Finally, we arrive at the loop diagram (sometimes called a loop sheet) for the compressor surge control system…
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A powerful mathematical concept useful for analyzing practically any physical system – electrical…
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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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A temperature switch is one detecting the temperature of some substance. Temperature switches often use…
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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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Regardless of valve type, all stem-actuated control valves require some form of seal allowing motion of the…
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Linearity of Measurement Instruments The purpose of calibration is to ensure the input and output of an…
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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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The fundamental principle of electromagnetism is that an electric current will create a magnetic field at…
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A much simpler alternative to continuous vibration sensors (displacement or acceleration) and monitoring…
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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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As defined previously, calibration means the comparison and adjustment (if necessary) of an instrument’s…
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The electrical conductivity of liquids is an important analytical measurement in many industrial processes.…
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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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A chemical reaction resulting in a net release of energy is called exothermic. Conversely, a chemical reaction…
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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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Multiple accessories exist for pressure-sensing devices to function optimally in challenging process…
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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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Learning how to tune PID controllers is a skill born of much practice. Regardless of how thoroughly you may…
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Take for instance the problem of measuring fluid flow through a pipe. To the layperson, this may seem to be a…
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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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One of the great benefits of digital technology is the ability to communicate vast amounts of information over…
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Non-dispersive analysis, while newer in discovery than dispersive analysis (Isaac Newton’s 17th-century…
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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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The reason why a pneumatic control valve’s stem position corresponds linearly to the amount of air…
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The efficient identification and correction of instrument calibration errors is an important function for…
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Volumes could be written about poor diagnostic technique. The following mistakes are not intended to comprise…
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Virtually any mass above absolute zero temperature emits electromagnetic radiation (photons, or light) as a…
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Human-machine interfaces, or HMIs, are a critical part of nearly all control systems, complementing the…
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Control strategies such as cascade, ratio, feedforward, and those containing limit and selector functions can…
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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 bridge circuit is basically a pair of voltage dividers where the circuit output is taken as the difference…
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Imagine a major marathon race, where hundreds of runners gather in one place to compete. When the starting gun…
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“Polyphase” means “many phases,” describing a form of AC electrical system where…
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An extremely important topic in engineering is that of transfer functions. Simply defined, a transfer function…
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One of the most important accessories for any temperature-sensing element is a pressure-tight sheath known as…
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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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Although it seems each model of PLC has its own idiosyncratic standard for programming, there does exist an…
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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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One of the fundamental laws of electric circuits is Kirchhoff’s Current Law, which states the algebraic…
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Most of these formulae appear in molecular chemical form rather than structural form. For example, ethanol…
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A number of different sensors used in instrumentation generate DC voltage signals proportional to the process…
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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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Light is known to interact with matter in very specific ways, which may be exploited as a means of measuring…
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Current is the name we give to the motion of electric charges from a point of high potential to a point of low…
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A very common method for directly controlling low flow rates of fluids is to use a device known as a metering…
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The concepts of calibration (trimming) and ranging are often difficult for new students of instrumentation to…
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Take for instance the problem of measuring fluid flow through a pipe. To the layperson, this may seem to be a…
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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 Ohm’s Law, we have a set of rules describing how voltages, currents, and resistances…
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The following photograph shows a large air blower in a wastewater treatment facility equipped with a…
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The digital multimeter (DMM) is quite possibly the most useful tool in the instrument technician’s…
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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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Sample sizes of chemical substances are often measured in moles. One mole of a substance is defined as a…
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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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The majority of flowmeter technologies operate on the principle of interpreting fluid flow based on the…
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A great many chemical composition measurements may be made indirectly by means of electricity, if those…
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Mechanical pressure-sensing elements include the bellows, the diaphragm, and the bourdon tube. Each of these…
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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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An on/off valve is the fluid equivalent of an electrical switch: a device that either allows unimpeded flow or…
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