Showing papers on "Voltage published in 1989"

Electrode models for electric current computed tomography

Abstract: A mathematical model for the physical properties of electrodes suitable for use in electric current computed tomography is discussed. The model includes the effects of discretization, shunt, and contact impedance. The complete model was validated by experiment. Bath resistivities of 284.0, 139.7, 62.3, and 29.5 Omega -cm were studied. Values of effective contact impedance used in the numerical approximations were 58.0, 35.0, 15.0, and 7.5 Omega -cm/sup 2/, respectively. Agreement between the calculated and experimentally measured values was excellent throughout the range of bath conductivities studied. It is desirable in electrical impedance imaging systems to model the observed voltages to the same precision as they are measured in order to be able to make the highest-resolution reconstructions of the internal conductivity that the measurement precision allows. The complete electrode model, which includes the effects of discretization of the current pattern, the shunt effect due to the highly conductive electrode material, and the effect of an effective contact impedance, allows calculation of the voltages due to any current pattern applied to a homogeneous resistivity field. >

Calcium currents in rat thalamocortical relay neurones: kinetic properties of the transient, low‐threshold current.

Abstract: 1. Calcium currents were recorded with whole-cell voltage-clamp procedures in relay neurones of the rat thalamus which had been acutely isolated by an enzymatic dissociation procedure. 2. Low-threshold and high-threshold Ca2+ currents were elicited by depolarizing voltage steps from holding potentials more negative than -60 mV. A transient current, analogous to the T-current in sensory neurones, was activated at low threshold near -65 mV and was completely inactivating at command steps up to -35 mV. Voltage steps to more depolarized levels activated a high-threshold current that inactivated slowly and incompletely during a 200 ms step depolarization. 3. The high-threshold current contained both non-inactivating and slowly inactivating components which were insensitive and sensitive to holding potential, respectively. 4. A 'T-type' current was prominent in relay neurones, in both absolute terms (350 pA peak current average) and in relation to high-threshold currents. The average ratio of maximum transient to maximum sustained current was greater than 2. 5. T-current could be modelled in a manner analogous to that employed for the fast Na+ current underlying action potential generation, using the m3h format. The rate of activation of T-current was voltage dependent, with a time constant (tau m) varying between 8 and 2 ms at command potentials of -60 to -10 mV at 23 degrees C. The rate of inactivation was also voltage dependent, and the time constant tau h varied between 50 and 20 ms over the same voltage range. With command potentials more positive than -35 mV, the inactivation of Ca2+ current could no longer be fitted by a single exponential. 6. Steady-state inactivation of T-current could be well fitted by a Boltzman equation with slope factor of 6.3 and half-inactivated voltage of -83.5 mV. 7. Recovery from inactivation of T-current was not exponential. The major component of recovery (70-80% of total) was not very voltage sensitive at potentials more negative than -90 mV, with tau r of 251 ms at -92 mV and 23 degrees C, compared to 225 ms at -112 mV. A smaller, voltage-sensitive component accounted for the remainder of recovery. 8. All kinetic properties, including rates of activation, inactivation, and recovery from inactivation, as well as the amplitude of T-current, were temperature sensitive with Q10 (temperature coefficient) values of greater than 2.5.(ABSTRACT TRUNCATED AT 400 WORDS)

Microprocessor controlled arthroscopic surgical system

Abstract: An apparatus for controlling the speed of a plurality of DC motors, comprises a device for supplying voltage to one of the plurality of DC motors, first selector for selecting one of the DC motors to be connected to the device for supplying voltage, second selector for selecting a desired speed for the selected DC motor, a device for producing a feedback signal representative of an electrical current drawn by the selected DC motor and a controller for: (i) producing a reference voltage in response to the first and second selectors (ii) producing a load voltage in response to the feedback signal and (iii) outputting a control signal which is the sum of the reference voltage and the load voltage to the device for supplying voltage so that the selected DC motor is operated at the desired speed.

