Semiautomatic mutual inductance bridge for magnetic susceptibility measurements

A semiautomatic Hartshorn bridge has been designed to improve the complicated adjusting procedures of the bridge in the measurements of magnetic susceptibilities. The bridge is useful for a continuous recording of the susceptibility of a sample, especially when it varies with time.     

Mutual inductance bridge for low-temperature thermometry and susceptibility measurements

We describe a solid-state mutual inductance bridge suitable for low-temperature thermometry and susceptibility measurements. The design features an electronically simulated variable mutual inductance. Particular care is taken to reduce spurious capacitive effects. The bridge is highly stable and linear. It has a resolution of 10(-4) over the range 15 microH to 150 mH, and a noise limited sensitivity of 55 I(p) (-1) nH with a l-s time constant, where I(p) is the rms primary current in mA. Application to thermometry is discussed.     

Op-amp mutual inductance bridge

A mutual inductance bridge constructed from operational amplifiers is described.     

High-resolution dc-voltage-biased ac conductance bridge for tunnel junction measurements

A simple, low-cost conductance bridge circuit, which provides high-resolution measurements of dI/dV and d 2I/dV2 for a voltage-biased load, is presented. A resolution in dI/dV for a 90-Omega tunnel junction of several parts in 10(5) has been measured using a 35-microV-rms modulation level and a 1-s postdetection time constant (Bn=0.25 Hz). The output impedance of the voltage source and the error in the conductance measurement are discussed. The output impedance of the circuit with an AD119 operational amplifier is 0.02 Omega. A detailed discussion of Johnson-Nyquist, tunnel junction, and amplifier noise is presented.     

Automatic bridge for comparison of inductance standards

A high-precision multi-range unbalanced transformer bridge KWL5 designed for calibration of standard inductors of the same nominal value is described. The basic theory of the bridge is presented. Design, application and characterisation of the instrument which enables the direct measurement of differences of both impedance components (real and imaginary) is presented. The instrument was designed to compare inductors of values from 100 μH to 10 H in the frequency range from 100 Hz to 10 kHz with the smallest uncertainty possible. Repeatability of the results obtained by the use of the KWL5 bridge is better than 10 ppm. Coherence equal to or better than 5 ppm for frequency range up to 10 kHz was obtained.     

Vertical impedance measurements on concrete bridge decks for assessing susceptibility of reinforcing steel to corrosion

Corrosion is a pressing problem for aging concrete infrastructure, especially bridge decks. Because of its sensitivity to factors that affect corrosion of reinforcing steel in concrete, resistivity is an important structural health indicator for reinforced concrete structures. In this research, an instrument was developed to measure vertical impedance on concrete bridge decks. Measurements of vertical impedance on slabs prepared in the laboratory, on slabs removed from decommissioned bridge decks, and on an in-service bridge deck in the field demonstrate the utility of the new apparatus.     

Wide bandwidth constant current source for ac galvanomagnetic measurements

A simple one-op-amp constant current source which has great versatility is described. Its important features include a wide bandwidth ( greater, similar10 kHz) and the ability to float from third-wire ground. Applications to three separate types of measurement are included, ac conductivity measurements on ionic conductors, Double-ac Hall effect measurements, and tunneling measurements.     

Wheatstone bridge technique for magnetostriction measurements

A basic Wheatstone bridge, with additional electronic instrumentation, has been used in the measurement of magnetostriction. This method allows a resolution of approximately 10% on measurements of magnetostrictions less than 0.75 parts per million.     

Resonant torsional apparatus for contactless measurements of electrical conductivity and magnetic susceptibility of solids

We have constructed a torsional resonance apparatus for contact-free measurements of the electrical conductivity of solids. Owing to its use of modulation spectroscopy, the technique achieves considerable enhancement of sensitivity compared to previous contactless methods. Conductivities in the range 10(-5) mho/cm to 10(-6) mho/cm can now be measured by the contactless technique. Measurements of magnetic susceptibility as low as 10(-12) can be made. This sensitivity allows for investigation of magnetic impurities as dilute as 1 part in 10(7). In samples which display both phenomena of electrical conductivity and magnetic susceptibility, the two effects can be sorted out via analysis of frequency and/or temperature dependence. The present apparatus has potential for considerable improvement.     

Proposal for the direct comparison of the standards of,capacitance and inductance to ac QHR

The representation of the ohm by the quantum Hall effect permits the reproduction of the farad unit by tracing capacitance to dc resistance. Many R–C bridge’s types are used in these determinations. In effect a chain of some bridges must be used.     

Circuitry for ac thermometry and dc heating in measurements of thermal properties

An instrument is described in which the resistance of a metal wire thermometer is measured by an ac bridge and sampled at a fixed rate. A superimposed dc pulse heats the wire during a selectable time interval. The temperature may be recorded before heating, during heating, and during cooling.     

