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Proportional-only Control

Proportional-only Control

Imagine a liquid-level control system for a vessel, where the position of a level-sensing float directly sets…


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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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Proximity Switches

Proximity Switches

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


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Instrument Identification Tags

Instrument Identification Tags

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


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True Mass Flowmeters

True Mass Flowmeters

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


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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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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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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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Input/Output (I/O) Capabilities of PLCs

Input/Output (I/O) Capabilities of PLCs

Every programmable logic controller must have some means of receiving and interpreting signals from real-world…


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Velocity-based Flowmeters

Velocity-based Flowmeters

The Law of Continuity for fluids states that the product of mass density (\(\rho\)), cross-sectional pipe area…


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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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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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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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Root Mean Square (RMS) Quantities

Root Mean Square (RMS) Quantities

It is often useful to express the amplitude of an alternating quantity such as voltage or current in terms…


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4-wire (“self-powered”) Transmitter Current Loops

4-wire (“self-powered”) Transmitter Current Loops

DC electric current signals may also be used to communicate process measurement information from transmitters…


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Laminar Flowmeters

Laminar Flowmeters

A unique form of differential pressure-based flow measurement deserves its own section in this flow…


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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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Insertion Flowmeters

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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Pressure Switches

Pressure Switches

A pressure switch is one that detects the presence of fluid pressure. Pressure switches often use diaphragms…


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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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Auxiliary and Lockout (86) Relays

Auxiliary and Lockout (86) Relays

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


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Logic Programming in PLCs

Logic Programming in PLCs

Although it seems each model of PLC has its own idiosyncratic standard for programming, there does exist an…


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Analog to Digital Conversion and ADCs

Analog to Digital Conversion and ADCs

In order to provide an interface between the internal (digital) world of a computer and the external (analog)…


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Techniques for Analyzing Control Strategies

Techniques for Analyzing Control Strategies

Control strategies such as cascade, ratio, feedforward, and those containing limit and selector functions can…


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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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The Basics of Control Relays

The Basics of Control Relays

An electromechanical relay is an electrical switch actuated by an electromagnet coil. As switching devices,…


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Digital Representation of Text

Digital Representation of Text

Binary patterns are not just able to represent numerical values. Given a standardized code, they may represent…


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Using Manometers for Measuring Pressure

Using Manometers for Measuring Pressure

A very simple device used to measure pressure is the manometer: a fluid-filled tube where an applied gas…


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Numerical Integration

Numerical Integration

As we have seen, the concept of integration is finding the accumulation of one variable multiplied by another…


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National Institute of Standards and Technology (NIST) Traceability

National Institute of Standards and Technology (NIST) Traceability

As defined previously, calibration means the comparison and adjustment (if necessary) of an instrument’s…


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Transfer Function Analysis

Transfer Function Analysis

An extremely important topic in engineering is that of transfer functions. Simply defined, a transfer function…


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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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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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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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Introduction to Protective Relaying

Introduction to Protective Relaying

Circuit breakers used in residential, commercial, and light industrial service are self-tripping devices: they…


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DC Motor Speed Control

DC Motor Speed Control

DC electric motors generate torque by a reaction between two magnetic fields: one field established by…


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Filled-bulb Temperature Sensors

Filled-bulb Temperature Sensors

Filled-bulb systems exploit the principle of fluid expansion to measure temperature. If a fluid is enclosed in…


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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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Input/Output (I/O) Capabilities of PLCs

Input/Output (I/O) Capabilities of PLCs

Every programmable logic controller must have some means of receiving and interpreting signals from real-world…


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Material Volume Measurement

Material Volume Measurement

A variety of technologies exist to measure the quantity of stored material in a vessel. For liquid…


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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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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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Electrical Pressure Elements

Electrical Pressure Elements

Several different technologies exist for the conversion of fluid pressure into an electrical signal response.…


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Use of Line Reactors

Use of Line Reactors

Regulating the electric power sent to an electric motor is a task performed by high-speed switching…


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Analytical Measurements of Chemical Compositions

Analytical Measurements of Chemical Compositions

A great many chemical composition measurements may be made indirectly by means of electricity, if those…


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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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The Difference Between Series and Parallel Circuits

The Difference Between Series and Parallel Circuits

In addition to Ohm’s Law, we have a set of rules describing how voltages, currents, and resistances…


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Understanding the “Normal” Status of a Process Switch

Understanding the “Normal” Status of a Process Switch

Perhaps the most confusing aspect of discrete sensors is the definition of a sensor’s normal status.…


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Input/Output (I/O) Capabilities of PLCs

Input/Output (I/O) Capabilities of PLCs

Every programmable logic controller must have some means of receiving and interpreting signals from real-world…


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Understanding Electrical Power Grids

Understanding Electrical Power Grids

The term “grid” refers to the conductors and equipment interconnecting power sources to power…


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Dimensional Analysis

Dimensional Analysis

An interesting parallel to the “unity fraction” unit conversion technique is something referred to…


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Equivalent Series and Parallel Circuits

Equivalent Series and Parallel Circuits

Impedance in a series circuit is the orthogonal sum of resistance and reactance: \[Z = \sqrt{R^2 + (X_L -…


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Conservation Laws

Conservation Laws

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


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Pilot Valves and Pneumatic Amplifying Relays

Pilot Valves and Pneumatic Amplifying Relays

Self-balancing mechanisms consisting solely of a baffle/nozzle detector coupled to a feedback bellows, while…


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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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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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Formulae for Common Chemical Compounds

Formulae for Common Chemical Compounds

Most of these formulae appear in molecular chemical form rather than structural form. For example, ethanol…


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Periodic Table of the Elements

Periodic Table of the Elements

All substances are comprised of various elements in various combinations and proportions. Elements may thus be…


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Teaching Technical Theory

Teaching Technical Theory

Learning is not merely a process of information transfer. It is first and foremost a transformation of…


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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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