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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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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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Pressure Sensor Accessories

Pressure Sensor Accessories

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


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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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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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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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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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The s Variable: Euler’s Relation and Phasor Expressions of Waveforms

The s Variable: Euler’s Relation and Phasor Expressions of Waveforms

A powerful mathematical concept useful for analyzing practically any physical system – electrical…


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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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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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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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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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Analytical Measurements of Chemical Compositions

Analytical Measurements of Chemical Compositions

A great many chemical composition measurements may be made indirectly by means of electricity, if those…


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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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Pneumatic Actuator Response

Pneumatic Actuator Response

A limitation inherent to pneumatic valve actuators is the amount of air flow required to or from the actuator…


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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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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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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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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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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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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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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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Flow Switches

Flow Switches

A flow switch is one that detects the flow of some fluid through a pipe. Flow switches often use…


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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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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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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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Introduction to Optical Analysis

Introduction to Optical Analysis

Light is known to interact with matter in very specific ways, which may be exploited as a means of measuring…


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On/off Shut-off Valves

On/off Shut-off Valves

An on/off valve is the fluid equivalent of an electrical switch: a device that either allows unimpeded flow or…


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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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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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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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Flow Measurement from Differential Pressure

Flow Measurement from Differential Pressure

In our first signal characterization example, we tackle the problem of measuring fluid flow through a pipe. To…


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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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An Analogy for Calibration Vs Ranging

An Analogy for Calibration Vs Ranging

The concepts of calibration (trimming) and ranging are often difficult for new students of instrumentation to…


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Tube and Tube Fittings

Tube and Tube Fittings

Tube, like pipe, is a hollow structure designed to provide an enclosed pathway for fluids to flow. In the case…


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Displacement and Displacer Level Instrumentation

Displacement and Displacer Level Instrumentation

Displacer level instruments exploit Archimedes’ Principle to detect liquid level by continuously…


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The Concept of Differentiation

The Concept of Differentiation

Suppose we wished to measure the rate of propane gas flow through a hose to a torch: Flowmeters appropriate…


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Atomic Theory and Chemical Symbols

Atomic Theory and Chemical Symbols

The three “elementary” particles of matter comprising all atoms are electrons, protons, and…


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Mathematical Problem-solving Techniques

Mathematical Problem-solving Techniques

Some problem-solving techniques are unique to quantitative problems, involving mathematical calculations. In…


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Digital PID Algorithms

Digital PID Algorithms

Instrument technicians should not have to concern themselves over the programming details internal to digital…


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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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Electrical Sensors: Potential Transformers (PTs) and Current Transformers (CTs)

Electrical Sensors: Potential Transformers (PTs) and Current Transformers (CTs)

The two “process variables” we rely on most heavily in the field of electrical measurement and…


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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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Techniques for Analyzing Control Strategies

Techniques for Analyzing Control Strategies

Control strategies such as cascade, ratio, feedforward, and those containing limit and selector functions can…


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