Bishop, Robert H. - The Mechatronics Handbook [CRC Press 2002] Part 18 doc

This form of divider is useful from low frequencies up through frequencies of several megahertz. A common application is in the scaling of large voltages. Inductive Dividers If the elements in the chain divider are inductors, then an autotransformer results. Inductive dividers are useful over frequencies from a few hertz to several hundred kilohertz. Errors in the parts-per- billion range are achievable. Voltage Transformers Voltage transformers constitute one of the most common means of accomplishing voltage scaling at line frequencies. Standard double-wound configurations are useful unless voltages above about 200 kV are to be monitored. For very high voltages, alternative configurations such as the capacitor voltage transformer and the cascade voltage transformer are employed (Gregory, 1973). Current Scaling Current scaling is typically accomplished via either a current shunt or a current transformer. A current shunt is essentially an accurately known resistance through which the current to be measured is passed. The voltage developed across the shunt as a result of the current is the quantity measured. Shunts are useful at DC and frequencies through the audio range. Two disadvantages are (1) the shunt consumes power, and (2) the measurement circuitry must be operated at the same potential as the shunt. The current transformer overcomes the mentioned disadvantages of the current shunt. Typically, the current transformer consists of a specially constructed toroidal core upon which the secondary (sense) winding is wrapped and through which the primary winding is passed. A single-turn primary is com- monly used, although mutiturn primaries are available. Other Attenuators In addition to the aforementioned means of voltage and current scaling are attenuator pads, which provide, in addition to voltage or power reduction, the ability to be matched in impedance to the source and load circuits between which it is connected. The common pads include the T, L, and Π types, either balanced or unbalanced. Resistive attenuator pads are discussed in most textbooks on circuit design (e.g., Cuthbert, 1983). They are useful from DC through several hundred megahertz. Impedance Transformation Oftentimes the impedance of the transducer must be transformed to a value more acceptable to the remainder of the measurement system. In many cases maximum power must be transferred from the transducer’s output signal to the remaining circuitry. In other cases it is sufficient to provide buffering that presents a very high impedance to the transducer, a very low impedance to the rest of the system, and a voltage gain of unity. Matching transformers, passive matching networks such as attenuator pads, and unity-gain buffers are standard means of accomplishing impedance transformation. Unity-gain buffers are available in IC form. Linear Filtering Although, in general, digital signal processing offers many advantages over analog techniques for filtering signals, there are many relatively simple applications for which frequency-selective analog filtering is well suited. Filters are used within signal conditioners (1) to reduce the effects of noise that corrupts the input signal, (2) as part of a demodulator, (3) to limit signal bandwidth, or (4) if the signal is to be sampled, to limit its bandwidth in order to prevent aliasing. These filters can be built either entirely of passive components or based on active devices such as op amps. ©2002 CRC Press LLC 48 Computer-Based Instrumentation Systems 48.1 The Power of Software 48.2 Digitizing the Analog World 48.3 A Look Ahead Today’s computer-based and networked measurement and automation systems contain powerful software that brings high-performance in a familiar environment. By using these systems, engineers lower their costs while increasing productivity and create more customized solutions that directly match their needs. Electrical and electronics test instruments have always borrowed from contemporary technology that was widely used elsewhere. The jeweled movement of the nineteenth century used in clocks was first adapted to build analog meters. In the 1930s, when the variable capacitor, variable resistor, and vacuum tubes began to be widely accepted pieces of the radio, the first electronic instruments were introduced using the same components. As display technologies were improved for use on the first televisions, oscillo- scopes and analyzers began using the same technology to display the user’s measurements (see Fig. 48.1). These first steps toward computer-based instrumentation met significant challenges. Computerized ins- trument systems of the 1960s required custom hardware interfaces and low-level assembly languages. The development of standards, such as the introduction in 1976 of the general-purpose interface bus for instrument-to-computer connections, provided the foundation for revolutionary improvements in the development and use of computer-based instruments. Using the general-purpose interface bus, engineers began writing programs, first in BASIC, then C- based languages, and ultimately graphical development environments, that transformed their computers into efficient instrument controllers that also had the capability of electronically storing data. In the 1980s, digitizers and computer plug-in boards for data acquisition became widely accepted alternatives to expensive standalone instruments. With this combination of software and hardware, engineers began creating “virtual instruments.” Throughout the 1980s and 1990s, the idea of virtual instruments gained wider acceptance as the power of desktop computers increased exponentially. First consumer and then corporate demand for faster, more efficient CPUs, more capable and compact ASICs, faster and larger hard drives, and more capable interface buses played right into the hands of those designing computer-based instrumentation systems. Today’s instrumentation