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On/off Electric Motor Control Circuits

On/off Electric Motor Control Circuits

An electric motor is often used as a discrete control element in a control system if driving a pump, conveyor…


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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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Phasors, Phase Shift, and Phasor Algebra

Phasors, Phase Shift, and Phasor Algebra

Phasors are to AC circuit quantities as polarity is to DC circuit quantities: a way to express the…


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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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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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Ladder Diagram (LD) Programming Contacts and Coils

Ladder Diagram (LD) Programming Contacts and Coils

In the United States, the most common language used to program PLCs is Ladder Diagram (LD), also known as…


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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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Diagnosing Feedback Control Problems

Diagnosing Feedback Control Problems

Negative feedback systems, in general, tend to cause confusion for those first learning their fundamental…


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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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Controller Output Current Loops

Controller Output Current Loops

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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VSD and VFD Motor Drive Features

VSD and VFD Motor Drive Features

Modern DC and AC motor drives provide features useful when using electric motors as final control elements.…


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Digital PID Controllers

Digital PID Controllers

The vast majority of PID controllers in service today are digital in nature. Microprocessors executing PID…


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Basics of Bridge Circuits

Basics of Bridge Circuits

A bridge circuit is basically a pair of voltage dividers where the circuit output is taken as the difference…


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Integral (Reset) Control

Integral (Reset) Control

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


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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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Non-contact Temperature Sensors

Non-contact Temperature Sensors

Virtually any mass above absolute zero temperature emits electromagnetic radiation (photons, or light) as a…


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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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Self-regulating, Integrating, and Runaway Process Characteristics

Self-regulating, Integrating, and Runaway Process Characteristics

Perhaps the most important rule of controller tuning is to know the process before attempting to adjust the…


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Basic Feedback Control Principles

Basic Feedback Control Principles

Feedback Control System Components Before we begin our discussion on process control, we must define a few key…


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AC Motor Braking

AC Motor Braking

There are several different methods useful for causing an AC induction motor to brake, or slow down: DC…


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Self-balancing Pneumatic Instruments Principles

Self-balancing Pneumatic Instruments Principles

A great many precision instruments use the principle of balance to measure some quantity. Perhaps the simplest…


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Transmitter Damping Adjustments

Transmitter Damping Adjustments

The vast majority of modern process transmitters (both analog and digital) come equipped with a feature known…


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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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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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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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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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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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FOUNDATION Fieldbus H1 Protocol Data Link Layer

FOUNDATION Fieldbus H1 Protocol Data Link Layer

Like so many other industrial data networks, FOUNDATION Fieldbus is an “unswitched” or…


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Resistance, Reactance, and Impedance

Resistance, Reactance, and Impedance

Electrical Resistance Resistance (\(R\)) is the dissipative opposition to an electric current, analogous to…


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Change-of-quantity Flow Measurement

Change-of-quantity Flow Measurement

Flow, by definition, is the passage of material from one location to another over time. So far this chapter…


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Actuator Bench-set

Actuator Bench-set

Valve actuators provide force to move control valve trim. For precise positioning of a control valve, there…


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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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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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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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Transformer Basics and Principles of Operation

Transformer Basics and Principles of Operation

The transformer is one of the most important components in all of AC circuitry. Principally used to…


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Quantitative PID Tuning Procedures

Quantitative PID Tuning Procedures

A quantitative PID tuning procedure is a step-by-step approach leading directly to a set of numerical values…


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Electronic Structure

Electronic Structure

Earlier in this chapter you were shown a model of a nitrogen atom with a dense nucleus (comprised of protons…


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Differential (87) Current Protection

Differential (87) Current Protection

One of the fundamental laws of electric circuits is Kirchhoff’s Current Law, which states the algebraic…


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Introduction to Power System Automation

Introduction to Power System Automation

Those familiar with industrial instrumentation will find much within the electric power industry remarkably…


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Examples of PLC Systems

Examples of PLC Systems

Programmable logic controllers are essentially nothing more than special-purpose, industrial computers. As…


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AC Motor Braking

AC Motor Braking

There are several different methods useful for causing an AC induction motor to brake, or slow down: DC…


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Relation Control

Relation Control

A control strategy similar to ratio control is relation control. This is similar to ratio control in that a…


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4 to 20 mA Analog Current Signals

4 to 20 mA Analog Current Signals

In modern industry, the most popular form of field-level signal transmission for variable industrial…


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Phasor Analysis of Transformer Circuits

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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Controller Output Current Loops

Controller Output Current Loops

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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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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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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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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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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The International System of Units

The International System of Units

The very purpose of physics is to quantitatively describe and explain the physical world in as few terms as…


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Limit Switches

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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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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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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Open-ended, Shorted, and Properly Terminated Transmission Lines

Open-ended, Shorted, and Properly Terminated Transmission Lines

Many years ago, when I was first learning about electricity, I happened to discover a length of coaxial…


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Practical PID Controller Features

Practical PID Controller Features

In order for any PID controller to be practical, it must be able to do more than just implement the PID…


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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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Integral (Reset) Control

Integral (Reset) Control

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


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Standardized Volumetric Flow

Standardized Volumetric Flow

The majority of flowmeter technologies operate on the principle of interpreting fluid flow based on the…


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Chemical Reactor Temperature Control Example

Chemical Reactor Temperature Control Example

Sometimes we encounter a diversity of instrument signal standards in one control system. Such is the case with…


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Pneumatic Sensing Elements

Pneumatic Sensing Elements

Most pneumatic instruments use a simple but highly sensitive mechanism for converting mechanical motion into…


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