Showing papers in "Journal of Scientific Instruments in 1953"
TL;DR: In this paper, a combined Dewar vessel and double absorption cell is described for use in the quantitative measurement of the ultra-violet absorption spectra of solutions between + 100 and - 196°C.
Abstract: A combined Dewar vessel and double absorption cell is described for use in the quantitative measurement of the ultra-violet absorption spectra of solutions between + 100 and - 196° C. The apparatus is particularly convenient when used in conjunction with the Cary recording spectrophotometer. Temperature confraction data are given for a number of useful solvents.
46 citations
TL;DR: By this method analyses may be carried out more rapidly and it has been found that the results are reproducible to ±0.02% from day to day, this compares with 0.1% precision obtained with single collection methods in this laboratory.
Abstract: A conventional 90° mass spectrometer has been modified to permit the simultaneous collection and measurement, by means of a null method, of the ion currents due to the isotopic species of sulphur dioxide at masses 64 and 66. The design of a magnetic valve system to facilitate the rapid change from one sample to the other is described, as well as an improved ion source and collector assembly. By this method analyses may be carried out more rapidly and it has been found that the results are reproducible to ±0.02% from day to day, this compares with 0.1% precision obtained with single collection methods in this laboratory. The analytical procedure is outlined.
43 citations
TL;DR: In this paper, a self-balancing photoelectric densitometer is described, which employs a high speed telegraphic relay for the conversion of the photoelectric currents into 50 c/s a.c., and the use of a two-phase servomotor for selfbalancing.
Abstract: An a.c. operated self-balancing photoelectric densitometer is described. It measures photographic density over a range of 0-3, and has reproducibility and sensitivity of better than 0.01 over the entire range. A pair of emissive photoelectric cells are employed, and the measurement is made by a wedge substitution method. Special features are the employment of a high-speed telegraphic relay for the conversion of the photoelectric currents into 50 c/s a.c., and the use of a two-phase servomotor for self-balancing. The system gives high sensitivity, freedom from zero drift, while the simplicity of operation and rigid construction make this densitometer suitable for factory use.
35 citations
TL;DR: In this paper, the authors describe the use of the Pantograph-punch for the observation of diffraction patterns of holes punched in thin card to represent atomic arrangements, and the instrument that is used to observe these patterns and also the pantographpunch used to prepare the cards.
Abstract: The methods described involve the observation of the diffraction patterns of holes punched in thin card to represent atomic arrangements. Details are given of the instrument that is used to observe these patterns and also of the pantograph-punch that is used to prepare the cards. Several examples of diffraction patterns are given; some illustrate the performance of the instrument with lenses of various optical qualities and others illustrate the use of the instrument in the teaching of physical optics.
25 citations
TL;DR: In this article, constructional and operating details for a high-intensity flash-discharge tube, used for generating a continuous emission spectrum which serves as background for the observation of far ultra-violet absorption spectra, are given.
Abstract: Constructional and operating details are given for a high-intensity flash-discharge tube, used for generating a continuous emission spectrum which serves as background for the observation of far ultra-violet absorption spectra.
24 citations
TL;DR: In this paper, a diaphragm vacuum gauge covering the pressure range 1 to 100 μ with an accuracy of better than 0.5 μ is described, which is suitable for measurement of mass-spectrometer sample inlet pressures.
Abstract: A diaphragm vacuum gauge covering the pressure range 1 to 100 μ with an accuracy of better than 0.5 μ is described. Movement of the diaphragm is followed by measurement of capacity change. The electronic circuit involves only a single valve. The gauge is suitable for measurement of mass-spectrometer sample inlet pressures.
22 citations
TL;DR: In this paper, the electron-optical aberrations due to mechanical defects in magnetic lens pole-pieces are calculated, for several lens geometries and a range of excitations, by a slight modification of the computational procedure of Sturrock.
