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State-of-the-art of battery state-of-charge determination

From the early days of its discovery, humanity has depended on electricity, a phenomenon without which our technological advancements would not have been possible. With the increased need for mobility, people moved to portable power storage—first for wheeled applications, then for portable and finally nowadays wearable use. Several types of rechargeable battery systems, including those of lead–acid, nickel–cadmium, nickel–metal hydride, lithium ion and lithium-ion polymer exist in the market. The most important of them will be discussed in this review. Almost as long as rechargeable batteries have existed, systems able to give an indication about the state-of-charge (SoC) of a battery have been around. Several methods, including those of direct measurements, book-keeping and adaptive systems (Bergveld et al 2002 Battery Management Systems, Design by Modelling (Philips Research Book Series) vol 1 (Boston: Kluwer)) are known in the art for determining the SoC of a cell or battery of cells. An accurate SoC determination method and an understandable and reliable SoC display to the user will improve the performance and reliability, and will ultimately lengthen the lifetime of the battery. However, many examples of poor accuracy and reliability can be found in practice (Bergveld et al 2002, cited above). This review presents an overview on battery technology and the state-of-the-art of SoC methods. The goal of all the presented SoC indication methods is to design an SoC indication system capable of providing an accurate SoC indication under all realistic user conditions, including those of spread—in both battery and user behaviour, a large temperature and current range and ageing of the battery.

State-of-charge indication in portable applications

The known methods of state-of-charge (SoC) indication in portable applications are not accurate enough under all practical conditions. The method presented in this paper aims at designing and testing an SoC indication system capable of predicting the remaining capacity of the battery and the remaining run-time with an accuracy of 1 minute or better under all realistic user conditions, including a wide variety of load currents and a wide temperature range. The basis of the proposed algorithm is current measurement and integration during charge and discharge state and voltage measurement during equilibrium state. One of the main problems in designing an accurate SoC indication system is aging of the battery. A simple method of adapting the maximum battery capacity used in the system with the aging effects is presented in this paper. A first set of experimental results shows the effectiveness of our novel approach for improving the accuracy of the SoC indication.

Measurement Errors and Uncertainty

No matter what precautions are taken, there will always be a difference between the result of a measurement and the true value of a quantity. This difference is called the measurement error. A measurement is useless without a quantitative indication of the magnitude of that error. Such an indication is called the uncertainty. Without knowing the uncertainty, the comparison of a measurement result with a reference value or with results of other measurements cannot be made. This chapter addresses the problem of how to define measurement errors, uncertainty, and related terms. The chapter also addresses the question of how to determine the uncertainty in practice. Under this, it summarizes the related statistical issues. Further, various sources of errors and the various types of errors is discussed. Methods to specify these errors are also highlighted. The chapter concludes with some techniques used to reduce the effects of errors.

Time-of-flight estimation using extended matched filtering

The problem considered is the estimation of the ToF (time-of-flight) of an acoustic tone burst in a reflective environment. Secondary echoes cause a complex interference pattern. Only the ToF of the first echo is of interest. Conventional matched filtering (MF) cannot cope with overlapping echoes. An explicit model for overlapping echoes leads to a generalized MF consisting of a parallel bank of filters rather than just a single filter. The new method is evaluated with a dataset of 150 records of observed waveforms using 3-fold cross validation.

Design of Measurement Systems

This chapter reviews the essential steps in the design and decision process. The design process is decomposed into a number of basic steps, with feedback loops and iteration sequences. Most of these studies distinguish three major levels—task definition, concept generation, and evaluation. Any design should start with a description of the requirements the system should finally be able to meet. Important specifications of a measurement system concern information handling performance; technical performance; environmental conditions; and economically related aspects. The design of a measurement system is not a trivial task. Even for the measurement of a single parameter, a variety of measurement principles is available, and for each principle many sensor types, measurement configurations and different ways of signal processing and data handling are available. This leads to an almost infinite number of possible measurement systems for each measurand.

