Parallel Condenser Research Articles

Analysis of Single-Phase Back-to-Back SCR Circuit Having Condenser in Parallel

Analysis of Single-Phase Back-to-Back SCR Circuit Having Condenser in Parallel

Analysis of the Junction Potential of a Small Nerve

Fatt and Katz1 demonstrated with the aid of an intracellular microelectrode that the end-plate potential was produced in the region of the motor end-plate by a sudden and transient reduction in the membrane potential as a result of neuromuscular transmitter action. They further pointed out that the prolonged decline of the end-plate potential was almost exponential and was determined by the electrical properties of the resting muscle membrane. An equivalent circuit of the resting muscle membrane is represented as a condenser in parallel with a battery (membrane potential) with a series resistance (membrane resistance). In the active phase of the end-plate potential, the membrane resistance at the junctional region is suddenly reduced by the transmitter action, that is, the muscle membrane is shortened by a shunting resistance1. To demonstrate the active process of the end-plate potential, Takeuchi and Takeuchi2 and Oomura and Tomita3,4 recorded a current flowing through the end-plate region of the muscle membrane by stimulating the nerve under conditions where the membrane potential was kept at the resting level, using the voltage-clamp technique5,6. On the other hand, the small motor nerve fibres which innervate the slow muscle fibres and relate to the tonic function in the maintenance of posture, also produce the junction potential of the small nerve at the junction region by its stimulation7. A distinctive feature of this junction potential is that it displays two phases with a terminal phase of hyperpolarization7. In the present work an attempt has been made to analyse the mechanism of production of the junction potential of the small nerve, using the voltage-clamp technique.

Periodic Sampling Logarithmic Amplifier

The logarithmic response of the amplifier described in this paper is derived by extracting an output proportional to the time required for the voltage across a parallel resistance condenser combination to decay to a small fixed value. The input voltage is sampled with a 400-cy converter. Accordingly, the amplifier is restricted to a resolving time of 1/400th of a second. A logarithmic response over four decades with a deviation of less than 1% of the maximum output is secured. The immediate purpose of the amplifier is to aid in the study of the transients associated with photocells.

Spark quenching at relay contacts interrupting d.c. circuits

Quenching by resistors and by condensers in parallel with a switch having silver contacts is discussed, and a number of experiments are described which throw light on it. Explanations for the major phenomena in terms of the known properties of arc and glow discharges are offered which appear to be consistent with the experimental facts. The data and reasoning appear to be a sufficient basis from which to decide the approximate values of components needed to effect quenching in any given conditions within the range covered by the experiments.

The Vibration of Piezoelectric Plates

The characteristic frequencies of infinite piezoelectric plates vibrating between the grounded electrodes of a plane parallel condenser have been rigorously investigated. It is found that the frequencies depend on the piezoelectric constants as well as the elastic constants of the crystal. The effective elastic constants for a piezoelectric crystal do not in general satisfy the same symmetry relations as the true elastic constants. For odd harmonics, which are the only modes which can be excited by a uniform electric field, the strain does not vanish at the surface of the plate for a finite gap between the electrodes. Consequently, the frequencies of free vibration also depend on the separation of the electrodes, and the rigorous theory shows this dependence should not be linear as hitherto supposed. The effect of the gap decreases as the square of the harmonic number and hence the higher frequencies of vibration are not exactly harmonics of the fundamental.

A radio-frequency bridge for impedance and power-factor measurments

A radio-frequency bridge for impedance and power-factor measurments

A radio-frequency bridge for impedance and power-factor measurements

A radio-frequency bridge for impedance and power-factor measurements

Note on the correction of frequency error in moving iron voltmeters

The article examines the method of correcting the frequency error in a moving iron voltmeter by connecting a condenser in parallel with the series resistance. The commonly accepted theory is shown to involve unjustified approximations and an accurate investigation is made. The results agree with practical experience, which was not so in the case of the accepted theory. A numerical example is given.

