共查询到20条相似文献,搜索用时 31 毫秒
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When magnetic cores with a square hysteresis loop are used for a time delay Crcuit or a pulse counter circuit, and if these circuits are designed by the use of the static hysteresis loop, the ac magnetization curve, or the control magnetization curve (CMC) which is the basic characteristic of a magnetic amplifier, there is apt to be a marked discrepancy between their design values and measured values. Since, in the flux control of magnetic cores used for a time delay circuit or a pulse counter circuit, the flux, contrary to the case with a magnetic amplifier, arrives at the negative saturation from the positive saturation by many intermittent signal voltages, a new characteristic quite different from CMC and other characteristics must be adopted as the standard of the design in this case. It was for this reason that instantaneous relation between the rate of flux change and the exciting current was examined in the case in which real flux resetting behaviors of a time delay circuit or a pulse counter circuit were taken into consideration, by using grain-oriented 50 per cent permalloy as the sample, with a view to obtaining core characteristics serviceable enough for exact design methods of a time delay circuit or a pulse counter circuit. Various useful results have been obtained as to: 1) how the correlation between rate of flux changedPhi/dt and instantaneous values of exciting current ic changes in proportion to the flux values, 2) how the amount of reset fluxDeltaPhi_{r} will change according to the flux valuePhi and the rate of flux changedPhi/dt , and 3) how the above-mentioned relations are connected to the tape thickness of the magnetic core. This paper reports the results of this investigation. 相似文献
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A new group of magnetic circuits that can count the number of magnetic bubbles and display them in any binary, ternary, ..., decimal basis is proposed. Feasibility of the concept was demonstrated by successful operation of a binary counter circuit. A design of a decimal counter is given. 相似文献
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针对数字电视机顶盒的重要功能——多节目解码对播放同步的需求,设计了一种双时钟计数器(STC)的时钟恢复电路,并在支持先进音视频编码标准(AVS)的高清解码芯片中得到实现。该电路使用主从两个STC,主STC由一个混合型的锁相环驱动,该锁相环产生的27MHz时钟同时用于产生音视频解码时钟;从STC则由一个全数字的锁相环驱动,它仅用于与展示时间戳(PTS)比较产生显示同步控制信号。同时提出了一个硬件的低通滤波算法,该算法保证了STC在稳态下追踪传输流中的节目时钟参考(PCR)的变化,并且提供稳定的时钟输出,同时有效降低了主控CPU的负荷。仿真实验结果表明,所提出的时钟恢复电路和低通滤波算法具有较好的性能和较低的计算复杂度,并有效地降低了硬件开销。 相似文献
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An electrical equivalent circuit is derived for the electrospray process. It is a series circuit which consists of the power supply, the electrochemical contact to the solution, the solution resistance (R(s)), a constant-current regulator which represents the processes of charge separation and charge transport in the gap between the spray needle aperture and the counter electrode, and charge neutralization at the counter electrode. A current i, established by the constant-current regulator flows throughout the entire circuit. Current-voltage curves are developed for each element in the circuit. From these it is shown that in the case where R(s) is negligible (the power supply is connected directly to a conducting needle) the shape of the current-voltage curve is dictated by the constant-current regulator established by the charge separation process, the gap, and the counter electrode. The solution resistance may be significant if a nonconducting needle is used so that the electrochemical contact to the solution is remote from the tip. Experiments with a nonconducting spray needle quantify the effect of the solution resistance on the current-voltage curve. Subtracting the iRs voltage from Vapp (power supply voltage) yields the current-voltage curve for the constant-current regulator. When iRs drop is a significant fraction of Vapp, the current-voltage curve of the constant-current regulator is changed substantially from the case when the solution resistance is negligible. 相似文献
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Carbon nanotube (CNT) films have been used as counter electrodes in natural dye-sensitized (anthocyanin-sensitized) solar cells to improve the cell performance. Compared with conventional cells using natural dye electrolytes and platinum as the counter electrodes, cells with a single-walled nanotube (SWNT) film counter electrode show comparable conversion efficiency, which is attributed to the increase in short circuit current density due to the high conductivity of the SWNT film. 相似文献
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本文介绍以可逆计数器为核心的通用型测控系统的硬件组成,对其中主要电路工作原理进行了分析。既能解决稳定控制的问题,也能实现随动控制功能。文章的最后对该系统的实际应用作了论述。 相似文献
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《IEEE transactions on instrumentation and measurement》1985,34(3):470-471
A simple circuit for the measurement of very low angular speeds is described. It uses a potentiometric transducer along with a modified astable multivibrator. Using an up-down counter the speed measured can also be displayed. 相似文献
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Dye sensitized solar cells (DSSC) with surface modified carbon fiber fabric (CF) counter electrodes were prepared and tested. Four different type of CF were used; carbon fiber (CF); carbon fiber etched with NaOH (ECF); carbon fiber with thermally deposited platinum (CFPt); and carbon fiber etched with NaOH followed by thermal deposition of platinum (ECFPt). For comparison, DSSC with thermally Pt deposited fluorine doped tin oxide (FTO/Pt) glass counter electrode was also prepared and tested. Scanning electron microscope (SEM) proved that surface morphology of the carbon fiber was roughened by the etching process and platinum deposition process. The I-V curves of each DSSC were measured under simulated light (1 Sun, AM 1.5) to get open circuit voltage (Voc), short circuit current density (Jsc), fill factor (FF) and efficiency (eta). Electrochemical impedance spectroscopy of each cell was measured also. It was found that higher efficiency is obtained in order of using ECFPt > CFPt > FTO/Pt > ECF > CF counter electrode. 相似文献
