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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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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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Level Sensor Accessories

Level Sensor Accessories

Disturbances in the liquid tend to complicate liquid level measurement. These disturbances may result from…


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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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Vibration Monitoring Hardware

Vibration Monitoring Hardware

The following photograph shows a large air blower in a wastewater treatment facility equipped with a…


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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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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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Feedforward Control

Feedforward Control

“Feedforward” is a rather under-used control strategy capable of managing a great many types of…


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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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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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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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Fiber Optic Data Communication

Fiber Optic Data Communication

Light has long been used as a long-range signaling medium. While communication by light through open air is…


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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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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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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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WirelessHART Radio Communication Standard

WirelessHART Radio Communication Standard

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


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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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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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Pressure Sensor Accessories

Pressure Sensor Accessories

Multiple accessories exist for pressure-sensing devices to function optimally in challenging process…


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Human-Machine Interfaces (HMIs)

Human-Machine Interfaces (HMIs)

Human-machine interfaces, or HMIs, are a critical part of nearly all control systems, complementing the…


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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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Hand Switches and Stackable Switches

Hand Switches and Stackable Switches

A hand switch is exactly what the name implies: an electrical switch actuated by a person’s hand motion.…


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Directional Overcurrent (67) Protection

Directional Overcurrent (67) Protection

While 50 and 51 (instantaneous and time overcurrent) relay functions monitor line current magnitude and guard…


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Fundamental Principles of Industrial Instrumentation

Fundamental Principles of Industrial Instrumentation

Shown here is a partial listing of principles applied in the subject matter of this chapter, given for the…


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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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Circuit Failure Analysis

Circuit Failure Analysis

Perhaps the most valuable skill an instrument technician can possess is the ability to efficiently diagnose…


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Analog Signal Conditioning and Referencing

Analog Signal Conditioning and Referencing

Modern analog-to-digital converters are phenomenally accurate, dependable, repeatable, and surprisingly…


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Relating 4 to 20 mA Signals to Instrument Variables

Relating 4 to 20 mA Signals to Instrument Variables

A 4 to 20 mA current signal represents some signal along a 0 to 100 percent scale. Usually, this scale is…


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Vibration Sensors

Vibration Sensors

Sensors used to measure vibration come in three basic types: displacement, velocity, and acceleration.…


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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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FOUNDATION Fieldbus H1 Protocol Physical Layer

FOUNDATION Fieldbus H1 Protocol Physical Layer

Layer 1 of the OSI Reference Model is where we define the “physical” elements of a digital data…


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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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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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Bi-metal Temperature Sensors

Bi-metal Temperature Sensors

Solids tend to expand when heated. The amount that a solid sample will expand with increased temperature…


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The Stuxnet Virus

The Stuxnet Virus

In November of 2007 a new computer virus was submitted to a virus scanning service. The purpose of this new…


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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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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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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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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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The Concept of Integration

The Concept of Integration

Suppose we wished to measure the consumption of propane over time for a large propane storage tank supplying a…


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