【正文】 Virtual instrumentation software Article Outline 1. Introduction 2. Dynamic test methods for waveform recorders based on plugin boards 3. Sound card as a waveform recorder 4. Test software and setup characteristics 5. Examples of achieved test results 6. Conclusions References 1. Introduction Sound cards, sometimes called sound blasters, are very mon and are often used as ponents of many puters (PC) nowadays. They can be considered as their ―standard‖ audio (analogue) interface. Sound cards are much cheaper than multifunction and industrial data acquisition plugin boards—usually more than 10–100 times. On the other hand, the parameters of analogue inputs and outputs declared by vendors, . at least 16bit resolution of analoguetodigital and digitaltoanalogue converters (ADCs and DACs), indicate the possibility to apply such a card in low cost and lowfrequency dataacquisition systems acquiring signals from chemical, pressure, vibration and other sensors. The frequency bandwidth of a sound card can be extended on DC or quasiDC signals by applying a chopper or a 本科畢業(yè)設(shè)計(jì)（論文）外文翻譯 14 modulation amplifier on card input followed by a digital demodulation in the PC. These ideas, as well as the challenge in the industry, led the authors to perform some tests of analogue signal recording channels according to IEEE Standards 1057 and 1241 and DYNAD drafts to verify the application possibilities of sound cards in the examples indicated herein before. New proprietary virtual instrument (VI) software had to be developed to perform the experiments and tests. 2. Dynamic test methods for waveform recorders based on plugin boards The standard test methods for waveform recorders are generally well known, and they were brought out in a prehensive form in IEEE Std. 1057 [1]. Nowadays, the new, about to be accepted standards IEEE Std. 1241 [2] and DYNAD [3] are ing with some new ideas and test procedures described in more detail. Moreover, many researchers have contributed with lots of ideas and approaches to solve AD and DA converter test problems. Probably the widest survey of those ideas was made in [4]. Comparing the standards, IEEE Std. 1057—―Standard for digitising waveform recorders‖—is the closest to the task of sound card testing. However, this standard covers mostly the static and quasistatic tests methods based mainly on the histogram testing and there is a deficiency of procedure and data processing details on testing and determining the dynamic parameters of ADC especially in the frequency domain. The histogram based methods are generally not very convenient for sound card characterisation because of the AC coupling on signal input of the cards (Fig. 1). Fullsize image (9K) Fig. 1. Typical function block diagram of analogue and digital circuits for signal recorder part in sound cards. View Within Article Both oning standards are more focused on testing standalone ADCs but they contain much more specific details on execution and evaluation of some dynamic tests. Particularly, the DYNAD draft contains very detailed descriptions of data processing for estimation of the ADC dynamic parameters in the spectral domain. These facts, as well as many similarities in testing ADCs and digitising waveform recorders, led to the decision to apply many procedures referred in DYNAD and in IEEE Std. 1241 for evaluation of ADC dynamic parameters on PC sound card testing in the role of waveform recorder. 本科畢業(yè)設(shè)計(jì)（論文）外文翻譯 15 Testing waveform recorders in the form of PC plugin boards have some specifics. The interior of PC is generally illic it for a precise digitalisation of an input signal. The test methods developed and suggested, as well as some achieved test results for multifunction industrial plugin boards in various circumstances, have been published in [5, 6 and 7]. The authors preferred the dynamic test methods based on FFT spectrum or sinusoidal curve fit with determining effective number of bits (ENOB) versus test frequency as the main quality characterisation parameter of the tested board. In the software area, two universal versions of VI test software have been developed and published—one in LabVIEW [9] and another in Matlab [8]. Both versions of software have very general assignations—they process data from any measurement recorded in a file and they do not contain any data acquisition part. 3. Sound card as a waveform recorder Sound cards are generally dedicated to recording and playing sound signals. This results in a restriction of input and output frequencies span, usually to the frequency bandwidth from 20 Hz to 20 kHz, which prevents application of the static test methods and leads to the application of the dynamic test methods using the sinusoidal input test signal. The typical function block diagram of sound blaster input recording channels is shown in Fig. 1 ( [10 and 11] and others). The analoguetodigital conversion usually employs sigma–delta converters that can work in at least two precision modes—8 and 16 bits. Data can be coded into a few nonlinear and linear formats. The linear format (PCM), which is the most suitable format for the performance test, was chosen in the developed testing procedure. A variety of optional sampling frequencies depending on the sound card model—at least 8, 11, and kHz—are monly offered. The stability and, eventually, a frequency shift of these frequencies are not usually explicitly indicated in sound card manuals. Digitising input may be switched by an analogue multiplexer. A microphone input and a less sensitive linein (aux) input are builtin for linking external analogue signal sources. Sound cards are probably most often used in PCs with operational systems (OS) Windows 9x/NT/20xx/ME/XP. Any sound application under Windows can use some of th