Abstract: The electron-optical aberrations due to mechanical defects in magnetic lens pole-pieces are calculated, for several lens geometries and a range of excitations, by a slight modification of the computational procedure of Sturrock. The condition that these aberrations shall not predominate over the combination of spherical aberration and diffraction is taken as a criterion of mechanical tolerance. Tolerances for the alinement of the pole-pieces are shown to be well within the limits of normal workshop practice (for a typical lens: the axes of the two pole-pieces must not be laterally separated by more than 30 μ, nor must the angle between them exceed 0.005 radian). Tolerances for ellipticity of the bore and corrugation of the pole-faces are more stringent (typically: the variation in radius or in distance of the pole-face from the mid-plane must not exceed 0.1 μ). The results are generalized in the form of universal curves, designed to facilitate the assignment of tolerances in the case of lenses of any magnitude or accelerating voltage.
18 citations
TL;DR: In this paper, a microphotometer was used to record the transmission in the primary image of an object down to 2-3 μ2 under visual control, and the accuracy was less than 1% for the photographic-photometric procedure in X-ray microradiography.
Abstract: The microphotometer records the transmission in the primary image of an object down to 2-3 μ2 under visual control. The electrical construction gives a linear amplification in the transmission range actually used. The object is moved across the measuring light beam and, synchronously, the transmission curve is recorded by the writer. The accuracy of the apparatus was found to be less than 1%. When the test included the photographic-photometric procedure in X-ray microradiography the standard error was ±1.5%.
16 citations
TL;DR: In this paper, a pinhole in a metal foil mounted next to the specimen is used as a reference point, through which the X-ray beam is sent by taking readings from an electronic counter placed behind the foil.
Abstract: A camera is described which allows the orientations of pre-selected individual grains in an aggregate to be accurately determined. A pinhole in a metal foil mounted next to the specimen is used as a reference point, through which the X-ray beam is sent by taking readings from an electronic counter placed behind the foil. The principles of X-ray collimation are discussed.
16 citations
TL;DR: A scintillation counter designed for the standardization of radio-active isotopes by 4π-β-counting and for the radioactive assay of small biological samples by γ counting is described in this article, using a liquid luminophor in conjunction with an uncooled end-window photomultiplier tube.
Abstract: A scintillation counter designed for the standardization of radio-active isotopes by 4π-β-counting, and for the radioactive assay of small biological samples by γ-counting is described. The instrument uses a liquid luminophor in conjunction with an uncooled end-window photomultiplier tube. Details are given of performance with various commonly used radioactive isotopes.
15 citations
TL;DR: In this article, an oximeter consisting of an earpiece and associated electronic apparatus provides continuous estimation of oxygen saturation in human arterial blood, including an incandescent lamp, two selenium barrier layer photocells fitted with suitable gelatin filters, and a pressure capsule.
Abstract: An oximeter consisting of an earpiece and associated electronic apparatus provides continuous estimation of oxygen saturation in human arterial blood. The earpiece, made of Duralumin, contains an incandescent lamp, two selenium barrier-layer photocells fitted with suitable gelatin filters, and a pressure capsule. An oscillator supplies the lamp with direct current interrupted at 91 c/s. The a.c. signals from each of the photocells are amplified. The amplified alternating voltages are rectified and each applied to a valve voltmeter. With the earpiece mounted on the pinna of the ear, air pressure (300 mm of mercury) is applied to the pressure capsule, thus removing blood from the transilluminated area. Sufficient positive bias is then applied to each rectifier to set the meters to a fixed point. On release of pressure, blood returns to the ear; the current in one meter (thickness indicator) rises to a finite value depending on the amount of blood in the illuminated vascular bed; the current in the other meter (saturation indicator) rises to a value depending on both the amount of blood in the vascular bed and its state of oxygen saturation. The saturation meter is calibrated to read percentage oxygen saturation directly when a variable shunt has been adjusted according to the reading on the thickness meter. Instrument accuracy, expressed as standard deviation measured with three earpieces, was ? 3.8, ? 3.3 and ? 3.2% respectively.
TL;DR: In this article, it has been shown that a modification of the concentric cylinders method is most suitable for adaptation for high temperature measurements on molten silicates, for which the range 0.1-10 000 P is the most important.
