计量室人工接地体接地电阻的应用

众所周知,埋入地中与大地紧密接触并与大地形成电器连接的一个或一组导电体成为接地体,连接至接地端子的导体也就是接地线,这样构成接地极系统.随着现代计量科学技术的发展,对接地的要求越来越高.如要求阻值低,更稳定、经费少、占地少等等,本文根据设计、施工、到最终测试结果,说明合理采用降阻剂,是目前较理想的办法.     

接地与接地电阻测量

接地与接地电阻测量福州市计量所严晓玲接地电阻表属国家列入安全防护方面强制检定的计量器具，如何正确使用接地电阻表，对保证安全生产意义重大。现结合工作实践，谈谈我们对接地电阻测量的一些体会。１接地的几种方式为了将电流泄放入地，需要在土壤中埋设金属导体（接...     

接地电阻的确定方法

本文介绍了接地电阻的常用确定方法，阐明了不同测量方法的原理和适用范围，并分析了如何精确测定接地电阻值；同时，对土壤电阻率的测取、接地电阻的分类及关系进行了论述。     

降低输电线路接地电阻的方法研究

在电力建设中,良好的接地装置是保证电网安全稳定运行的重要措施,它的作用主要是防止设备和线路遭受雷击的损坏,预防火灾及静电损害,从而对电力系统正常运行提供有效保障。本文作者结合山区特点,主要对电力线路施工中如何降低接地体的接地电阻的方法进行了分析,同时就降低土壤电阻率进行了阐述。     

大电流接地电阻测量仪检测方法探讨

介绍了检测大电流接地阻测量仪的三种方法。对每一种方法的原理、技术关键以及误差情况等做了较全面的阐述，并分别用三种方法进行了模拟实验和比较，从而检测了检测大电流接地电阻测量仪的切实可行的方法。     

对25安培接地电阻仪检测方法的探讨

目前，我国地市计量部门使用的一组标准电阻或电阻箱允许工作电流达不到25安培，对检测工作带来不便。本探讨了采用普通铜线为载体，对大电流接地电阻仪的检测方法。     

钳形接地电阻测试仪校准方法探讨

钳形接地电阻测试仪是用来测量任何有回路系统之接地电阻值,在国外已成功应用多年,由于其测量方法简便,重复性好等优点,近年来在我国逐步地推广使用,目前我国还没有正式发布的校准规范。本文经过实际工作的实践,提出了钳形接地电阻测试仪的校准方法供探讨。     

Frequency domain methods for reducing transducer variability

A major objective of quantitative nondestructive evaluation is to formulate defect detection, classification, and sizing algorithms that are insensitive to variations in transducer characteristics, material type, and defect depth. With the data used in this research, ultrasonic signals were found to vary significantly with changes in the transducer and only secondarily with changes in material and depth. It is shown that the method for minimizing signal variations due to transducer and material changes is to deconvolve the test signal with respect to the transducer response from a reference defect in a block of the same material. Since depth variation primarily affects signal amplitude and has minor impact on shape, detection, classification, and sizing, insensitivity to depth is achieved by avoiding the use of amplitude-dependent parameters. The notion of a standard transducer is introduced. Its mathematical properties and methods of realization are given. It is shown how the effects of variability from different test transducers can be removed by signal processing. When these procedures are applied to the test transducer, the effect is to cause it to resemble the standard transducer and, thereby, to place all ultrasonic waveforms on a common basis.     

Suppression methods of radon emanation from phosphorus fertiliser and diatomaceous earth

The present paper shows methods to suppress radon emanation from artificial porous materials such as phosphorous fertiliser or diatomaceous earth with a small amount of radium. The basic concept of suppression is making the radon emanation mechanism 'null', which comes from the fact that recoil is the main mechanism of radon emanation at room temperature. Nullifying may be done through removal of water in the pore volume by heating and through removal of pores by melting or filling with sulphur. These radon emanation suppression methods were tried for phosphorous fertiliser and diatomaceous earth with a small amount of radium. The melting method was the most effective of all. Sustainability of these methods was also studied. The melting method was the most sustainable. The heating method was also sustainable for diatomaceous earth in spite of a long-term immersion in water.     

Comparison of methods for reducing the effects of scattering in spectrophotometry

Light scattering provides a problem in optical spectroscopy as the relationship between attenuation and absorption in the presence of scattering is nonlinear. Three simple methods of reducing the effects of scattering and hence returning to an approximately linear relationship are considered in this paper, namely, extracting light that has maintained its original polarization state through subtraction of orthogonal polarization states, use of an added absorber, and spatial filtering. These can all be applied relatively easily to conventional spectrophotometers. However, there is an inevitable trade-off between the accuracy of the measurement and the signal-to-noise ratio as scattered light is rejected from the detector. It is demonstrated that polarization subtraction is the most efficient technique at selecting weakly scattered photons from a scattered light background as it enables the relationship between attenuation and absorption coefficient to become more linear while maintaining a higher number of detected photons. In practical use, the drawback of polarization subtraction over added absorber and spatial filtering methods is that a large dc background light level is maintained, which contributes to a higher shot noise. This means that when the scattering coefficient is high (micros > or = 7 mm(-1)) the added absorber method offers better performance for shot noise limited detection.     

Two methods of reducing the dynamic range of a holographic filter

Two methods of reducing the dynamic range of the transmittance of computer-generated interconnection holograms are presented and compared. The holograms are used in an optical implementation of an associative memory to connect the input and the output planes but are representative of more generalN(4) interconnection holograms. Because the holograms play a double correlation-reconstruction role, the standard spectrum-smoothing techniques (e.g., random phase) cannot be applied. We show, in computer simulations and optical experiments, that by using deterministic phase functions that can be realized in the optical system (defocusing the hologram or controlling the phases of the diffraction spots of a Dammann grating used in the system input) the hologram dynamic range can be lowered, reducing the errors during the hologram binarization and increasing the hologram's diffraction efficiency.     

碱土金属离子对微晶玻璃性能的影响研究

根据玻璃工艺学原理,选取相同摩尔含量的不同周期碱土金属氧化物制备微晶玻璃,采用DSC分析、XRD测试和力学性能、介电性能、热膨胀性能测试来研究其析晶特性以及各项物理性能随其中碱土金属离子R2 的变化.揭示出几点规律:随R2 周期数的增大,玻璃的析晶峰值温度降低,但烧结温度范围减小;微晶玻璃的抗弯强度随R2 周期数的增加先降低后增加;介电常数随R2 周期数增加而增大,介质损耗则随之减小;热膨胀系数随R2 周期数增加而增大.