A new low-cost voltage-to-voltage transducer for distorted signals

During the last years, measuring equipment has evolved toward the massive use of digital techniques and devices. The performance of analog-to-digital converters (ADC) and computing devices has constantly improved, and very accurate and flexible instruments can now be realized with bandwidths up to several kilohertz. Unfortunately, the transducers used to adapt the input signals to a suitable ADC input levels have not improved to the same extent so that the metrological characteristics of a DSP-based measuring instrument are mainly determined by the input transducers. Improving the performance of such transducers is thus of the utmost importance. This paper proposes a new voltage-to-voltage transducer, based on a capacitive divider and the Σ-Δ modulation techniques, that features a bandwidth wider than that of the traditional magnetic and capacitive voltage transformers. Specifications are provided on the transducer design, and the results of experimental tests on a lab prototype with primary voltage up to 500 V are reported     

Best linear unbiased estimation of the Fourier coefficients ofperiodic signals

Fourier coefficients of periodic signals are usually estimated by the discrete Fourier transform (DFT). Since DFT is equivalent to ordinary least squares, it might be expected to be best linear unbiased only if the errors in the observations are not covariant. Fortunately, for covariant errors, the DFT achieves this optimum property asymptotically     

A programmable self-adaptive digital frequency multiplier

Existing self-adaptive frequency multipliers work well if the master clock frequency is an integral multiple of the input signal frequency; otherwise they lose an output pulse after a certain interval of time. The frequency of this missing pulse could be as high as half of the input frequency. Since existing self-adaptive frequency multipliers are not programmable, the multiplication factor can not be changed without doing some major changes in the hardware. The reason for missing an output pulse is explained, and design and implementation of a programmable self-adaptive digital frequency multiplier, that does not have this missing pulse problem are presented. The errors associated with the multiplier are discussed     

A novel differential synchronous demodulator for AC signals

We describe a new analog differential synchronous demodulator for AC signals where (i) the signal is synchronously demodulated using the floating-capacitor technique after being amplified, if necessary, by an AC amplifier with differential input and differential output, thus yielding a very high CMRR; and (ii) the differential-to-single-ended signal conversion is performed after demodulation, that is, on a low-frequency signal that can be amplified by low-cost, high-performance circuits. The possible signal-to-noise ratio degradation because of synchronous sampling is prevented by using bandpass differential filters     

非整周期采样信号相位差估计的相频匹配方法

To improve the precision and anti-interference performance of phase difference estimation for non-integer periods  sampling signals,a phase and frequency matching based phase difference estimation method  was proposed.The phase difference estimation  was obtained by means of the segmented Hilbert transform to suppress the effect of non-integer periods  sampling sinusoidal signals on the Hilbert transform.The simulation results demonstrate that compared with the methods of cross-correlation,Hilbert transform and data extension-based correlation, the proposed method has better phase difference estimation performance for non-integer periods sampling signals in terms of its estimation precision and anti-interference performance.Its phase difference estimation errors are closer to Cramer-Rao lower bound (CRLB).The measurement experiments  on the flow rates of Coriolis mass flowmeter validate the effectiveness of the proposed method.     

Feedback compensated synchronous and multiplier type phasesensitive detectors

A feedback technique for phase sensitive detection (PSD) is developed, which is suitable for both synchronous and multiplier modes of implementation. The feedback-compensated PSD straightaway provides a DC output proportional to the amplitude of the measurand. The technique is very useful in a noisy environment where post-processing of the in-phase and quadrature components would otherwise deteriorate the stability, accuracy, and sensitivity. Quantitative comparison of the extent of compensation obtained experimentally with that estimated by PC-simulation indicates good agreement     

跟踪测量视频的高精度同步采集系统

设计了一种无损实时跟踪测量视频和测控数据同步采集系统。根据测控信息同步信号及其对视频采集时刻的规定,以测控信息采集卡上高精度定时器为时钟,由视频采集卡通过软件修正摄像机曝光信号,实现对曝光时刻的精密调节。采用高速总线实现数据无失真存储和转储、AVI技术组织文件,充分利用了测量视频图像空间。     

A digital method of frequency measurement for harmonic signals

Conclusions A new method and an algorithm are described for determining the frequency or period of a harmonic signal no matter what the period of the signal. The principle can be used in digital measuring systems, particularly at low and infralow frequencies.Translated from Izmeritel'naya Tekhnika, No. 11, pp. 71–73, November, 1973.     