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It is pointed out that a circuit given in Fig.4 of the above-titled paper (ibid., vol.36, no.3, p.711-16, 1987) will not operate if the output of the divide by 2 counter is connected to the AND gate as it is shown 相似文献
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《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》1999,361(2-3):502-510
The counting statistics of a scintillation counter, with a preamplifier saturated by an overloading input, are investigated. First, the formulae for the variance and the mean number of counts, accumulated within a given gating time, are derived by considering counting-loss effects originating from the saturation and a finite resolving time of the electronic circuit. Numerical examples based on the formulae indicate that the saturation makes a positive contribution to the variance-to-mean ratio and that the contribution increases with count rate. Next the ratios are measured under high count rates when the preamplifier saturation can be observed. By fitting the present formula to the measured data, the counting-loss parameters can be evaluated. Corrections based on the parameters are made for various count rates measured in a nuclear reactor. As a result of the corrections, the linearity between count rate and reactor power can be restored. 相似文献
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《IEEE transactions on instrumentation and measurement》1964,13(4):159-163
The problem of measuring a time interval using a crystal oscillator as a time base is discussed. A statistical analysis is made of the free-running oscillator and gated counter when the time interval to be measured is repetitive. Using the equivalent circuit of a quartz crystal, the difficulties involved in using a pulsed crystal oscillator as a time base are investigated. A method is described to measure, at a random instant, the instantaneous phase of a free-running oscillator and use this information as the last significant figure in a time interval or pulse delay method. The method consists of sensing the coincidence between oppositely-traveling pulses on a delay line. A digital-delay generator was constructed using this technique. The accuracy of the delay was measured as ±0.01 us ±crystal time-base accuracy. The construction and testing of this device is discussed. 相似文献
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《IEEE transactions on instrumentation and measurement》1970,19(4):286-290
This instrument uses pulsewidth modulation techniques in which a crystal oscillator, frequency divider, and preset counter replace the resistive divider to form a precision potentiometer. The smoothing of the time-division intervals to a steady-state direct current without introducing prohibitive time constants is solved by a "sectional average" integrating circuit. This utilizes a short time-constant integrator combined with a switched unity-gain buffer amplifier in the feedback to integrator input. This switch, integrate, and sample-and-hold circuit provides output within ±0.1 percent of the eventual steady-state value in less than 400 ms after a step change and within ±0.001 percent in 600 ms. The system provides digital compatibility with tape, cards, digital voltmeters, etc. An engineering prototype has 7 decade dials covering a 0-100.0000-volt range with ±(0.1 ppm + 5?V) voltage-ratio accuracy and, ±0.05 ppm/50°C temperature coefficient and ±0.05 ppm/ 10-week long-term stability, and it is expected that this may be improved. 相似文献
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We present a direct-to-digital capacitive sensor readout circuit that converts capacitance changes of a sensor element to changes of the duty cycle of a square-wave oscillator, which, in turn, is converted to a digital output by a counter. The readout circuit resembles a single-slope analog-to-digital converter structure. There are several advantages of this readout scheme. First, due to its simplicity and low number of components, the power consumption of the circuit is expected to be significantly smaller than in similar digital readout designs. Furthermore, linearization of the output may be achieved using an EEPROM lookup table. Another advantage is the possibility of performing adaptive measurements where the sensor resolution and bandwidth may be changed via the readout circuit software. Finally, we present a theory of the adaptive measurement and an analysis of the design tradeoffs. The capacitance-to-duty cycle readout circuit may achieve large bandwidth and high resolution in a modern low-voltage, low-power CMOS implementation. The performance of a prototype readout circuit built from discrete components is 13-bit effective resolution with a 1-kHz bandwidth. 相似文献
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分别以气煤、焦煤、瘦煤为原料制备了低成本、高性能煤基炭对电极(counter electrodes, CEs), 并使用煤基炭CE同时代替导电玻璃基底和催化层, 分别考察了浸渍和表面修饰对煤基炭CE结构和光电性能的影响。采用X射线衍射、扫描电镜和电化学阻抗谱等表征手段, 对煤基炭CE的结构和性能进行了表征。结果表明: 浸渍后煤基炭CE形成了底层致密表层多孔的一体化结构; 经过表面修饰的煤基炭CE表现出良好的光电性能, 其开路电压(Voc)、短路电流密度(Jsc)和填充因子(FF)分别为0.79 V、13.48 mA/cm2和0.67, 光电转化效率(η)达到了7.16%, 与传统Pt电极的效率相当, 比石墨电极效率提高30%。煤基炭CE是传统Pt/FTO电极的良好替代材料。 相似文献
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《IEEE transactions on instrumentation and measurement》1968,17(3):186-192
This paper discusses the design and operation of a digital voltmeter employing a new technique in the analog-to-time converter. The circuit is based on dual-slope integration, which eliminates the necessity of a highly stable clock. Any long term drift in the clock is canceled, so that a simple two-transistor multivibrator clock is used. With the aid of a special diode circuit, the ramp-generating integrator also serves as an accurate comparator, so that no separate comparator is needed for analog-to-digital conversion. Finally, the new circuit requires only a single up counter, and no special polarity switching circuits for automatic polarity indication are needed. The new voltmeter, developed for the University of Arizona's new Locust Computer, has full-scale ranges of ±1 volt and ±10 volts. Tests on the instruments have shown its accuracy to be ±0.02 percent of half-scale. The sampling rate can be varied from 80 ms to 1 second, and the input impedance is 2 MU on the 10-volt range. 相似文献