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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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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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Disassembling a Globe Valve

Disassembling a Globe Valve

The following collection of photographs chronicles the complete disassembly of a Fisher E-body globe valve…


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Fluid Power Systems

Fluid Power Systems

Given the ability of pressurized fluids to transmit force over long distances, it is not surprising that many…


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Analysis of Practical Pneumatic Instruments

Analysis of Practical Pneumatic Instruments

To better understand the design and operation of self-balancing pneumatic mechanisms, it is helpful to examine…


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Teaching Diagnostic Principles and Practices

Teaching Diagnostic Principles and Practices

Diagnostic ability is arguably the most difficult skill to develop within a student, and also the most…


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Dampers and Louvres

Dampers and Louvres

A damper (otherwise known as a louvre) is a multi-element flow control device generally used to throttle large…


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Displacement and Displacer Level Instrumentation

Displacement and Displacer Level Instrumentation

Displacer level instruments exploit Archimedes’ Principle to detect liquid level by continuously…


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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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What is Hydrostatic Pressure?

What is Hydrostatic Pressure?

A vertical column of fluid generates a pressure at the bottom of the column owing to the action of gravity on…


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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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Tube and Tube Fittings

Tube and Tube Fittings

Tube, like pipe, is a hollow structure designed to provide an enclosed pathway for fluids to flow. In the case…


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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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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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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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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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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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Solenoid Valves

Solenoid Valves

A very common form of on/off valve used for pneumatic and hydraulic systems alike is the solenoid valve. A…


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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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Cascade Control

Cascade Control

A simple control system drawn in block diagram form looks like this: Information from the measuring device…


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Chromatography: Methods, Detectors and Species

Chromatography: Methods, Detectors and Species

Imagine a major marathon race, where hundreds of runners gather in one place to compete. When the starting gun…


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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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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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Heuristic PID Tuning Procedures

Heuristic PID Tuning Procedures

In contrast to quantitative tuning procedures where definite numerical values for P, I, and D controller…


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Pipe and Pipe Fittings

Pipe and Pipe Fittings

Pipe is a hollow structure designed to provide an enclosed pathway for fluids to flow, usually manufactured…


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Learn Fundamental Principles, not Procedures

Learn Fundamental Principles, not Procedures

“As to methods there may be a million and then some, but principles are few. The man who grasps…


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The s Variable: Euler’s Relation and Phasor Expressions of Waveforms

The s Variable: Euler’s Relation and Phasor Expressions of Waveforms

A powerful mathematical concept useful for analyzing practically any physical system – electrical…


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Difference Between Calibration and Re-ranging

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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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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Process/Instrument Suitability

Process/Instrument Suitability

Every flow-measuring instrument exploits a physical principle to measure the flow rate of fluid stream.…


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Disassembling a Globe Valve

Disassembling a Globe Valve

The following collection of photographs chronicles the complete disassembly of a Fisher E-body globe valve…


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Null-balance Voltage Measurement

Null-balance Voltage Measurement

A number of different sensors used in instrumentation generate DC voltage signals proportional to the process…


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Memory Maps and I/O Addressing

Memory Maps and I/O Addressing

A wise PLC programmer once told me that the first thing any aspiring programmer should learn about the PLC…


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Understanding the Calculus Concepts of Differentiation and Integration

Understanding the Calculus Concepts of Differentiation and Integration

The following animation shows the calculus concepts of differentiation and integration (with respect to time)…


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Teaching Diagnostic Principles and Practices

Teaching Diagnostic Principles and Practices

Diagnostic ability is arguably the most difficult skill to develop within a student, and also the most…


Textbook

What is Hydrostatic Pressure?

What is Hydrostatic Pressure?

A vertical column of fluid generates a pressure at the bottom of the column owing to the action of gravity on…


Textbook

Instantaneous and Time-overcurrent (50/51) Protection

Instantaneous and Time-overcurrent (50/51) Protection

Perhaps the most basic and necessary protective relay function is overcurrent: commanding a circuit breaker to…


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Control Valve Sizing

Control Valve Sizing

When control valves operate between fully open and fully shut, they serve much the same purpose in process…


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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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the Negative Consequences of Poor PID Controller Tuning

the Negative Consequences of Poor PID Controller Tuning

Much has been written about the benefits of robust PID control. Increased productivity, decreased equipment…


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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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Thermistors and Resistance Temperature Detectors (RTDs)

Thermistors and Resistance Temperature Detectors (RTDs)

One of the simplest classes of temperature sensor is one where temperature effects a change in electrical…


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P, I, and D Responses Graphed

P, I, and D Responses Graphed

Visualizing the actions of P, I, and D tuning parameters using graphs is extremely useful in predicting the…


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