Thermoelectric temperature control device for vapor pressure measurements

The static method of measuring equilibrium vapor pressure requires locating the sample at the coldest part of the apparatus to avoid errors due to evaporation and recondensation elsewhere. This paper describes a device that can hold the sample 1 K below the temperature of the surrounding air without a liquid bath. It comprises a pair of thermoelectric elements and two thermometers attached to an insulated aluminum block. The device can operate as high as 200?°C while controlling the sample with a precision of 0.02 K; below 110?°C, the precision is 2 mK. Also described is a method to measure the small temperature offset due to heat flow between the sample and the surrounding aluminum block. The uncertainty due to the offset is small compared to the 6 mK uncertainty due to the thermometer.     

单压吸收式Einstein循环制冷机的设计

介绍了单压吸收式Einstein循环制冷机的设计方案,阐述了制冷机的组成、工作原理及主要部分的设计说明.     

Wave-number stability of a laser diode mounted in a closed cycle helium refrigerator

The wave-number stability of a laser diode mounted in a closed cycle helium refrigerator was examined using a CO(2) laser heterodyne spectrometer. The set current supplied by a commercial laser diode supply appeared stable enough over the time periods normally used. Temperature control was achieved through both passive and active loop control. A stage of open loop control of the cold tip allowed the closed loop control of diode heat sink to be operated at higher gains than conventionally used. Long-term stability of the center of the line shape function was better than 10 MHz per hour and the 1-min average was better than +/-5 MHz. Vibration of the diode mount determined the instrument line shape in spite of steps taken to eliminate the vibrations. The line shape had a half-width of 10 MHz with broad shoulders out to 50 MHz.     

一种应用于液压闭式回路的冷却装置

液压闭式回路以其能耗低、结构紧凑并容易实现无级调速等优点,广泛应用于工程机械及工业液压系统中.但由于闭式回路油箱一般较小,油液循环较快;又因为马达和油泵壳体所承受压力低,冲洗油路要求畅通无阻,使得闭式系统散热成为一大难题.该文介绍一种新型的冷却装置,既能产生很好的冷却效果,又不增加冲洗油路背压.     

自动循环采油装置控制系统研究

针对自动循环采油装置,设计了一种控制系统,其原理是基于可编程控制器(PLC),采用变频器作为变频电动机的调速器;同时,通过RS422总线实现触摸屏与PLC的通信,进而控制采油装置的运行.整个控制系统简单、可靠,能耗低,大大提高了工效,且制造和维护成本较低,收到了良好的效果.     

闭式油箱通气增压系统气压变化规律

本文简述了飞机油箱通气增压系统的分类,介绍了封闭式油箱通气增压系统的原理,以典型闭式系统为例,分析了飞机在起飞、爬升、不同高度稳定平飞、加减速平飞、空中应急放油以及油箱增压输油等典型工况下油箱气压的变化规律,为后续飞机油箱通气增压系统的设计和试飞方法研究提供依据,具有很高的工程试验价值。     

Hall measurements to 40 kilobars under hydrostatic pressure in a piston-cylinder device

A technique for Hall measurements under truly hydrostatic pressures to 40 kilobars is described. The method employs the piston-cylinder apparatus with a Teflon cell to contain a suitable fluid. The necessary magnetic field is generated by a coil placed inside the cell. Hall data can be obtained over the full pressure range, at temperatures from 150 to 300 K. Results for an Al(x)Ga(1-x)As sample are presented as an example.     

水压试验机液压系统噪声控制的研究

这里通过对水压试验机液压系统各部位产生的噪声进行深入分析,并针对各种不同情况,提出如何控制及降低其噪声的方法。     

Simple PID parameter tuning method based on outputs of the closed loop system

Most of the existing PID parameters tuning methods are only effective with pre-known accurate system models, which often require some strict identification experiments and thus infeasible for many complicated systems. Actually, in most practical engineering applications, it is desirable for the PID tuning scheme to be directly based on the input-output response of the closed-loop system. Thus, a new parameter tuning scheme for PID controllers without explicit mathematical model is developed in this paper. The paper begins with a new frequency domain properties analysis of the PID controller. After that, the definition of characteristic frequency for the PID controller is given in order to study the mathematical relationship between the PID parameters and the open-loop frequency properties of the controlled system. Then, the concepts of M-field and θ-field are introduced, which are then used to explain how the PID control parameters influence the closed-loop frequency-magnitude property and its time responses. Subsequently, the new PID parameter tuning scheme, i.e., a group of tuning rules, is proposed based on the preceding analysis. Finally, both simulations and experiments are conducted, and the results verify the feasibility and validity of the proposed methods. This research proposes a PID parameter tuning method based on outputs of the closed loop system.     

