Showing papers on "Electrical impedance published in 1977"

Analysis for the change of skin impedance

Abstract: Skin impedance, for various reasons, changes in a very complex fashion. The range of change of skin impedance is determined experimentally and analysed theoretically. The equivalent circuit of the skin impedance, the theoretical relationships among the variable parameters in this circuit, and the impedance space are proposed as powerful concepts for the analysis of impedance changes. The experimental examples are practically analysed and can well be understood. A theoretical foundation taking into consideration the mechanism of the change has been established in this paper.

Impedance measurement on Pb/H2SO4 batteries

Abstract: Relatively few works have been carried out on Pb/H2 SO4 batteries from an electrochemical kinetics point of view This is partly due to the complexity of the chemical and electrochemical reactions occurring on plates but mainly because the system is not a constant one The current continuously modifies the electrode structures and their properties [1-3], so that, strictly speaking, no steady-state can be defined in this system Thus, it is scarcely possible to use the classical methods of electrochemical kinetic investigations such as the analysis of polarization curves The use of transient methods seems to be more adequate to investigate the electrode processes of such systems If the system is disturbed by a very small measuring signal so that its response remains linear, its impedance can be defined This allows the analysis of the dynamic behaviour of the system [4] If the direct polarizing current (bias current) I is equal to zero and also if the autodischarge of the battery is negligible, the structure and properties of both plates may be regarded as constant In this particular case, the steady-state can be defined On the contrary, during the charge or discharge processes of a battery, if the measuring period is short enough, the evolution of the electrode structure and other properties affecting cell impedance may be kept to the same order of magnitude or smaller than the errors of measurement In this case, the system under investigation is considered to be in quasi-steady-state Of course, the lowest frequency at which the impedance can be properly explored depends on the measuring error and also on the rate at which the system changes The purpose of this note is to demonstrate that it is technically possible to measure the impedances of electrochemical generators by means of a transfer function analyser over a very wide frequency range The impedance measurements are performed between two terminals of a battery, corresponding to the overall dynamic behaviour of the cell, as well as separately on positive and negative plates Some preliminary results obtained on a commercially available Pb/H2 SO4 battery during a charge and discharge cycle are given

Ink jet device

Abstract: PROBLEM TO BE SOLVED: To provide an ink jet device capable of solving in a simple structure a problem of accumulation of a residual electric charge on a protection layer and of achieving stable ejection. SOLUTION: A voltage applying means 8 for applying, across a diaphragm 11 and a substrate layer 25 of an individual electrode substrate 2, a voltage of which the pole is different from that of a voltage to be applied across the diaphragm 11 and an individual electrode 21 by a driving means 7. In terms of the voltage applying means 8, the voltage of the individual electrode 21 in a condition that a switch array in the driving means 7 is in an ON state is determined by a driving signal. When the switch array is in an OFF state, the individual electrode 21 becomes a floating condition (a high impedance condition) and the individual electrode 21 has a voltage which is obtained such that the voltage of the voltage applying means 8 is divided by a capacity between the individual electrode 21 and the diaphragm 11 and a capacity between the individual electrode 21 and the substrate layer 25. As the poles of the driving means 7 and the voltage applying means 8 are different from each other, a reverse electric field is applied to the individual electrode 21 and the diaphragm 11 so that it is possible to suppress the accumulation of the residual electric charge. It is not necessary to directly apply a voltage having a reverse pole to the individual electrode 21, thereby simplifying the structure.

Reply to "Comments on 'RF Impedance of United States and European Power Lines'"

Abstract: Impedance measurements were made of 86 commercial 50-Hz AC power distribution systems throughout the LF-HF (0.02-30 MHz) spectrum in six European countries. The impedances are those presented to devices/appliances connected to the ac power source. The European results are presented in graphic and tabular form and are compared to impedances of U.S. power lines.

