Learn about Modbus function codes, the structure of Modbus message packets, and the various types of channels used to transmit Modbus telegrams between controllers.
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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 bridge circuit is basically a pair of voltage dividers where the circuit output is taken as the difference…
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“Radio” systems use electromagnetic fields to communicate information over long distances through…
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Programmable logic controllers are essentially nothing more than special-purpose, industrial computers. As…
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At the next OSI Reference Model layer (layer 4) is a set of protocols specifying how reliable communication…
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An exciting development in industrial instrumentation is the WirelessHART radio communication standard,…
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Light has long been used as a long-range signaling medium. While communication by light through open air is…
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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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A flow switch is one that detects the flow of some fluid through a pipe. Flow switches often use…
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This animation shows the basic operation of a gas chromatograph, showing the separation of different molecular…
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Multiple accessories exist for pressure-sensing devices to function optimally in challenging process…
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A much simpler alternative to continuous vibration sensors (displacement or acceleration) and monitoring…
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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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Up until this point, we have explored various types of instrumentation diagram, each one making reference to…
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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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Imagine a liquid-level control system for a vessel, where the position of a level-sensing float directly sets…
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The next level of detail is the Process and Instrument Diagram, or P&ID. Here, we see a “zooming…
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In reliability engineering, it is important to be able to quantity the reliability (or conversely, the…
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Suppose we wished to measure the consumption of propane over time for a large propane storage tank supplying a…
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Creative Commons Attribution 4.0 International Public License By exercising the Licensed Rights (defined…
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Several different technologies exist for the conversion of fluid pressure into an electrical signal response.…
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Valves can experience a number of problems, most of them either preventable or repairable. These problems can…
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To review, voltage is the measure of potential energy available to electric charges. Current is the uniform…
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As we have seen, the concept of integration is finding the accumulation of one variable multiplied by another…
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“Radio” systems use electromagnetic fields to communicate information over long distances through…
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An electromechanical relay is an electrical switch actuated by an electromagnet coil. As switching devices,…
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A damper (otherwise known as a louvre) is a multi-element flow control device generally used to throttle large…
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Perhaps the most valuable skill an instrument technician can possess is the ability to efficiently diagnose…
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Visualizing the actions of P, I, and D tuning parameters using graphs is extremely useful in predicting 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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Suppose we wished to measure the consumption of propane over time for a large propane storage tank supplying a…
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When I began teaching full-time in 1998, most of what I thought I understood about good teaching was actually…
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The term “grid” refers to the conductors and equipment interconnecting power sources to power…
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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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An electric motor is often used as a discrete control element in a control system if driving a pump, conveyor…
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A great many precision instruments use the principle of balance to measure some quantity. Perhaps the simplest…
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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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Like so many other industrial data networks, FOUNDATION Fieldbus is an “unswitched” or…
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One of the marks of a successful problem-solver is a habit of applying general principles to every new problem…
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Human-machine interfaces, or HMIs, are a critical part of nearly all control systems, complementing the…
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There are many process control applications in the industry where it is desirable to have multiple control…
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Perhaps the most basic and necessary protective relay function is overcurrent: commanding a circuit breaker to…
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Certain types of nuclear radiation easily penetrates the walls of industrial vessels, but is attenuated by…
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The electrical conductivity of liquids is an important analytical measurement in many industrial processes.…
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To understand just how different FOUNDATION Fieldbus is from other digital instrument systems, consider a…
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Cyber-security seems to have its own vocabulary, ranging from unwieldy technical acronyms to slang terms…
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