives a process variable (PV) signal as a variable air pressure, compares that…
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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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Phasors are to AC circuit quantities as polarity is to DC circuit quantities: a way to express the…
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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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There is much to be said for neatness of assembly in electrical signal wiring. Even though the electrons…
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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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Measuring the flow rate of liquid through an open channel is not unlike measuring the flow rate of a liquid…
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Every programmable logic controller must have some means of receiving and interpreting signals from real-world…
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Capacitance Any two electrical conductors separated by an insulating medium possess the characteristic called…
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DC electric current signals may also be used to communicate process measurement information from transmitters…
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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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A limitation inherent to pneumatic valve actuators is the amount of air flow required to or from the actuator…
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Every flow-measuring instrument exploits a physical principle to measure the flow rate of fluid stream.…
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In modern industry, the most popular form of field-level signal transmission for variable industrial…
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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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An important type of “accessory” relay, especially for legacy electromechanical protective relays,…
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The fundamental principle of electromagnetism is that an electric current will create a magnetic field at…
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A powerful mathematical concept useful for analyzing practically any physical system – electrical…
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Perhaps the most confusing aspect of discrete sensors is the definition of a sensor’s normal status.…
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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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A number of different sensors used in instrumentation generate DC voltage signals proportional to the process…
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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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Many years ago, when I was first learning about electricity, I happened to discover a length of coaxial…
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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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Recall that an exothermic chemical reaction is one that releases a net sum of energy, as opposed to an…
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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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A Safety Instrumented Function, or SIF, is one or more components designed to execute a specific…
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The disadvantages of pneumatic instruments are painfully evident to anyone familiar with both pneumatic and…
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A great many chemical composition measurements may be made indirectly by means of electricity, if those…
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An important legacy technology for all kinds of continuous measurement is the self-balancing system. A…
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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 Law of Continuity for fluids states that the product of mass density (\(\rho\)), cross-sectional pipe area…
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I remember first learning about the world-wide Internet, and wondering what it actually looked like. The first…
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Capacitance Any two electrical conductors separated by an insulating medium possess the characteristic called…
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Perhaps the most basic and necessary protective relay function is overcurrent: commanding a circuit breaker to…
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Capacitive level instruments measure electrical capacitance of a conductive rod inserted vertically into a…
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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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All substances are comprised of various elements in various combinations and proportions. Elements may thus be…
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Flow, by definition, is the passage of material from one location to another over time. So far this chapter…
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Temperature measurement devices may be classified into two broad types: contact and non-contact. Contact-type…
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Creative Commons Attribution 4.0 International Public License By exercising the Licensed Rights (defined…
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Most of these formulae appear in molecular chemical form rather than structural form. For example, ethanol…
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