systems are being greatly influenced by the personal computer and Internet revolutions. Personal computers are now equipped with powerful computational engines that can be combined with software to create a sophisticated measurement instrument. The data that are acquired by the computer-based instrumentation system can then be easily transferred to anyone anywhere in the world who is connected to the instrumentation machine via the Internet. Kris Fuller National Instruments, Inc. ©2002 CRC Press LLC 49 Software Design and Development * 1 49.1 The Notion of Software 49.2 The Nature of Software Engineering 49.3 Development Before the Fact Language • Technology • Process 49.4 Experience with DBTF 49.5 Conclusion A software-based system can be neatly compared with a biological entity called a superorganism. Com- prising software, hardware, peopleware and their interconnectivity (such as the Internet), and requiring all to survive, the silicon superorganism is itself a part of a larger superorganism—for example, a medical system including patients, drugs, drug companies, doctors, hospitals, and health care centers; a space mission including the spacecraft, the laws of the universe, mission control, and the astronauts; a system for researching genes including funding organizations, funds, researchers, research subjects, and genes; a financial system including investors, money, politics, financial institutions, stock markets, and the health of the world economy; or it could be just the business itself. Whether that business be government, academic, or commercial, the software-based system, like its bio- logical counterpart, must grow and adapt to meet rapidly changing requirements. And, like other organisms, the business has both physical infrastructure and operational policies, which guide and occasionally constrain its direction and the rate of evolution, which it can tolerate without becoming dysfunctional. Compared to a biological superorganism, which may take many generations to effect even a minor hereditary modification, software can be modified immediately. This makes it far superior in this respect to the biological entity in terms of its evolutionary adaptability. Continuity of business rules and/or the physical infrastructure provides a natural tension between “how fast the software can change” and “how rapidly the overall system can accept change.” Software, the brain of the silicon superorganism, controls the action of the entire entity. Keep in mind, however, it was a human being that created the software. In this chapter we will discuss the tenets of software, what it is and how it is developed, as well as the precepts of software engineering, which are the methodologies by which ideas are turned into software. 2 1 * Parts of this chapter were taken from Object Thinking: Development Before the Fact , M. H. Hamilton and W. R. Hackler, in press. 2 001, 001 Tool Suite, DBTF, Development Before the Fact, SOO, and System Oriented Objects are all trademarks of Hamilton Technologies, Inc. Margaret H. Hamilton Hamilton Technologies, Inc. ©2002 CRC Press LLC 50 Handbook of Mechatronics—Data Recording and Logging 50.1 Overview 50.2 Historical Background 50.3 Data Logging Functional Requirements Acquisition • Sensors • Signal Connectivity • Signal Conditioning • Conversion • Online Analysis • Logging and Storage • Offline Analysis • Display • Report Generation • Data Sharing and Publishing 50.4 Data-Logging Systems Software Options • Hardware Options 50.5 Conclusions Related Information 50.1 Overview Data logging and recording is a very common measurement application. In its most basic form, data logging is the measurement and recording of physical or electrical parameters over a period of time. These parameters can be temperature, strain, displacement, flow, pressure, voltage, current, resistance, power, or any of a wide range of other measurement types. Real-world data-logging applications are typically more involved than just acquiring and recording signals, typically involving some combination of online analysis, offline analysis, display, report generation, and data sharing. Also, many data-logging applications are beginning to require the acquisition and storage of other types of data. One example would be recording sound and video in conjunction with the other parameters measured during an automobile crash test. Data logging is used in a broad spectrum of applications. Chemists record data like temperature, pH, and pressure when performing experiments in a lab. Design engineers log performance parameters like vibration, temperature, and battery level to evaluate product designs. Civil engineers record strain and load on bridges over time to evaluate safety. Geologists use data logging to determine mineral formations when drilling for oil. Breweries log the conditions of their storage and brewing facilities to maintain quality. The list of applications for data logging goes on and on, but all of these applications have similar common requirements. The purpose of this chapter is to provide a general background on data logging, discuss the various functional requirements that are common to most logging applications, and examine some of the modern hardware and software options available that allow scientists and engineers to implement powerful PC-based data-logging systems. Tom Magruder National Instruments ©2002 CRC Press LLC . across the shunt as a result of the current is the quantity measured. Shunts are useful at DC and frequencies through the audio range. Two disadvantages are (1) the shunt consumes power, and (2) the. instrument. The data that are acquired by the computer-based instrumentation system can then be easily transferred to anyone anywhere in the world who is connected to the instrumentation machine via the. upon which the secondary (sense) winding is wrapped and through which the primary winding is passed. A single-turn primary is com- monly used, although mutiturn primaries are available. Other