Some notes on grid circuit and diode rectification

The equivalent input resistance of a grid leak and condenser in parallel and the combination in series with a diode or the grid-cathode circuit of a triode are calculated for various combinations by means of the static I g -E g , characteristics and an extension of the work of Colebrook and Peterson and Llewellyn. The equivalent internal resistance of the diode is also calculated and an expression for the equivalent generator is also derived. The relations between X, the grid condenser modulation frequency reactance, R, the grid leak, and m, the percentage modulation, to give good quality are considered theoretically and experimentally. The part played by the values of X, R, and m in the quality of the audio-frequency output was first considered by Terman and Morgan. Limiting values of X and R for the cases of the triode and diode are also estimated.

A New Type of Low Frequency Low Voltage Discharge in a Neon Lamp

IN recent years a good deal of work has been done on the neon lamp as a means of producing oscillatory discharges of high frequencies. The arrangement for this purpose usually consists in placing a variable condenser in parallel with the two electrodes inside the lamp and connecting this in series with an adjustable resistance to a supply of D.C. voltage. The phenomenon of periodic ‘flashing’ owes its existence to the peculiar characteristics of the neon lamp, namely, to the fact of its having two ‘critical’ voltages. When the voltage across the condenser and the lamp in parallel approaches a value equal to that required to start a flash, a flash is visible. During the flash, the resistance of the gap falls and so does also the P.D. between the electrodes. The flash, however, does not disappear until the P.D. between the electrodes falls below the lower critical voltage. As soon as the flash ceases the condenser again begins to charge up to the upper critical value, and the process is automatically repeated. This explanation was given by Mecke and Lambrez (Phys. Zeit., 27, 86; 1926). Using the above arrangement, periodic discharges of high frequencies have been obtained by a number of workers.

The Dielectric Constant of Air at Radio Frequencies

A radio frequency method has been used to measure the dielectric constant $K$ of dry air free from C${\mathrm{O}}_{2}$, the value obtained being 1.0005893 for standard conditions of temperature and pressure. The probable error in $K\ensuremath{-}1$ due to accidental variations is 0.34 percent. The method is a modification of the usual heterodyne beat arrangment. Capacity changes produced when the pressure in the test condenser is changed are compensated by a suitable condenser in parallel. The beat note frequency is compared with that of a fork by means of Lissajous' figures. The test condenser is made of invar to avoid temperature effects. Short connecting wires are used to minimize lead-inductance effects. A few preliminary measurements made with a large direct current voltage superimposed on the high frequency voltage across the condenser indicate no change in the dielectric constant of air, hydrogen, or ammonia. There is some indication that a discharge through the gas decreases its dielectric constant but the effect is probably spurious.

The Piezo-Electric Resonator and Its Equivalent Network

The theory of the piezo-electric and the mechanical behavior of a quartz resonator is stated following Voight and Cady. The functions of the quartz as dielectric and as vibrator are shown to be separable and replaceable by a condenser in parallel with an electrical resonator, i.e., a series chain of inductance, resistance, and capacity. For a Curie-cut quartz rod excited lengthwise through the transverse piezo-electric effect into compressional vibration at the frequency the series elements become L=M/4ϵ2b2; R= N/4ϵ2b2; C=4b2ϵ2/g. This of vibration may be termed the fundamental normal mode since the vibration direction is normal to the electric field. For a Curie-cut quartz plate excited through the longitudinal piezo-electric effect into compressional vibration at the thickness frequency, the series elements become L =e2M/4ϵ2l2b2; R=e2N/4ϵ2l2b2; C=4ϵ2l2b2/e2g. This of vibration may be termed the fundamental parallel mode since the vibration direction is parallel to the electric field. M, N, and g are respectively the half-mass, mechanical resistance factor, and equivalent stiffness of the rod or plate whose thickness along the field is e, and dimensions normal to the field are l and b, the latter being along the optic axis. The parallel capacity is shown to be less than that for a quartz dielectric which is free to assume piezo-electric strain and to be equal to that for unstrained quartz. Phase and amplitude variations of current to the resonator are shown as obtained with the cathode ray oscillograph.

