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Authors of various books published with Artech House Publishing blog about current topics in microwave technology that are covered in their recent books.

How inductive sensors work – from basics to advanced applications with Sorin Fericean

June 8, 2020

Sorin Fericean’s book, Inductive Sensors for Industrial Applications, primarily deals with sensors containing inductive primary sensing elements.  “Inductive” is one of most widely used elements in the market (see Section 3.4) and the author acted mainly in the R & D, manufacturing and tests fields for inductive sensors for more than 25 years.

A volume for all experts in inductive sensors industry

It is absolutely necessary to underline the universality of this technical reference book. The VOLUME implicitly ADDRESSES ALL SENSORS EXPERTS having industrial sensor preoccupations, either through industrial applications or due to the activity in sensor design and validation, manufacturing and tests, sales and marketing, etc., at different levels.

The Artech House Insider Blog excellently distinguishes some main attributes of the volume, namely:

  • Useful for professionals and students;
  • Comprehensive description of every chapter beginning with classical, traditional solutions and ending with state-of-the art realizations;
  • Consistent application in parallel of three evaluation methods: analytic computation, graphical methods but particularly computer assisted tools;
  • Plethora of numerical examples;
  • Abundance of specified commercial components (electronics, materials, soft-tools).

In addition to this 360 degree-view reading, in this post, the author would like to give a book presentation from a new different perspective, responding to the question: “What are the benefits offered to the professionals who deal with miscellaneous sensors like capacitive, ultrasonic, photoelectric, magnetic, microwave based, etc.”?

Review and order the book Inductive Sensors for Industrial Applications .

Key benefits for professionals from the basics to advanced industry applications for inductive sensors – a book overview

Looking at this enumeration, the volume should cover a large theoretical and practical knowledge area relative to the industrial sensors, and that is fulfilled. This challenge is better recognized if the book content is divided in four virtual parts.

Inductive sensors basics  – Which are the features of the industrial sensors, in general, and of the inductive sensors, in particular?

The first two chapters theoretically cover the first PartChapter 1 reviews the basics and the definitions of the position or displacement of the inductive sensors but also of other sensor types. Section 1.3 summarizes the main features (supply conditionssensing rangehysteresis, sensitivity and nonlinearity, accuracy, resolution, and repeatability, etc). They are valid for all the aforementioned sensors. In technical publications and specifications of sensor providers there are several divergent definitions and interpretations of some sensor performances. The author succeeded in offering a general review of these features but also of the characterizing parameters regarding the sensor output types, temperature and dynamic behaviors. Moreover, the proposed lexicon is based on the international standards which are valid world-wide and will systematically be used in the book.

Subsequently, Chapter 2 addresses the people who need more terms and definitions in order to evaluate an inductive sensor from a practical point of view but – again – also another type of sensors/other types of sensors. Applications with these devices are advantageous and reliable in all application fields, beginning with the traditional industries and ending with medicine or aerospace. That is the reason for the larger volume of technical references regarding the contactless methods and products: standards, papers and white papers, catalogues and flyers, etc.

Resuming, the goal of the first chapter is to provide preliminary basics – let’s say academic terms – relative to the sensors for industrial applications in general, and regarding the inductive sensors in particular. This information generally represents theoretical and metrological profound knowledge. They are necessary but not sufficient. At the same time, terms and definitions with distinctive engineering and practical character are very important.

Now, chapter 2 refers to the international and/or national standards, which are highly suitable information sources for the sensors. The interoperability with several automation systems requires the fulfillment of a wide variety of standard demands regarding operation parameters and conditions, electromagnetic compatibility (EMC) and electromagnetic influence (EMI), CE Mark for the European Union countries, shock and vibration, etc. These requirements are minutely described in this chapter and have to be meticulously followed.

On the other hand, these publications are extensive. For this reason, the author offers a complete but compact summary of the product standards (Section 2.1). The same is valid for the basic and sensor specific electromagnetic compatibility and interference (EMC/EMI) in Section 2.2. Finally, very specific features, such as shock and vibrations, international protection classes for dirt, dust and humidity as well as the reliability and availability are subjects of the next sections of Chapter 2.

Functionality and technology of inductive sensors

The second Part of the Inductive Sensors for Industrial Applications book is effectively more specific to inductive sensors and debuts with Chapter 3. At the beginning, a large overview tries to comprise all classes of inductive sensorsSeven main types are presented with deep details (structure, operation, characteristic formulae, but also records of the electromagnetic fields and sensor features that are offered by running a field simulator – Maxwell Software from Ansoft, concretely). The chapter ends with statistics of the global sensor market and some relevant submarkets, which overviews the author’s summaries of ten extensive market research studies and reports.