Multiple-frequency permittivity tester

Abstract: As in prior testers, a capacitive cell in which material is placed to be tested is connected in a voltage divider circuit. However, signal generating means connected to the voltage divider applies voltages at different predetermined frequencies selected for the material being tested, and frequency selective means connected to the cell develop voltages at the applied frequencies having values dependent on the impedance of the filled cell at the respective frequencies. These voltages developed across the cell are applied to a computer that provides an output according to an equation that has been derived statistically from many samples of the material being tested for the substance or quality of the material being measured.

Single wire transmission of multiple switch operations

Abstract: Each of a plurality of switches is connected in parallel with an impedance and the switches are coupled to form a series circuit. A reference voltage is coupled to one end of the series circuit and a termination impedance is coupled to the other end to form a voltage divider. The voltage divider ratio is determined by the switches that are operated and the divided voltage is coupled to an analog-to-digital converter producing a binary output signal that indicates which combination of switches is operated. Another embodiment of the invention uses a constant current generator instead of a termination impedance to provide linear ratios in the voltage divider.

Highway line detector

Abstract: A highway line detection system for an automobile which provides an output signal when a traffic line on a pavement under an automobile is about to be crossed. It includes a photoelectric sensor connected to an electrical bridge circuit, and the bridge circuit includes an impedance element which is varied in impedance responsive to the integrated output of the bridge circuit, and thereby the bridge circuit is maintained in balance for ambient light conditions. Further, the threshold of detection of the system, at which point an alarm is sounded, is varied as a function of the ambient light state, whereby the sensitivity of the system is increased for low light conditions and decreased for high light conditions to compensate for an opposite characteristic of the photosensor.

Impedance Measurements at the N‐ and P‐Type GaP Single Crystal Electrode

Abstract: Impedance measurements were made at the dark n- and p-type GaP single crystal electrodes in aqueous indifferent electrolyte solutions as a function of applied voltage and of frequency. The results allow the determination of the flatband potential and hence of the position of the Fermi level and the conduction and valence band edges at the electrode surface. The observed frequency dependence of the capacitance can be attributed to dipole relaxation phenomena in the space-charge layer of the semiconductor electrode. The influence of preliminary etching on the frequency behavior is discussed.

A simple voltage controlled oscillator with grounded capacitors

Abstract: A simple voltage controlled oscillator circuit using capacitors, all of which are grounded, is presented. The circuit is thus attractive from the point of view of monolithic or hybrid IC fabrication. The frequency of oscillation can be varied over a wide range, with the amplitude of oscillation remaining relatively stable over the range. Experimental results are given that agree closely with the theoretical predictions.

Circuit for the protection of telephone lines

Abstract: Arrangement for protecting telephone lines and electronic circuits connected thereto from overvoltages. A first pair of diodes clamp the voltage of each wire versus the supply voltages in cooperation with a current limiting impedance. A second pair of (Zener-) diodes, separated from the first pair by means of a current limiting impedance, clamp the forward "transient" produced across the first pair versus the same or slightly deviating supply voltages.

Inductor simulation using a current conveyor

Abstract: Two schemes of simulating grounded inductors using a second generation current conveyor are reported. Both schemes provide simulated inductors that are relatively frequency independent, with suitable design, at moderately high-Q values.

Circuit for automatic load sharing in parallel converter modules

Abstract: A nondissipative circuit for automatic load sharing in parallel converter modules having push-pull power transistors, each transistor having a separate current-sensing transformer and an impedance-adjusting transformer in series with its collector. The impedance-adjusting transformer functions as a current-controlled variable impedance that is responsive to the difference between the peak collector current of the transistor and the average peak current of all collector currents of power transistors in all modules, thereby to control the collector currents of all power transistors with reference to the average peak collector current.

