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Split-Range Control

Split-Range Control

There are many process control applications in the industry where it is desirable to have multiple control…


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Calibration Standards to Produce and Measure Physical Quantities

Calibration Standards to Produce and Measure Physical Quantities

As previously defined, calibration refers to the checking and adjustment of an instrument so that its output…


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Analyzer Sample Systems

Analyzer Sample Systems

Some analyzers measure the composition of a process stream by directly immersing the sensing element in that…


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Comparison of  Op-Amp Circuits With Analogous Pneumatic Mechanisms

Comparison of Op-Amp Circuits With Analogous Pneumatic Mechanisms

Self-balancing pneumatic instrument mechanisms are very similar to negative-feedback operational amplifier…


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Rotary-stem Valves

Rotary-stem Valves

A different strategy for controlling the flow of fluid is to insert a rotary element into the flow path.…


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Sliding-stem Valves

Sliding-stem Valves

A sliding-stem valve body is one where the moving parts slide with a linear motion. Some examples of…


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Basics of Electrical Current

Basics of Electrical Current

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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Overpressure Protection Devices

Overpressure Protection Devices

Fluid pressure exerts force on any surface area it contacts, as described by the formula \(F = PA\). One…


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Pneumatic Actuator Response

Pneumatic Actuator Response

A limitation inherent to pneumatic valve actuators is the amount of air flow required to or from the actuator…


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Fluorescence Measurement

Fluorescence Measurement

When a high-energy photon strikes an atom, it may eject one of the lower-level electrons from its shell,…


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Circuit Breakers and Disconnects

Circuit Breakers and Disconnects

Disconnect Switches Disconnects are switches designed to isolate sections of a power system in case of damage…


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What are Simple Machines?

What are Simple Machines?

A machine in the broad sense of the word is any device designed to translate some form of energy into useful…


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Control Valve Actuators

Control Valve Actuators

The purpose of a control valve actuator is to provide the motive force to operate a valve mechanism. Both…


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Common Control Valve Problems

Common Control Valve Problems

Valves can experience a number of problems, most of them either preventable or repairable. These problems can…


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Valve Failure Modes

Valve Failure Modes

An important design parameter of a control valve is the position it will “fail” to if it loses…


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Ratio Control

Ratio Control

Most people reading this book have likely had the experience of adjusting water temperature using two hand…


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Valve Positioners

Valve Positioners

The reason why a pneumatic control valve’s stem position corresponds linearly to the amount of air…


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Mathematical Problem-solving Techniques

Mathematical Problem-solving Techniques

Some problem-solving techniques are unique to quantitative problems, involving mathematical calculations. In…


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Proper Care and Feeding of Pneumatic Instruments

Proper Care and Feeding of Pneumatic Instruments

Perhaps the most important rule to obey when using pneumatic instruments is to maintain clean and dry…


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Legal Code

Legal Code

Creative Commons Attribution 4.0 International Public License By exercising the Licensed Rights (defined…


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Valve Packing

Valve Packing

Regardless of valve type, all stem-actuated control valves require some form of seal allowing motion of the…


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Stoichiometry and the Law of Mass Conservation

Stoichiometry and the Law of Mass Conservation

Stoichiometry is the accounting of atoms before and after a chemical reaction. It is an expression of the Law…


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Motives for Compromising the Security of an Industrial Control System

Motives for Compromising the Security of an Industrial Control System

There are multiple motives for compromising the security of an industrial control system, some of which…


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AC Motor Speed Control

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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Safety Gas Analyzers

Safety Gas Analyzers

Process analyzers measure the concentration of specific substances for the purpose of measuring and/or…


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Glossary of Cyber-security Terms

Glossary of Cyber-security Terms

Cyber-security seems to have its own vocabulary, ranging from unwieldy technical acronyms to slang terms…


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The Stuxnet Virus

The Stuxnet Virus

In November of 2007 a new computer virus was submitted to a virus scanning service. The purpose of this new…


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General Problem-solving Techniques

General Problem-solving Techniques

A variety of problem-solving techniques have been presented for students over the years which are all helpful…


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Safety Instrumented Functions and Systems

Safety Instrumented Functions and Systems

A Safety Instrumented Function, or SIF, is one or more components designed to execute a specific…


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Introduction to Inductors and Inductance

Introduction to Inductors and Inductance

Any conductor possesses a characteristic called inductance: the ability to store energy in the form of a…


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Flow Measurement in Open Channels

Flow Measurement in Open Channels

Measuring the flow rate of liquid through an open channel is not unlike measuring the flow rate of a liquid…