Digital synchronous detector and frequency control loop for cesiumbeam frequency standard

A setup that includes a digital synchronous detector and a digital frequency control loop and is designed for use in a cesium beam frequency standard is described. It is based on the TMS 32010 signal microprocessor. When associated with a high-quality HP 5061A option four cesium beam tube, it makes it possible to achieve the same levels of short-term and medium-term frequency stability as its original analog counterpart. It is thus expected that the setup will fit the improved short- and long-term frequency stability capability of optically pumped cesium beam tubes     

极低频信号的一种离散频谱校正新方法

对于振动工程中常见的极低频、极短时、极高频(接近奈奎斯特频率)等极端频率信号,常用的离散频谱分析与校正方法存在较大误差.对极端频率信号的典型情形进行了分析,针对极端频率信号中的极低频信号,提出了一种计及负频率成分干涉影响的离散频谱校正新方法.该方法基于Blackman窗,利用局部谱峰附近的三条谱线,建立包含正负频率贡献的离散频谱校正模型,通过对模型的求解获得频率、幅值和相位校正公式.采用频段内扫描的方式对频谱校正公式进行了仿真验证,结果表明所提方法有效降低了负频率成分的干涉影响,对极低频信号的频率、幅值和相位校正有较高的精度.     

Multi-order sampling for digital beamforming of wide-band signals

After proving that the second-order sampling method introduces too much error for beamforming of the wide-band signal generally used in ultrasound imaging systems, we suggest a new multi-order sampling method that significantly reduces sampling error but maintains advantages of the second-order sampling method with relatively simple hardware     

Phase fluctuations in a heterodyne multistage frequency multiplier

Conclusions The inherent phase instability and error of these multipliers are not inferior (as regards frequency stability) to those found in other methods of frequency multiplication.Multiplication with heterodyning is especially justified in frequency comparison of atomic clocks, where the mutual deviation and output frequency instability are much less than the limiting values permissible for undistorted multiplication. A transistorized multiplier is simple, so one can provide reliability over long periods with continuous comparison.The main component in the phase fluctuations in a multiplier is due to noise in the coupling and transformation circuits, so in principle it is possible to improve the stability further via advances in this part of the device.The input stages are of broad bandwidth and have low temperature coefficients, so one can compare frequencies over periods up to 100 sec without thermostatic control without appreciable loss of accuracy.Translated from Izmeritel'naya Tekhnika, No. 11, pp. 41–43, November, 1972.     

外置式非标准视频同步信号发生器的设计

采用TMS320F206作为USB接口芯片PDIUSBD12的控制器,实现对高速数据采集卡的同步控制。主机从荻得的非标准视频数据中提取同步信号参数,通过USB接口及时传输给DSP,DSP对分频系数实行模糊控制,产生精度可达7ps的视频同步信号,实现非标准视频信号的采集和稳定显示。分别对行频为15．625kHz、场频为50Hz的CCD视频信号,及行频为48．656kHz、场频为60Hz的计算机显示器视频泄漏信号进行了采集与显示,证实了此方案的可行性。     

Compact ultrahigh-frequency antenna designs for low-cost passive radio frequency identification transponders

Compact planar antennas for low-cost radio frequency identification (RFID) passive transponders are disclosed. The proposed ultrahigh-frequency antenna takes advantage of its unique topology to assure conjugate matching with essentially complex impedance of the electronic chip directly embedded into the radiator. Rectenna design issues are also emphasised. An original method to characterise IC chips and antennas as taken in its entirety of transponders is presented. The characterisation of the chip takes into account the impact of connecting antennas to the rectifier by flip-chip bonding process. The proposed experimental method allows finding chip impedance exactly as it seen by antennas. Refined rectifier circuitry effectively overcomes dependence of transponder performances on the type deviation of the connected antennas. Very good antenna performance is predicted theoretically and validated experimentally over an operating bandwidth of actual RFID systems.     

A low-frequency multiplier

A low-frequency multiplier is described whose operation is based on filling the period of the multiplied frequency with a constant number of pulses maintained by a frequency-controlled generator.Translated from Izmeritel'naya Tekhnika, No. 7, pp. 57–58, 1994.