气相色谱热导检测器的信号测量与电源电路研究

在气相色谱仪中,采用热导检测器检测物质成分的浓度变化,具有构造简单、测定范围广、稳定性好、线性范围宽等优点。针对气相色谱热导检测器的弱信号失真和电源不稳定问题,研究与设计热导检测器的弱信号测量电路、信号放大电路以及电源电路。实践表明,该方法有效提高气相色谱热导检测系统的可靠性。     

8710型热导池检测器

本文叙述了8710型热导池检测器(TCD)的特性。检测器中的导线从池的两端引出,使池体积减小到44μL。热丝元件的弓架在池中极短,弓架引起的热效应大大减少,全部热效应能够最大限度地作用在热丝上。文中对各设计参数做了较精确的计算。     

气相色谱的近代热导检测器

本文从设计实践的角度评述了气相色谱的近代热导检测器。它包括检测器体积和几何形状、温度控制、敏感元件以及热丝和热敏电阻两者的电学性质。     

基于MEMS技术的微型热导检测器的研制

文中采用MEMS技术加工研制了一种新型热导检测器,这种微型热导检测器采用电阻率高、电阻温度系数大的Pt热敏电阻,利用MEMS技术将Pt薄膜沉积在Pyrex 7740玻璃上并通过剥离技术获得热敏电阻,而气体通道以及热导池是通过深刻蚀在硅片上刻蚀得到,热导池的体积为0.4 μL.这种热导检测器具有灵敏度高,不受气流影响,不易氧化等特点,适用各种混合气体分离检测.     

带前置放大器的热导检测器

在通用型热导检测器直流电桥的基础上 ,增加了内含倍乘× 1、× 2、× 4、× 8的前置放大器 ,使检测器的灵敏度达到 12 0 0 0 m V· m L /mg,比不加前置放大器的热导检测器的灵敏度提高了 4～ 5倍 ,已成功地应用在商品化 GC- 80 0 0 N气相气色谱仪上     

应用热导池检测器的注意事项有哪些

热导池检测器(TCD)是气相色谱仪中应用较为广泛的检测器，尤其是在气体分析中心用最多。由于不断的研究和发展，越来越多应用于ppm级气体成份的微量分析，在许多分析应用中取代了FID，然而，热导池检测器损坏的因素很多，通过对此方面的了解，能使我们在仪器使用中，避免不必要的损失。     

新型气体热导传感器及其应用设计

气体热导传感器是利用被测组分和参考气的热导系数不同而响应的浓度型传感器。文中介绍了一种新型气体热导传感器TCS208F的特点、结构及指标,由于其输出是微弱信号,所以设计出其信号调理电路。传感器检测到的微弱信号由测量电桥调理输出,通过集成芯片AM402中的仪表放大器进行差分放大,由于远距离传输的需要,再将电压信号送入U/I变换器转换成0~20 mA的工业标准电流信号,最后再把电流信号转换为电压信号送入单片机。     

基于单片机的相位差测量系统的设计

从硬件电路和软件设计两方面介绍了一种以单片机为主控器件的相位差测量系统的设计方案,此系统可用于两个同频率的正弦信号的相位差测量,并具有硬件电路简单、测量精度高、显示直观等优点,有一定的使用价值。     

色谱仪热导检测器电桥自动调衡的方案研究

本文针对色谱仪热导检测器电桥的工作特点。分析了用数字电位器替代机械电位器实现电桥自动调衡的两种方案，并根据较好的方案制作了热导检测器电桥的自动调衡电路，在实际应用中达到了理想的效果。     

毛细管气相色谱热导检测器的设计与应用

根据对负压下热导检测器(TCD)响应特性的研究,新设计并研制出适用于程序升温气相毛细管色谱的TCD及恒流系统。所研制TCD的最小等效池体积为1.3μl,几何尺寸为100μl。热丝敏感区内无死角,无气流突变。内径为0.2mm以上的毛细管柱可以直接与该TCD连接而不需用尾吹气。该检测器的动态线性范围为4个数量级,对丁烷的灵敏度为0.005%(v/v),响应速度≤0.1秒。所设计的毛细管进样装置。能在程序升温条件下保证流经毛细管的流量恒定,进样分流比恒定。因此解决了程升条件下毛细管色谱用TCD检测的定量问题。文中给出了应用实例,说明该检测器和整个系统的适用性。     

电导检测器离子色谱法测氰根的应用

利用电导检测器离子色谱建立了氰根的分析方法,考察了该分析方法的检测下限、线性范围、标准误差(RSD)以及加标回收率.在高频热解设备中对神府煤和稻草进行了快速热解实验,利用NaOH溶液吸收法将热解气中的HCN转化为氰根离子,利用所建立的检测方法对氰根进行定量.结果表明,信噪比为3时该分析方法的检测下限为0.01 mg/L,在0.1～50 mg/L范围内线性关系良好,标准误差(RSD)小于3%,加标回收率为90%～105%.对HCN吸收液样品进行检测时发现氰根与其他杂质离子分离效果较好,3次重复实验的重现性良好.所建立的HCN吸收方法和氰根检测方法能够满足煤和生物质热解时HCN生成率的考察要求.     

The measurement of thermal conductivity variation with temperature for solid materials

An apparatus was designed to routinely measure the thermal conductivity variation with temperature for solid materials. The apparatus was calibrated by measuring the thermal conductivity variations with temperature for aluminum, zinc, tin and indium metals. The variations of thermal conductivity with temperature for the Zn-[x] wt.% Sb alloys (x = 10, 20, 30 and 40) were then measured by using the linear heat flow apparatus designed in present work. From experimental results it can be concluded that the linear heat flow apparatus can be used to measure thermal conductivity variation with temperature for multi component metallic alloys as well as pure metallic materials and for any kind of alloys. Variations of electrical conductivity with temperature for the Zn-[x] wt.% Sb alloys were determined from the Wiedemann–Franz (W–F) equation by using the measured values of thermal conductivity. Dependencies of the thermal and electrical conductivities on composition of Sb in the Zn–Sb alloys were also investigated. According to present experimental results, the thermal conductivity and electrical conductivity for the Zn-[x] wt.% Sb alloys decrease with increasing the temperature and the composition of Sb.     

