Cathode-ray Oscillograph Research Articles

An instrument for the rapid production of a decimal series of potentials and its application to ballistic measurements

An instrument for producing decimal subdivisions of a chosen potential was developed for calibrating a cathode-ray oscillograph, often within a few milliseconds after the ballistic record had been obtained. The maximum potential could be chosen as any integral multiple of 10 millivolts, with a maximum of 100 millivolts. To permit this choice, ten 10-ohm coils were connected in series, and a current of 1 milliampere was sent through them. Then the drop in potential over each coil was 10 millivolts, and the maximum output potential was the product of 10 millivolts and the number of coils included between the output terminals. The decimal subdivisions of the chosen potential were obtained by varying the current in the ten 10-ohm coils in steps of 0.1 milliampere from 0 to 1.0 milliampere by shunt resistances. The calibration started with zero voltage when the shunt resistance was zero, and the shunt resistance increased in such steps that the current in the 10-ohm coils increased in 0.1 miJliampere steps and hence the output voltage in decimal steps of the chosen maximum potential. The shunt resistances were inserted by opening switches that normally short-circuited them. For oscillograph calibration these switches were opened in succession by a falling weight. The numerical data used for illustration are based on decimal subdivision of the maximum available potential. The general case is treated, however, showing that a calibrator of this type may be used for any desired number of potential steps.

Illumination of Cathode-Ray Oscillograph Screen for Photography

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3—LOOM STUDY BY MEANS OF THE CATHODE RAY OSCILLOGRAPH: I. Variations in individual warp-thread tension during the weaving cycle

3—LOOM STUDY BY MEANS OF THE CATHODE RAY OSCILLOGRAPH: I. Variations in individual warp-thread tension during the weaving cycle

A critical study of the Hopkinson pressure bar

The first part of this paper (§§ 1 to 9) contains a description of an electrical method for measuring the relation between pressure and time in experiments on high pressures of short duration. As in the method devised by Hopkinson, the pressure is applied normally to one end of a cylindrical steel bar, producing a stress pulse which gives rise to radial and longitudinal displacements in the bar. The radial displacement, or the longitudinal displacement at the end of the bar remote from the applied pressure, is used to produce a change in the capacity of a suitable condenser unit which is charged to a high potential and connected through a feed circuit and an amplifier to a double-beam cathode-ray oscillograph. The change in capacity of the condenser unit gives rise to a vertical deflexion of one of the beams of the oscillograph, the other beam being used for time-marking. At the appropriate instant, the two beams are traversed rapidly in a horizontal direction across the screen by a sweep circuit triggered by a switch on the pressure bar. By photographing the traces on the screen, an oscillogram , giving the variation with time of the displacement in the bar, is obtained, and from this record the variation of the applied pressure with time can be deduced. The second part of the paper (§§ 10 to 12) begins with a theoretical discussion of the propagation of extensional stress waves and pulses in a bar, using the exact equations due to Pochhammer and to Chree (§ 11), and also a less accurate wave equation due apparently to Love (§ 12). These investigations show that, owing to dispersion, a stress pulse is modified in its passage down the bar, the shorter waves lagging behind the longer ones. The theory provides a satisfactory explanation of certain features of the experimental results which are incompatible with elementary theory. It is found, for example, by the theory of group velocities, that a pulse whose initial duration is very short, becomes extended as it travels along the bar, its duration at distance x cm . from the origin being about 3.3 x /i sec. In the early stages of the disturbance, extending for the first 1.4 x /t sec., only one dominant group exists; the later portion, extending over 1.9 x sec., is com posed o f two dominant groups which give the characteristic pattern of two superposed oscillations. These conclusions are confirmed by experiment. The theory is used to discuss the errors in the experiments caused by the pressure bar itself, and it is shown that bars about 2 ft. long and 1 in. and 0.5 in. diameter can be used to measure pressures which last for about 20 and 10 /i sec. respectively with an accuracy of about 2 to 3 % . T his was confirmed by experiments with bullet impacts and detonation waves in gaseous mixtures, in which the measured values of the pressure could be checked by calculation.

