TBQ—2型总日射表热滞后效应的理论分析

总日射表自曝光至热稳定经历了从非稳态传热到稳态传热的过程。采用集总热容法建立了热端的换热微分方程，通过求解得到了达到热稳定之前，总日射表输出电压随时间变化的函数关系，估算了热稳定时间的数量级，得到了热稳定时间与总日射表的物性参数，工作条件之间的关系。与实验结果作了对比。     

TBQ－2型总日射表热滞后效应的理论分析

总日射表自曝光至热稳定经历了从非稳态传热到稳态传热的过程。采用集总热容法建立了热端的换热微分方程，通过求解得到了在达到热稳定之前，总日射表输出电压随时间变化的函数关系，估算了热稳定时间的数量级，得到了热稳定时间与总日射表的物性参数、工作条件之间的关系。与实验结果作了对比。     

分光总日射表校准因子的迭代计算法

详细讨论了分光总日射表的校准方法。论证了以一台直接日射表和一台遮蔽的总日射表为标准的校准方法优于仅用一台直接日射表为标准的校准方法，并提出了分光总日射表校准因子的迭代计算法。该方法可以解决由于遮蔽的总日射表校准因子不准确而产生的误差。最后还讨论了在校准过程中时间准确的重要性，指出至少应准确到分，否则每分的误差通过太阳高度角的正弦会给直接日射值带来０．２％的系统误差。     

PSP总日射表热偏移特征及其测量总辐射误差分析

根据2004年7月～2006年5月期间北京上甸子大气区域本底站Eppley PSP总日射表观测太阳辐射数据,分析了PSP表的热偏移特征及其影响因子,并以Eppley8-48型日射表和NIP直射表分别观测的散射和直射辐射之和作为总辐射的标准值,分析了PSP总辐射的误差特点及其影响因素.研究表明:PSP总日射表的热偏移呈现正态分布特征,平均值为-8.8±2.7W·m-2;PSP表热偏移显著受到净长波辐射、风速、相对湿度和温度的影响,其中与风速和相对湿度的相关性最为明显.与标准的太阳总辐射观测值(水平面上的散射与直射辐射之和)相比,未做热偏移订正的PSP总辐射的平均误差约为-20.0W·m-2,经过当日平均热偏移订正后,平均误差接近-11.0W·m-2.PSP表测量的总辐射绝对误差也呈准正态分布特征,但晴天与云天略有区别.PSP总辐射的相对误差与太阳天顶角的变化以及云量均有相关关系,反映了半球型辐射表的余弦效应对PSP总日射表测量精度的影响.太阳辐射的强弱变化或总辐射中散射与直射所占比率的相对变化也对PSP总日射表的测量精度有一定影响.研究表明:总日射表测量的总辐射应考虑热偏移订正,总日射表标定还应考虑云的影响.     

标准传递中日射表光谱误差的模拟计算

工作直接日射表一般都有窗口，而标准直接日射表却没有窗口。校准时，由于窗口都有一定的波长范围，必然会截去部分日射，利用ＬＯＷＴＲＡＮ６对其影响进行了光谱模拟计算。结果表明，石英玻璃窗口的影响不大，相对误差一般均在±１％以内；如果采用ＷＧ２９５窗口，则其影响不容忽视。利用ＬＯＷＴＲＡＮ６并配合Ｉｑｂａｌ方法，对总日射表进行类似的研究表明，窗口对总日射表的影响不像直接日射表那样明显，相对误差一般均不超过±１％。根据光谱计算结果，认为与分光总日射表配合使用的总日射表在校准时，作一标准用的直接日射表应加上ＷＧ２９５窗口，以便与其它分光总日射表的长波端的截止波长一致，否则将会引起１－２％的系统误差。     

国产紫外总日射表性能测试(Ⅱ):室外测试及与国外同类产品比较

介绍了几种国产紫外总日射表与美国YankeeUVB-1型紫外总日射表和EppleyTUVR型紫外总日射表在室外进行半年对比试验的结果。发现:在几种国产紫外总日射表中,从性能上讲,无论是与TUVR型的相关性,还是余弦响应,均以UVB-2型总日射表为佳,另外,该总日射表还具有自动恒温装置,从而可免受环境温度的干扰;原计划在对比中以YankeeUVB-1型紫外总日射表作为UVB波段总日射表的相对标准,通过试验发现,它与任何一种紫外总日射表之间的关系均呈非线性。通过对其余弦响应实际测量发现,由于该紫外总日射表并无余弦修正装置,余弦响应不良也就不足为奇了。YankeeUVB-1型总日射表虽与EppleyTUVR型总日射表在测量波段上并不一致,但通过理论计算发现,在太阳高度较高时(>40°),二者之间还是存在着较好的线性关系。可以借此判断仪器性能之优劣。     