Measurement of Chemical Quantities

This chapter discusses the basics of electrochemical sensing and sensors. As is the case with physical sensors in the electrical domain, the retrieved information can be represented by a voltage, a current, or an impedance. For chemical sensors based on electrochemical measuring principles, this subdivision turns out to be a fundamental one because different means of mass transport are involved. Information represented by a voltage, a current or an impedance is retrieved by potentiometric sensors, by amperometric sensors or by electrolyte conductivity sensors, respectively. This chapter describes some fundamentals of potentiometry, amperometry, and electrolyte conductivity.

Basics of Measurement

This chapter discusses the basic aspects of measurement science. The chapter also presents the system of units is and discusses the materialization of a unit quantity. It is shown that at present all standards (except for the kilogram) are related to fundamental physical constants. Further, an overview of the most important quantities and properties, used in various physical domains—the geometric, electrical, thermal, mechanical, and optical domain is presented. Relations between quantities from different domains that are fundamental to the measurement of non-electrical quantities and parameters is also discussed. Finally, the chapter describes some general aspects of sensors, and discusses the devices that convert information from one domain to another.

Analogue Signal Conditioning

This chapter discusses amplification, analogue filtering, and modulation and demodulation conditioning functions. Most analogue amplifier circuits consist of operational amplifiers, combined with resistance networks. An operational amplifier is in essence a differential amplifier with very high voltage gain, a high common mode rejection ratio and a very low input current and offset voltage. The amplifier is composed of a large number of transistors and resistors and possibly some capacitors, but no inductors. The most important imperfections of an operational amplifier are the offset voltage and the input bias currents—they limit the accuracy of measurements where small sensor voltages or currents are involved. Further, modulation is a particular type of signal conversion that makes use of an auxiliary signal, the carrier. One of the parameters of this carrier signal is varied correspondingly to the input signal. The result is a shift of the complete signal frequency band to a position around the carrier frequency. Due to this property, modulation is also referred to as frequency conversion. Several parameters of the carrier can be modulated by the input signal, for instance the amplitude, the phase, the frequency, the pulse height or the pulse width. These types of modulation are referred to as amplitude modulation (AM), phase modulation, frequency modulation (FM), pulse height, and pulse width modulation.

Measurement of Mechanical Quantities

There is an overwhelming number of sensor types for the mechanical domain available, operating on various physical principles. A particular mechanical construction converts the displacement or force to be measured into an electrical, optical, or magnetic quantity that can then be measured by one of the methods discussed before. This chapter discusses sensors for measuring linear and rotational displacement, and force. Principally, a force sensor consists of a displacement sensor with a spring element. An accelerometer can be derived from a force sensor using a seismic mass. The following classes of sensors for the measurement of displacement and force is reviewed: resistive sensors, capacitive displacement sensors, magnetic and inductive displacement sensors, optical sensors, piezoelectric force sensors and accelerometers, and finally ultrasonic displacement sensors.

Chapter 10 – Imaging Instruments

Publisher Summary The purpose of imaging instruments is to measure aspects of the 2- or 3-dimensional geometrical structure of physical objects. Imaging instruments use radiation as the carrier of information. This chapter discusses general principles of imaging instruments. An imaging instrument typically exists of a radiator (illuminator) and an image formation device (camera). Radiant energy is emitted into space. Eventually, it reaches the surfaces of objects where it interacts with the material. In the case of reflection, each surface patch acts as a new radiator that emits energy. Other examples of light-material interactions are absorption and transmission. The image formation device intercepts part of the energy and distributes it over a plane. The chapter also presents an overview of different types of modalities. It appears that the wavelength of the radiation is a parameter that controls many of the properties of the radiation including resolving power and diffraction, spectral radiation, quantum effects, and light-material interactions. In addition, different types of imaging techniques using visible light as the physical modality, including a short review of multi-spectral imaging is discussed.