Simultaneous Recording of Related Oscillograph Traces

DURING the War, the frequent need in such fields as ballistics, and the study of mechanical shock and vibration, to obtain information about the temporal variation of quantities, and in particular the interrelationship of these variations, led to a considerable use of the cathode ray oscillograph and moving-film technique. The methods of obtaining several records at once so as to permit a study of this interrelationship included the use of double-beam oscilloscopes, electronic switches for beam splitting, ganged cameras, and the photographing of a number of screens on the same film. Messrs. Cossor designed a unit comprising a 70-mm. film camera facing the screens of two double-beam tubes, and provision was made for ganging three such instruments together. The problem became more difficult, however, when it was desired to record some fifteen traces on the same film, as it was obviously impracticable to photograph fifteen oscilloscopes in line and still retain reasonable trace amplitude. To meet such a requirement, Messrs. Avimo Ltd., Taunton, have produced a series of units, employing up to fifteen ½-in. cathode ray tubes photographed through mirrors on 70-mm. film or paper. The apparatus is robust and portable, and has a range of film speeds of 1-50 in./sec. The optical reduction factor is 2·5, and a microscope is provided to allow observation of the traces during recording. Of particular importance is the provision of adjustments to permit the alignment of the tubes so that each deflexion shall be normal to the film motion and all the deflexions shall be colinear.

Ionization Processes in a Long Discharge Tube with Application to Lightning Mechanism

Properties of the progressive breakdown, occurring when an impulsive potential is applied to an electrode in one end of a discharge tube 14 cm in diameter and 12 meters long, have been investigated, principally by means of a high speed cathode-ray oscillograph. Potentials from 25 kv to 115 kv and pressures from 0.006 to 8.0 mm Hg were used, with dry air and hydrogen in the tube. Conditions in the discharge, when comparatively large over-voltages are impressed, have been discussed by several investigators, particularly with respect to impulses of positive polarity and in tubes of smaller diameter. These observations now have been extended to include the negative polarity. In addition, a low speed, low potential process has been obtained and its properties analyzed.A possible application of the lightning theory to such discharges is given. The low speed impulse resembles the hypothetical lightning pilot streamer as to speed and current, and the speed is of the order of magnitude of the drift speed of electrons in the tip field, as assumed for the pilot streamer. The high speed processes are more similar to the lightning dart leaders. It is pointed out that conditions in the tube are such that propagation in this case may be controlled more by the presence of photo-electrons ahead of the tip than by a preliminary ionizing leader.

Note on the Ionization Time of an Argon-filled Relay

Details are given of some experiments in which the voltage collapse across an Osram GT1C argon-filled relay when triggered by a steep-fronted rectangular impulse voltage on the grid, was recorded on a high-speed cathode ray oscillograph. Curves showing the variation of ionization time with grid over-voltages up to 50 V. and with anode voltages up to 240 V. are given, and typical oscillograms showing the marked effect of the amplitude of the grid impulse are reproduced. Ionization times ranging from 0.16 to 2.2 μsec. were measured. A brief discussion of the oscillograms with reference to previous studies is included.

Fluctuations in Gas Discharges

Examination of the light output of discharge tubes, using the multiplier-type photo-tube in conjunction with a cathode-ray oscillograph, is suggested as a powerful aid to the usual electrical measurements in understanding the behavior of electrical discharges in gases. Exhaustive experiments of this type are under way, the preliminary results of which are reported in this paper. A striking characteristic of these results is the appearance of oscillations not only in the voltage and current, but particularly in the light intensity. These oscillations appear to be very general, and are not due to the external circuit used. They are only of a few percent magnitude in the case of the voltage and current, but often nearly 100 percent in the case of the light intensity. It seems certain that the theory of electrical discharges should in many cases be revised to take these oscillations into account.

Cathode-ray Recording Micrometer and Force Gauge

A description is given of a device using a cathoderay oscillograph in conjunction with a moving-coil system to record and measure rapidly varying movements of the order of 3 mm. to an accuracy of 0.0025 mm. By attaching the moving coil to a specially designed force gauge of natural period of about 1/5000 sec. the device has been applied to record and measure rapidly varying forces and to a preliminary study of rapid shear.