The physics of the inductive sensors, i.e. the implemented methods to evaluate the target influence on the sensor’s primary sensing element by monitoring of different magnitudes (inductance, impedance, admittance and immittance, quality factor, etc.), are described in Chapter 4 using modern methods (complex representations, frequency dependences, Smith charts). How to measure these parameters and the suitable procedures implemented in inductive sensors is a second important aspect of this chapter.

Finally, as already mentioned before, the book dives into the world of the modern computer-assisted analysis and synthesis. A state-of-the-art application of the electromagnetic field analysis based on the word-wide known Maxwell-Ansys field simulator is described step-by-step in Section 4.3. Starting with the fundamentals of a computer-aided electromagnetic field simulation (Maxwell’s equations as well as constitutive relations and material definitions), the section explains how the simulator solves the field to compute the primary field quantities (magnetic and electric field intensities, induction, magnetic vector potential, electric current density, etc.) and how the equivalent physical values (AC-resistance, inductance, impedance, etc.) can finally be calculated. Certainly, to consolidate this profound knowledge, a numerical example leads the reader through the preprocessing, processing and postprocessing computation levels.

A such approach is singular, compact and partially original. Similarly, comparative basic knowledge is difficult to find in professional publications.

Designers, manufacturers and users of sensors for industrial applications need information about inductors in several embodiment versions. Chapter 5 seeks to give in a compact presentation formula the knowledge base (construction, inductance calculation, loses computation, impedance with its general equivalent electrical circuit) of the fundamental inductors (solenoid, toroid), and derivative shapes with or without magnetic cores (wire-wound coils, PCB printed flat spiral coils, integrated COS coils on silicon substrate and active gyrators).

Similar to miscellaneous suppliers, the producer of magnetic materials for coil cores and plungers offers a large informational support. In Chapter 6, the author summarizes several worldwide known sources and deals with the three most important components: ferrites, Permalloy and Mu-metals and soft iron alloys, respectively. The record of parameter definitions (16 at least), materials properties and metallurgy manufacturing processes, as well as the established standardized shapes should be sufficient for the broad audience.

What are the component electronic parts of the industrial sensors? And applications.

The third Part of the book addresses the evaluation electronics of the inductive sensors, and also the entire extremely wide family of sensors for industrial applications, starting with capacitive, thermal, optical, magnetic, chemical, etc. sensors and ending with microwave, gas and electrolytic conductivity meters. This book part has a dominant position and extension (277 pages from 525 pages, totally) and consists of the following seven chapters:

  • Chapter 7 succeeds in the aggregation of all possible, realistic sensor block diagrams into a universal generic functional diagram. The evolutive versions of electronics that partially or fully embody these functionalities and topologies are amply described: discrete electronics (in the 70s, 80s up to the present, exceptionally for low-cost products), integrated electronics (bipolar or MOS metal-oxide semiconductors technologies), realizations with single- or multi-ASICs (application specific integrated circuit), SOC structures (system-on-chip) and – last but not least – prospective SDS-embodiments (software-defined sensor) are discussed in this chapter;
  • Chapter 8 dives in the profound knowledge of the oscillators. The electronic oscillator is the core piece of every inductive sensor. At the same time, evaluation electronics of the otherwise sensor majority contain an oscillator. For this reason, the chapter is an interesting part of the book. Researching into the worldwide professional publications, a significant number of knowledge sources regarding the oscillators’ structure and operation can be found. Unfortunately, the reader has real difficulty in finding references relative to the theoretical basics of this electronic centerpiece. The author identified suchlike fundamental books and compactly summarized herewith the theory of resonant LC circuits (series versus parallel) as well as the general theory of the oscillators (harmonic, linear with losses and with losses cancellation oscillator). Subsequently, the chapter describes almost all classical but also up-to-date current LC-oscillators and functional generators (e.g. the worldwide famous circuit 555) giving analytical and practical descriptions and characteristics. PSpice simulation tool is applied, naturally;
  • Chapter 9 addresses electronic circuits, which are essential for each and every sensor, namely:
    • Signal amplifiers;
    • Precision AC/DC signal converters;
    • Sample-and-Hold systems;
    • Signal linearization systems;
    • Comparators, window discriminators;
    • Regenerative comparators (Triggers);
    • PLL Phase-Locked Loop circuits;
    • DAC Digital-to-Analog and ADC Analog-to-Digital Converters;

In a similar way to the previous chapters, the functional description of the numerous electronic circuits is attended by computation formula and also by applied classical graphic methods (frequency response, Bode plot, Nyquist diagram, etc.). Analog but also digital solutions are effectively discussed.