Temperature measuring apparatus

Abstract: An apparatus for measuring the temperature of a metallic body in a non-contact maner includes an electronic circuitry for measuring a change in the impedance of a detecting coil arranged oppposite to the metallic body The electronic circuitry comprises an operational amplifier, a negative feedback circuit with adjustable feedback factor, a positive feedback circuit, an oscillator, a phase shifter circuit and a synchronous detection circuit The change in the impedance of the detecting coil is caused by the effect of eddy current produced by the application of alternating field to the metallic body, and this impedance change is dependent on change in the temperature of the metallic body By adjusting the negative feedback factor βN of the negative feedback circuit and the phase angle θ of the phase shifter circuit in the electronic circuitry, the relationship between the distance measured between the detecting coil and the metallic body and the measured output level, the temperature measuring sensitivity relative to the temperature of the metallic body and the temperature measuring sensitivity relative to the measuring distance can be determined as desired

A mathematical model for the impedance of the cavity-backed slot antenna

Abstract: A mathematical model is derived that relates the impedance of a cavity-backed slot antenna to that of an identical slot which is free to radiate on both sides of a large ground plane The model, which utilizes empirical constants from a previous experimental investigation, provides a continuously variable function of frequency and cavity depth for the impedance of a cavity-backed slot of fixed length and cavity cross section This function is then compared with previously found experimental values and two theoretical solutions, one using a variational method and the other using the complex Poynting theorem

Two-wire transmitter with totalizing counter

Abstract: A two-wire transmitter operating in conjunction with a meter whose output signal varies in frequency as a function of the metered variable. The meter signal is changed into an analog voltage that is converted by the transmitter into a corresponding output current and conveyed to a receiving station over a two-wire line which also supplies operating voltage to the transmitter. In the transmitter, the analog voltage is applied to a differential amplifier which converts the voltage into an output current via a transistor acting as a variable impedance across the line to make up the difference between the operating current drawn by the transmitter and the output current. This make-up current is stored to provide an energy source for operating a totalizing counter coupled to the meter to determine the total amount of the variable passing through the meter.

Input Impedance of Coaxial Line to Circular Waveguide Feed

Abstract: The expressions for the real, imaginary parts of the input impedance seen by a coaxial line driving a thin cylindrical probe in a dominant TE/sub 11/ mode circular waveguide are derived. The analysis is carried out by assuming that the cylindrical post is replaced by a curvilinear strip having maximum width equal to the diameter of the probe. Theoretical results on input VSWR and input impedance seen by a coaxial line are in close agreement with experimental data.

Rotary electric machine and power conversion system using same

Abstract: A power conversion system for converting between electrical power at different frequencies, including a rotary electrical machine including a rotor, a stator, first and second independently controllable field windings, and at least one armature winding for each phase; a switching circuit including a plurality of switching devices and having first terminal means interconnected with the armature winding which carries a high frequency signal established by the machine, and a second terminal for interconnection with an impedance establishing a lower frequency signal; the first field control circuit for monitoring the machine to sense phase difference between the optimum zero crossings and actual zero crossings of the higher frequency signal for driving the first field winding to adjust the phase of the higher frequency signal to minimize the phase difference; a second field control circuit for modulating the higher frequency signal carried by the armature winding with the lower frequency signal and for monitoring the second terminal means to sense amplitude difference between a selected one of the voltage and current parameters of the lower frequency signal and a reference level for driving the second field winding to adjust that parameter towards the reference level; and a switch firing circuit responsive to the machine voltage and one of the voltage and current parameters of the lower frequency signal at the second terminal means for selectively triggering to the on state and self-commutating to the off state the switching devices synchronously with the zero crossings of the higher frequency signal for transferring power between the higher and lower frequency signals through the switching circuit.

