利用光学方法测量实验室标准传声器的前腔深度

实验室标准传声器的前腔深度是耦合腔互易法校准其声压灵敏度的主要不确定度分量之一.为了控制声压灵敏度校准的不确定度,利用光学三坐标自动测量系统,分别通过直测法和块规法测量3只LS1P和3只LS2P传声器的前腔深度.测量结果表明,在传声器外环面放置高精度的块规,较好匹配了传声器与平面波耦合腔进行声学耦合时的物理模型,其前腔深度测量不确定度优于3.0 μm(k=2).对于LS1P传声器20 Hz～10 kHz频率范围内的声压灵敏度,前腔深度引入的不确定度分量优于0.005 dB(k=2);对于LS2P传声器,20 Hz～25 kHz频率范围内的不确定度分量优于0.012 dB(k=2),能够实现实验室标准传声器声压灵敏度的高精度校准.     

光学三坐标测量仪在传声器参数测量中的应用

将光学三坐标测量仪应用到实验室标准传声器前腔深度的测量过程中,其测量结果表明,利用光学三坐标测量仪可以对传声器的前腔深度进行高精度的测量,其测量不确定度优于3．4μm（k=2）,较好控制了耦合腔互易法校准声压灵敏度的不确定度分量。     

平面波耦合腔中热传导和声泄漏对低频互易校准的影响

针对低频耦合腔互易校准中存在的热传导和声泄漏问题,通过理论计算和不同长度耦合腔的系列实验研究,探讨其对互易校准结果的影响规律。首先阐述了互易校准原理及电容传声器低频时的频响特征,传声器均压孔在声场外时,低频声压灵敏度随着频率降低而逐渐增加;其次,对发射传声器-耦合腔-接收传声器构成的耦合腔系统中的热传导修正因子进行计算,结果表明,随着耦合腔长度变长,热传导修正因子变小,不确定度分量变小;通过不同长度的耦合腔组成的互易校准系统研究声泄漏的影响并探讨其优化方案,实验结果表明,10 mm和15 mm耦合腔对互易校准结果影响较小,重复性高,该实验结果与传声器的低频响应特性一致。     

实验室标准传声器静压和温度修正系数的测量

为测量实验室标准传声器的静压和温度修正系数,在耦合腔互易法声压基准的基础上建立了静压调节系统和温度控制装置。对不同静压和温度条件下利用耦合腔互易法获得的传声器声压灵敏度进行线性拟合,得到不同频率条件下的静压修正系数和温度修正系数。实验结果表明低频段静压修正系数和温度修正系数基本保持不变,频率值在传声器膜片谐振频率值的1/2处,静压修正系数和温度修正系数分别存在最大值和最小值。     

时选窗技术在传声器自由场互易校准中的运用

实验室标准传声器的自由场互易校准是复现声压量值的一种基本方法,在测量过程中需要测试系统具有很高的信噪比.在空气声自由场声压基准装置中采用了步进正弦信号扫描和时间延迟谱技术测量传声器转移阻抗复频率响应,并采用IFFT得到脉冲响应,通过时域窗口消除反射,有效提高了信噪比,在体积较小的消声箱内完成了互易校准.     

耦合腔互易法声压国家计量基准

耦合腔互易法声压基准建立于1965年，于1986年批准为国家计量基准，并于1990年进行了技术改造。它采用耦合腔互易技术，通过精确确定基准传声器声压灵敏度的方法来复现声压量值。该基准装置包括：互易校准仪、一级基准传声器、一套耦合胜、信号发生器、差分电压表以及其他配套设备。国家计量基准介绍主要技术指标为：频率范围：SOth－ZqUth；不确定度：0．05dB（k＝3）；重复性：o．o川B；其主要技术指标接近国际先进水平。耦合腔互易法声压基准承担着我国声压量值传递及国内外比对的任务，为科研、生产、环保、医学等领域的声压量值准确…     

LS2F传声器的高频自由场互易校准

为满足空气超声声压量值的溯源需求,利用PULSE分析仪和互易校准仪,采用时间加窗技术对频域信号转换得到的时域信号进行处理,建立了LS2F传声器的高频互易校准装置,实现了实验室标准传声器的20~51 kHz的自由场灵敏度校准。通过对比时间加窗处理前后的实验数据,分析了驻波和墙体发射波对传声器灵敏度的影响。结果表明,高于40 kHz时,时间加窗处理技术能够减小1.0 dB的偏差。     

噪声变送器电流输出声压灵敏度测量结果的不确定度评定

介绍了一种直接测量噪声变送器电流输出声压灵敏度的不确定度评定方法,对频率1000Hz、声压级84. 0dB时的噪声变送器电流输出声压灵敏度的测量不确定度进行评定,得到测量结果的扩展不确定度为0. 0011mA/d B(k=2),为噪声变送器电流输出声压灵敏度的准确校准提供了技术参考。     

