The calibration of CERL-Planer capacitance strain gauges

CEGB-Planer capacitance strain gauges are used extensively for monitoring the deformation of components operating in the creep range. However, there are significant differences between the way the gauges are installed for use and the way they are installed for calibration. This paper describes the various types of calibrations that have been carried out to identify the errors associated with these differences and the results show that, providing the manufacturers' recommendations are adhered to, the errors are acceptably small.     

A temperature calibration of a temperature/strain transducer based on two strain gauges

The operation of a temperature/strain transducer, called “duplex gauge”, based on two electrical resistance strain gauges, that are temperature compensated for use on materials with different coefficients of linear expansion, was briefly recalled. Three steel specimens were equipped with “duplex gauges” and were subjected to temperature variations and no external loads were applied. The chosen experimental setup (i) to measure the outputs of the gauge temperature compensated for steel and titanium silicate and (ii) to impose known temperature, assured good accuracy and precision in evaluation of the temperature calibration curve. The obtained results showed that the strain differences could be considered, at least for the experimental arrangement examined, a linear function of temperature over the range of 20 to over 140°C. The prepared calibration chart, that allows the correction of temperature induced apparent strain, will be used in future research when generic temperature and strain fields are applied to specimens.     

Experimental evaluation of a method for separating axial and bending stresses from strain gauge measurements taken on one surface by three-element rosettes

A method is described and results presented for the separation of axial and bending components of stress taken on one surface of a structure with a two-tier, three-element rosette assembly.     

Theoretical design of calibration beams for strain gauge factor measuring apparatus

By starting with theoretical analysis and combining with the needs of practical applications, this article carries out a preliminary theoretical investigation of optimum design of the cross sectional shape and dimensions of calibration beams for strain gauge factor measuring apparatus. A new formula is derived in this paper that shows the quantitative relationship among strains on the beam surfaces, the strain non-uniformity within a certain range of the beam and beam thickness, which provides a theoretical basis for the accuracy improvement of the measuring apparatus and for correct application of the calibration beams, and also for drawing up and improving items concerning with calibration beams in strain gauge standards internationally. It is proven through experiments that the neutral axis of the bent calibration beam of rectangular cross section under pure bending moments is actually not circular but parabolic.     

The use of vibrating wire strain gauges for long term measurements on buried gas mains

A trial agreement concerned with the effect of adjacent deep excavations on the risk of failure of buried cast iron gas and water mains was implemented by British Gas and National Water Council on 1 January 1983. To complement this agreement, field experiments are being carried out at selected sites throughout the UK. The British Gas Engineering Research Station (ERS) is working in cooperation with the Water Research Centre to install instrumentation to measure pipe strains, joint movement, ground temperature and ground movement.
Field measurements impose environmental and operating conditions of much greater severity than those encountered in a laboratory. This note outlines the site techniques developed by ERS which allow reasonably quick and reliable installation of equipment capable of withstanding the adverse conditions typical of backfilled trenches. The principle of operation of the VW gauge, its method of fixing, the factors affecting its output and the interpretation of the readings themselves are described.     

An assessment of a frictional strain gauge probe for dynamic strain measurement

A probe for the measurement of surface strains on dynamically loaded structures has recently been tested at the National Engineering Laboratory (NEL). The procedure for estimating the amplitude of the conditioned signals from the frictional strain gauge attached to the probe is described and the usefulness of the technique is discussed. Calibration data are presented from comparative tests of the performance of the frictional gauge and bonded gauges on an axially loaded testpiece subjected to sinusoidal and random loading conditions.     

真空比对法校准装置的研究

真空比对法校准装置采用了动态直接比对法、静态直接比对法和静态膨胀法,在一台装置上复合了三种方法,满足了拓宽量程的需求.该装置可以1×105-5×10-4 Pa范围内的各类真空规进行校准,是一种结构简单、操作方便、检定效率高、实用性强的真空标准装置.整套装置由涡轮分子泵、校准容器、副标准真空计和金属膨胀阀等部件组成,主要技术指标符合国际标准化组织和国内有关真空标准的规定.     

A prototype for a resistive extensometer as a strain measuring standard

The design, handling and calibration of a prototype to a resistive extensometer with 10 mm measuring length is described.
It stands on the test specimen via pins with conical tips. These end in hard metal spherical calottes with 16 micron nose radius. The manufacturing and maintenance of these tips was described earlier.
The extensometer is calibrated on a bending beam to 1 mm/m strain, using the loading and deflection equipment developed at the FFA and described earlier.
The total extensometer inaccuracy, i.e. the sum of estimated systematic errors and random errors, the latter expressed as the 2σ confidence interval about the mean, is about 400 × 10^-4%, for 60 reproduced calibration tests.
With the extensometer, it was shown that the beam, which was machined and hardened from an alloy with 1.4% Cr and 1.4% Ni and has a moderate hardness of H_v 430, does not show any kind of inhomogeneity in Young's modulus, within the resolution of the indicator.
Therefore, the extensometer is suitable for the determination of bonded resistance gauge factors, even if a total error of only ±0.1% is required. The prototype described can therefore be used as a strain measuring standard.     