Ion concentrations in spark channels in hydrogen

Ion concentrations in hydrogen spark channels may, it is shown, be found by observing the Stark broadening of the Balmer lines. The line breadths are measured in two ways: by the normal techniques of photography or by plotting the line breadths with a photoelectric electron multiplier, amplifier and cathode-ray oscillograph. The advantages of the latter method is that the light emission/time relation can be studied. Representative oscillograms are shown in the paper. Full account must be taken of the fine structure of the lines in assessing their true breadths, and Holtsmark's theoretical analysis of the Stark effect for inhomogeneous fields is used for that purpose.

Application of the Cathode Ray Oscillograph to Measurements of Short Life-Periods of Radioactive Sources

The most accurate determinations of the life-periods of short-lived radioactive nuclei have been made using either coincidence circuits with variable resolving times1, or the method of delayed coincidences2.

Use of the Cathode Ray Oscillograph for Studying the Near Infra-Red Solar Spectrum

An apparatus has been developed in the Radiation Laboratory of the Meteorological Office at Poona for the measurement of absorption due to atmospheric water vapour in the near infra-red region of the solar spectrum by means of a cathode ray oscillograph. The working principle of this apparatus and the object for which it was developed are entirely different from those described by Daly and Sutherland and by King, Temple and Thompson1, and it was developed independently of their work. A short paper describing it was read by me at the symposium on “Atmospheric Processes” held at the Royal Institute of Science, Bombay, under the auspices of the National Institute of Sciences of India in August 1946. This paper is at present in course of publication in a special issue of the Transactions of the National Institute of Sciences of India.

Measurement of Transient Hydraulic Pressures

In experiments in which it was necessary to record transient pressure waves in water, a recording instrument was sought which possessed the following characteristics: (1) a frequency response which was the same over a range from ½ cycle to 10 kilocycles per second, (2) a continuous pressure-time relationship in the recordings, (3) a range of sensitivity from about minus 200 pounds per square inch to several thousand pounds per square inch on the positive side, (4) the ability to be calibrated through the use of known hydrostatic pressures, and (5) relative freedom from artifacts. Several methods involving the use of piezoelectric crystals, electromagnetic pick-ups, balanced diaphragms, high speed stoboscopic pictures of small rubber balloons, and cylindrical wire strain gauges were employed and their characteristics analyzed. Only the cylindrical wire strain gauge met all of the requirements. It consisted of a length of fine resistance wire wound on a thin-walled, closed cylinder. The gauge operated through a bridge circuit into an amplifier and cathode-ray oscillograph. The structure, operation, and characteristics of this gauge are considered and compared with the other methods used for recording transient hydraulic pressures.

Statistical analysis of spontaneous electrical fluctuations

Electrical fluctuations, generated either as shot-effect in a saturated diode or as thermal in a tuned circuit, were produced in a receiver of high natural frequency (similar 100 kc./s.-1 Mc./s.) and narrow band-width (similar 1-6 kc./s.), and (after suitable amplification) photographically recorded by means of a cathode-ray oscillograph operating on the single-stroke system. In these circumstances the fluctuations have the character of rapid oscillations (with the natural frequency of the receiver) whose amplitude R varies slowly and irregularly in time. The study of the statistical properties of this time variation of R, as represented by the envelope of the fluctuation record, was the subject of the present investigation. In particular, the distribution function of R within a statistically stationary series of observations and the correlation between values of R separated by a finite time interval were thoroughly investigated and, in general, found to be in good agreement with the statistical theory of the phenomenon in question.

Note on a short-range radio position-finding system using modulated continuous waves

The paper describes a position-finding system by which the polar co-ordinates of any suitably equipped aircraft can be determined at a single base station using phase-comparison range-finding apparatus and a v.h.f. automatic direction-finder in conjunction with conventional communication equipment.‡An experimental model is described in which azimuth and range are displayed on a single cathode-ray oscillograph, which may be installed in an airport control tower. Range is indicated without ambiguity up to 100 nautical miles, and there is no azimuthal ambiguity. So far, the model has been used primarily to demonstrate the principles of the system, in conjunction with an aircraft fitted with an experimentally modified Service type of v.h.f. communication equipment. The results of a limited number of tests suggest that, with airborne equipment specifically designed for use with the system, the probable error in range measurement should be less than 1 mile. Azimuthal accuracy is not here discussed, but in a companion paper it is shown that the probable instrumental error of the direction-finder is less than 1.5 deg, implying a probable lateral error less than 2.5 miles at the maximum non-ambiguous range of 100 nautical miles.