Magnetic field detection apparatus

Abstract: A magnetic field detector for determining the presence of a magnetic field disturbance in the vicinity of the apparatus senses the difference in magnetic fields at two spaced-apart locations. A pair of field sensors, each including a body of polarizable liquid and a probing coil, are connected in series and provide an output signal that is produced in the coils by the free precession of the protons of the liquid bodies in the earth's magnetic field. A timer circuit controls a relay to alternately connect the magnetometer coils to a source of polarizing current during a polarizing period, and to detection circuitry during a listening period. The detection circuitry includes a high gain signal channel comprising a multi-stage, high input impedance preamplifier and a bandpass amplifier tuned to the frequency range of the signals generated in the probing coils. The output signal from the high gain signal channel is applied to a rectifying circuit that rectifies the amplified free precession signals at a selected bias level to produce a signal that reduces to zero as the free precession signals in the coils decay. Filtering and amplifying of the rectified signal is provided, with the signal being finally applied to a meter operable to follow a low frequency beat signal and provide for the observation and timing of the length of the interval between the beginning of the listening period and the occurrence of the first subsequent minimum value of the beat signal. The time interval is marked by deflections of the meter movement and characterizes the size and distance of a detected object.

Electronically tunable microwave frequency FET discriminator

Abstract: A microwave frequency discriminator comprising a field effect transistor (FET) amplifier including an electronically variable capacitor (varactor), a biasing circuit and a detector. The FET is biased to generate an output RF signal within a predetermined frequency bandwidth in response to an input RF signal of substantially constant power level. The variable capacitor is biased to electronically provide a predetermined impedance to the transistor to augment the frequency roll-off characteristic of the FET. The biasing circuit is used to electronically match the impedance of the FET output to the input of the detector. At such impedance conditions the dc output voltage of the detector varies substantially linearly throughout the frequency bandwidth as a function of the frequency of the input RF signal, approximating the characteristic of a frequency discriminator.

Oxygen sensor temperature monitor for an engine exhaust monitoring system

Abstract: A vehicle engine includes an exhaust monitoring system with an exhaust mounted oxygen sensor and apparatus for processing the sensor output voltage into an exhaust constituent signal which may, for example, be used to control the air-fuel ratio of the engine fuel supply to a substantially stoichiometric ratio, the apparatus including a low pass filter which suppresses components of the signal greater in frequency than a predetermined cutoff frequency. An alternating voltage generator effective to generate a square wave of at least the cutoff frequency is connected through a reference impedance, a capacitor and the oxygen sensor in series to ground, thus creating a voltage divider with an output between the reference impedance and the sensor internal impedance, the voltage at the output having a peak-to-peak amplitude which varies inversely with sensor temperature. The voltage at the output is provided to a peak detector, which generates therefrom a signal representing the temperature of the oxygen sensor. The low pass filter in the closed loop fuel control and the capacitor protect the exhaust constituent signal from distortion by the alternating voltage.

