Pulsed measurement of transistor-base charge against collector current

A transistor measurement is described in which a pulse is applied to the emitter, and the base and collector current waveforms are measured and recorded using a sampling oscilloscope and data logger. The measurements are then processed by computer to determine the variation of the charge and the fT with the collector current under large-signal transient conditions     

Emitter-junction temperature measurement under nonuniform current and temperature distribution

A computer analysis of the temperature dependence of emitter junction voltage under an assumed nonuniform temperature distribution is presented, which demonstrates a temperature averaging effect when using junction voltage as an indicator of junction temperature.     

Microwave measurement of temperature and current dependences ofsurface impedance for high-Tc superconductors

Perturbation formulas for TE₀₁₁-mode dielectric rod resonator and for a TE₀₁₁-mode circular cavity resonator are derived to determine the surface impedance Z_s of superconductors from measured values of resonant frequencies and unloaded Q. The relation between the maximum surface current density of a superconductor, J_s, and output power from a signal generator is derived. On the basis of these analytical results, a measurement technique is proposed to evaluate the temperature and J_s dependencies of Z_s for superconductors. The measured results of the temperature dependence of Z_s for YBCO and copper plates are presented. From these results, it is verified that the dielectric resonator is suitable for measuring the surface reactance for YBCO. From these Z_s values the temperature dependences of the skin depth and the penetration depth and those of the complex conductivity are obtained on the basis of the two-fluid model. These measured values agree well with the theoretical curves     

一种基于电流环的温度测量系统

为了实现核电站的无电磁辐射在役设备的温度状态实时监测,提高设备使用安全性,设计并实现了一种满足核电站环境要求的基于电流环的有线温度测量系统。系统以C8051F系列单片机为控制器,用电流环实现有线数据传输,通过温度传感器DS18B20进行设备温度的实时获取,最后,应用后端模块对前端的温度数据进行接收和解析,并且实现测温结果在液晶屏上的直观显示。该系统目前已应用于多种核电设备中。     

一种恒流源驱动的高精度温度测量系统设计

为提高温度测量精度,利用REF200提供的0.4mA恒定电流驱动串联的四线制温度传感器PT1000和精密电阻,在传感器和精密电阻两端分别提取电压信号并对其进行调理,通过高精度AD7712对所得到的电压信号进行放大和A/D转换,设计了一种高精度温度测量系统。为了减小高精度温度测量中铂电阻非线性所引起的误差,在上位机中对数字信号进行了最小二乘法算法处理。测试结果表明,该系统稳定可靠,其随机误差和系统误差均小于0.1℃,实现了高精度温度测量。     

New measurement method of Gunn-diode impedance

Using a suitably designed cavity, the negative conductance of X band Gunn diodes is derived from oscillation buildup characteristics when a steep bias voltage step is applied. By this method, a quick assessment of the diode negative conductance as a function of r.f. voltage amplitudes can be made.     

屏蔽对阻抗测量的影响

屏蔽对抑制电磁场耦合干扰起着重要的作用.为了研究屏蔽在阻抗测量中的影响,通过屏蔽原理以及实现等电位屏蔽,了解屏蔽对电容、电感、电阻测量值影响的重要性,进而保证测量值的可靠性.     

High input impedance current conveyor filters

Two new active RC canonic band pass filters are presented. The new configurations offer a very high input impedance and employ single grounded resistors for independent adjustments of ω₀, Q and gain.     

Phase retrieval from impedance amplitude measurement

In this letter, we propose a numerical method for computing the phase spectrum of impedance. The developed method is based on the maximum entropy model (MEM) and enables one to retrieve the phase spectrum directly from an impedance amplitude spectrum. The validity of the method is tested with an input impedance measurement of a distribution transformer in the frequency band 100 kHz-30 MHz, where both the amplitude and the phase spectrum of the impedance are measured. According to the tests carried out, the method is useful and it may be applied, for example, in the research of active filters, power line communication, and electromagnetic interference.     

