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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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Temperature Sensor Accessories

Temperature Sensor Accessories

One of the most important accessories for any temperature-sensing element is a pressure-tight sheath known as…


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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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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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Circuit Breakers and Disconnects

Circuit Breakers and Disconnects

Disconnect Switches Disconnects are switches designed to isolate sections of a power system in case of damage…


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Classified Areas and Electrical Safety Measures

Classified Areas and Electrical Safety Measures

Any physical location in an industrial facility harboring the potential of explosion due to the presence of…


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Electromagnetism Basics

Electromagnetism Basics

The fundamental principle of electromagnetism is that an electric current will create a magnetic field at…


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Comparison of  Op-Amp Circuits With Analogous Pneumatic Mechanisms

Comparison of Op-Amp Circuits With Analogous Pneumatic Mechanisms

Self-balancing pneumatic instrument mechanisms are very similar to negative-feedback operational amplifier…


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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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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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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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Valve Failure Modes

Valve Failure Modes

An important design parameter of a control valve is the position it will “fail” to if it loses…


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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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Thermocouple Types, Junctions, Connector and Tip Styles

Thermocouple Types, Junctions, Connector and Tip Styles

RTDs are completely passive sensing elements, requiring the application of an externally-sourced electric…


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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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Feedforward with Dynamic Compensation

Feedforward with Dynamic Compensation

As we have seen, feedforward control is a way to improve the stability of a feedback control system in the…


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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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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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Laser Spectroscopy

Laser Spectroscopy

A laser is a light source emitting waves of light that not only share the exact same frequency (color)…


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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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2-wire (“loop-powered”) Transmitter Current Loops

2-wire (“loop-powered”) Transmitter Current Loops

It is possible to convey electrical power and communicate analog information over the same two wires using 4…


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Temperature Sensor Accessories

Temperature Sensor Accessories

One of the most important accessories for any temperature-sensing element is a pressure-tight sheath known as…


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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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Relay Circuits and Ladder Diagrams

Relay Circuits and Ladder Diagrams

Electromechanical relays may be connected together to perform logic and control functions, acting as logic…


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Antennas and Resonant Circuits (Tank Circuits)

Antennas and Resonant Circuits (Tank Circuits)

Capacitors store energy in electric fields, proportional to the square of voltage. Inductors store energy in…


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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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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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True Mass Flowmeters

True Mass Flowmeters

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


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Periodic Table of the Ions

Periodic Table of the Ions


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References

References

Lipták, Béla G. et al., Instrument Engineers’ Handbook – Process Measurement and Analysis Volume I,…


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Ions in Liquid Solutions

Ions in Liquid Solutions

Many liquid substances undergo a process whereby their constituent molecules split into positively and…


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Pressure-based Flowmeters

Pressure-based Flowmeters

All masses require force to accelerate (we can also think of this in terms of the mass generating a reaction…


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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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Single-line Electrical Diagrams

Single-line Electrical Diagrams

Electrical power grids primarily consist of three-phase AC circuits. This means most power lines (transmission…


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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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Common Educational Fallacies

Common Educational Fallacies

When I began teaching full-time in 1998, most of what I thought I understood about good teaching was actually…


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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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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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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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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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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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Mechanical Vibration Switches

Mechanical Vibration Switches

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


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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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