光电型总日射表性能的初步研究

对光电型总日射表与ＰＳＰ型总日射表进行了对比测试。在带有圆柱形余弦修正器时光电型总日射表的灵敏度尚佳。在太阳高度角小型３５°、没有温度补偿或将传感器与二次仪表做成一体时其误差较大     

太阳辐射测量仪表

TBQ-1总日射表和TBS-1直接辐射表的主要性能示干表1。 DZR、DR、JZR、PR日射记录仪是一种数字化专用仪器。采用国产低漂移、低功耗集成运算放大器和CMOS中规模集成电路。其特点是:精度高、性能稳定可靠、耗电少、连续工作时间长、有较远的有线遥测距离(≥150米)、交直流两用。主要性能示于表2。     

总日射表倾斜效应的研究(Ⅱ)——物理机制初探

本文从总日射表传感器的热平衡出发,分别对黑白型和全黑型总日射表内各种传热方式随倾角的变化进行了分析和讨论,并得出总日射表内对流换热随倾角的变化是造成倾斜效应主要原因的结论。文中还指出了影响总日射表体内对流换热变化的各项因素,并对黑白型表的倾斜效应大于全黑型表以及首次发现的方位和辐照水准对倾斜效应的影响等原因作了解释。     

总日射表的积分球校准

本文报道了总日射表用积分球校准的结果。改进后的积分球构造简单,体积小,测试台面上的光线平均入射角比一般校准积分半球小,有利于减少余弦响应误差。该积分球校准总日射表的重复性为±0.5％。三种总日射表的积分球校准结果同太阳光下校准结果的偏差为3.3％。本文还对减小校准偏差进行了讨论。     

Measurement and analysis of the step response of pyranometers requiring second-order correction

We have measured the time response of Kipp and Zonen CM-5 pyranometers to a step function of radiation and observed that the pyranometer output varied significantly from a single exponential function of time. Using a multi-exponential function to fit the experimental data, we extracted the two dominant exponential components of the signal to obtain the analytic function describing the pyranometer response. A thermal model of the pyranometer has been developed, whose response displays the observed time behaviour. The model was applied to correct the time response error of the pyranometers subject to a step function of incident radiation, and compared with a single exponential correction scheme.     

宽温域中碳纤维导热特性研究

碳纤维作为一种被广泛应用的微纳米材料,对其导热性能的测量研究一直被作为对碳纤维性能研究的重要内容。在利用氦气的气体液化基础上搭建的超低温实验环境中,基于瞬态电热法对处于290到10 K温度内的碳纤维样品的导热性能进行研究。实验发现,当实验温度低于某一特定温度后,材料的热扩散率表现出与声子散射分析相反的实验结果。通过引入热扩散系数倒数这一理论研究声子热阻在低温下的变化,分析得出,当实验环境温度低于某一特定温度后,低温会造成碳纤维材料内的石墨微晶体结构发生变化,从而造成材料热扩散率下降。     

A method to calibrate a solar pyranometer for measuring reference diffuse irradiance

Accurate pyranometer calibrations, traceable to internationally recognized standards, are critical for solar irradiance measurements. One calibration method is the component summation, where the pyranometers are calibrated outdoors under clear sky conditions, and the reference global solar irradiance is calculated as the sum of two reference components, the diffuse and subtended beam solar irradiances. The beam component is measured with pyrheliometers traceable to the World Radiometric Reference, while there is no internationally recognized reference for the diffuse component. In the absence of such a reference, we present a method to consistently calibrate pyranometers for measuring the diffuse component with an estimated uncertainty of ±(3% of reading+1 W/m²). The method is based on using a modified shade/unshade method, and pyranometers with less than 1 W/m² thermal offset errors. We evaluated the consistency of our method by calibrating three pyranometers four times. Calibration results show that the responsivity change is within ±0.52% for the three pyranometers. We also evaluated the effect of calibrating pyranometers unshaded, then using them shaded to measure diffuse irradiance. We calibrated three unshaded pyranometers using the component summation method. Their outdoor measurements of clear sky diffuse irradiance, from sunrise to sundown, showed that the three calibrated pyranometers can be used to measure the diffuse irradiance to within ±1.4 W/m² variation from the reference irradiance.     

An improved pyranometer

This paper outlines the sources of error of changes in calibration that can occur in pyranometers. Several new prototype pyranometers have been constructed and tested. These pyranometers, by suitably choosing the materials of construction, have output signals independent of ambient temperature. Measured data presented shows that they are superior to the current pyranometers in use throughout the world, particularly when mounted in an inclined position.     

