低温漂过温保护带隙基准源研究

通过对Brokaw带隙基准电压电路的改进,设计出具有基准启动电路、带隙基准电压源核心电路、曲率补偿电路、输出过温保护电路的低温漂过温保护带隙基准电压源,它具有低温漂、功耗低、电源抑制比高、结构简单、易于集成等特点。     

高稳定度可调恒流源的设计与实现

针对影响恒流源稳定性的因素,制定相应的改进解决方案以确保输出电流的稳定,通过设计基于场效应管和运算放大器组成的串联反馈电路来保证电流的稳定性。实验测试的结果表明,串联反馈电路中加入运放的隔离电路使得前后级的电路更加稳定,同时基准电压越稳定,恒流源的输出电流越稳定,在市电供电情况下,经过预热可以产生更加稳定的基准电压。通过实验测试,恒流源样机达到10-6量级稳定度以及输出电流范围在0～1 A可调的设计要求。     

高稳定度直流恒流源的设计

高精度直流电位差计UJ52型所使用的专用高稳定度直流恒流源，其设计采用六节锌汞电池作为恒流源基准。由于该电池极易损坏（正常使用时每年都需换新），而且其他部件损坏在本地无法购置，使仪器·的使用受到极大的影响，故设计一高稳定度恒流源电路以代替原电路，是非常必要的。1电路设计原理电路设计采用了两级稳压稳流结构，首先由两稳压管LM7815和LM7915输出30V稳定的直流电压，尔后由低噪声、低漂移运算放大器Opo7等组成恒流输出的控制部分所控制。电路。设计的关键是采用了Lto99高精度基准电压源.作为恒流源的基础。LMi99为自带温…     

一种新型的铜电阻测温电路

目前,铜电阻已广泛地用作测温元件,但是,铜电阻的电阻-温度特性直接用于温度测量是有困难的,一般是采用将电阻变化转换成电压变化,并使电压变化量与温度变化量成正比关系的办法,即利用具有将电阻变化量转换为电压变化量的变换电路。本文介绍一种将变换、放大、补偿三位一体的新型变换电路。如果配接数字电压板表,可作为数字式温度显示仪,配接电压——电流变换器又可以构成铜电阻温度变送器。这种电路即为双恒流源变换电路。一、双恒流源变换电路本文所提出的新型变换电路如图1所示,也称之为双恒流源变换电路。图1中,R_1代表测温铜电阻,r_1、r_2、r_3为铜电阻的引线电阻,工厂中习惯于采用三线制,尽可能地使三条线长度相同、电阻值相等。I_1和I_2是两个电流源,I_1是I_2的二     

高耐腐蚀锌钙系中温磷化液的研制

阐述了以锌、钙盐为主要成膜物质，以硝酸盐和自制TL促进剂为促进剂，以有机酸和TL添加剂为稳定剂，合成了一种具有高耐腐蚀性的锌钙系中温磷化液。探讨了游离酸度、总酸度、温度、时间以及钙离子对磷化成膜的影响。     

智能温湿度变送器的精密测温电路研究

研究一种基于铂热电阻的智能温度变送器精密信号检测电路。该电路由测量回路、多路模拟开关、高分辨率A／D转换器构成,可对零点、增益误差、温度时间漂移及参数电压变化等进行补偿,其输出精度仅取决于一只精密参数电阻的精度。     

包装自动化中一种自适应可调直流电源的设计

介绍了在包装自动化中一种自适应可调制式电网的开关电源的设计.它主要是通过检测负载的电流变化,来改变PWM输出的占空比,用以驱动MOSFET管,实现恒压输出,采用改变UC3842内部集成运算放大器的基准电压来实现本电源可调的功能.另外,采用交流输入电路和整流滤波电路为反激式电路提供直流电源,在高频变压器的二次侧设置了由光电耦合器与TL431组成的保护电路,用以加强反激式自适应可调直流电源的稳定度和可靠性.     

SF—3A型石英晶体膜厚监控仪

以往研制的各种石英晶体膜厚监控仪.都不同程度的保留了模拟电路.不仅限制了频率检测的精度.而且未解决频率变化与质量厚度非线性关系所造成的测厚误差问题.SF-3A 型石英晶体膜厚监控仪的主要设计思想是:提高晶体切角精度.采用孪生晶体技术,大大改善频温特性;选用小的电极面积和开孔.减小频漂:选择考毕兹振荡电路和二极管大讯号混频电路.以提高可靠性;检测电路都作数字化处理.提高检测精度.避开了频率变化与质量厚度非线性关系的问题.研制的 SF-3A 频漂小.运用温度范围宽.具有若干状态监测点和数据保护手段.性能指标达国外同类产品水平.介绍了仪器的电路原理和使用方法.     

PSD 信号处理电路的研究

目的简化PSD信号处理电路,降低噪声信号和温漂的技术.方法用软件代替部分硬件电路的方法.结果简化了电路,提高了信噪比.结论这种方法适于多PSD计算机信号处理的智能测试系统.     