A hybrid experimental-numerical investigation of dynamic shear fracture

Dynamic shear fracture is investigated by a hybrid experimental-numerical approach. The numerical simulations rely on LEFM assumptions and crack-tip stationarity. Violation of these assumptions is related to fracture or adiabatic shear banding and can be used to identify these events in a typical experiment. Firstly, the reliability of numerical model is verified by comparing our results with the analytical results of Lee and Freund [J. Appl. Mech. 57 (1990) 104]. Then a numerical simulation of Guduru et al.'s experiments is compared with their results to assess the onset of adiabatic shear banding in terms of a critical K_II value. Finally, dynamic shear experimental results are reported and analyzed using this approach for commercial PMMA and Maraging 250 steel specimens. In these experiments, the stress intensity factors are determined from miniature strain gauge measurements. A very good agreement is obtained between the present and previous values of K_II. The numerical exercises and the experimental results validate the use of hybrid experimental-numerical techniques for the identification of the onset of fracture, with a potential application to large-scale testing.     

Analysis of strain averaged data from finite length gauges and predictions of peak strain for planar notch and fillet problems

From a previously derived modal (i.e., series) representation of the stress and strain fields in stress concentration regions, exact analytical expressions are obtained for the averaging effects of finite length gauges located on the boundary of a notch fillet. A simple method of analysing such data is described. It is then applied to two problems to show i) how easily poor or faulty data can be detected and ii) how a very reliable estimate can be made of the magnitude and location of the peak stress (or strain), even when using data from gauges beyond the very highly stressed (strained) region.     

Using strain rate sensitivity measurements to determine phase relations in A430 stainless steel

Precision strain rate sensitivity measurements have been used to determine the solid solution component of interstitials in ferritic stainless steel. The measurements are based on activation volume of dislocation-solute interaction. Under an instantaneous strain rate change, a load drop occurs which is inversely proportional to the activation volume. By correlating the measured response with heat treatments a pseudo-binary Nb(C,N) solvus was determined. Such a phase diagram for a specific stainless steel alloy is useful for delineating hot-working conditions. The technique was also able to detect the presence of fine Guinier-Preston zone type of precipitates that formed during quenching and were aligned with the {001} planes of the matrix.     

低温压力传感器校准系统研制与应用

介绍了一种用于低温压力传感器校准装置,该装置能在试验室对低温压力传感器进行校准,可满足压力传感器复杂低温环境的要求,准确、客观地反映低温压力传感器的性能指标,具有较高的测量精确度.利用该校正装置在20 K、77 K条件下成功对某压力传感器进行标定,证明此套校验装置的有效性和可靠性.     

大型机械高精度安装校准基准给定的新方法

介绍一种大型机械安装校准的新方法，论述了利用拉直的钢丝和新型电容测微仪及多功能核准检具对大型机械安装校正给定高精度基准的方法。同时还简要介绍了电容测微仪在校准中的应用及其标定方法，以及多功能检具的功能特点和设计原则等。     

激光量块干涉测量中传感器的应用和校准

本文介绍了双波长激光量块干涉仪中使用的温度、湿度和气压传感器,描述了其工作原理、设计方案、测量不确定度以及校准方法。这些传感器同样可用于其他高准确度长度测量的激光干涉系统中。     

Microcomputer system for logging vibrating wire gauges

A microcomputer controlled logger for controlling and monitoring up to 256 vibrating wire strain gauges is described. Sophisticated data loggers have been developed for use with various sensors producing voltage outputs. The logger described here is capable of handling VWGs in a similar manner enabling long term monitoring to be carried out without operator intervention but with a high degree of confidence in the results obtained. The system represents a low-cost solution to the intelligent logging of VWGs.     

用应变片法确定混凝土动态起裂时间的研究

在混凝土等准脆性材料的动态起裂韧度K_(1d)测试中,准确确定试件裂尖的起裂时间是测试工作的关键。采用分离式霍普金森压杆系统,对圆孔裂纹平台巴西圆盘混凝土试件进行动态径向冲击试验,通过在裂尖粘贴应变片的方法来确定起裂时间。讨论了应变片在裂纹尖端的粘贴位置、粘贴方向等因素对起裂时间测试值的影响,结果表明裂尖应变片的最佳粘贴方式是:在裂纹延长线上或在裂尖并与裂纹垂直的线上,都距离裂尖3 mm左右,且粘贴方向与裂纹延长线垂直。给出了考虑贴片位置和试件厚度的起裂时间计算公式。     

钟罩式气体流量标准装置自动检定系统的设计与实现

介绍了一种钟罩式气体流量标准装置自动检定系统.系统在现有钟罩装置的基础上,增加了由单片机与上位机组成的二级系统,实现了检定过程的自动控制与数据采集,并且将检定结果存入数据库,便于对检定数据进行管理.该自动检定系统的实现,对于提高气体流量仪表检定的效率和准确度具有实际意义.     

Multivariate calibration of non-replicated measurements for the factored noise model

The accuracy of a multivariate calibration (MVC) model for relating concentrations of multicomponent mixtures to their spectral measurements depends on effective handling of errors in the measured data. For the case when error variances vary along only one mode (either along mixtures or along wavelengths), a method to estimate the error variances simultaneously along with the spectral subspace was developed by Narasimhan and Shah (Control Engineering Practice, 16, (2008), 146–155). This method was exploited by Bhatt et al. (Chemom. Intell. Lab. Syst., 85, (2007), 70–81) to develop an iterative principal component regression (IPCR) MVC model, which was shown to be more accurate than models developed using PCR. In this work, the IPCR method is extended to deal with measurement errors whose variances vary along both modes, by using a factored noise model. As a first step, an iterative procedure is developed to estimate the error variance factors along with the spectral subspace, which is subsequently used in developing the regression model. Using simulated and experimental data, it is shown that the quality of the MVC model developed using the proposed method is better than that obtained using PCR, and is as good as the model obtained using Maximum Likelihood PCR, which requires knowledge of the error variances. For dealing with large data sets, a sub-optimal approach is also proposed for estimating the large number of error variances.