PREFACE
Smart sensors are of great interest in many fields of industry, control systems, biomedical applications, etc. Most books about sensor instrumentation focus on the classical approach to data acquisition, that is the information is in the amplitude of a voltage or a current signal. Only a few book chapters, articles and papers consider data acquisition from digital and quasi-digital sensors. Smart sensors and microsensors increasingly rely on resonant phenomena and variable oscillators, where the information is embedded not in the amplitude but in the frequency or time parameter of the output signal. As a rule, the majority of scientific publications dedicated to smart sensors reflect only the technological achievements of microelectronics. However, modern advanced microsensor technologies require novel advanced measuring techniques.
Because data acquisition and signal processing for smart sensors have not been adequately covered in the literature before, this book aims to fill a significant gap.
This book is based on 40 years of the authors' practical experience in the design and creation of sensor instrumentation as well as the development of novel methods and algorithms for frequency–time-domain measurement, conversion and signal processing. Digital and quasi-digital (frequency, period, duty-cycle, time interval and pulse number output) sensors are covered in this book.
Research results, described in this book, are relevant to the authors' international research in the frame of different R&D projects and International Frequency Sensor Association (IFSA) activity.
Who Should Read this Book?
This book is aimed at PhD students, engineers, scientists and researchers in both academia and industry. It is especially suited for professionals working in the field of measuring instruments and sensor instrumentation as well as anyone facing new challenges in measuring, and those involved in the design and creation of new digital smart physical or chemical sensors and sensor systems. It should also be useful for students wishing to gain an insight into this rapidly expanding area. Our goal is to provide the reader with enough background to understand the novel concepts, principles and systems associated with data acquisition, signal processing and measurement so that they can decide how to optimize their sensor systems in order to achieve the best technical performances at low cost.
How this Book is Organized
This book has been organized into 10 chapters.
Chapter 1, Smart sensors for electrical and non-electrical, physical and chemical quantities: the tendencies and perspectives, describes the main advantages of frequency–time-domain signals as informative parameters for smart sensors. The chapter gives an overview of industrial types of smart sensors and contains classifications of quasi-digital sensors. Digital and quasi-digital (frequency, period, duty-cycle, time interval and pulse number output) sensors are considered.
Chapter 2, Converters for different variables to frequency–time parameters of electric signals, deals with different voltage (current)-to-frequency and capacitance-toperiod (or duty-cycle) converters. Operational principles, technical performances and metrological characteristics of these devices are discussed from a smart sensor point of view in order to produce further conversion in the quasi-digital domain instead of the analog domain. The open and loop (with impulse feedback) structures of such converters are considered. (Figures 2.11, 2.12, 2.13, 2.14, 2.15 and some of the text appearing in Chapter 2, section 2.1, are reproduced from New Architectures of Integrated ADC, PDS ’96 Proceedings. Reproduced by permission of Maciej Nowinski.)
Chapter 3, Data acquisition methods for multichannel sensor systems, covers multichannel sensor systems with cyclical, accelerated and simultaneous sensor polling. Data acquisition methods with time-division and space-division channelling are described. The chapter contains information about how to calculate the time-polling cycle for a sensor and how to analyse the accuracy and speed of data acquisition. Main smart sensor architectures are considered from a data acquisition point of view. Data transmitting and error protection on the basis of quasi-ternary cyclic coding is also discussed.
Chapter 4, Methods of frequency-to-code conversion for smart sensors, discusses traditional methods for frequency (period)-to-code conversion, including direct, indirect, combined, interpolation, Fourier conversion-based counting techniques as well as methods for phase-shift-to-code conversion. Such metrological characteristics as quantization error, conversion frequency range and conversion speed as well as advantages and disadvantages for each of the methods are discussed and compared.
Chapter 5, Advanced and self-adapting methods of frequency-to-code conversion, discusses reciprocal, ratiometric, constant elapsed time (CET), M/T, single-buffered, double-buffered and DMA transfer advanced methods. Comparative and cost-effective analyses are given. Frequency ranges, quantization errors, time of measurement and other metrological performances as well as hardware and software requirements for realization from a smart sensor point of view are described. This chapter is very important because it also deals with the concepts, principles and nature of novel self-adapting methods of dependent count (MDC) and the method with non-redundant reference frequency. The chapter covers main metrological performances including accuracy, conversion time, frequency range as well as software and hardware for MDC realization. Advanced conversion methods for frequencies ratio, deviations and phase shifts are also described. Finally, some practical examples and modelling results are presented.
Chapter 6, Signal processing for quasi-digital smart sensors, deals with the main frequency signal manipulations including multiplication, division, addition, subtraction, derivation, integration and scaling. Particular attention has been paid to new methods of frequency multiplication and scaling with the aim of frequency signal unification. Different wave shapes (sine wave, sawtooth, triangular and rectangular) of a sensor's output are considered. It is also shown how the weight function averaging can be used for noise and quantization error reduction.
Chapter 7, Digital output smart sensors with software-controlled performances and functional capabilities, discusses program-oriented methods for frequency-, period-, duty-cycle-, time-interval-, phase-shift- and pulse-number-to-code conversion and digital smart sensors. The design methodology for optimal program-oriented conversion methods, correction of systematic errors and the modified method of algorithms merging are considered. Examples are given. This chapter also describes specific errors and features.
Chapter 8, Multichannel intelligent and virtual sensor systems, describes smart sensor systems with time- and space-division frequency channelling. Both are based on the method of dependent count. Comparative analysis is given. Performances and features are illustrated by an ABS smart sensor microsystem example. Multiparameters sensors are also considered. The chapter includes information about virtual sensor instrumentation and how to estimate the total error of arranged system. Definitions and examples (temperature, pressure, rotation speed virtual instruments) are given.
Chapter 9, Smart Sensor Design at Software level, deals with embedded microcontroller set instruction minimization for metering applications (to save chip area) and low-power design techniques–optimal low-power programming (for power consumption reduction). Many practical ‘hints’ (e.g. instruction selection and ordering, jump, call and cycle optimization, etc.), recommendations and examples are given.
Chapter 10, Smart sensor buses and interface circuits, describes sensor buses and network protocols from the smart sensor point of view. Modern sensor interface circuits are discussed. Particular attention has been given to the Universal Transducer Interface (UTI) and Time-to-Digital Converter (TDC), which allow low-cost interfacing with different analog sensors elements such as Pt resistors, thermistors, potentiometer resistors, capacitors, resistive bridges, etc. and convert analog sensor signals to the quasi-digital domain (duty-cycle or time interval).
Finally, we discuss what the future might bring.
References. Apart from books, articles and papers, this section includes a large collection of appropriate Internet links, collected from the Sensors Web Portal launched by the authors.