Current waveform distortion in power factor correction circuits employing discontinuous-mode boost converters

Abstract: For active power factor correction circuits employing discontinuous-mode boost converters, the line current will automatically follow the sinusoidal line-voltage waveform. However, due to the modulation of the input inductor current discharging time, there is certain distortion in the AC line-current waveform. It is found that the modulation of inductor current discharging time is a function of the line voltage and the output voltage of the boost converter. For practical design considerations, the waveform distortion and the maximum power factor achievable are derived and presented in a graph form as functions of the ratio of line voltage to output voltage. >

Circuit for measuring the capacity of a battery

Abstract: The discharge capacity of a secondary battery, e.g. a Ni-Cd battery, has a maximum value at room temperature and gradually decreases both with an increase and decrease of ambient temperature. The battery discharge capacity also varies inversely with the number of battery charge/discharge cycles of the battery. A circuit for measuring the remaining discharge capacity of the secondary battery comprises a capacitor (23) whose temperature and age-variation characteristics are very similar to those of the discharge capacity of the secondary battery. The current flowing through the battery and motor (13) is detected by a series resistor (17). A voltage follower (20) responds to the detected voltage and drives a resistor (24), so that capacitor (23) is discharged at a rate determined by the resistor (24) current. The capacitor voltage is compared with a predetermined value by a hysteresis comparator (29) which controls the ON/OFF state of a transistor (21) in accordance with the comparison. The comparator output pulses, i.e., the capacitor charge/discharge cycles, are counted by a counter (31). Since the capacitance variation of the capacitor corresponds to the variation in battery discharge capacity with ambient temperature and also with the time of use, the counter (31) indicates very accurately the remaining battery capacity

A self-calibration technique for monolithic high-resolution D/A converters

Abstract: A self-calibration technique based upon charge storage on the gate-source capacitance of CMOS transistors is presented. The technique can produce multiple copies of a reference current. Therefore, it is suitable for the calibration of high-resolution D/A (digital/analog) converters which are based upon equal current sources. As the storage capacitor is internal, no external components are required. A calibrated spare current source is used to allow continuous converter operation. This implies that no special calibration cycles are required. To show the capabilities of the calibration technique, it was implemented in a 16-b D/A converter. Measurement results show a total harmonic distortion of 0.0025% at a power consumption of 20 mW and a minimum supply voltage of 3 V. The design was fabricated in a 1.6- mu m double-metal CMOS process without special options. >

Electronic battery testing device

Abstract: An electronic device for testing storage batteries and other dc sources is disclosed. The testing device passes a small, time-varying, current through the battery and observes the resulting time-varying voltage response. This response is then digitized and inputted to a microprocessor. In one embodiment of the invention, the microprocessor numerically inverts the level of the response voltage to obtain a quantity proportional to the battery's conductance and hence proportional to its available power. In a second embodiment, the microprocessor compares the observed voltage response level with a reference value based upon the battery's rating to obtain a qualitative assessment of the battery.

High frequency electrosurgical apparatus for thermal coagulation of biologic tissues

Abstract: A high frequency surgical apparatus for the thermal coagulation of biologic tissues is described, in which for monitoring the fluctuations in amplitude of the high frequency current during each coagulation process a current monitor (25) is provided, which by means of a current-to-voltage coverter generates an electrical voltage proportional to the amplitude fluctuations of the high frequency current, from which voltage, by means of a first detector, a first direct voltage proportional to the amplitude fluctuations is formed and, by means of a second detector acting as a peak value detector, a second direct voltage is formed that rises in proportion to the amplitude of the high frequency current. The first direct voltage (Ua) and the second direct voltage (kUb), which is divided downward by an adjustable factor by means of a voltage divider, are supplied to a voltage comparator, the output signal of which sets a bistable circuit as soon as the first direct voltage (Ua) becomes lower than the downwardly divided second direct voltage (kUb). The output signal of the bistable circuit switches the high frequency current off until the high frequency current is switched back on again by actuation of a manual switch and/or by means of an automatic switch. Instead of or in addition to this current monitor (25), and electric arc monitor (26) for monitoring the generation of anharmonic frequencies of the base frequency of the frequency generator can be connected to the output of the surgical apparatus, the arc monitor including a filter which passes at least one of the anharmonic frequencies, generated by the electric arc, of the base frequency of the high frequency generator. The output signal of the filter is supplied to a voltage comparator, the output signal of which resets a bistable circuit such that its output signal switches off the high frequency current.

Current-forced single-phase reversible rectifier

Abstract: A 7 kW voltage-sourced reversible rectifier (VSRR) which achieves bidirectional power flow between a single-phase AC supply and a DC busbar voltage is described. A current-forced control (CFC) strategy is used to switch two power transistors, enabling the device to operate with a unity power factor and a sinusoidal line current to produce a regulated DC busbar voltage. The advantages of the scheme are its simplicity, an extremely fast and well damped response and its adaptive nature to nonlinear effects such as transistor switching delays. The device operates with a DC busbar voltage which is greater than the peak-to-peak voltage of the utility supply so that it is especially suitable for use as a source of power in a variable-speed AC induction-motor drive.

