A Simple Fast Frequency Detector for a Constant Amplitude Sinusoid

The frequency of a constant-amplitude sinusoidal signal is measured within a small fraction of a cycle. This is accomplished by carrying out computations on two successive samples of the input signal. System delay expressed in a fraction of a cycle is given by two times the ratio of the input-to-sampling frequencies. An inverse sine function is computed using digital hardware, giving a digital output representing the frequency.     

Five-Point Amplitude Estimation of Sinusoidal Signals: With Application to LVDT Signal Conditioning

A simple algorithm for the amplitude estimation of sinusoidal signals is proposed. It is first shown that three well-spaced samples are sufficient to calculate the amplitude of a harmonic signal. However, the three-point estimator is sensitive to deviation of the sampling rate. To deal with errors that were caused by noncoherent sampling, a modified algorithm that uses two more samples is developed. With the five-point algorithm, estimation errors fall below 0.04% for 1% of frequency deviation. As a demonstration of its simplicity, the five-point estimator is applied to the signal conditioning of a linear variable differential transformer (LVDT) using moderate-speed devices. By implementing the proposed algorithm with a low-cost 16-b microcontroller, a digital LVDT signal conditioner is built and tested with satisfactory performance.      

A Simple Method for Design of Adaptive Filters for Sinusoidal Signals

Filtering of input signals in algorithms for measurement of power system electrical parameters is very important. Filters are used to minimize the noise effect and eliminate the presence of higher order harmonics. In addition to that, a number of measurement algorithms apply orthogonal signal components obtained by two orthogonal finite-impulse response filters. The frequency response of the filters must have nulls at the higher order harmonic frequencies that are expected to be present in the signal and must have a unity gain at the main harmonic frequency. In the case of a time-varying frequency, the filter parameters have to be adapted during frequency estimation. In this paper, a simple method for online design of digital filters for sinusoidal signals is proposed. It is based on closed-form solutions for calculating filter coefficients. A simple linear algorithm for frequency estimation was used, and a derived algorithm for online adaptation of the filter coefficients is computationally very efficient. The number of subsections in the cascade and data window lengths can also be changed, depending on the frequency variations during measurement.      

The Contrast Transmission of a Sinusoidal Signal of Large Amplitude by Photographic Materials

Interference patterns are used to determine the transmitted contrast of sinusoidal signals of large amplitude by photographic plates. The mean transmitted contrast is deduced from microdensitometer records. The whole curve-contrast (i.e., spatial frequency) can be considered as the response function of the emulsion. A statistical and objective definition of the microdensitometric resolving power follows directly from this curve.     

声光快速分光装置与微机控制

本文介绍了一个以声光可调滤光器为分光元件的快速分光装置,它具有光波长电调谐,易与微机接口,全固态结构等优点。文章详细讨论了快速分光装置各个单元部份电路设计。在Z—80A CPU控制下,分光装置以5nm波长间隙扫描500～700nm光谱范围只需0.74ms。通过模拟实验,快速分光扫描的结果被证明是正确的。     

高速倾斜镜的频率响应函数测量

在用四象限管测量法测量高速倾斜镜频率响应函数的基础上,设计了一种利用位移传感器－电涡流传感器来测量频率响应函数的方法。分别给出了两种方法对同一个四点驱动高速倾斜镜的测量结果,并对两种方法的优缺点进行了分析和讨论。     

Phase and Amplitude Modulation Effects in a Phase Detector Using an Incorrectly Balanced Mixer

A very simple theoretical model of a phase detector using a double-or single-balanced mixer is described. The main characteristics of this device are depicted and the effect of the balance in the mixer is analyzed. Experiments show that the model describes the behavior of the unbalanced phase detector in a satisfactory way.     

一种低信噪比正弦信号高精度频率测量方法

在研究噪声对低信噪比正弦信号频率测量的影响、分析触发误差对多周期同步频率测量影响的基础上,提出了一种多-多周期同步频率测量方法,推导了频率测量计算公式和误差计算公式,并对两种测频方法的触发误差做了对比分析;最后给出了用STM32单片机实现多-多周期同步频率测量的方法。实验表明:该方法能有效压制噪声,提高低信噪比正弦信号频率测量精度。     

Oscillators with Frequency and Amplitude Outputs for the Measurement of Two Parameters

A class of harmonic oscillators is described which has the frequency of oscillation determined by one parameter of an RC or RL circuit and the amplitude of oscillation by the other parameter. These oscillators are useful in the impedance measurement of physical or biological objects when two attributes of the object are related to two electrical parameters of the equivalent circuit. A pole or zero is derived from the measured object by isolating it from the oscillator. The remainder of the oscillator contains linear elements and a single memoryless nonlinearity. Second-order oscillators containing a hard nonlinearity and third-order oscillators containing a soft nonlinearity are presented. The frequency and amplitude relationships are derived using linear theory and the describing function method. The theoretical results are verified by analog computer simulations. The oscillators are described in general terms by means of flow graphs.     