A Simple Method for the Determination of the Electrostatic Capacity of Electroscope

The determination of the electrostatic capacity of the electroscope-iontoquantimeter by either the potential-drop or radio frequency method requires special apparatus and is, at best, an extremely delicate procedure. The following simple method necessitates no apparatus not found in any roentgen department or roentgenologist's office, and seems to give very uniform results. Assuming that one has a standard condenser checked by the Bureau of Standards or other authoritative source, we proceed as follows: Place a small amount of radium element on or near the ionization chamber, screening it properly with lead from the rest of the system. Time the fall of the leaf over any convenient part of the scale. Then connect the standard condenser in parallel with the system (that is, connect one side of the standard to the post supporting the leaf and ground the other side), and again time the fall over the same scale. Of course, if there IS an error caused by leak it must be corrected for in the usual manner. As the...

Condenser Shunt for Measurement of Higi-Frequency Currents of Large Magnitude

The necessity for an accurate ammeter for large high-frequency currents is pointed out. A new device consisting of a large condenser in parallel with a small condenser, and the latter carrying the current to a small thermo-couple ammeter, is described. A device of this nature can be made very accurate; in fact, comparable in accuracy to any available standards. The construction of the device includes provisions for reducing and restricting the electrostatic and electromagnetic field, due to large current, the reduction of distributed inductance and capacity, and a provision to prevent the resonance effect of high harmonics of the operating current. Provisions are also made for locating the measuring instrument at a distance from the circuit. Large ratings are possible by connecting a number of condenser units in parallel.

Condenser Shunt for Measurement of High-Frequency Currents of Large Magnitude

The necessity for an accurate ammeter for large high-frequency currents is pointed out. A new device consisting of a large condenser in parallel with a small condenser, and the latter carrying the current to a small thermocouple ammeter, is described. A device of this nature can be made very accurate; in fact, comparable in accuracy to any available standards. The construction of the device includes provisions for restricting the electrostatic and electromagnetic field, due to large current, the reduction of distributed inductance and capacity, and a provision to prevent the resonance effect of high harmonics of the operating current. Provisions are also made for locating the measuring instrument at a distance from the circuit. Large ratings are possible by connecting a number of condenser blocks in parallel.

On the excitation of the band spectrum of helium

It is now generally agreed that the band spectrum of helium, which was first observed by Curtis (‘Roy. Soc. Proc.,’ A, vol. 89, p. 146, 1913) and by Goldstein (‘Verh. d. Deutsch. Phys. Gesell.,’ vol. 15, p. 402, 1913), is to be attributed to some molecule of helium. This band spectrum is peculiar in the fact that the heads of the bands have been shown by Fowler (‘Rov. Soc. Proc.,’ A, vol. 91, p. 208, 1915) to follow the law usually associated with line spectra, though the individual lines composing the bands can be represented by the parabolic arrangement appropriate to band series. More recently, Curtis has carried out a series of investigations (‘Roy. Soc. Proc.’) on the structure of the bands in terms of the quantum theory. Attention may here be drawn to two peculiarities in the spectrum. There is one isolated band with a head at about λ = 5733 A., which is degraded to the violet, whilst all the remaining bands are degraded to the red. Also Goldstein ( loc. cit. ) observed a number of faint band lines in the region about λ = 5390 A. to λ = 5270 A., which were not recorded in Curtis’s paper ( loc. cit .). It is well known that in vacuum tubes excited by uncondensed discharges only faint traces of the principal band heads are visible in the positive column though the complete band spectrum appears in the negative glow. The band spectrum can be excited with much greater intrinsic brightness by using a discharge tube with a wide tube in place of the usual capillary, and exciting it by means of a discharge from an induction coil or transformer, with a condenser in parallel and a small spark gap in series with the discharge tube, the band spectrum under these conditions appearing throughout the tube. There appears to be an optimum length of spark gap and the spectrum tends to become weaker when the length is increased beyond a certain point. Curtis ( loc. cit .) has found that the band spectrum is not strongly developed at low pressures, and this condition appears to be independent of other conditions of excitation. In the present investigation we have found that under certain conditions the band spectrum can be greatly modified. It was observed that when a vacuum tube, containing pure helium, which had been made with the capillary in several sections of different bore, was excited with an uncondensed discharge the narrowest section, which was of the finest thermometer tubing that could be worked conveniently in the blowpipe, showed nothing but the line spectrum, but in the wider sections on either side the band spectrum was quite strongly developed. This seems to show that a high-current density is not an essential condition for the excitation of the band spectrum, but it was remarkable that with these tubes it appeared in the wider parts, where it would not have been seen if the capillaries had not been provided with a section of narrow bore.

