In order for any PID controller to be practical, it must be able to do more than just implement the PID…
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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 simple control system drawn in block diagram form looks like this: Information from the measuring device…
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As discussed at the beginning of this chapter, instrumentation safety may be broadly divided into two…
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Perhaps the most important rule of controller tuning is to know the process before attempting to adjust the…
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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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The vast majority of PID controllers in service today are digital in nature. Microprocessors executing PID…
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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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Perhaps the most basic and necessary protective relay function is overcurrent: commanding a circuit breaker to…
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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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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 directly performing logic functions, electromechanical relays may also be used as interposing…
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Non-dispersive analysis, while newer in discovery than dispersive analysis (Isaac Newton’s 17th-century…
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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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Feedback Control System Components Before we begin our discussion on process control, we must define a few key…
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In the United States, the most common language used to program PLCs is Ladder Diagram (LD), also known as…
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An electric motor is often used as a discrete control element in a control system if driving a pump, conveyor…
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The simple PLC ladder diagram (LD) commands consist of contacts and coils, arranged in sequences that mimic…
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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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Imagine a liquid-level control system for a vessel, where the position of a level-sensing float sets the…
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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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Layer 1 of the OSI Reference Model is where we define the “physical” elements of a digital data…
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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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Constructing PID control systems using discrete components is a fairly simple method involving operational…
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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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The advent of “smart” field instruments containing microprocessors has been a great advance for…
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A technological advance introduced in the late 1980’s was HART, an acronym standing for Highway…
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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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The concepts of calibration (trimming) and ranging are often difficult for new students of instrumentation to…
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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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“Feedforward” is a rather under-used control strategy capable of managing a great many types of…
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Disturbances in the liquid tend to complicate liquid level measurement. These disturbances may result from…
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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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It is often useful to express the amplitude of an alternating quantity such as voltage or current in terms…
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Stoichiometry is the accounting of atoms before and after a chemical reaction. It is an expression of the Law…
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Some of the simplest types of digital communication networks found in industry are defined by the EIA…
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Solids tend to expand when heated. The amount that a solid sample will expand with increased temperature…
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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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The fundamental principle of electromagnetism is that an electric current will create a magnetic field at…
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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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