A probe for organ impedance measurement

In this paper, we describe the theory and practical implementation of an electrical impedance probe for making in vivo measurements of the electrical admittance of living tissue. The probe uses concentric annular electrodes and is shown to sample a more localized, yet greater, volume of tissue than the standard four-electrode probe. We have developed a mathematical model for the conduction of current between the probe electrodes assuming that we are investigating a uniform, isotropic, semi-infinite region and taking into account the contact impedance between the electrodes and the organ. The electric fields produced by the probe have been calculated by solving a weakly singular Fredholm integral equation of the second kind. The size and position of the probe electrodes have been optimized to maximize both the accuracy in the admittance measurement and insensitivity to contact impedance. A probe and driving hardware have been constructed and experimental results are provided showing the accuracy of admittance measurements at 50 and 640 KHz.     

Comparison of applied and induced current electrical impedance tomography

Several papers on induced current electrical impedance tomography (IC-EIT) have dwelt on potential advantages of this technique over conventional EIT which uses applied current (AC-EIT). Experimental evidence that IC-EIT could surpass AC-EIT in similar imaging conditions is lacking. In this paper, we describe a system that can switch rapidly between both AC-EIT and IC-EIT. The system makes it possible to image objects in a saline-filled tank, providing data acquired in identical test conditions for comparing the performance of the two modes. The system uses eight circular coils and 16 electrodes to acquire 120 linearly independent measurements in IC-EIT and 104 in AC-EIT. Difference images were reconstructed from data acquired with both modes using the maximum a posteriori method. Spatial resolution was lower in IC-EIT images than in AC-EIT, especially in the radial direction. IC-EIT also exhibits a bias toward the center for positioning a conductivity perturbation. These results were obtained for a typical coil configuration widely used in the literature and may not be representative of alternate coil configurations. The system described in this paper provides stable experimental conditions for comparing the performance of the two EIT imaging modes and would be a valuable tool for validating new coil configurations.     

Electrical impedance measurement of urinary bladder fullness

A tetrapolar 75-kHz, 0.2-mA constant-current electrical impedance measuring system was used to monitor urinary volume change over 12 four-hour sessions in 20 male and 20 female normal human subjects. Two spot voltage electrodes (E) and two spot current electrodes (I) were applied 5 cm above the symphysis pubis at 15 cm interelectrode distances, 7.5 cm bilaterally from the midline. Five measurements of impedance and skin temperature were made at 15-minute intervals over 4 hours. Specific gravity, impedance change, and volume were recorded with each voided specimen. Suprailiac and infrascapular skinfolds, and circumference at iliac crests were measured. The subjects drank 175 ml of fluids per hour during the testing session. Subjects remained in the supine position during measurements. They walked to the lavatory to void. Bladder fullness is defined as the urge to void. Results include: (1) a poor negative correlation between specific gravity of urine and impedance (r2 = 0.1240, p less than or equal to 0.01); (2) baseline impedance was dependent upon individual subject characteristics: in males skin area, skinfold thickness, and suprailiac circumference; in females skinfold thicknesses and time since last menstrual period; (3) impedance decreased with urinary bladder filling and increased upon voiding (p less than or equal to 10(-10)); (4) the cumulative sum test (CUSUM) predicted time to void in 78.9% of voids (p less than or equal to 0.05) and no void (when voiding did not occur) in 66.8% of no voids (p less than or equal to 0.05). Overall accuracy of the CUSUM test was 74.6% (p less than or equal to 0.05).     

嵌入式电阻抗测量系统研究

为提高阻抗测量的便捷性及数字化应用,基于ARM架构的S3C2440处理器和Linux3.0.4内核,研发了一套嵌入式电阻抗测量系统。系统采用AD5933作为阻抗传感器,利用I2C通信协议实现AD5933与S3C2440处理器之间的数据通讯,开发QT用户界面实现测量结果的显示,通过操作触摸屏实现阻抗参数的采集、显示、保存及曲线绘制等功能。实验结果表明图像重建质量较好,信噪比达65.6dB,验证了系统软硬件设计的可靠性与稳定性。该研究有助于推动阻抗测量技术在数字化医疗及临床应用的发展。     

比色测温法的最优波段及测温精度的研究

目前火炮膛温测试存在测试难度大、精准度低和条件恶劣等问题。针对此类问题,本文设计了基于比色测温的火炮膛温测试系统。论证了波长的选择和标定误差是影响比色测温精度的两大重要因素,并通过分析波长与采集电压之间的灵敏度关系,得出最优波段为0960μm和1000μm,提高了比色测温法的测温精度。分别使用最小二乘法和遗传算法(GA)对实验数据进行拟合,对系统进行测试验证。结果表明:选择最优波长能够提高测温精度,遗传算法在精度上对比最小二乘法有明显提高,整体测量误差小于4 ‰。     

Dependence of receiver noise-temperature measurement on source impedance

When calculating the uncertainty in measuring the effective input noise temperature Te of a receiver, it is essential to take account of the dependence of receiver noise on source impedance. This applies even when the receiver is adjusted for minimum Te with the nominal source impedance connected. The calculation is carried out, and an example is given.     

