When control valves operate between fully open and fully shut, they serve much the same purpose in process…
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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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Many years ago, when I was first learning about electricity, I happened to discover a length of coaxial…
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The term “grid” refers to the conductors and equipment interconnecting power sources to power…
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RTDs are completely passive sensing elements, requiring the application of an externally-sourced electric…
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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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Any conductor possesses a characteristic called inductance: the ability to store energy in the form of a…
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Electrical Resistance Resistance (\(R\)) is the dissipative opposition to an electric current, analogous to…
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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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A form of protection against faults on long-distance power lines is called distance relaying, so named because…
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The disadvantages of pneumatic instruments are painfully evident to anyone familiar with both pneumatic and…
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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 simple control system drawn in block diagram form looks like this: Information from the measuring device…
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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 powerful mathematical concept useful for analyzing practically any physical system – electrical…
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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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Diagnostic ability is arguably the most difficult skill to develop within a student, and also the most…
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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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A very simple device used to measure pressure is the manometer: a fluid-filled tube where an applied gas…
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In modern industry, the most popular form of field-level signal transmission for variable industrial…
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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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By definition, a source is a device delivering energy into a system, while a load is a device extracting…
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Like so many other industrial data networks, FOUNDATION Fieldbus is an “unswitched” or…
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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 fluid is any substance having the ability to flow: to freely change shape and move under the influence of a…
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Any physical location in an industrial facility harboring the potential of explosion due to the presence of…
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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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Multiple accessories exist for pressure-sensing devices to function optimally in challenging process…
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pH is the measurement of the hydrogen ion activity in a liquid solution. It is one of the most common forms of…
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Perhaps the most valuable skill an instrument technician can possess is the ability to efficiently diagnose…
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Modern analog-to-digital converters are phenomenally accurate, dependable, repeatable, and surprisingly…
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DC electric motors generate torque by a reaction between two magnetic fields: one field established by…
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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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A completely different way of measuring liquid level in vessels is to bounce a traveling wave off the surface…
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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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A level switch is one detecting the level of liquid or solid (granules or powder) in a vessel. Level switches…
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Using filter cells to eliminate wavelengths associated with interfering gases is called positive filtering in…
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Classical mechanics (often called Newtonian mechanics in honor of Isaac Newton) deal with forces and motions…
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The concepts of calibration (trimming) and ranging are often difficult for new students of instrumentation to…
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In this section I will show screenshots from a process loop simulation program illustrating the effectiveness…
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An extremely important topic in engineering is that of transfer functions. Simply defined, a transfer function…
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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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Modern analog-to-digital converters are phenomenally accurate, dependable, repeatable, and surprisingly…
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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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A Safety Instrumented Function, or SIF, is one or more components designed to execute a specific…
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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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Developed by the Modicon company (the original manufacturer of the Programmable Logic Controller, or PLC) in…
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“Feedforward” is a rather under-used control strategy capable of managing a great many types of…
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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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Linearity of Measurement Instruments The purpose of calibration is to ensure the input and output of an…
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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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Nearly every technical course teaches and tests students on definitions, basic concepts, and at least some…
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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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In contrast to quantitative tuning procedures where definite numerical values for P, I, and D controller…
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Using filter cells to eliminate wavelengths associated with interfering gases is called positive filtering in…
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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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The very purpose of physics is to quantitatively describe and explain the physical world in as few terms as…
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DC electric current signals may also be used to communicate process measurement information from transmitters…
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A number of different sensors used in instrumentation generate DC voltage signals proportional to the process…
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Labwork is an essential part of any science-based curriculum. Here, much improvement may be made over the…
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