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Electrical Sources and Electronic Load

Electrical Sources and Electronic Load

By definition, a source is a device delivering energy into a system, while a load is a device extracting…


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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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Troubleshooting Current Loops

Troubleshooting Current Loops

A fundamental principle in instrumentation system troubleshooting is that every instrument has at least one…


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Digital Multimeter (DMM) Tips and Tricks

Digital Multimeter (DMM) Tips and Tricks

The digital multimeter (DMM) is quite possibly the most useful tool in the instrument technician’s…


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Concepts and Laws of Probability

Concepts and Laws of Probability

While the term “probability” may evoke images of imprecision, probability is in fact an exact…


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Basics of Bridge Circuits

Basics of Bridge Circuits

A bridge circuit is basically a pair of voltage dividers where the circuit output is taken as the difference…


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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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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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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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Input/Output (I/O) Capabilities of PLCs

Input/Output (I/O) Capabilities of PLCs

Every programmable logic controller must have some means of receiving and interpreting signals from real-world…


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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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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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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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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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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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Null-balance Voltage Measurement

Null-balance Voltage Measurement

A number of different sensors used in instrumentation generate DC voltage signals proportional to the process…


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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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Root Mean Square (RMS) Quantities

Root Mean Square (RMS) Quantities

It is often useful to express the amplitude of an alternating quantity such as voltage or current in terms…


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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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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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Common Control Valve Problems

Common Control Valve Problems

Valves can experience a number of problems, most of them either preventable or repairable. These problems can…


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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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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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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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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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4 to 20 mA Analog Current Signals

4 to 20 mA Analog Current Signals

In modern industry, the most popular form of field-level signal transmission for variable industrial…


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Pneumatic Sensing Elements

Pneumatic Sensing Elements

Most pneumatic instruments use a simple but highly sensitive mechanism for converting mechanical motion into…


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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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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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Process Flow Diagrams

Process Flow Diagrams

To show a practical process example, let’s examine three diagrams for a compressor control system,…


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Level Switches

Level Switches

A level switch is one detecting the level of liquid or solid (granules or powder) in a vessel. Level switches…


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How to Teach Yourself PLC Programming

How to Teach Yourself PLC Programming

Learning PLC programming is a very important skill. If your job involves programming, then you will likely…


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Chemical Reactor Temperature Control Example

Chemical Reactor Temperature Control Example

Sometimes we encounter a diversity of instrument signal standards in one control system. Such is the case with…


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What is Internet Protocol (IP)?

What is Internet Protocol (IP)?

I remember first learning about the world-wide Internet, and wondering what it actually looked like. The first…


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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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Change-of-quantity Flow Measurement

Change-of-quantity Flow Measurement

Flow, by definition, is the passage of material from one location to another over time. So far this chapter…


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Derivative (Rate) Control

Derivative (Rate) Control

The final element of PID control is the “D” term, which stands for derivative. This is a calculus…


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Electrical Signal and Control Wiring

Electrical Signal and Control Wiring

There is much to be said for neatness of assembly in electrical signal wiring. Even though the electrons…


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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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Fluorescence Measurement

Fluorescence Measurement

When a high-energy photon strikes an atom, it may eject one of the lower-level electrons from its shell,…


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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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Weight-based Level Measurement

Weight-based Level Measurement

Weight-based level instruments sense process level in a vessel by directly measuring the weight of the vessel.…


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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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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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