A current limiter for DC/DC regulators with compensation against process and temperature variations

A low-voltage current limiter suitable for both linear and switching regulators is presented. Although the approach relies on absolute values of sense resistance and MOSFET threshold voltage on subsequent I/V and V/I conversions of the sensed current, a reference current in the process and temperature (PT) compensator is derived in such a manner that the dependence of clamping threshold I _TH on PT-spread is first-order canceled out. Furthermore, the current sensor embodies a transconductor build up with either p-MOSFET depletion-mode device or a level-shifter with enhancement-mode transistors, meeting low-dropout requirements. For nominal value of 750 mA, Monte Carlo data express boundaries for I _TH of 523 and 1,075 mA, accounting for broad PT-variation, as well as operating voltages and mismatching. A linear regulator with 400 mA-current rate and 250 mV-dropout incorporating the limiter on its depletion p-MOSFET version was integrated on a smart-power process. The limiter occupies an area of 0.052 mm² and consumes only 65 μA. Experimental data attest the clamper functionality and accuracy against PT-variations. From samples of distinct lots, I _TH spans from 615 to 996 mA. Owing to its simplicity and open-loop operation in case of switchers, the limiter reacts upon overcurrent in only 20 ns, making it compatible with converters functioning in MHz range and under low duty-cycles. Moreover, the limiter suits supply voltages as low as 1 V.     

Very low input impedance low power current mirror

In this paper a novel low input impedance current mirror/source is proposed. The principle of its operation compared to that of the simple current mirror is discussed. Also are given the comparative simulation results with HSPICE in TSMC 0.18 μm CMOS which verify the theoretical formulation and operation of the proposed structure. Simulation results show an input resistance for the proposed current mirror about 0.006 Ω. This is 4 × 10⁵ times lower than that of the simple one while both working with 1.5 V supply and 50 μA bias current. It consumes only 161 μW and exhibits an excellent current error value of Zero at 55 μA which remains below 0.6% up to 100 μA. Favorably its minimum output voltage is reduced to 0.2 V.     

On optimal current patterns for electrical impedance tomography

We develop a statistical criterion for optimal patterns in planar circular electrical impedance tomography. These patterns minimize the total variance of the estimation for the resistance or conductance matrix. It is shown that trigonometric patterns (Isaacson, 1986), originally derived from the concept of distinguishability, are a special case of our optimal statistical patterns. New optimal random patterns are introduced. Recovering the electrical properties of the measured body is greatly simplified when optimal patterns are used. The Neumann-to-Dirichlet map and the optimal patterns are derived for a homogeneous medium with an arbitrary distribution of the electrodes on the periphery. As a special case, optimal patterns are developed for a practical EIT system with a finite number of electrodes. For a general nonhomogeneous medium, with no a priori restriction, the optimal patterns for the resistance and conductance matrix are the same. However, for a homogeneous medium, the best current pattern is the worst voltage pattern and vice versa. We study the effect of the number and the width of the electrodes on the estimate of resistivity and conductivity in a homogeneous medium. We confirm experimentally that the optimal patterns produce minimum conductivity variance in a homogeneous medium. Our statistical model is able to discriminate between a homogenous agar phantom and one with a 2 mm air hole with error probability (p-value) 1/1000.     

多光谱瞬态测温系统最优测温波段的分析研究

针对多光谱瞬态温度的测量系统中波长的选择问题。研制了一套适用于反演爆炸场瞬态温度的测试系统,该系统从辐射测温的原理出发,通过分析温度随波长灵敏度的变化关系,确定温度精度最高时的波长,并结合天鹰优化器约束算法,对蜡烛燃烧的火焰现场测试加以验证,结果表明：选择各个波段的最优待测波长测量时,测量的温度误差最小,不超过±2.1%,减小因波长的选择而引起的误差。