Abstract: Previously reported measurements have been marked by an upper temperature limit of 1650° C and by the poor agreement obtained between different authors working on the same system. The present paper shows how, by the use of molybdenum apparatus, the temperature range may be increased to an upper limit of 1820° C and a method for the measurement of torque, not previously used in this field, permits a higher degree of accuracy than previously attained. It is shown that, of the methods available for room temperature viscosity measurements, a modification of the concentric cylinders method is most suited to adaptation for high temperature measurements on molten silicates, for which the range 0.1-10 000 P is the most important. By the use of an electromagnetic method of torque measurement, it has been found possible to cover the range 0.05-14 000 P without modification of the apparatus and an accuracy of ±0.5% has been obtained with the apparatus at room temperature. A method of calibration is demonstrated whereby the appratus constant is obtained for any depth of liquid and an accuracy of ±6.9% with a reproducibility of ±3.0% has been obtained at 1800° C. The construction of the apparatus is briefly described and details are given of the operation and method of calibration.
TL;DR: In this article, a servo-operated pen-recording microdensitometer is described which is particularly applicable to the measurement of densities in photographs of biological material.
Abstract: A servo-operated pen-recording microdensitometer is described which is particularly applicable to the measurement of densities in photographs of biological material. It is a double beam instrument, recording density directly, which allows the immediate summation of densities to to give, for example, the integrated absorption due to a particular biological structure.
TL;DR: In this article, a general review is made of double-beam systems in absorption spectroscopy, in which the two beams of radiation fall alternately on to a fast thermopile, the latter being in the primary circuit of a step-up transformer designed to work at low frequencies.
Abstract: A general review is made of double-beam systems in absorption spectroscopy Apparatus is described in which the two beams of radiation fall alternately on to a fast thermopile, the latter being in the primary circuit of a step-up transformer designed to work at low frequencies The output goes to a low-noise wide-band amplifier capable of a maximum overall voltage gain exceeding 109 The amplified signals from the two beams are separated and rectified by a simple mechanical switch on the radiation interrupter shaft, thus making the amplifier selective for frequency and phase, and enabling response time to be varied between 1 and 100 sec Finally, the ratio of the outputs is measured on a potentiometer recorder The reference beam output is used to regulate a slit monitor, so maintaining a constant reference energy level on the thermopile through the whole spectral range The performance of the equipment is illustrated
TL;DR: In this article, the conditions governing high resolving power in electron diffraction cameras are discussed, and, in particular, those determining the quality of resolution of the fine-structure in single-crystal reflexions.
Abstract: The conditions governing high resolving power in electron diffraction cameras are discussed, and, in particular, those determining the quality of resolution of the fine-structure in single-crystal reflexions. Limitation of resolution may arise from large source size, instability of electrical supplies, misalinement of the electron-optical system, interference from mechanical vibration and stray magnetic fields, grain in the photographic emulsion or too high an operating gas pressure in the camera. A camera designed to minimize these limitations is described, and its performance illustrated. Detailed fine structure, such as the subsidiary maxima of the shape transforms for small crystals, has been resolved.
TL;DR: In this paper, a detailed account of the construction and manipulation of a fused silica micro-balance is given, and the theory of an idealized balance is discussed, as well as its theory of idealized balances.
Abstract: A detailed account is given of the construction and method of manipulation of a fused silica micro-balance. The theory of an idealized balance is discussed.
TL;DR: In this article, a single prism spectrometer is described which uses a photoconductive detector of short response time to display spectra in the near infra-red region at a high repetition rate on a cathode-ray tube.
Abstract: A single prism spectrometer is described which uses a photoconductive detector of short response time to display spectra in the near infra-red region at a high repetition rate on a cathode-ray tube. The performance of the instrument is briefly discussed and illustrated by photographs of typical spectra. Using a lead-telluride cell, the long wave limit is about 5.5 μ. The instrument could be made to work at longer wavelengths by using a bolometer or pneumatic detector, but at a sacrifice of speed or resolution, and in the visible and ultra-violet by using a photoemissive cell or other suitable detector.
