Auxiliary and Lockout (86) Relays

An important type of “accessory” relay, especially for legacy electromechanical protective relays,…

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Conservation Laws

The Law of Mass Conservation states that matter can neither be created nor destroyed. The Law of Energy…

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The Concept of Integration

Suppose we wished to measure the consumption of propane over time for a large propane storage tank supplying a…

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Capacitive Level Measurement

Capacitive level instruments measure electrical capacitance of a conductive rod inserted vertically into a…

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Difference Between Calibration and Re-ranging

What is Calibration? To calibrate an instrument means to check and adjust (if necessary) its response so the…

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FOUNDATION Fieldbus Design Philosophy

To understand just how different FOUNDATION Fieldbus is from other digital instrument systems, consider a…

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AC Motor Speed Control

AC induction motors are based on the principle of a rotating magnetic field produced by a set of stationary…

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Phasor Analysis of Transformer Circuits

Three-phase AC is the dominant mode of electric power generation and distribution in modern societies.…

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True Mass Flowmeters

Many traditional flowmeter technologies respond to the volumetric flow rate of the moving fluid.…

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Insertion Flowmeters

This section does not describe a particular type of flowmeter, but rather a design that may be implemented for…

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Variable-area Flowmeters

An variable-area flowmeter is one where the fluid must pass through a restriction whose area increases with…

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Temperature Sensor Accessories

One of the most important accessories for any temperature-sensing element is a pressure-tight sheath known as…

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Instrument Identification Tags

Up until this point, we have explored various types of instrumentation diagram, each one making reference to…

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Metric Prefixes and Prefix Scale

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Supervisory Control

In a manually-controlled process, a human operator directly actuates some form of final control element…

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Molecular Quantities

Sample sizes of chemical substances are often measured in moles. One mole of a substance is defined as a…

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Concepts and Laws of Probability

While the term “probability” may evoke images of imprecision, probability is in fact an exact…

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Limit Switches

A limit switch detects the physical motion of an object by direct contact with that object. An example of a…

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The HART Digital/Analog Hybrid Standard

A technological advance introduced in the late 1980’s was HART, an acronym standing for Highway…

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Circuit Failure Analysis

Perhaps the most valuable skill an instrument technician can possess is the ability to efficiently diagnose…

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