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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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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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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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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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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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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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Understanding How Three-phase Electric Motors Work

Understanding How Three-phase Electric Motors Work

The key to understanding how three-phase electric motors work is to have an accurate mental picture of the…


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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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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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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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Digital Representation of Numerical Data

Digital Representation of Numerical Data

Process measurements are often of an analog nature: the temperature of a furnace, the rate of fluid flow…


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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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High-reliability Control Systems

High-reliability Control Systems

As discussed at the beginning of this chapter, instrumentation safety may be broadly divided into two…


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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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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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Understanding How Three-phase Electric Motors Work

Understanding How Three-phase Electric Motors Work

The key to understanding how three-phase electric motors work is to have an accurate mental picture of the…


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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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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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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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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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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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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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“Normal” status of a Process Switch

“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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Supervisory Control

Supervisory Control

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


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The HART Digital/Analog Hybrid Standard

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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Introduction to Modbus

Introduction to Modbus

Developed by the Modicon company (the original manufacturer of the Programmable Logic Controller, or PLC) in…


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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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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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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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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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Transmission Control Protocol (TCP) and User Datagram Protocol (UDP)

Transmission Control Protocol (TCP) and User Datagram Protocol (UDP)

At the next OSI Reference Model layer (layer 4) is a set of protocols specifying how reliable communication…


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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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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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