Intensities in the helium spectrum

Merton and Nicholson made a quantitative study of the distribution of intensities in the spectra of hydrogen and helium under different conditions. Among other things, they studied the distribution of intensities in the helium spectrum as a function of the distance from a flat cathode in a wide vacuum tube. They also investigated the effect of admixture of other gases, and the effect of putting a condenser in parallel with a vacuum tube. The results were extremely interesting; but it seems that, in most cases, the changes were brought about by a simultaneous change in more than one variable, or that they were changes of a kind not capable of simple specification in terms of atomic processes. Thus when a condenser is put in parallel with a vacuum tube, the energy of impact of the electron on the atom and the density of the current are altered. Moreover, both of these vary rapidly with the time, since the current is necessarily alternating. To account for the observed distribution of intensities under such conditions is a formidable problem when we consider that the quantitative explanation of the intensity of any spectrum line would be a different problem, on any atomic theory, even when the conditions are reduced to the very simplest.

The conductance of unicellular organisms

The electrical conductance of bacteria (B. coli and B. butyricus) unicellular algæ (Chlorella sp.) yeasts (Saccharomyces sp.) and mammalian red-blood cells has been studied by a method which yields figures for the gross conductance dependable within 1/10 per cent. Polarization capacity was compensated for by variable condensers in parallel with the variable resistance. While most of the studies here reported were made on the alga, Chlorella, there is apparently no fundamental difference between this and the other organisms. The difference between the conductance of the suspending fluid and that of the suspension of cells is expressed in per cent. of the former and called the net conductance. This will always be negative in sign, because living cells are poor conductors of electricity. Rather large variations in the net conductance are produced by factors, such as irregular distribution of cells in the suspension, which it is impracticable to eliminate and which may affect the net conductance of any one sample by several per cent. For this reason enough samples were used in each experiment to make the error of the mean less than three per cent. It is possible to calculate the limits between which the observed net conductance should fall, the relative conductance of the cells themselves and their volume concentration being known. If r is the resistance of the suspending fluid and kr that of the cells and n the concentration of the cells in volume per cent., then the total resistance should lie between These formulas give curves convex to the axis of concentrations when they are plotted against resistances as ordinates. But when the cells form less than about 65 per cent. of the total volume the observed curves are nearly linear, possibly because of variations in the relative extent to which the current lines are able to evade the more highly resistant cell material.

The Neon Tube as a Means of Producing Intermittent Currents

The Paper relates to an experiment in which a neon tube and a condenser in parallel are connected in series with a high resistance and source of current. In these circumstances intermittent current is found to pass through the lamp, and the Paper discusses the conditions governing the frequency and duration of the resulting flashes.

On The Use of Anderson's Bridge for the Measurement of the Variations of the Capacity and Effective Resistance of a Condenser with Frequency

An analysis of the effect of residuals and earth capacities in Anderson's Inductancecapacity bridge is made, and it is shown that if balances are obtained by balancing the bridge with direct currents; by making the alternating current adjustments by means of a small series resistance (s') and parallel condenser (C') in the condenser arm; then the changes required in s' and C' to hold the balance at different frequencies are equal and opposite to the variations of the effective (series) resistance and capacity of the condenser with frequency. The assumptions made in obtaining the above conclusions are that the residual inductances and resistances of the non-inductive arms of the bridge are invariable with frequency and that the resistance of the inductive arm varies as the square of the frequenc y No knowledge of the absolute values of the residuals, &c., is required for the method. The method is illustrated by results obtained with a condenser of capacity 0.5μF, and details are given showing how the chief experimental trouble, viz., drift in D.C. balance owing to temperature variations, may be overcome.