Automatic gain and return loss compensating line circuit

Abstract: The disclosed T-type line compensation circuit reduces the gain and return loss variations when customer equipment is connected to a central office or PBX over telephone lines of various lengths. A linear resistor of a first series leg is thermally coupled, as a heat source, to a positive temperature coefficient (PTC) resistor of a second series leg. The shunt leg consists of a series connection of a bilateral zener diode, linear resistor, and varistor. The resistance value of both the second series leg and the shunt leg of the line circuit vary automatically with the direct current in the line to minimize gain variation due to telephone line length variation. The thermal feedback to the PTC resistor varies automatically with the direct current in the line to minimize return loss variations seen by the customer equipment. FIELD OF THE INVENTION This invention relates to a line circuit for compensating telephone loop line and return loss variations due to variations in line lengths. BACKGROUND OF THE INVENTION In the telephone loop plant it is frequently necessary to transmit and receive signals over telephone lines of various lengths. These telephone loop length variations arise because of the varying distances between the subscriber locations and the associated central office location. The length of the telephone line from the central office to the subscriber determines the magnitude of the direct current which flows to the subscriber telephone set. Thus, when a modern telephone set is connected at the subscriber's premises, an equalizer incorporated therein will equalize transmitting and receiving levels and side-tone levels in accordance with the magnitude of the direct current flowing from the central office. The circuit disclosed in U.S. Pat. No. 2,629,783 issued to H. F. Hopkins on Feb. 24, 1953 is typical of telephone equalizer circuitry. In Hopkins a current-sensitive resistance element is placed across the line terminals of the telephone circuit. As the loop length varies the direct current flowing through the loop will vary and if the current-sensitive element has the proper degree of nonlinearity, the received and the transmitted levels at the telephone terminals will be held substantially constant, assuming constant inputs at the telephone transmitter. In Hopkins, the current-sensitive element is placed in shunt across the telephone circuit. A variable shunt across the telephone circuit imposes an additional burden on the side-tone balancing circuit, since with the variable shunt the loop impedance "looking out" from the telephone terminals will vary over a greater range than without the variable shunt. This additional burden is alleviated in Hopkins by employing in combination with the variable shunt equalizing circuit, a variable line balancing circuit which is also responsive to the loop direct current. Thus, Hopkins and other prior art does not compensate the telephone line to match a fixed impedance, but rather balances the telephone equipment to the varying line impedance. A problem exists, however, when subscriber equipment has a conference capability in which multiple central office (CO) lines are connected to a single telephone. Since each CO line will be supplying current the total current received by the telephone will bear no relationship to the length of the connected CO lines. Additionally, in some customer equipment the telephones at the subscriber location are dc isolated from the CO lines and hence not supplied with a direct current which varies with loop length. Thus, the equalization approach used in the prior art will not be applicable. In addition, the diversity of customer premises communication equipment has grown rapidly in recent years with some equipment requiring a constant impedance "looking out" from the customer's terminals, towards the central office or private business exchange (PBX), to match the impedance of the customer's equipment. In the telephone system any impedance mismatch between the telephone loop lines and the connecting central office or customer equipment may result in echoes or singing. A measure of this characteristic is called return loss which is an inverse measure of the transmission energy loss due to an impedance mismatch. Accordingly, a need exists in the art for a line circuit which will automatically compensate for variations in line impedance to effect a better impedance match when connected to fixed impedance communications equipment. Another need exists in the art for a line circuit which will automatically compensate for variations in line impedance as well as gain variations due to different telephone loop lengths. Another need is to provide a gain and return loss compensating line circuit which reduces the unbalance caused by connection of multiple central office lines to one telephone. Another need is to provide a gain and return loss compensating line circuit which operates independent of the telephone dc currents. Another need is to provide a gain and return loss compensating line circuit which can be inserted in cascade with existing lines at the subscriber's location. Yet another need is to provide a gain and return loss compensating line circuit which is economical, small and mechanically rugged. SUMMARY OF THE INVENTION In the instant application one embodiment of a gain and return loss compensating line circuit is disclosed which satisfies the existing needs. The disclosed four-terminal compensating line circuit is inserted in cascade with each CO line at a transformer input to the customer equipment. The transformer isolates the line dc currents from the dc currents of the telephone set. Since each CO line has its own compensating line circuit, unbalance is reduced when multiple CO lines are connected together. One embodiment of the disclosed circuit is arranged as a "T" type attenuator having a first series leg, a shunt leg and a second series leg with a common connection node for one terminal of each leg. The shunt leg, which provides gain compensation, consists of a series connection of a bilateral zener diode, linear resistor, and bilateral varistor. A linear resistor of the first series leg is thermally coupled, as a heat source, to a positive temperature coefficient (PTC) resistor of the second series leg. Alternately, if the PTC can be made with low enough thermal inertia the first series leg is not necessary as an additional heat source and may be eliminated along with its audio bypass capacitor. This circuit would be better adapted to applications where the series resistance must be kept low for supervisory applications. Normally any such resistance in series with the line adds signal loss which decreases the effectiveness of the gain compensating circuit. However, the linear resistor of the first series leg is required to limit current and avoid saturation of the transformer on short CO loops. Since the PTC resistor is placed in series with the line such that the gain compensator's current flows through the PTC resistor, any gain variations caused by the PTC resistor are minimized by the gain compensating circuit while enabling the PTC resistor to provide the desired return loss improvement. Return loss improvement requires the value of series resistance for short loops to be greater than the resistance for long loops. Thus, a PTC resistor was used as the series resistance. Since short loops have higher dc current, more heat is developed in the PTC resistor, and the thermally coupled linear resistor thus increasing the temperature and hence resistance of the PTC resistor. The temperature rise, and hence the resistance increase, of the PTC resistor is more pronounced when heat is coupled to it from an additional heat source, the linear resistor of the first series leg, of the compensator circuit. Thus, the impedance value of both the second series leg and the shunt leg of the line circuit vary automatically with the direct current in the CO loop in a manner to minimize gain variations when connected to CO loops of various lengths. The thermal feedback to the PTC resistor varies automatically with the direct current in the line in a manner to change its resistance to minimize return loss variations at both the customer and central office locations. Accordingly, it is a feature of my invention to provide both an automatic gain and return loss compensating line circuit which uses series and shunt regulation circuitry to compensate for impedance and signal variations of various telephone loop lengths. It is a feature of my invention to provide an automatic gain and return loss compensating circuit, utilizing a PTC resistor with thermal feedback, which can be used with protective coupler devices. It is another feature of my invention to provide an automatic gain and return loss compensating circuit, utilizing a PTC resistor with thermal feedback, which can be used in a telephone station set. Finally, it is a feature of my invention to provide a small, solid state mechanically rugged, yet economical compensating line circuit.