New International Electrical Reference Standards Based on the Josephson and Quantum Hall Effects

Abstract: We give here the background and basis for the new international electrical reference standards of voltage and resistance that are to come into effect worldwide starting on 1st January 1990. Founded on the Josephson and quantum Hall effects, respectively, these new reference standards will improve significantly the international uniformity of electrical measurements and their consistency with the SI.

Dynamics of a collisional, capacitive RF sheath

Abstract: A self-consistent solution for the dynamics of a high-voltage, capacitive RF sheath driven by a sinusoidal current source is obtained, under the assumptions of time-independent, collisional ion motion and inertialess electrons. Values of the ion current density, the sheath capacitance per unit area for the fundamental voltage harmonic, and the conductance per unit area for stochastic heating by the oscillating sheath are calculated. The ratio of the DC to the peak value of the oscillating voltage is found to be 0.40, while the second and third voltage harmonics are, respectively, 19.3% and 5.3% of the fundamental. >

Method and apparatus for the calibration of electrosurgical apparatus

Abstract: A method and apparatus for the calibration of electrosurgical apparatus utilizes a non-volatile, read-write storage device (U2) to store calibration parameters. A programmed microprocessor (U3) and an EPROM memory (U1) for the microprocessor (U3) control the flow of data to and from the storage device (U2). For the calibration of the RF power output a test resistor of known value provides a test power reading and the RF power output is adjusted by the adjustment of up/down power select keys until the RF power output substantially equals the test power so that the values stored in the storage device (U2) control subsequent RF power output levels. For the calibration of a return electrode contact monitor (35), a low resistance of known value is input into the storage device (U2) by depressing a key and a high resistance value is input into the storage device (U2) by depressing the same key. These values are stored in the storage device (U2) and provide a transfer function from which a particular output voltage value is generated for each return electrode resistance measurement.

Flash EEPROM array with negative gate voltage erase operation

Abstract: A flash EEPROM cell array is erased by applying a zero reference voltage to the bulk substrate of the cell, a relatively high negative voltage to the control gate of the cell and a relatively low positive voltage to the source region of the cell. Because of a relatively low reverse voltage developed between the source region of the cell and the bulk substrate, the generation of hot holes is inhibited and improved performance may be obtained. The source region is preferably single diffused rather than double-diffused so that the cell can occupy a minimum area for a given design rule. The low positive voltage applied to the source is preferably less than or equal to the voltage, V CC presented at a +5V chip power supply pin. This makes it possible for the +5V pin to directly supply source current during erasure.

The fundamentals of the pseudospark and its applications

Abstract: The pseudospark, an axially symmetric gas discharge at low pressures of typically 10 to 100 Pa and high voltages (of some hundred volts up to several hundreds of kilovolts), has become of interest in fast high-power switching, in producing well-pinched high intensity electron or ion beams, and as an X-ray source. The essential features of this type of discharge are described. The results of fast time-resolved spectroscopic investigations and breakdown delay statistics of the pseudospark are discussed. >

Angle controlled current regulated rectifiers for AC/AC converters

Abstract: Rectifier control schemes for use in AC-DC-AC voltage-sourced resonant link converters with controlled rectifiers are discussed. Resonant link converters require the use of discrete pulse modulation. Control of the AC-to-DC converter by means of averaging methods or duty-cycle control is not inherent with this type of modulation. However, it is shown that the voltage-sourced rectifier cannot be operated solely on the basis of instantaneous quantities. A bang-bang control scheme is developed which independently controls the angle and the magnitude of the AC line current vector. The magnitude of the current is controlled using a linear combination of the link voltage error and the current magnitude error. The current reference is derived by the use of load torque estimation. In addition, the current vector that satisfies the sliding-mode criteria and results in the lowest voltage ripple is chosen to further minimize the size of the link capacitor. >

Monitoring device for electric storage battery and configuration therefor

Abstract: An electric storage battery is provided having a monitoring device for indicating the state-of-charge of the battery and particularly indicating whether a discharged battery is healthy and capable of being recharged or unhealthy and impending on a state of failure. The monitoring device achieves the foregoing by testing the open circuit voltage of the battery and determining if the voltage of the battery drops below a first preset value after application of a load and subsequently fails to rise above a second preset value after the load has been removed. Also, the monitoring device for the battery includes the capability of sensing when the battery has been placed into a system such as an engine system for an automobile and in response thereto modifying testing certain parameters. Preferably, the monitoring device is made integral with the battery case by providing a receptacle for receiving the device and a pair of connecting arms at least partially embedded in the battery container or cover.

