Maxwell-Wien Bridge Research Articles

Maxwell-Wien bridge with vector voltmeter system for measurement small and rapid changes in inductive-loop sensor impedance components

The paper presents a low-cost electronics system for impedance measurement of an inductive-loop sensor as well as small, rapid changes in impedance components. The idea of the system is based on the adaptation of a vector voltmeter instead of the Maxwell-Wien bridge balance indicator and supporting the system with a microcontroller. The proposed procedures, based on the complex voltage of bridge unbalance, allow to calculate the resistance that can balance the bridge in a short time. This, in turn, allows to measure the sensor impedance components, identically, as in the case of a well-known balanced bridge method. However, what is original in this work, is that measurements can be taken in a state of bridge imbalance and with high relative accuracy to small changes in sensor impedance.

Study of the effect of distance and misalignment between magnetically coupled coils for wireless power transfer in intraocular pressure measurement.

An analysis of the effect of distance and alignment between two magnetically coupled coils for wireless power transfer in intraocular pressure measurement is presented. For measurement purposes, a system was fabricated consisting of an external device, which is a Maxwell-Wien bridge circuit variation, in charge of transferring energy to a biomedical implant and reading data from it. The biomedical implant is an RLC tank circuit, encapsulated by a polyimide coating. Power transfer was done by magnetic induction coupling method, by placing one of the inductors of the Maxwell-Wien bridge circuit and the inductor of the implant in close proximity. The Maxwell-Wien bridge circuit was biased with a 10 MHz sinusoidal signal. The analysis presented in this paper proves that wireless transmission of power for intraocular pressure measurement is feasible with the measurement system proposed. In order to have a proper inductive coupling link, special care must be taken when placing the two coils in proximity to avoid misalignment between them.

Novel rotor position estimation technique for switched reluctance motor (SRM)

This article presents a new and novel method which is designed to detect the rotor position at standstill and at low speeds in switched reluctance motor. Since the inductance parameter plays a significant role both in the steady state and in the dynamic characteristics of an electromagnetic device, the rotor position can be determined using inductance bridge systems to measure unknown inductance and resistance values. In this method we use motor winding in Maxwell–Wien Bridge, with the standard capacitor and the resistor in parallel with it adjusted to achieve balance in an aligned position when the maximum inductance occurs. The supply voltage, in conjunction with the drive transistor, produces short pulses for this AC bridge. The condition of the balanced bridge v 0 = 0 leads to the relation between the impedances of the bridge branches. The phase inductance varies with the rotor position. Therefore the motor goes into an unaligned position and the Maxwell–Wien Bridge goes into an unbalanced condition thus causing variation in the state of the bridge output. It then continues to sense the rotor position with the motor running by applying the same procedure, but only to the un-energised phases winding. The simulation and experimentally obtained results demonstrate the feasibility and practicability of this method.

Modification of the Maxwell–Wien Bridge for Accurate Measurement of a Process Variable by an Inductive Transducer

The small inductance of an inductive transducer generally linearly changes with a process variable, but their measurement by the usual inductive bridge circuit like the Maxwell bridge, the Maxwell-Wien Bridge, the Hay bridge, etc., suffers from errors due to the effect of the stray capacitance between bridge nodal points and the ground and the stray inductance on the inductive coil, respectively. The conventional Wagner-Earth technique is not suitable for continuous measurement. In this paper, a modified operational-amplifier-based Maxwell-Wien bridge measurement technique has been proposed in which the effect of stray capacitance and inductance is minimized. In the first phase of the experiment, the bridge performance has been studied with a known variable inductor, and in the second phase, the same experimentation was done by replacing the variable inductor with an inductive coil having an adjustable core position for the measurement of displacement. The linear characteristics over a wide range of displacement with good repeatability, linearity, and variable sensitivity have been described.

Compact Inductance Standard

A portable Maxwell-Wien bridge as a part of the Korea Research Institute of Standards and Science (KRISS) inductance standard has been developed. Two auxiliary resistive-capacitive networks (analogous to a Wagner ground) provide excellent stability of the bridge balance and impose less strict requirements on the components of the networks. Removable capacitance and ac/dc resistance standards used in the bridge arms make it possible to realize the inductance unit in terms of capacitance and resistance in the frequency range 500 Hz to 3 kHz. Investigations of the standard and results of preliminary (trial) comparison with the Mendeleyev Institute for Metrology demonstrate that the bridge can be used for measurement of 10 and 100 mH inductance standards with an uncertainty within (1-3) /spl mu/H/H at frequencies of 1 and 1.6 kHz. The use of this bridge as a constituent part of a transportable standard gives an opportunity to eliminate any uncertainty arising from instability of the standard inductors.

Magnetic aftereffects in nickel ferrites

We have studied the magnetic aftereffects in the Ni x Fe3−x−ΔO4 system, for 0≦x≦1 and 10−5≦Δ≦2×10−1, between 80 and 500 K. The samples were obtained by sintering at 1400°C in an appropriate gas atmosphere. The measurements are based on the deviation from equilibrium that is produced in a Maxwell-Wien bridge when the self-induction of a coil with ferrite core varies because of the phenomenon of magnetic aftereffects. The numerical analysis of the results shows the presence of relaxation processes at 300 K (III), 330 K (IIa), and above 500 K (I). The Processes III and IIa are related to the concentration of nickel,x, and of vacancy, Δ. It is seen that the IIa peak can be attributed to a process of diffusion of Ni ions in the spinel lattice by means of vacancies on octahedral sites.

Calibration of inductance standards in the Maxwell-Wien bridge circuit

Calibration of inductance standards in the Maxwell-Wien bridge circuit

Measurement of the Ohm in Absolute Units

This paper describes an experiment for the measurement of resistance in absolute units, based on the bridge method developed by H. L. Curtis and R. W. Curtis [Bur. Standards J. Research 12, 665–734 (1934)]. The main modifications introduced in the work were the use of a mica instead of an air capacitor, a simplified method of measuring its capacitance in terms of resistance, and the use of the Anderson bridge in place of the Maxwell-Wien bridge for the determination of a relation between capacitance and inductance. A simple formula accurate to 0.4 percent was derived for the evaluation of the inductance of the single layer solenoid used in this work.

The corona voltmeter

The paper presents a low-cost electronics system for impedance measurement of an inductive-loop sensor as well as small, rapid changes in impedance components. The idea of the system is based on the adaptation of a vector voltmeter instead of the Maxwell-Wien bridge balance indicator and supporting the system with a microcontroller. The proposed procedures, based on the complex voltage of bridge unbalance, allow to calculate the resistance that can balance the bridge in a short time. This, in turn, allows to measure the sensor impedance components, identically, as in the case of a well-known balanced bridge method. However, what is original in this work, is that measurements can be taken in a state of bridge imbalance and with high relative accuracy to small changes in sensor impedance.