Electrical Degrees Research Articles

Ion Phase Measurements on the Birmingham Cyclotron

The ion phase in the internal beam of the Birmingham cyclotron at distances from the ion source from 8 mm up to 69 cm has been determined by measurements of the target current waveform. The equipment consisted of a screened target and a specially built oscilloscope based on the sampling technique. The results obtained are discussed and compared with theory. Ions are grouped in phase at early stages of acceleration over approximately 20 electrical degrees, which is about 5 times larger than predicted by the uniform electric field approximation. At later stages the measured phase changes are in good agreement with Rose's equation.

A radio-frequency nondestructive readout for magnetic-core memories

It is possible to read information nondestructively from two- and three-dimensional magnetic-core digital computer memories in several microseconds by exciting selected cores with rf currents. If two co-ordinate lines of a core in a memory array plane are driven at slightly different frequencies, a beat-frequency signal is generated whose phase may take on one of two values which are separated by 180 electrical degrees. These two possible phases correspond to the 0 and 1 information states of the core. The beat-frequency signal, separated from the inevitable noises by tuned linear filters, may be phase detected to yield the desired information.

Commutation in Universal-Type Motors

The problem of commutation has always been one of the most important problems in the satisfactory operation of both d-c and a-c commutator motors. The universal motor has the problems of both a-c and d-c motors. The many factors influencing satisfactory commutation such as electrical and magnetic conditions, mechanical condition of the armature, carbon brush condition, and in some applications such as portable electrical tools, atmospheric conditions may be such as to influence commutations. In both the d-c and a-c motors, the armature conductors cutting across the magnetic field set up by the combined armature and field winding generate electromotive forces in the short-circuited coils which are proportional to the product of the speed of the armature, the flux which the armature conductors cut, and the number of turns in series. However, in the a-c motor, there is a voltage generated by the reversals of the main field flux just as the voltage is generated in the secondary of a transformer. In the noncompensated motor, commutation can be somewhat improved by using a strong main field and weak armature field and moving the brushes backward. However, this has no effect upon the transformer voltage. In the compensated universal motor there is a compensating winding distributed at 90 electrical degrees to the main field and opposing the armature field, or in the single fied distributed winding the brushes are moved back a predetermined amount which compensates for the voltage due to the armature field.

High-voltage rectifier equipment for tube testing

MERCURY-ARC rectifier equipment of high capacity and voltage rating and special design for tube-testing service has been installed in the RCA-Victor Company Advanced Development Laboratory at Lancaster, Pa. The equipment provides 2,000 kw at 12,000 volts d-c with two rectifier units connected in parallel, and 2,000 wk at 24,000 volts d-c with the two units in series. In each case, the d-c windings of the rectifier transformers are displaced 30 electrical degrees so as to achieve, effectively, 12-phase rectification. The basic power circuit of the installation is shown in Figure 1.

Television Resolution as a Function of Line Structures

A labor-saving method is developed for obtaining complex wave shapes by means of evaluating integrals. This method is applied to the problem of square-wave pulse shapes containing large numbers (not infinite) of harmonic components. The method is applicable for any value of cutoff frequency, expressing this value in terms of electrical degrees. A theory of processes is developed by mathematical induction, and it is shown that the finite width of a pulse (line structure of an image) is mathematically equivalent to the pulse width obtained from an image of infinite detail scanned by a finite aperture. The finiteness of the pulse width in either case, constitutes in itself an aperture process. An approximate rule of thumb is given for defining the resolution of an image, in terms of the lines-of-resolution involved in each process imposed upon it during optical-electrical conversions. This is applicable to discussions conceming the effect of quality in the televised subject as it affects quality in the received image: as, for example, concerning the relative merits of 16- and 35-millimeter film.

The Calculation of Class C Amplifier and Harmonic Generator Performance of Screen-Grid and Similar Tubes

In this paper it is shown how to predetermine the performance of harmonic generators and class C amplifiers which employ screen-grid and similar tubes in which the plate current is substantially independent of plate voltage over the working part of the characteristic. The sum of the plate and grid currents in such tubes is very nearly proportional to (E g +E sg /μ sg )α, where α is usually very close to 3/2, and is always between 1 and 2 in practical tubes. The resulting current impulses are analyzed by the Fourier method for α = 1 and α = 2, and are presented in curves which give the various frequency components in terms of the number of electrical degrees during which current flows, and the peak value of (I p +I g ). In the case of the alternating components it is shown that to a good approximation the effect of the grid current is to reduce the current component in the plate circuit below the value that would be obtained if there were no grid current by an amount twice the direct grid current. It is shown how the results of the above analysis may be applied in a straightforward manner to lay out class C amplifiers and harmonic generators on paper, and to predict the voltage and power output, power input, plate loss, etc., for any particular set of operating conditions.