Variable speed DC motor controller apparatus particularly adapted for control of portable-power tools

Abstract: A portable electric power tool having a DC motor for driving tool bit is controlled according to speed and torque by employing a zero displacement switch means which is coupled to the tool and operative to provide an output voltage porportional to the pressure applied to the switch means via the hand of the user. The zero displacement switch interfaces with a piezoresistive array which produces a voltage output proportional to the pressure applied to the zero displacement switch. The voltage output of the array is applied to control circuit means which are coupled to the motor and which controls the speed of the motor according to the pressure applied to the switch. There is further included motor control circuitry which operates to monitor the current through the DC motor to control the speed of the motor according to the torque imparted upon the tool bit being accommodated by the portable electric tool.

Electronic battery testing device with state-of-charge compensation

Abstract: A self-contained electronic device for testing storage batteries that may be partially discharged is disclosed. The testing device performs small-signal measurements of the battery's dynamic conductance and provides either a proportional numerical readout, displayed in appropriate battery measuring units, or a corresponding qualitative assessment of the battery's relative conduction based upon its electrical rating. In addition, the testing device measures the battery's open-circuit (unloaded) voltage and provides adjustable means for correcting the dynamic conductance test result in inverse correspondence with the battery's open-circuit voltage relative to its fully-charged value. By virtue of this correction, the quantitative or qualitative information displayed to the user in the dynamic conductance test is adjusted to comport with that of a fully-charged battery even through the battery may, in actual fact, be only partially charged when tested.

Radiofrequency sheaths and impurity generation by ICRF antennas

Abstract: In general, Faraday screen elements in an ICRF antenna are not aligned precisely along the combined toroidal and poloidal magnetic fields. When plasma of density n > 20V/eg2 ~ 109cm−3 (V being the voltage across the gap and g the gap spacing) is present in the gap between the elements, the electron response to the parallel electric field shorts out the electric field over most of the gap, leaving a narrow sheath of positive space charge and an intense electric field. This intense electric field accelerates ions up to an appreciable fraction of the gap voltage (~1 kV), sufficient to cause physical sputtering of the screen material. Impurities so generated constitute the principal limitationon power density for ICRF antennas. Principles of ICRF antenna and Faraday screen design which minimize sputtering are discussed.

Power factor improvement

Abstract: A boost convertor power supply comprising an electronic switch controlling current through a boost inductance, rectifier means for charging capacitor means which accumulate the resulting boost charge from the boost inductance, and means for repeatedly switching the electronic switch. Pulse width modulation means vary the relative on/off period of each cycle of switching to cause the peak switch current to follow a variable amplitude wave of shape corresponding to the input voltage applied to the boost convertor and amplitude controlled by an error amplifier and multiplier thereby regulating the output voltage. A ramp signal generator provides for pulse width stability. Means correct for the difference between average current in the boost inductor and peak switch current to modify the pulse width modulation means to reduce distortion of the line current waveform.

An improved understanding for the transient operation of the power insulated gate bipolar transistor (IGBT)

Abstract: It is shown that a nonquasi-static analysis must be used to describe the transient current and voltage waveforms of the IGBT (insulated-gate bipolar transistor). The nonquasi-static analysis is necessary because the transports of electrons and holes are coupled for the low-gain, high-level injection conditions, and because the quasi-neutral base width changes faster than the base transit speed for typical load circuit conditions. To verify that both of these nonquasi-static effects must be included, the predictions of the quasi-static and nonquasi-static models are compared with measured current and voltage switching waveforms. The comparisons are performed for different load circuit conditions and for different device base lifetimes. >

Equivalent circuit models for resonant and PWM switches

Abstract: The nonlinear switching mechanism in pulsewidth-modulated (PWM) and quasi-resonant converters is that of a three-terminal switching device which consists only of an active and a passive switch. An equivalent circuit model of this switching device describing the perturbations in the average terminal voltages and current is obtained. Through the use of this circuit model the analysis of pulsewidth modulated and quasiresonant converters becomes analogous to transistor circuit analysis where the transistor is replaced by its equivalent circuit model. The conversion ratio characteristics of various resonant converters and their relationship to a single function, called the quasi-resonant function, is easily obtained using the circuit model for the three-terminal switching device. The small-signal response of quasi-resonant converters to perturbations in the switching frequency and input voltage is determined by replacing the three-terminal switching device by its small-signal equivalent circuit model. >

Method for monitoring aircraft battery status

Abstract: An aircraft storage battery is monitored to determine battery capacity, state of charge and certain fault conditions. The ambient temperature, battery voltage on-board charger output voltage and current to and from the battery are continuously measured. Current voltage (I-V) data is analyzed to determine the internal resistance and polarization of the battery. A determination is made regarding state of charge and fault conditions produced by corroded terminals and low electrolyte level. The low temperature starting limit is determined by comparing the battery's power output capability with starting power requirements of the aircraft. Data produced by the comparison are indicated on the dashboard of the vehicle.