New device and method for measuring thermal conductivity of thin-films

Thermal sensitive paints (TSPs) are used for global nonintrusive detection of boundary layer transition in flow over the surface of wind tunnel research models. Since the transition is a transient process, the TSP should have a fast response characteristic. A low paint thermal conductivity is required for fast response. A thin-film thermal conductivity meter (TFTCM) was designed and built to measure thermal conductivity of the TSPs, which are typically between 50 and 150 microm thick. In this paper, the design and operating features of the TFTCM are described. Measurement of the thermal conductivity with this TFTCM of three standard thin-film low conductivity specimens, Kapton, Teflon, and Borofloat glass, showed good agreement with the manufacturer quoted values, thus validating the instrument and the procedure. Consistently repeatable values for thermal conductivity (k=0.41 +/- 0.02 W/m K) were also obtained for the TSP specimen (TSB-B, 75 microm) tested.     

Determination of the thermal conductivity of composted material

The objective of this study was to develop a reliable method for the determination of the thermal conductivity of composted material using the TP08 probe. Study was set out to determine whether the selection of a signal fragment used to establish thermal conductivity (λ), has a significant influence on the results. Also minimum number of measurements was determined for every phase of the composting process. No significant differences were reported between results, but certain changes in the value of λ were noted. In successive stages of the process, thermal conductivity of composted material were: 0.31 ± 0.09, 0.45 ± 0.14, 0.27 ± 0.03 and 0.37 ± 0.17 W m⁻¹ K⁻¹.     

平板式稳态导热仪的设计及实现

基于一维无限大平板稳态传热模型开发改进平板式稳态导热仪,采用K级热电偶和数字温度仪表进行温度数据采集,数据控制系统与数字温度表通过RS232串口进行数据通讯,读取温度数据,在输入加热电压、加热板电阻、试件面积、厚度等数据后可直接获得并显示试件的导热系数.利用设备进行试验,测定了方形橡胶试样和圆形橡胶试样的导热系数,方形橡胶试样比圆形橡胶试样更适合于设备.与LFA447导热仪测定的标准数据相比,在正常操作下利用设备测定的数据误差小于(5～10)%,基本可满足高等学校实验室和实际工程测量的需要.     

Radiative heat losses in thermal conductivity measurements: a correction for linear temperature gradients

A method for the quantification of the radiative heat losses in a steady-state thermal conductivity measurement set-up is developed based on the Stefan–Boltzmann radiation law with the assumption of a linear temperature distribution along the specimen. The resulting expression can be applied to any regular-shaped sample with well-defined side surfaces and cross-section. Owing to the quantification of the radiative heat losses the accuracy of the steady-state thermal conductivity measurement method is improved and the measurement range can be extended to higher temperatures. An exemplary application in a commercial device is presented. The results are in an excellent agreement with the independently measured high temperature thermal conductivity.     

Online conductivity calibration methods for EIT gas/oil in water flow measurement

Electrical Impedance Tomography (EIT) is a fast imaging technique displaying the electrical conductivity contrast of multiphase flow. It is increasingly utilised for industrial process measurement and control. In principle, EIT has to obtain the prior information of homogenous continuous phase in terms of conductivity as a reference benchmark. This reference significantly influences the quality of subsequent multiphase flow measurement. During dynamic industrial process, the conductivity of continuous phase varies due to the effects from the changes of ambient and fluid temperature, ionic concentration, and internal energy conversion in fluid. It is not practical to stop industrial process frequently and measure the conductivity of continuous phase for taking the EIT reference. If without monitoring conductivity of continuous phase, EIT cannot present accurate and useful measurement results. To online calibrate the electrical conductivity of continuous phase and eliminate drift error of EIT measurement, two methods are discussed in this paper. Based on the linear approximation between fluid temperature and conductivity, the first method monitors fluid temperature and indirectly calibrates conductivity. In the second method, a novel conductivity cell is designed. It consists of a gravitational separation chamber with refreshing bypass and grounded shielding plate. The conductivity of continuous phase is directly sensed by the conductivity cell and fed to EIT system for online calibration. Both static and dynamic experiments were conducted to demonstrate the function and accuracy the conductivity cell.     

GC-14A气相色谱仪热导检测器三种故障的处理方法

热导检测器 (ＴＣＤ)是ＧＣ - 14Ａ气相色谱仪常用检测器之一。但ＴＣＤ故障往往不易准确判断 ,处理不当还会扩大故障部位。本文在排除电路和气路方面的原因外 ,分析了ＴＣＤ常见的三种故障现象 ,提出了相应的处理方法。(1)开机后基线不稳 ,噪声大或基线严重漂移。故障分析 :可能是ＴＣＤ被污染 ,从ＴＣＤ工作时间长短可粗略推断ＴＣＤ受污染的程度。处理方法 :对于轻微污染 ,可将ＴＣＤ的气路进口和出口拆下 ,用 5 0ｍＬ注射器依次将丙酮、无水乙醇和蒸馏水从进气口反复注入 5～ 10次 ,用吹气球从进气口处缓慢吹气 ,吹出杂质和残余液体 ,然…     

用标准样法测量材料的导热系数

在对导热系数的稳态测量方法的综述与讨论的基础上,提出了测量材料导热系数的标准样比较方法。分析了该方法的简单性、经济性及可行性。