Power source circuit

Abstract: PURPOSE: To obtain a power source circuit which features a small power consumption as well as a small impedance with the steady output, by supplying the current intermittently to plural voltage division output route. COPYRIGHT: (C)1979,JPO&Japio

Measurement of Beam Stability and Coupling Impedance by RF Excitation

Abstract: The transverse stability limit and coupling impedance of proton beams in the CERN Intersecting Storage Rings have been measured by external excitation of the beam. The impedance values at low frequencies thus obtained are in good agreement with the sum of the skin-effect and the wall-inductance which has been measured previously. The method can be extended to higher frequencies if the beam can be stabilized against low-frequency oscillations, e.g. by feedback.

Improvements on the measurements of dielectric constant and dissipation factor in a wide frequency range

Abstract: This paper describes an improved micrometer electrode system for the measurements of dielectric constant, dissipation factor, and mean thickness of sheet specimens in a wide frequency range and its appplication to a series of measuring methods. The influence of the edge capacitance and the residual impedance of this electrode system has been decreased to a negligibly small amount by the adoption of a shield ring and improvements in construction of the electrode system. The characteristics of the system are easily examined by using its electrode gap fine adjustment mechanism, which is developed for a series of measuring methods. In case the varying gap immersion method is adopted, the imperfect contact between the electrodes and the specimen and the residual impedance of the system do not affect the results, even at the highest frequency. Furthermore, the measurements are limited to only the gap variations and the resonance voltage ratio, and are freed from those of the electrode gap length, the electrode ...

The current dependency of the output conductance of voltage-driven bipolar transistors

Abstract: The current dependency of the output conductance of voltage-driven bipolar junction transistors (BJTs) is discussed. It is shown that by combining the established theories about basewidth modulation and thermal feedback the output admittance of voltage-driven BJTs can be accurately predicted over a large range of current levels. The current dependency of the output admittance of some basic IC configurations is discussed in detail.

Dual liquid level monitor

Abstract: A liquid level monitoring system functions by applying an alternating voltage to a probe. When the liquid level in a reservoir touches the probe, a low impedance to ground is present, thereby permitting current to flow to ground. When the liquid level falls below the probe, a high impedance to ground is created and current flows to a detector. The detector switches on an alarm which flashes an appropriate warning.

Multiple circuit switch assembly

Abstract: A switch apparatus is provided which closely approximates transmission medium parameters for reducing impedance discontinuities by utilizing a high frequency contact arrangement permitting high bandwidth operation. The apparatus is adaptable for use with both high and low impedance circuitry.