Transformers with peaked wavs

Special purpose transformers now can built to provide a secondary voltage wz less than 2 electrical degrees wide from sinusoidal primary voltage source. Transformers construction of such a transformer and some of its uses are described in this article.

Commutation in alternating-current machinery

As is now well known, the inductive reactive effect of a commuted winding in a revolving magnetic field decreases directly with the increase in speed from standstill to synchronism, when its value becomes zero. As first pointed out by the author some years ago, it becomes negative at speeds above synchronism, under which condition the rotor of a motor operates as a capacity. The author introduces into the discussion of the commutating characteristics of alternating-current commutating motors, his theory that perfect commutation in a continuous-current motor depends substantially on the production of a mean resultant neutral field in the region where commutation is taking place, and shows that the production of a perfect revolving field in a polyphase commutator motor assists in insuring perfect commutation at exact synchronism. In a single-phase commutator motor a “polyphase”. revolving field can be produced at synchronism by utilizing supplementary brushes, short-circuited upon themselves, displaced by 90 electrical space degrees from the main single-phase brushes on the commutator. As in the case of polyphase motors, the problem of securing perfect commutation at synchronism becomes that of producing a perfect rotating field. It is shown by the author that the use of fractional-pitch windings on the rotor and a sinusoidal distribution of conductors on the stator is of much assistance in this connection. In a motor built in accordance with the principles set forth, the commutator difficulties are not serious, the overload range is in excess of that of an induction motor, and the machine can act as a condenser on the system.

Commutation in Alternating-Current Machinery

As is now well known, the inductive reactive effect of a commuted winding in a revolving magnetic field decreases directly with the increase in speed from standstill to synchronism, when its value becomes zero. As first pointed out by the author some years ago, it becomes negative at speeds above synchronism, under which condition the rotor of a motor operates as a capacity. The author introduces into the discussion of the commutating characteristics of alternating-current commutating motors, his theory that perfect commutation in a continuous-current motor depends substantially on the production of a mean resultant neutral field in the region where commutation is taking place, and shows that the production of a perfect revolving field in a polyphase commutator motor assists in insuring perfect commutation at exact synchronism. In a single-phase commutator motor a ``polyphase'' revolving field can be produced at synchronism by utilizing supplementary brushes, short-circuited upon themselves, displaced by 90 electrical space degrees from the main single-phase brushes on the commutator. As in the case of polyphase motors, the problem of securing perfect commutation at synchronism becomes that of producing a perfect rotating field. It is shown by the author that the use of fractional-pitch windings on the rotor and a sinusoidal distribution of conductors on the stator is of much assistance in this connection.

Alternating-Current Magnets

IT follows from the well-known law of pull of an electromagnet that if the magnetic field alternates between positive and negative values the pull is unidirectional and intermittent. Unless means are provided to reduce the consequent chattering and vibration, the magnet is rendered useless. In the present experiments a phase-splitting device has been adopted, and consists in surrounding a portion of the pole-piece of the magnet with a short-circuited coil. The portion of the pole-piece so surrounded is sometimes said to be shaded, and the coil referred to as a coil. The effect of this coil is to alter, not only the relative amplitudes, but the phase of the magnetic fields passing through the shaded and unshaded portions of the pole-face. The magnet used in the experiments varies the length of its gap when in action, and the influence of the gap length upon this phase displacement has been studied. When the resistance of the shading coil is such that the magnetic induction B over the whole face is substantially uniform and the gap closed, the phase displacement was 72 electrical degrees (360 deg. = 1 period). A gap length of 0.15 cm. reduces the phase-displacement to 18 deg., and consequently the minimum or hold pull drops. This minimum or hold pull is, of course, smaller than the average, and has to be taken into consideration in the design of the magnet. The arrangement of the shading coil above described is very effective in preventing vibration and chattering when the magnet is closed, and renders the alternating-current magnet a practical success. With constant alternating voltage impressed upon the magnetising coils of the magnet the net pull exerted diminishes rapidly at first as the gap length increases, and tends to become more nearly constant. The R.M.S. amperes, on the other hand, steadily increase as the pull diminishes, owing to the increase in the gap length. The observed net pull in the case of the magnet experimented upon is less than the calculated average pull, varying from 83 to 59 per cent. as the gap length varies from 0 to 1 cm.

Single-Phase Induction Motors

Self-starting, single-phased induction motors can be constructed using a rotor and a stator in which the magnetic poles caused by the current flowing through the coils of the stator and caused by induced currents in the bars of the rotor are preferably displaced from one another about 90 electrical degrees around the axis of the rotor at one of the ends of the motor, while they are positioned opposite one another in a conventional manner at the other end of the motor. In a motor of this invention, auxiliary windings are located at the first of these ends in the stator displaced from the stator winding. Preferably they are displaced an amount of about 90 electrical degrees.