Soiling of irradiation sensors and methods for soiling correction

Access to exact solar irradiation data is indispensable for planning and dimensioning of applications as e.g. solar power plants. The expectable amount of yearly solar irradiation has an over-proportional impact on the financing and therefore has to be known very precisely. For this reason, DLR performs investigations at PSA to improve the accuracy of irradiation data, which are measured at several locations in southern Spain and Morocco. Devices as Rotating Shadowband Pyranometers (RSP) as well as thermal pyranometers and a pyrheliometer are used. Besides well-documented and known technical aberrations, soiling of the sensors is an important source for underestimation of the measured irradiation, especially at offside stations where daily maintenance is not possible. In this paper, we present soiling characteristics of these sensors and a corresponding method for its correction.     

国产紫外辐射仪器性能测试(I)——室内静态性能测试

对国产3种UVB和2种UV辐射表的余弦响应、非线性、带外杂光水准、温度特性和光谱特性等仪器静态性能进行了细致的测试。对不同型号仪器性能有所了解,便于对仪器的选用和改进。     

Dust-induced degradation of pyranometer sensitivity

The effect of dust accumulation on the sensitivity of pyranometers is studied in order to estimate the possible loss of accuracy associated with leaving the instruments unattended for extended periods of time. Under the arid conditions of Sede Boqer, Israel, the dust effect reduces the sensitivity of a horizontal pyranometer by one permille per day. For periods extending up to several weeks, the degradation rate appears to be constant, and no saturation effects are observed. The propagation of the measurement errors associated with dust accumulation on pyranometers to the errors on the beam and global radiation values derived from a stationary multipyranometer system is discussed.     

The distribution of global solar radiation over the land surfaces of the earth

The history, present world distribution and accuracy of measurements of global solar radiation are briefly reviewed. 221 annual total values measured during 1975 with thermopile pyranometers, were used to map the world distribution of solar irradiation and statistically analyze its variation with latitude, altitude and longitude in the northern and southern hemispheres. The pole-to-pole distribution of irradiation was fitted by cubic splines with seven knots giving a standard deviation that was 12 per cent of the average irradiation over the Earth's land surface. The distribution based on the 1975 data is compared with previously published analyses and current uncertainties and gaps in the world measurement network are discussed.     

A multisensor pyranometer for determination of the direct component and angular distribution of solar radiation

This paper describes a technique for determining the direct component and the angular distribution of the diffuse component of solar radiation. The information is obtained by measurement of the total radiation on slopes of different orientations. This has been done using a new multidirectional pyranometer, called a multipyranometer, specially developed for this purpose. The instrument incorporates 25 radiation sensors mounted on a metal hemisphere. Each sensor consists of a blackened copper plate with a semiconductor temperature transducer. Sensors are enclosed in an evacuated glass envelope and each of them is connected to its own digital integrator. Computer programs have been developed for data quality control, monitoring and computations. Some of the results from laboratory tests and solar radiation measurement obtained over a period of two years are given. Comparisons are made between observations obtained with the multipyranometer and those obtained with conventional pyranometers. Experimental observations are also compared with some radiation models.     

Ground reflectance estimation by means of horizontal and vertical radiation measurements

The importance of an accurate estimation of the ground reflectance is well-recognized in energy balances involving solar radiation. Despite there are methods to estimate it directly it is still a hard task in highly reflective environment or in urban areas. In those areas it is also hard to find measurements of the ground-reflected component of the solar radiation. However, data coming from solar energy installations could be employed to estimate the local ground reflectance. To achieve this goal a method to estimate the ground reflectance from global radiation measurements in several orientations is needed.In this work the question of the estimation of the ground reflectivity from measurements of the global solar radiation on orientations typical from the energy installations is addressed.Two different approaches are presented to solve the same problem. First, by direct solution of global radiation models the ground reflectivity is deduced from the measurements (known as direct problem approach). In second place, from physical hypothesis about the behavior of the solar radiation such as isotropy and diffuse correlations the ground reflectance is approximated from experimental data (known as inverse problem approach) at the points where reality is closer to these conditions. In this framework, it is shown the need of mathematical tools such as Tikhonov regularization.The two approaches have been tested by means of the data produced at the CIEMAT’s test facilities from the Energy Efficiency in Building R&D Unit (UiE3) at Plataforma Solar de Almería (PSA) located at the South-East of Spain. Approaches are tested on data coming from several pyranometers on the rooftop of a building. Cross-validation is performed with measurements coming from an albedometer.It is shown that the inverse technique can solve the problem by taking near two weeks of measurements of global solar radiation on the horizontal and vertical surfaces. With the same set of experimental data the direct technique is unable to estimate the ground reflectance even with the inclusion of a third measurement on other surface.