TL;DR: In this paper, the specific ionic conductance of solid salts in the range 10-9 to 10-13 Ω-1 cm-1 was measured using a low-frequency pulse technique.
Abstract: An apparatus designed to measure the specific ionic conductance of solid salts in the range 10-9 to 10-13 Ω-1 cm-1 is described. The use of a low-frequency pulse technique to avoid polarization together with the precaution of making all measurements in high vacuum, have enabled values of κ as low as 5 × 10-15 Ω-1 cm-1 to be determined. The performance of the apparatus is illustrated by the results obtained in the determination of the specific conductance of potassium and strontium azides.
TL;DR: In this article, a high Q magnetostriction transducer is used in conjunction with a suitable step-up velocity transformer to generate the vibrations, which enables complicated machining operations to be performed rapidly and easily in most brittle materials.
Abstract: An instrument is described which uses intense mechanical vibrations at ultrasonic frequency for drilling and cutting brittle materials. To generate the vibrations, a high Q magnetostriction transducer is used in conjunction with a suitable step-up velocity transformer. The instrument is essentially a high-speed reciprocating drill which enables complicated machining operations to be performed rapidly and easily in most brittle materials.
TL;DR: In this article, an instrument is described in which a thermistor, immersed in the fluid system to be controlled, is connected in an ac Wheatstone bridge operated at 50 c/s.
Abstract: An instrument is described in which a thermistor, immersed in the fluid system to be controlled, is connected in an ac Wheatstone bridge operated at 50 c/s An error signal results when the thermistor is not at the required temperature, and is passed, after amplification, to a phasesensitive detector which operates a relay controlling the heating and/or cooling of the fluid Special attention is paid to the mounting of the thermistor Tests have shown that the unit can control a water bath of some 8 gallons capacity within ±002° C over a period of weeks
TL;DR: In this paper, a combination of steel screening, coincidence counting and pulse height selection was used to reduce the total background background to 30 c.p.m. at room temperature for a counting volume of 20 ml.
Abstract: Experiments with scintillation counters using p-terphenyl in benzene are described. By the use of a combination of steel screening, coincidence counting and pulse height selection the total background is reduced to 30 c.p.m. at room temperature for a counting volume of 20 ml. The 14C detection efficiency under these conditions is approximately 40%. Light interaction between the photomultipliers used is almost eliminated by the use of a suitable filter.
TL;DR: The omnidirectional photometer was originally designed for the measurement of daylight under grass swards; but the principle used in the instrument can be applied to measure the mean illumination at a point in other cases, for example, interior illumination as discussed by the authors.
Abstract: This omnidirectional photometer is intended for the measurement of daylight under grass swards; but the principle used in the instrument can be applied to measure the mean illumination at a point in other cases, for example, interior illumination. It consists of two small circular barrier layer cells, insulated from one another and mounted back to back, each being surmounted by a translucent diffusing hemispherical shell, diameter 5/8 in. The cell sensitivities are adjusted electrically to equality, the combined output being read on an indicating meter. Even for collimated light the response is uniform with orientation to better than ±5%.
TL;DR: In this article, an apparatus was assembled to turn the gauge length of Chevenard tensile specimens, which are only 1½ mm in diameter, by electrochemical means instead of by normal lathe turning.
Abstract: An apparatus was assembled to turn the gauge length of Chevenard tensile specimens, which are only 1½ mm in diameter, by electro-chemical means instead of by normal lathe turning. The latter causes undesirable surface deformation. Specimens about 3/4 × 1/8 in (19.0 × 3.18 mm) diameter were rotated at 2000 rev/min and moved to and fro along the axis of rotation at constant velocity while a stationary jet of electrolyte impinged radially on to the surface to be removed. Using a hydrochloric acid/copper ammonium chloride solution, the diameter of iron specimens could be reduced by 0.065 in (1.6 mm) in 15 min and a good polish produced on the surface. The stress strain curves of normalized pure iron specimens produced by electro-turning and by machining were compared. The yield point, which is easily obliterated by cold work, was shown only on the curves of the electrolytically produced specimens.