拟合测量正弦信号频率的不确定度

介绍了用四参数最小二乘曲线拟合法评价正弦信号频率时不确定度的分析和评价.通过使用国军标GJB 3756-1999"测量不确定度的表述及评定"中推荐的方法,讨论了影响评价结果不确定度的几个主要误差来源,包括采集速率误差、采集序列的谐波失真、采集序列的噪声及非谐波失真、采集序列中信号周期的抖动、软件拟合运算误差的影响等,给出了正弦信号频率的测量不确定度及减小不确定度的主要措施.结合一个实际例证的评价结果,验证了该过程的正确性和可行性.     

振幅分割无掩模激光干涉光刻的实现方法

无掩模激光干涉光刻中的分束方法一般有波前分割和振幅分割。研究和比较了振幅分割无 掩模激光干涉光刻方法和系统,包括振幅分割双光束干涉系统、三光束干涉系统、液浸式深紫外干涉系统及全自动干涉光刻系统。建立了双光束双曝光干涉光刻实验系统。模拟和实验结果表明,对点阵或孔阵图形,在同样的图形尺度下,无掩模干涉光刻比传统光刻简单得多。     

Digital Frequency Multiplier for Spectrum Measurement of Periodic Signals

Frequency multipliers find applications in the Fourier and Walsh spectrum measurements of periodic signals. Earlier digital frequency multipliers use two counters: 1) An upcounter which is partitioned into a fractional counter of kbits in cascade with an integral counter. This determines the period of the input signal by the number of clock pulses that are accumulated in a period of the signal. 2) A downcounter which is next fed from the same clock, and which is periodically preset to the contents of the integral counter whenever the downcounter reaches zero. In this process an error is introduced in the output frequency because the fractional counter contents are ignored in the frequency multiplication phase. To minimize this error, a high clock frequency is required so that the fractional count is small compared with the integral count. The maximum output pulse frequency is limited by the speed of the counters used. A new method is described which also uses the contents of the fractional counter. The clock frequency is reduced substantially and the maximum output pulse frequency is limited by the settling time of a D/A converter: If the settling time is 200 ns, the maximum output frequency is ten times that of earlier methods.     

A Varactor Null Detector for Aduio Frequency Capacitance Bridges

A two-varactor, double-sideband up-converter pumped at 30 MHz has been constructed. Operated at room temperature with a signal frequency of 104 rad/s, the device has an optimum source resistance of 105 ohms and a minimum noise figure of 0.01 dB. Immersed in liquid N2, minimum noise figures below 0.001 dB referred to a room temperature source have been measured. The device is particularly useful as a null detector for audio frequency capacitance bridges. At 104 rad/s, a signal current of 10-14 amperes through a capacitance of 1000 pF can be detected in less than one second with this instrument. Techniques for suppressing microphonics and other extraneous sources of noise are described.     

涡街流量传感器信号的幅值和频率特征

基于实验数据建立了涡街流量传感器输出信号的数学模型,提出了用混合高斯分布来描述涡街流量传感器信号幅值的自然衰减现象,采用频率调制信号来表示涡街流量信号的宽带特征,通过频谱分析确定机械振动噪声信号为窄带信号.     

Adaptive Wide-Range Multichannel Module for the Input of Pulsed Frequency Signals into a Computer

A method of adaptive measurements and the structural scheme of a module for the input of data into a computer are proposed. An analysis is made of the accuracy, speed, and range of the measurements.     

单探测器复合轴伺服系统解耦技术的研究与实现

本文分析了单探测型复合轴系统探测器大视场与高帧频之间的矛盾以及主轴与子轴单元控制输入耦合的问题。采用智能相机控制技术,在线调整CCD探测器的工作参数,实现了探测器在捕获/粗跟踪阶段大视场与精跟踪阶段高探测帧频状态之间的切换;将PZT位置输出与脱靶量进行位置信息的合成并将该信息作为主轴控制输入以保证子轴正常工作。并对系统控制方法进行了仿真,提出根据跟踪精度作为判断系统是否解耦的方法。实验结果表明该方法消除了系统的耦合,取得了较好的控制效果。