仿真耳的高频校准

仿真耳是听力计量的主要仪器之一,为满足听力计在8~16 k Hz高频范围内的计量需求,须对仿真耳进行高频校准。通过适配器的使用,解决了仿真耳高频校准中存在的测量结果不稳定的问题。同时,针对仿真耳中传声器声压灵敏度级和仿真耳声耦合腔声学特性这两项主要技术指标,建立了8~16 k Hz频率范围内的自动测量系统,对其进行测量。测量结果表明声压灵敏度级的标准偏差小于0.2 d B,表征耦合腔声学特性的频响测量标准偏差小于0.3 d B。     

静态质量法水流量标准装置校准流量计不确定度分析的讨论

文章主要讨论使用静态质量法水流量标准装置校准体积流量计,进行不确定度分析时应注意的问题。静态质量法装置获得的是质量流量,校准体积流量计时应换算为体积流量,换算过程需要获得准确的水密度值。我们一般采用测量水温查表法和密度计测量法获得水的密度值,这里主要讨论两种测量方法带来的不确定度分量的不同以及它们对扩展不确定度的影响的不同。     

Non-Contact Methods for Measuring Front Cavity Depths of Laboratory Standard Microphones Using a Depth-Measuring Microscope

To achieve an acceptable degree of accuracy at high frequencies in some standardized methods for primary calibration of laboratory standard (LS) microphones, the front cavity depth l_fc of each microphone must be known. This dimension must be measured using non-contact methods to prevent damage to the microphone diaphragm. The basic capabilities of an optical depth-measuring microscope were demonstrated by the agreement of its measurements within 0.7 μm of the known values of reference gage blocks. Using this microscope, two basic methods were applied to measure l_fc. One (D) uses direct measurements at the microphone front surface annulus and conventional data reduction techniques. The other (GB) uses measurements at the surface of a gage block placed on the annulus, and plane-fitting data reduction techniques intended to reduce the effects of the slightly imperfect geometries of the microphones. The GB method was developed to provide a smoother surface of measurement than the relatively rough surface of the annulus, and to simulate the contact that occurs between the annulus and the smooth, plane surface of an acoustic coupler during microphone calibration. Using these methods, full data sets were obtained at 33 measurement positions (D), or 25 positions (GB). In addition, D and GB subsampling methods were applied by using subsamples of either the D or the GB full data sets. All these methods were applied to six LS microphones, three each of two different types. The GB subsampling methods are preferred for several reasons. The measurement results for l_fc obtained by these methods agree well with those obtained by the GB method using the full data set. The expanded uncertainties of results from the GB subsampling methods are not very different from the expanded uncertainty of results from the GB method using the full data set, and are smaller than the expanded uncertainties of results from the D subsampling methods. Measurements of l_fc using the GB subsampling method with only nine measurement positions exhibit expanded uncertainties (with coverage factor k = 2) within 4 μm, and can improve the uncertainty of microphone calibrations by an order of magnitude over the result from use of generic standardized microphone type nominal l_fc values and tolerance limits.     

Analysis of the Effect of Microphone Parameters in Reciprocity Calibrations Using Taguchi Method

The paper presents parametric study investigating the relative influence of the various microphone parameters affecting the closed coupler reciprocity measurements while computing the sensitivity of reference standard microphones using the well known MP.EXE program used by National Metrology Institutes of various countries. A design of experiments perspective using L ₉ (3⁴) orthogonal array and analysis of variance (ANOVA) method is presented for LS1P and LS2P microphones. The relative importance of microphone parameters on its sensitivity is evaluated in terms of percentage contribution using ANOVA methodology.     

标准煤气表仪表系数测量不确定度分析

本文简略介绍了标准煤气表的测量方法，并依据JJG267-1996标准煤气表检定规程和JJF1059-1999测量不确定度评定与表示，对标准煤气表仪表系数测量结果进行不确定度的评定。具体分述各个不确定度分量（包括标准煤气表示值、气体流量标准装置通过的气体体积、装置内压力、标准煤气表前压力、装置内气温、标准煤气表前气温、装置内的饱和蒸汽压、标准煤气有处的饱和蒸汽压、装置内气体相对湿度、标准煤气表处的气体相对湿度）的产生，并合成标准不确定度及给出有效自由度。     

Measurement Accuracy of Secondary Standards of Sound Pressure in Comparison to Primary Standards

The paper presents the measurement uncertainty achieved in realizing the primary standard of sound pressure at NPL, India and comparison of the uncertainties of secondary calibrations with that of primary standard. The uncertainty associated with calibration of acoustic calibrators, working standard microphones and sound pressure level measurements is discussed. A comparison of the actuator response with that taken from reciprocity setup for working standard microphones is also presented. The major focus of the present work is to highlight the traceability chain established in measurement of sound pressure level and propagation of measurement uncertainties directly from the national primary standard to field measurements, which are very rigorously conducted in transportation noise monitoring, machinery noise diagnostics, noise labeling of electrical appliances and environmental impact assessment studies w.r.t noise abatement and control.     

