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Volume 48, Issue 474
Displaying 1-6 of 6 articles from this issue
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M. TAKAHASHI, J. MATURA1928 Volume 48 Issue 474 Pages 5-25
Published: 1928
Released on J-STAGE: November 20, 2008
JOURNAL FREE ACCESSIn our country, according to the recent development of mercury arc rectifiers, those of iron cylinder type for large direct current power source, especially for railway service, have become generally to be used in place of rotary converters. Though the mercury arc rectifier has many superior properties in comparison with rotary machines, hesitation is sometimes made tor their adaption on account of its inductive interference on weak current lines due to the pulsating rectified voltage wave. It is the inherent characteristic of mercury arc rectifier that the rectified voltage wave has many higher harmonics of supplied frequency and whatever improved the rectifier itself may be, this faulty point could, by no means, be avoided.
The inductive effects, however, can be eliminated for practical purposes by means of several methods, either on the rectifier side or the weak current one.
In this paper, the minimizing methods for voltage ripples on rectifier side arc chiefly described. At first the general voltage wave forms. on rectified circuits with or without load are discussed.
The best safety method of minimizing these ripples is to increase the number of phases of the rectifier. The increase of phase numbers, for example to increase to twelve phase, can economically be made using two ordinary six phase rectifiers each connected to the secondaries of both star-star and deltastar connected transformers of the same source. It is more desirable in view of voltage regulation and load division that the secondaries of both transformers compose of a pair of zigzag 6 phases windings having 30 degrees phase difference to each other.
Next the wave filting apparatus are described and the special theory on the rectified circuits is discussed.
The ideas of wave filters on weak current system, however, are also well applicable to the rectified circuits.
Authors recommend the use of series reactance and shunt reasonance circuits for harmonic frequencies as shown in Fig. 4.
The values of this series inductance and those of resonance circuits, and moreover the numbers of reasonance circuits according to the ripple frequencies, will suitably be changed by the actual grade of inductive effects.
Oscillographic studies for wave filters on rectified circuits are carried out on the 30 KW. iron cylinder rectifiers manufactured by the design of authors and the results are discussed.View full abstractDownload PDF (3950K) -
Shoichi NAKAI1928 Volume 48 Issue 474 Pages 26-37
Published: 1928
Released on J-STAGE: November 20, 2008
JOURNAL FREE ACCESSThe performance characteristics of a loud speaker having a very small horn shown in Fig. 1 and Fig. 11 was studied by means of the measurement of the motional impedance. The rhe result of which shows that it does not form a multi-resonant system like the ordinary loud speakers of prominent makers which had been studied by other authors up to the present, and the effect of the small horn upon the motional impedance, which is the measure of the velocity of the actuating element, is very limited to the narrow range of frequencies near the resonant frequency of the horn. When the resonant frequency of the horn coincides with that of the moving elemnt, the addition of horn changes the shape of the frequency characteristics as shown in Fig. 8 and Fig. 10. It is concluded that small horn such as treated here contributes very little to the improvement of the frequency response.View full abstractDownload PDF (716K) -
Jûichi OBATA1928 Volume 48 Issue 474 Pages 38-52
Published: 1928
Released on J-STAGE: November 20, 2008
JOURNAL FREE ACCESSIn the present article are described the detailed construction and various examples of applicatons of the "Ultramicrometer", a new instrument for measuring small displacement or motion utilizing a generating valve circuit. In its usual form the instrument consists of a tuned grid circuit, but it can easily be changed to the Colpitts-Hartley circuit. The displacement or motion to be measured is made to produce either a change in the capacity in the circuit or a change in the eddy-current loss, and in consequence a corresponding change in the anode current of the valve is resulted. This change in the anode current is measured with a galvanomter, or if a permanent record is needed, an Einthoven string galvanometer or a Duddell oscillograph is employed. The anode current itself is balanced by means of the potentiometer method or a small transformer is inserted in the anode circuit.
With this instrument the capacity method as well as the eddy-current method may be carried out, and the anode current may be balanced or a transformer may be inserted, all the necessary resistances and transformer being contained in the instrument.
As the examples of applications of the instrument are described the recording of earth-movements, direct recording of accelerations, an electrical indicator for high-speed internal-combustion engines, precise recording of sounds, pressure-variations and various mechanical vibrations.View full abstractDownload PDF (3242K) -
S. CHIBA1928 Volume 48 Issue 474 Pages 53-69
Published: 1928
Released on J-STAGE: November 20, 2008
JOURNAL FREE ACCESSThis paper studies the modulation in wireless telephony. Various systems of modulation are first mentined and the characteristics of some of them are considered.
The modulation character of systems commonly used is studied by means of a hot-cathode Braun tube. It is shown that in the constant-current method the stop condenser nsed in the ordinary oscillator circnit has much influence on the character of the modulation. Other methods of modulation, such as the grid control and the detuning are also tested. An example of the characteristic given by a magnetic modulator is also described.
Ordinary grid control systems are more or less of oscillation control type, which sometimes gives rise to serious distortion. The anthor tested a grid control method using a modulator which absorbs at the same time the high frequency power from the oscillation circuit. This system has extremely good character, having no distortion over the wide range of the modulator grid voltage. The circuit has another advantage that it can be easily adjusted in order to attain the distortionless condition. Tests show also that the system is adapted to a.c. filament heating. It is also suitable as the transmitter of duplex wireless Telephony. A sensitive relay controlled by speech currents is used to open or short-circuit the grid bias battery of the modulator, which in turn starts or stops The oscillation.View full abstractDownload PDF (1606K) -
Y. TORIYAMA1928 Volume 48 Issue 474 Pages 70-78
Published: 1928
Released on J-STAGE: November 20, 2008
JOURNAL FREE ACCESSThe author measured the voltage-current curves of various transformer oils as far as the break down voltage by using sphere and plate electrodes. The form of the curves is remarkably influenced by the form of electrodes and the existence of dust and moisture in the oil.
There are always dust and moisture in the transformer oil in practice. It is posible to exist dust only in well dried oil, but imposible to exist moisture only without dust in practical case. Therefore we must consider the effect of dust to discuss that of moisture upon the break down voltage of the oil.
In the later parts of the paper, the author describes the combined effects of fibrous dust and moisture upon the break down voltage under uniform electric field. As in well filted oil the fibrous dust is very thin, he assumes that the dusts are ellipsoids. By above assumption, he calculates the break down voltage of the transformer oil. The calculated result qualitatively coincides with the experiment of Friese.View full abstractDownload PDF (524K) -
Y. MURATA1928 Volume 48 Issue 474 Pages 79-88
Published: 1928
Released on J-STAGE: November 20, 2008
JOURNAL FREE ACCESSA new vector method which is a combination of the space vector and the well known symbolic vector expressing the time phase relation is treated in the former half of this article, and in the latter half, a solution is given, by means of the above mentioned vector method, regarding the primary current of a phase transformer for any given secondary current.View full abstractDownload PDF (545K)
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