  • Chapter 10 covers the circuits for the sensor output signal Independent of their output type: analog (voltage, current or ratiometric voltage) or digital, respectively, the sensors for industrial applications have to fulfil rugged requirements. The chapter reviews these features and presents large scale implemented circuits in this field, the majority being ASICs (application specific integrated circuits);
  • Chapter 11 examines the functionality and embodiments (series or shunt regulators), which convert the external supply power into internal, sensor suitable supply voltages. In parallel, the chapter shows high-level silicon-integrated solutions to perform the mandatory sensor protections against accidental evil supply conditions (over-voltages and high-energetic SURGE pulses on the supply lines, open-wire or reverse polarity protections);
  • Chapter 12 deals with the first action to be done if the sensor achieves the end of the production line, i.e. the adjustment and/or calibration. The challenge is to compensate the sample deviations of the rough sensors yielded by the line and to adjust these in such a way that the features, in general, and the sensor characteristic (output as a function of the physical measurand), in particular, fulfil the sensor specification and standard demands. This adjustment is very often applied acting upon a sensor electronic component (trimmable resistor, potentiometer, ) placed on the sensor carrier board and accessible before the sensor case is definitely closed. This procedure is a physical handicap for many sensor types, because the influence of the next constructive sensor changes; for instance, the presence of the body housing is no more compensated. The book intends to implement high-intelligent integrated trimming ASICs and exemplifies more possible versions. The fourth patent-protected teach-in solution is the author’s design and has been running for a long time with excellent, consistent and stable results, offering a sensor characteristic retention during a sensor permanent use more than 20 years;
  • Chapter 13 overviews a task, which is basically implemented in every sensor, namely the temperature compensation. Several sensor components, particularly the sensing elements, show temperature dependences that should internally be compensated in order to prevent or reduce the temperature drift of the sensor features. The sensing temperature device is the front part of signal compensation chain, hence the chapter starts with the presentation of conventional passive probes (NTC and PTC thermistor) as well as active temperature-dependent (VBE and PTAT) or temperature-independent references (bandgap). The sensor-internal hardware and software perform either passive or active temperature compensation. For the active procedure, the preliminary teach-in of the required behavior of the compensation unit and their subsequent workflow during the normal sensor operation are detailed by showing a concrete ASIC implementation for this task.

Intelligent sensor networks – more on AS Interface and IO-Link

The fourth Part of the book deals with a very topical matter and that is the networking of the intelligent sensors. The chapter name relates to inductive sensors, despite the fact that its content refers to all types of sensors for industrial applications. The chapter starts with an introductory section regarding the data communication systems. The reader can hereby find basic information about communication networks (more than 25 industrial communication systems are overviewed in a table), network access proceduresindustrial fieldbuses and the ISO/OSI network reference modelProfessional publications amply present the systems used on the superior layers of the ISO – 7 Layer – Stack (InterBus, PROFIBUS, CAN, etc.). The current networks applied on the sensor specific inferior layers, namely physical layer and data link layer, experience the lower resonance of the technical references. For this reason, the book focuses on two up-to-date networks for these layers (AS Interface and IO-Link).

After a 500-pages long diving into the sensor world, the volume ends with important information for the reader, namely lists with acronyms and abbreviationsnomenclature of electromagnetic quantities, and the index.

A book with essential knowledge on all sensors for industrial applications

The Inductive Sensors for Industrial Applications book makes good reading. A just-enough reminder about traditional electronic solutions that also includes a view of the modern digital implementations with increased software share. Many chapters dive into the microscopic world of the ASICs and show detailed layout images in parallel to the macroscopic presentation of the block diagram and electronic schematics.

After this book digest, the author believes the reader can easily conclude that the first, third and fourth Parts (Chapters 1 to 3 and 7 to 12) exceptionally fulfill the users’ , designers’, manufacturers’, marketing and sales people’s need of knowledge, which deal with all sensors for industrial applications.

For purchasing the book please go to our US website  or our UK website.

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