PSD信号处理电路的研究

目的 简化PSD信号处理电路，降低噪声信号和温漂的技术。方法 用软件代替部分硬件电路的方法。结果 简化了电路，提高了信噪比。结论 这种方法适于多PSD计算机信号处理的智能测试系统。     

交流磁场检测中激发频率与提离的影响分析

交流磁场检测是近年来电磁无损检测的重要进展之一,具有非接触、不需标定、检测速度快和适应性好等优点,在材料检测中具有广阔的应用前景。在检测过程中,激发频率的选取以及提离高度是影响信号分辨率的重要因素,以ANSYS软件系统为工具,建立了缺陷ACFM数值仿真模型,分析了信号对频率和提离高度的影响,结果显示ACFM方法更适合检测磁性材料。     

Detection and correction of distorted current transformer current using wavelet transform and artificial intelligence

Secondary current in a current transformer (CT) will become distorted if the CT becomes saturated because of a large primary current and a DC component. This distorted current may leads to a malfunction in the protective relay because it receives a smaller rms current during the period of the fault occurrence. Therefore detection and correction of the distorted current caused by the saturated CT is essential. The application of wavelet transform used to detect the occurrence time of the fault and identify all saturation periods is described. Two features of the fault current were extracted. Fuzzy-c-means was used to partition all possible currents into nine clusters according to their features. Nine multi-layer feed-forward neural networks (MFNNs) were trained individually with the corresponding smaller fault current data sets to obtain corrected secondary currents at the initial stage. Takagi-Sugeno-Kang fuzzy rules were then used to integrate all the MFNN output currents into the final corrected secondary current. The proposed method was verified by SIMUUNK/Visual C and was also implemented in a field programmable gate array (FPGA, Altera Stratix EP1S25F780C5 development board). The test results show the online applicability of the proposed method.     

Leakage current detection in cryogenic current comparator bridges

Several tests have been developed to locate leakage currents in cryogenic current comparator (CCC) resistance ratio bridges used at NIST to measure ratios of 1000 Ω/100 Ω, 6453.2 Ω/100 Ω, and 10 kΩ/100 Ω. The major advantage of the tests is that they can be performed in situ using the sensitivity of the CCC bridge. These test procedures have been used to reduce the leakage error uncertainty of CCC ratio measurements, linking working standards to the quantized Hall resistance (QHR) and to the NIST calculable capacitor experiment. CCC bridges require that the current which passes through a standard resistor must equal the current through the appropriate CCC winding to very high precision. This can be difficult to verify at or below 1 pA because a large number of possible leakage paths exist. Errors due to six important leakage current paths are given, and the calculated changes in the resistance ratio are compared with measurements made with a controlled leakage resistance in a 100 Ω/1 Ω CCC bridge     

Harmonic analysis of current waveforms using optical current sensor

This paper reports on the research and development of an optical current sensor for harmonic analysis within the electricity supply network. The device has a measurement capability, limited by the sampling frequency of the analog-to-digital converter, to around 20 kHz. We report on experimental verification of these measurements up to the 60th harmonic (3 kHz).     

Optimization of conduction-cooled current leads with unsteady operating current

A generalized optimization method is presented for conduction-cooled or cryocooled current leads whose operating current may vary over a period of time. This study is part of our ongoing efforts to reduce the cooling load in HTS power applications, where the actual current level varies considerably over a day and over a year. The presented method is also applicable to superconducting magnets that are not always operational at full current. When the operating current is given as a function of time, the total or accumulated cooling load at the cold end is calculated by integrating the instantaneous load over the period. The optimal length-to-area ratio of conductor is determined to achieve a minimum in the total load. After an accurate procedure taking into full account the temperature-dependent properties of conductor is developed with numerical calculations, a simple and reasonably accurate method based on Wiedemann-Franz approximation is suggested for practical use.     

Superconducting current switches for multiple superconducting critical current samples

A superconducting current switch is described, several of which can be stacked in a parallel array to allow the selection of a given sample to receive the high-current input from two current leads from the outside. The switch is a coil of superconducting wire which, when driven normal by a heater, shunts the current to a parallel, less-resistive leg. If such switches are stacked in parallel and (n ? 1) driven normal, all current goes through the superconducting member and its related sample. The configuration described here employs six switches with a test-current capability of 112 A to any sample.     

On the structure of Ni-S electrodeposits produced by direct current and pulse current methods

Ni-S electrodeposits have been produced by two plating methods, direct current (dc) and pulse current (pc) methods, in a nickel sulfate bath. The structure of electrodeposited layers has been studied in detail by X-ray diffraction methods. The electro-deposited layer produced by the dc method contains 21 at% S and consists of a microcrystalline state of Ni alloy. However, the layer by the pc method contains 46 at% S and consists of an amorphous alloy.