一种磁保持继电器驱动电路的设计

磁保持继电器是一种能耗低、稳定可靠的双稳态继电器,采用脉冲驱动。本文介绍了一种通用的驱动电路,中央控制单元输出的两路信号触发IR2110组成的驱动电路,驱动电路控制由MOSFET搭接的H桥主电路,实现磁保持继电器在两个稳态之间相互切换。总体结构简单、通用,工作可靠。     

A mutual-inductance bridge for analysis of magnetic fluids

A mutual-inductance bridge designed for measuring the dynamic susceptibility of magnetic fluids at temperatures ranging from ?50 to +90°C is described. A specific feature of the bridge is an extended frequency band of the probing field that ranges from infralow frequencies of ～0.05 Hz to 200 kHz. The formulas that establish relationships between the bridge output signals and the real and imaginary parts of the susceptibility, the testing technique, and the results of testing are presented.     

恒流变压供电方式的应变测量电桥电路

本文提出了一电阻应变片有源电桥电路。文章介绍了电路结构和工作原理以及消除引线电阻,电阻应变片的温度漂移和直流稳流电源供电质量对测量准确度的影响等问题。     

基于PLC控制的桥式起重机电路设计

1 总体方案 通过控制台或控制手柄上的按钮、开关等手动控制装置,输入信号给PLC的输入模块,信号经CPU模块,按照梯形图软件或者高级语言的指令进行处理,再由输出模块输出信号控制接触器、指示灯、报警器、显示装置等的工作。接触器的状态变化,进一步控制起重机主电路电机的启动,停止和正反转等动作。限位开关、过流继电器和超载限动器等也将反馈信号输入PLC,起到安全保护作用。系统总图见图1。     

Development of a miniature permanent magnetic circuit for nuclear magnetic resonance chip

The existing researches of miniature magnetic circuits focus on the single-sided permanent magnetic circuits and the Halbach permanent magnetic circuits. In the single-sided permanent magnetic circuits, the magnetic flux density is always very low in the work region. In the Halbach permanent magnetic circuits, there are always great difficulties in the manufacturing and assembly process. The static magnetic flux density required for nuclear magnetic resonance(NMR) chip is analyzed based on the signal noise ratio(SNR) calculation model, and then a miniature C-shaped permanent magnetic circuit is designed as the required magnetic flux density. Based on Kirchhoff’s law and magnetic flux refraction principle, the concept of a single shimming ring is proposed to improve the performance of the designed magnetic circuit. Using the finite element method, a comparative calculation is conducted. The calculation results demonstrate that the magnetic circuit improved with a single shimming has higher magnetic flux density and better magnetic field homogeneity than the one improved with no shimming ring or double shimming rings. The proposed magnetic circuit is manufactured and its experimental test platform is also built. The magnetic flux density measured in the work region is 0.7 T, which is well coincided with the theoretical design. The spatial variation of the magnetic field is within the range of the instrument error. At last, the temperature dependence of the magnetic flux density produced by the proposed magnetic circuit is investigated through both theoretical analysis and experimental study, and a linear functional model is obtained. The proposed research is crucial for solving the problem in the application of NMR-chip under different environmental temperatures.     

Nonmagnetic indenter-type high-pressure cell for magnetic measurements

An indenter-type high-pressure cell has been developed for electric and magnetic measurements in low-temperature and high-magnetic-field environments. The maximum pressure achieved at low temperatures is more than 4.5 GPa, which is higher than that of a conventional piston-cylinder cell. The typical sample space at maximum pressure is 1.6 mm in diameter and approximately 0.7 mm in depth, and magnetic measurements such as ac-susceptibility and nuclear magnetic resonance can be performed using a miniature coil. All the components of the indenter cell are made of nonmagnetic materials that have enough thermal conductivity for low-temperature experiments using a 3He/4He dilution refrigerator. Another indenter-type cell designed for a commercial superconducting quantum interference device magnetometer is also reported.     

Development and application of setup for ac magnetic field in neutron scattering experiments

We report on a new setup developed for neutron scattering experiments in periodically alternating magnetic fields at the sample position. The assembly consisting of rf generator, amplifier, wide band transformer, and resonance circuit. It allows to generate homogeneous ac magnetic fields over a volume of a few cm(3) and variable within a wide range of amplitudes and frequencies. The applicability of the device is exemplified by ac polarized neutron reflectometry (PNR): a new method established to probe remagnetization kinetics in soft ferromagnetic films. Test experiments with iron films demonstrate that the ac field within the accessible range of frequencies and amplitudes produces a dramatic effect on the PNR signal. This shows that the relevant ac field parameters generated by the device match well with the scales involved in the remagnetization processes. Other possible applications of the rf unit are briefly discussed.     

A magnetic transport electron spectrometer for in-beam measurements

A compact magnetic transport electron spectrometer has been built having an overall efficiency of 0.92%, a resolution Δp/p of 18% and a maximum transmitted energy of 3 MeV. Limitations to accuracy in intensity measurements due to non-isotropic electron angular distributions have been discussed.