A device for free-carrier recombination lifetime measurements

The design of a microwave system, the user interface, and the basic characteristics of noncontact equipment for measuring the recombination lifetime of free charge carriers in semiconductor materials by the photoconductivity-decay method are described. The features of the microwave-system design eliminate the need for a microwave circulator and other expensive elements of the systems without a loss in the equipment sensitivity. This substantially simplifies the design and provides automated measurements of the free-carrier lifetime in silicon single crystals in a range of 0.2 μs to tens of milliseconds. The upper measurement limit is determined by the geometrical dimensions of a sample and the surface treatment quality. The results of measuring the photoconductivity relaxation time in reference single-crystal silicon samples are presented.     

Simple pressure gauge for uranium hexafluoride

A sensitive detector and pressure gauge for uranium hexafluoride in high-vacuum systems is described. Negative surface ionization of UF(6) occurs on ribbon filaments operated at temperatures too low for electron emission to be significant. The ion current measured on a cylindrical collector surrounding the filament assembly varies regularly with UF(6) pressure below 10(-3) Torr. Different filament materials are considered, including rhenium, thoriated tungsten, and platinum. Rhenium is found to be the most satisfactory material for operation of diode emitters as a pressure gauge. Gauge constants (in A Torr(-1)) are derived from comparing negative surface ionization currents with the response of a capacitance manometer and are shown to be independent of temperature within a reasonable operating range. The effects of exposing the rhenium filament to various gases is considered, and it is shown that brief exposure to acetylene substantially improves the operating characteristics of the gauge.     

Simple low-noise power supply for electrical transient measurements

A very simple means is described for rapidly applying and briefly maintaining a large, essentially noiseless, dc voltage across a capacitive load. The technique is suitable for various nonrepetitive electrical transient measurements, such as carrier mobility determination, occurring over timescales ranging from tens of microseconds to several seconds; it essentially eliminates capacitive currents caused by noise in the power supply voltage, which can interfere with measurement of the true transient current. In an example, the noise on a 10-ms transient current (driven by 2000 V dc, and observed as a voltage across a 100-kOmega load resistor) was barely more than the Johnson noise ( approximately 2x10(-11) A rms) to be expected from the resistor.     

一种适用于热加工的CAPP系统

介绍一种适用于热加工的实用型CAPP系统ZTCAPP,具体分析了其功能模块、系统集成及接口技术问题,并简要介绍了其运行环境和特点.该系统已在某大型工程机械公司得到成功应用.     

Superconducting quantum interference device setup for magnetoelectric measurements

A commercial superconducting quantum interference device (SQUID) setup (MPMS 5S from Quantum Design), equipped with a magnetic ac susceptibility option, is modified for measurements of the linear magnetoelectric (ME) effect, i.e., of the magnetic moment induced by an applied external electric field in a ME sample. Test measurements on a Cr(2)O(3) (111) single crystal are in excellent agreement with previously reported data of its ME susceptibility. The main advantages of the proposed setup are the improved precision due to the high sensitivity of the SQUID magnetometer in combination with the lock-in technique and a relatively simple experimental realization.     

基于Windows的气瓶疲劳试验控制系统的研制

介绍了在Window98平台上使用VC6．0开发疲劳试验控制系统的方法，着重讲述了系统组成和所采用的主要技术，该系统可实现在恒温、恒湿条件下的气瓶疲劳试验。     

冰箱制冷能力快速评价系统硬件设计

为了能够缩短对冰箱制冷能力测试的时间,设计了一套快速评价系统。针对该系统,给出了该制冷能力快速评价系统的硬件框架及相关硬件电路。该系统采用铂热电阻温度传感器作为测温元件,利用芯片XTR105将电阻值随温度的变化量转变成电流并对铂热电阻温度进行线性补偿,采用低功耗、高性能的MSP430单片机对所采集的温度进行模/数转换,通过CAN总线实现工控机与各工位之间的数据可靠、实时地传输。测试结果表明,该系统能对冰箱制冷能力既快速又准确地做出评价。     

Simple mechanical device for orienting tissue blocks on the ultramicrotome

A simple and inexpensive modification of the specimen holder of the Porter-Blum model MT-1 has been devised, which allows fine adjustments of tissue block orientation in both horizontal and vertical planes. It consists of an additional ring mounted on the existing locking ring and fitted with four radial screws which push the shaft of the chuck.     

Simple apparatus for the multipurpose measurements of different thermoelectric parameters

A simple apparatus for the simultaneous measurement of Seebeck coefficient (α) and electrical resistivity (ρ) in the temperature range 100-600 K, Hall coefficient (R_H) and transverse Nernst-Ettingshausen coefficient (N) in the temperature range 300-600 K of the bar shaped samples has been fabricated. The instrument has been designed so simply that the sample can be easily mounted for the fast measurements of different thermoelectric parameters. The sample holder assembly of the apparatus has been designed so cleverly that any part of that section can be replaced in case of any damage; and so it can be regarded as a modular based system. The apparatus is relatively cheaper in cost and also portable.     

坚固耐用的直接测量系统

目前,MAG集团的Hüller Hille公司正在努力降低生产成本,与此同时还要提高质量和降低装配成本.利用Schneeberger Amsa测量系统及单轨导向装置取了可观成效.