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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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Continuous Float Level Transmitters

Continuous Float Level Transmitters

Perhaps the simplest form of solid or liquid level measurement is with a float: a device that rides on the…


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Ultrasonic (Sound) Echo Level Measurement

Ultrasonic (Sound) Echo Level Measurement

A completely different way of measuring liquid level in vessels is to bounce a traveling wave off the surface…


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FOUNDATION Fieldbus H1 Protocol Segment Troubleshooting

FOUNDATION Fieldbus H1 Protocol Segment Troubleshooting

Feedback obtained from industrial users of FF reveal a common pattern: Fieldbus is a powerful and reliable…


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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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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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FOUNDATION Fieldbus Design Philosophy

FOUNDATION Fieldbus Design Philosophy

To understand just how different FOUNDATION Fieldbus is from other digital instrument systems, consider a…


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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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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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Distance (21) Protection

Distance (21) Protection

A form of protection against faults on long-distance power lines is called distance relaying, so named because…


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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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Measuring Electrical Conductivity

Measuring Electrical Conductivity

The electrical conductivity of liquids is an important analytical measurement in many industrial processes.…


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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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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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WirelessHART Radio Communication Standard

WirelessHART Radio Communication Standard

An exciting development in industrial instrumentation is the WirelessHART radio communication standard,…


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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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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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Dispersive Spectroscopy

Dispersive Spectroscopy

The dispersion of visible light into its constituent colors goes all the way back to the 17th century with…


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Proportional-only Offset

Proportional-only Offset

A fundamental limitation of proportional control has to do with its response to changes in setpoint and…


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Pneumatic PID Controllers

Pneumatic PID Controllers

A pneumatic controller receives a process variable (PV) signal as a variable air pressure, compares that…


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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-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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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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Calibration Procedures in Linear, Non-Linear and Discrete Instruments

Calibration Procedures in Linear, Non-Linear and Discrete Instruments

As described earlier in this chapter, calibration refers to the adjustment of an instrument so its output…


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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 Calculus

Introduction to Calculus

Calculus. Few areas of mathematics are as powerfully useful in describing and analyzing the physical…


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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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Zero and Span Adjustments (Analog Instruments)

Zero and Span Adjustments (Analog Instruments)

Linearity of Measurement Instruments The purpose of calibration is to ensure the input and output of an…


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Tuning PID Controllers

Tuning PID Controllers

Learning how to tune PID controllers is a skill born of much practice. Regardless of how thoroughly you may…


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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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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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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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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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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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Mechanical Vibration Switches

Mechanical Vibration Switches

A much simpler alternative to continuous vibration sensors (displacement or acceleration) and monitoring…


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Pneumatic PID Controllers

Pneumatic PID Controllers

A pneumatic controller receives a process variable (PV) signal as a variable air pressure, compares that…


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Gas Filter Correlation (GFC) Spectroscopy

Gas Filter Correlation (GFC) Spectroscopy

Using filter cells to eliminate wavelengths associated with interfering gases is called positive filtering in…


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Indicators, Recorders, Process Switches and Alarms

Indicators, Recorders, Process Switches and Alarms

So far we have just looked at instruments that sense, control, and influence process variables. Transmitters,…


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PID Control Terminology

PID Control Terminology

PID control can be a confusing concept to understand. Here, a brief summary of each term within PID (P. I, and…


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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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Positive Displacement Flowmeters

Positive Displacement Flowmeters

A positive displacement flowmeter is a cyclic mechanism built to pass a fixed volume of fluid through with…


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