Travel time is the key point of system , its measure quality decides the survey precision of the stress . time to digital convertor ( tdc ) was applied to accomplish the precision time interval measurement . at the same time , one transmitter - two receivers probe arrangement and zero - crossing detecting method were also applied to reduce the errors in measurement 传播声时是整个测量系统中的关键量,其测量水平决定应力的测量精度,对此本文采用时间-数字转换器( timetodigitalconvertor , tdc )完成高精度时间间隔测量,在实现过程中又分别采用“单端发射-双端接收”的探头布局模式和“过零检测”手段来降低系统检测误差。
The working principle of pulsed eddy current ( pec ) nondestructive testing technology is analyzed , the pec testing system was been established to examined the specimen of multi - layered aircraft structure , peak and zero - crossing time of the time domain transient response signal of pec are extracted as the features to detect the corrosion in the second layer of aircraft structure quantificationally , the experiment results are consistent with that of the theory analysis , as the pec have the advantages of fast speed and quantification , this makes the method have the broad using foreground in the testing of aircraft structure corrosion 摘要对脉冲涡流无损检测技术的工作原理进行了分析，建立了脉冲涡流的检测系统对加工的模拟飞机多层结构的试件进行了测试，提取其时域瞬态感应信号的峰值和过零时间作为特徵量，对出现在飞机多层结构第二层中的腐蚀缺陷进行了定量检测，试验结果和理论分析相一致，证明了脉冲涡流检测方法的有效性，由于其具有快速和定量化的优点因而在飞机结构的腐蚀检测中具有广阔的应用前景。
In the system , control unit accomplishes back - emf zero - crossing information reading and closed loop commutation . the system eliminates the pwm interferences and the commutating interferences by filtering with software algorithm . in order to make the bldc commutate exactly , the method of three - point estimation is used for phase locking in the system . the system also accomplishes several important objects , such as tmppt of photovoltaic arrays , unmanned supervision of the system , fault detection etc . the results of the experiment show that the device , which is made on the base of the principle above , can control the motor to complete the exact commutation 系统以motorola单片机jl3为核心，完成了系统外围硬件电路和控制软件设计，实现了直流无刷电机反电势过零检测，利用软件滤波的方式消除了pwm波干扰及换相干扰；采用三点预估算法，进行相位锁定，以完成直流无刷电机准确换相；同时实现了光伏阵列工作点的tmppt跟踪、系统无人监控和故障检测等功能。
Such recognition algorithms the feature extraction based on a set of 2 - d gabor wavelet and computation of percentage mismatched bits hamming distance between a pair of iris representations developed by daugman , texture analysis methods developed by wildes and chinese academy of science , extraction of iris signatures by means of zero - crossing of the dyadic wavelet transform developed by boles and so on 深入研究了多种典型识别算法: daugman的基于2 - d复值gabor小波的虹膜相位编码和hamming距离的方法; wildes和中科院的基于虹膜纹理分析的方法; boles的基于小波过零检测的方法;上海交大的基于小波模极大值的方法等。并在此基础上,对虹膜识别系统中的图像预处理和识别的若干算法进行了改进。
The traditional detection algorithm , based on zero - crossing or energy , will not acquire ideal effect when the signal - to - noise is low or the signal is weaker . therefore , to resolve the real problem in the real environment that all kinds of random noise and speech signal exit together , some new algorithm must be put forward . account for the complexity of real noise , we integrate the wavelet transform and high - order statistics and advance a new algorithm ; the algorithm can effectively separate the speech signal and the non - gauss noise 基于过零率和能量的传统检测算法,在噪声环境比较复杂的情况下效果很不稳定,尤其是信噪比较低或者语音信号较弱时,检测效果很不理想,因此,在多种语言和噪声随机出现、噪声和语音强弱不一的实际噪声环境下,必须利用新的算法提取有用信号和噪声信号的有效特征,才能解决实际的问题。
According to the data character in well and the processing power of cpu , a kind of reduction coding technique is proposed to meet the demands of practical well logging . especially , noting that the continuous zero - passing character of sound wave signal , the error - transmitting effect causing by coding is constrained efficiently by using the zero - crossing information 并根据实际测井的需求，针对井下数据的特点和cpu的处理能力，提出了一种压缩编码方法，特别是根据声波信号不断过零的特点，利用过零信息，有效地抑制了编码所带来的误差传播效应。
Based on the tsc reactive compensation equipment , a new low - voltage intelligent controller is designed , which can slove switched - capacitor without instantaneous rush current by means of zero - crossing triggering of scr components , and can realize auto - tracking reactive power , compensating and auto - switching scb . msp430f149 mcu is used as its core controller . it is shown that the algorithm in hand has the vantage of decreasing power loss and lowers of voltage and increasing the distribution system efficiency , for example power factor 该控制器以msp430f149为控制核心，暂态投切控制晶闸管过零触发，避免了电容器投切时的电流冲击；稳态运行时接触器替代晶闸管，实现了无功补偿的自动跟踪和电容器的自动投切，解决了投切时的暂态电流冲击和稳态可靠运行的难题。