The development of single-receiver automatic adcock direction-finders for use in the frequency band 100–150 Mc/s

The paper describes the development of automatic direction-finders primarily intended for measuring the bearings of aircraft, on signals radiated in the frequency band 100–150 Mc/s. The basic system employs fixed elevated-H Adcock antennas and a single receiver, and, with the exception of the earliest model, all instruments give cathoderay oscillograph indication.An examination of the advantages and limitations of fixed*antenna automatic direction-finders employing two or more receivers leads to an account of the reasons for the adoption of a single-receiver system in the present development. The principles and evolution of this system are explained with reference to the original experimental models, whose performance is discussed.A naval direction-finder based on one of the experimental models is described in detail, and statistics are presented to show that the probable instrumental error varies from about 0.6–1.25 deg over the frequency band, after compensation for octantal error. Bearings can be measured on signals of field strength down to 7 μV/m or less.The paper concludes with a description of direction-finders for use on land. One of these, under current development, will be capable of unattended operation on two alternative frequency-channels, with bearing indication and full remote-control at points up to twenty miles distant.

The Interruption of Charging Current at High Voltage

The switching of high-voltage transmission lines and underground cables occasionally produces overvoltage surges on electric power systems. While operating experience generally has been satisfactory voltages of 66 kv and below, there have been transient disturbances of considerable magnitude at the higher voltages. The length of many of the transmission lines and the importance of maintaining continuity of service on heavily loaded interconnections have stimulated a critical analysis of the problem. However, in contrast to the extreme overvoltages predicted by theoretical studies, a review of several hundred field tests over the past ten years, including many tests with voltage records by cathode ray oscillographs, discloses practically no cases of line or bus surge voltages on solidly grounded systems reaching transient peaks as high as 2? times normal line-to-ground crest voltage. This paper attempts to evaluate the effect of both the circuit constants and the characteristics of the various types of interrupters used in modern high voltage oil circuit breakers on the magnitude of switching surges. Particular attention is given to the advantages and disadvantages of such oil flow pistons or low ohmic value resistors in parallel with the main arc extinguishing devices.

A 60-Cycle Hysteresis Loop Tracer for small Samples of Low-Permeability Material

The basic components of this instrument are (a). A large (35-pound) exciting coil with a pickup coil at its center. (b). An amplifier and integrating circuit. (c). A cathode-ray oscillograph. The instrument provides a convenient and rapid means of determining the magnetic properties of samples much smaller than can be used conveniently with the ballistic method. Absolute calibration provides greater accuracy and reliability than has been obtained previously in this type of apparatus. Phase errors are reduced to low values through the use of a compensated integrating network with absolute means of adjustment. This network provides a much higher output voltage than the usual circuit and thus makes practicable operation at the power line frequency and the consequent use of an exciting coil of sufficient size to minimize end effect errors and to allow operation at fields as high as 1,000 oersteds for long periods of time.

A cathode ray oscillograph for detection of low voltage D.C. signals

A cathode ray oscillograph for detection of low voltage D.C. signals

The Cathode Ray Oscillegraph in Industry

THIS excellent technological book on the industrial applications of the cathode ray oscillograph has been considerably enlarged in this second edition by the author, particularly by the incorporation of new photographs, for one of which a magnification of 200,000 is claimed. The author excludes television tubes, but includes full descriptions of straight and. pumped cathode ray tubes and varieties of the electron microscope, all of which in many forms have proved themselves key tools in recent scientific pro gress in industry. The Cathode Ray Oscillegraph in Industry Dr. W. Wilson By. Second edition revised. Pp. xii + 244. (London: Chapman and Hall, Ltd., 1946.) 18s. net.