TL;DR: In this article, an electrometer valve, combined with an ordinary pentode or triode valve, both acting as cathode followers, can provide a valve voltmeter of very high input impedance, low input capacity and of wide range.
Abstract: An electrometer valve, combined with an ordinary pentode or triode valve, both acting as cathode followers, can provide a valve voltmeter of very high input impedance, low input capacity and of wide range. By using two further ordinary pentodes as "tail" valves the range can be extended to ±500 V without difficulty and with an input to output magnification of 0.99. The input grid current is not increased by the wide range, while the presence of a very closely following output facilitates guard ringing and the reduction of input leakages and capacities. The arrangement will have several uses and has been especially designed for use for measurements of the atmospheric potential gradient using a radioactive collector, where it is more convenient and more rapid in response than most other methods.
TL;DR: In this paper, a circuit for use with Geiger-counter spectrometers which employ a second Geiger counter to monitor the X-ray output is described, and it allows neither counter to record while either is quenched, and thus ensures that the ratio of counts recorded is equal to a ratio of quanta received.
Abstract: A circuit is described for use with Geiger-counter spectrometers which employ a second Geiger counter to monitor the X-ray output. It allows neither counter to record while either is quenched, and thus ensures that the ratio of counts recorded is equal to the ratio of quanta received and is independent of the quench times, the mean X-ray output and the X-ray output waveform. The same principle should be applicable to other methods of monitoring. The circuit described also suppresses the background counts for the fraction of the cycle during which a self-rectified X-ray tube produces no characteristic radiation.
TL;DR: In this paper, a method of preparing plane diffraction grating replicas from helical rulings suggested by Merton and developed at the N.P.L. is described in further detail.
Abstract: A method of preparing plane diffraction grating replicas from helical rulings suggested by Merton and developed at the N.P.L. is described in further detail. Particular reference is made to the method of preparing the plastic "pellicle," and sources of error in this and other stages of the process are indicated.
TL;DR: In this article, the effect of temperature changes on capacitance pressure gauges is discussed and a theoretical treatment of their effect on the design of a sensitive differential pressure gauge with a temperature coefficient of capacitance of only - 100 p.p.m.
Abstract: A brief theoretical treatment is given of the effect of temperature changes on capacitance pressure gauges. Its use in the design of a sensitive differential pressure gauge of range 0-10 mm of water, having a temperature coefficient of capacitance of only - 100 p.p.m./°C, is illustrated.
TL;DR: In this article, it has been found that repeated measurements of turbulent velocity, under the same conditions but using different wires, differ from one another by 4% or more, and that a single wire can be used repeatedly; the sensitivity then remains constant to within 2%.
Abstract: When a hot-wire is exposed to an air-stream near an industrial area, it collects a deposit consisting of particles of soot and tar. The deposit, by changing the heat-loss from the wire, can decrease the sensitivity by as much as 20%. Even in cleaned air, the useful life of a hot-wire may be no more than 2 hours. It has been found that repeated measurements of turbulent velocity, under the same conditions but using different wires, differ from one another by 4% or more. A technique has therefore been developed for cleaning hot-wires, so that a single wire can be used repeatedly; the sensitivity then remains constant to within 2%. Making use of this technique, measurements of turbulent velocity have been reproduced to within ½%.
TL;DR: In this paper, an infra-red monochromator is split into two beams for the spectral response measurement of photocells, and one beam is used to control the energy output from the tungsten filament used as source.
Abstract: The apparatus described is primarily intended for the rapid measurement of the spectral response of photocells. Radiation emerging from an infra-red monochromator is split into two beams. One is used in conjunction with a radiation thermocouple to control the energy output from the tungsten filament used as source, providing a constant energy output from the monochromator, independent of wavelength. The other beam, constant in intensity, is used for the spectral response measurements.