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Ladder Diagram (LD) Structure Commands

Ladder Diagram (LD) Structure Commands

The simple PLC ladder diagram (LD) commands consist of contacts and coils, arranged in sequences that mimic…


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Valve Seat Leakage

Valve Seat Leakage

In some process applications, it is important that the control valve be able to completely stop fluid flow…


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Control Valve Characterization

Control Valve Characterization

Control valves are supposed to deliver reliable, repeatable control of process fluid flow rate over a wide…


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Error Corrections

Error Corrections

Abdelaziz, Ahmed (June 2014) Identified numerous typographical errors throughout the book, mostly repeated…


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Common Diagnostic Mistakes in Control Systems

Common Diagnostic Mistakes in Control Systems

Volumes could be written about poor diagnostic technique. The following mistakes are not intended to comprise…


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Design-based Fortifications

Design-based Fortifications

A design-based fortification is one rooted in technical details of system architecture and functionality. Some…


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Hand Switches and Stackable Switches

Hand Switches and Stackable Switches

A hand switch is exactly what the name implies: an electrical switch actuated by a person’s hand motion.…


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Digital Multimeter (DMM) Tips and Tricks

Digital Multimeter (DMM) Tips and Tricks

The digital multimeter (DMM) is quite possibly the most useful tool in the instrument technician’s…


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Interposing Relays in PLCs

Interposing Relays in PLCs

In addition to directly performing logic functions, electromechanical relays may also be used as interposing…


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Analyzer Sample Systems

Analyzer Sample Systems

Some analyzers measure the composition of a process stream by directly immersing the sensing element in that…


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Force-balance Pressure Transmitters

Force-balance Pressure Transmitters

An important legacy technology for all kinds of continuous measurement is the self-balancing system. A…


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How Derivatives and Integrals Relate to One Another

How Derivatives and Integrals Relate to One Another

Like many other mathematical operations, the derivative and the integral perform inverse operations from each…


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Process and Instrument Diagrams

Process and Instrument Diagrams

The next level of detail is the Process and Instrument Diagram, or P&ID. Here, we see a “zooming…


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Loop Diagrams (Loop Sheets)

Loop Diagrams (Loop Sheets)

Finally, we arrive at the loop diagram (sometimes called a loop sheet) for the compressor surge control system…


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Process Flow Diagrams

Process Flow Diagrams

To show a practical process example, let’s examine three diagrams for a compressor control system,…


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Radiation Level Measurement

Radiation Level Measurement

Certain types of nuclear radiation easily penetrates the walls of industrial vessels, but is attenuated by…


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Fundamental Principles of Industrial Instrumentation

Fundamental Principles of Industrial Instrumentation

Shown here is a partial listing of principles applied in the subject matter of this chapter, given for the…


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Functional Diagrams: the Flow of Information within a Control System

Functional Diagrams: the Flow of Information within a Control System

A unique form of technical diagram for describing the abstract functions comprising a control system (e.g. PID…


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Flow Switches

Flow Switches

A flow switch is one that detects the flow of some fluid through a pipe. Flow switches often use…


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Instrument and Process Equipment Symbols

Instrument and Process Equipment Symbols

This section shows some of the many instrument symbols found in different types of technical diagrams used to…


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What is Electrical Power?

What is Electrical Power?

Since we often use electricity to convey energy from one location to another, it is important to be able to…


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New Content

New Content

Coy, John J. et. al. (December 2012) Sampled graphic illustrations from his NASA Reference Publication…


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Rotating Magnetic Fields in Three-phase AC Induction Motors

Rotating Magnetic Fields in Three-phase AC Induction Motors

The following animation shows how the “rotating” magnetic field of a three-phase AC induction…


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Differential Pressure Transmitters

Differential Pressure Transmitters

One of the most common, and most useful, pressure measuring instruments in industry is the differential…


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Molecular Quantities

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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Non-dispersive Luft Detector Spectroscopy

Non-dispersive Luft Detector Spectroscopy

Non-dispersive analysis, while newer in discovery than dispersive analysis (Isaac Newton’s 17th-century…


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Proximity Switches

Proximity Switches

A proximity switch is one detecting the proximity (closeness) of some object. By definition, these switches…


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Troubleshooting Current Loops

Troubleshooting Current Loops

A fundamental principle in instrumentation system troubleshooting is that every instrument has at least one…


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On/off Shut-off Valves

On/off Shut-off Valves

An on/off valve is the fluid equivalent of an electrical switch: a device that either allows unimpeded flow or…


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