Electronic battery testing device with automatic voltage scaling.

Abstract: A self-contained electronic device for testing disparate storage batteries having any one of a fixed plurality of possible nominal voltages is disclosed. The testing device performs small-signal measurements of a battery's dynamic conductance and provides either a proportional numerical readout, displayed in appropriate battery measuring units, or a corresponding qualitative assessment of the battery's relative condition. Special voltage-sensing circuitry (52) within the testing device identifies the particular one of the possible nominal voltages possessed by the battery and scales (34) the dynamic conductance measurements accordingly. As a result, the quantitative or qualitative information provided to the user is automatically adjusted to comport with the nominal voltage of the battery undergoing test without the user having to actually input the battery's nominal voltage to the testing device.

High performance current control techniques for applications to multilevel high power voltage source inverters

Abstract: Several high-performance current-control techniques have been developed for applications to multilevel high-power voltage source inverters. The logical sequence of the design choices is described. They result in a very robust and reliable control system that allows an adequate switching optimization and excellent dynamic responses. The advantages of using various accessible DC potentials have been fully exploited. The results obtained by digital simulation refer to five-level voltage waveforms, but the current-control strategies developed can easily be applied to any multilevel inverter structure, even in the case of n-level voltage waveforms. The validity of the proposed schemes has been confirmed by both digital simulations and tests carried out on scale models. >

Apparatus for measuring internal resistance of wet cell storage batteries having non-removable cell caps

Abstract: Apparatus for measuring the total internal resistance of a multicell battery having positive and negative terminals employs a first transistor device having an input and an output and having mutually exclusive conductive and non-conductive electric states. An arrangement of resistances is connected in series with the device to form a network. The network is connected between the positive and negative terminals. An operational amplifier has an output connected to the input of the device and first and second inputs. The first input is connected to the network at a point connected to both of the device and the arrangement. A square wave signal alternating between a positive voltage and ground on alternate half cycles is applied to the second input. The device is in the conductive state when the alternating voltage is positive and is in the non-conductive state when the alternating voltage is at ground. The network conducts no current when the device is in the non-conductive state and conducts a current of constant value when the device is in the conductive state. The voltage appearing between the terminals as a result of the current in the network is monotonically related to the internal resistance of the battery.

Cognition device for battery residual capacity

Abstract: In a cognition device for battery residual capacity, battery voltage information and battery ambient temperature information are input to a microprocessor through an A/D converter. In the microprocessor, the voltage information is corrected with load information; the data conforming to the ambient temperature information are read out of the battery discharge characteristic data which are previously stored in memory, and the readout data are compared with the corrected voltage information so that the battery residual capacity can be computed from the result of the above comparison data. In this arrangement, it is therefore possible to accurately recognize battery residual capacity at an arbitrary point in time.

Micro-machined accelerometer

Abstract: A spring-mass-support structure and associated electrical circuitry for measuring acceleration applied to the support of the structure is disclosed According to one aspect of the invention, the spring-mass-support structure of the transducer is fabricated using micro-machining techniques of a silicon wafer The structure includes E-shaped leaf springs of silicon dioxide which suspend a mass from a support structure The springs as well as the support structure and the suspended mass, are formed by chemical etching through openings of opposite faces of a silicon wafer on which etch stop layer patterns are diffused Sense and force conductive patterns are diffused onto the opposite faces of the suspended mass The spring-mass-support structure is then sandwiched between opposite plates having corresponding sense and force conductive patterns which face such patterns on the suspended mass According to another aspect of the invention, electrical circuitry is provided by which a sense voltage and a force voltage are applied between opposite sense and force conductive patterns of the opposite plates creating a sense electric field and a force electric field across the sense and force patterns of the mass A feedback circuit arrangement is provided to substantially maintain the mass at a predetermined reference position between the support plates Forward circuitry of the feedback arrangement produces a displacement signal in response to a voltage induced on the sense area of the mass as it moves in response to acceleration applied to the support structure Feedback circuitry of the feedback arrangement produces an amount of charge in response to the displacement signal which is applied to the force conducting area of the mass The force on said mass is proportional to the product of that charge and the force electric field intensity which causes the mass to remain close to a reference position between the plates Alternative circuitry for providing analog or binary bit stream representations of acceleration is disclosed