New Measurement Service for Determining Pressure Sensitivity of Type LS2aP Microphones by the Reciprocity Method

A new National Institute of Standards and Technology (NIST) measurement service has been developed for determining the pressure sensitivities of American National Standards Institute and International Electrotechnical Commission type LS2aP laboratory standard microphones over the frequency range 31.5 Hz to 20 000 Hz. At most frequencies common to the new service and the old service, the values of the expanded uncertainties of the new service are one-half the corresponding values of the old service, or better. The new service uses an improved version of the system employed by NIST in the Consultative Committee for Acoustics, Ultrasound, and Vibration (CCAUV) key comparison CCAUV.A-K3. Measurements are performed using a long and a short air-filled plane-wave coupler. For each frequency in the range 31.5 Hz to 2000 Hz, the reported sensitivity level is the average of data from both couplers. For each frequency above 2000 Hz, the reported sensitivity level is determined with data from the short coupler only. For proof test data in the frequency range 31.5 Hz to 2000 Hz, the average absolute differences between data from the long and the short couplers are much smaller than the expanded uncertainties.     

Cylindrical Acoustic Resonator for the Re-determination of the Boltzmann Constant

The progress towards re-determining the Boltzmann constant k _B using two fixed-path, gas-filled, cylindrical, acoustic cavity resonators is described. The difference in the lengths of the cavities is measured using optical interferometry. Thus, a literature value for the density of mercury is not used, in contrast with the presently accepted determination of k _B. The longitudinal acoustic resonance modes of a cylindrical cavity have lower quality factors Q than the radial modes of gas-filled, spherical cavities, of equal volume. The lower Qs result in lower signal-to-noise ratios and wider, asymmetric resonances. To improve signal-to-noise ratios, conventional capacitance microphones were replaced with 6.3 mm diameter piezoelectric transducers (PZTs) installed on the outer surfaces of each resonator and coupled to the cavity by diaphragms. This arrangement preserved the shape of the cylindrical cavity, prevented contamination of the gas inside the cavity, and enabled us to measure the longitudinal resonance frequencies with a relative standard uncertainty of 0.2 × 10⁻⁶. The lengths of the cavities and the modes studied will be chosen to reduce the acoustic perturbations due to non-zero boundary admittances at the endplates, e.g., from endplate bending and ducts and/or transducers installed in the endplates. Alternatively, the acoustic perturbations generated by the viscous and thermal boundary layers at the gas–solid boundary can be reduced. Using the techniques outlined here, k _B can be re-determined with an estimated relative standard uncertainty of 1.5 × 10⁻⁶.     

小孔流导测量方法的研究

在分子流条件下,给出了定容法和恒压法测量流导的方法,分析了测量不确定度.采用定容法气体微流量校准装置和恒压法气体微流量校准装置分别对小孔流导进行了测量,对2种测量方法进行了比对,一致性好于1.0%.     

标准气体气瓶体积膨胀的精确测量

目前普遍采用称量法制备标准气体,在此过程中气瓶体积膨胀所引入的空气浮力的不确定度贡献不可忽视。设计了一个气瓶充气膨胀率测量装置,该装置可以控制气瓶内充入气体的压力,并利用精密移液管测量气瓶体积的膨胀量,从而准确计算出气瓶的充气膨胀率。利用该装置对国内常见的2L、4L和8L铝合金气瓶进行了测量,结果显示气瓶体积的膨胀与充入气体的压力近似成线性正相关。而且气瓶外观体积越大,充气膨胀率的数值越大,量值之间也呈现出较强的相关性。基于获得的气瓶充气膨胀率数据,可以进一步降低气瓶体积膨胀对瓶内充入气体质量的不确定度贡献,从而使气体质量的计算更加精确。     

矢量水听器自动校准系统的研究及实现

研制的矢量水听器自动校准系统在水声计量领域具有重要的应用价值,能够实现低频范围内矢量水听器的自动校准。利用动态信号采集卡采集被测信号和标准水听器的输出信号,对驻波管内的声场分布进行了测量分析,对系统的测量不确定度进行了分析评定,对声压灵敏度进行了比对测试。该系统校准矢量水听器的扩展不确定度为1.6dB。