Special operational features of a variometer for measuring small pressure change rates

Conclusions In principle, the time lag of a variometer designed to measure small pressure change rates can be made as small as one pleases. However, when the time lag of the variometer is decreased, so too is the pressure drop between the static and dynamical chambers. This means that highly sensitive membranes of large dimensions must be used, and, in the final analysis, that the sensitivity of the variometer as a whole is lessened. To obtain the necessary sensitivity of the instrument, it is necessary to increase the volume of the static chamber, and, at the same time, to keep the time lag unchanged, it is necessary to lessen the effective resistance of the capillary.Translated from Izmeritel'naya Tekhnika, No. 11, pp. 33–35, November, 1971.     

Evaluating errors of thermocouple manometric transducers LT-2

Conclusions A more precise thermal computation method can be used for reducing the errors of thermoelectrical vacuum gauges and developing multichannel wide-band instruments for measuring pressure. The latter circumstance is particularly important for mass measurements of vacuum, when the application of multichannel vacuum gauges may provide a considerable saving. The physically substantiated computation method makes it possible to utilize the previously neglected potentialities of LT-2 transducers almost without changing their design and production technology.Translated from Izmeritel'naya Tekhnika, No. 7, pp. 14–16, July, 1968.     

Measurement of small friction moments

Conclusions The most widespread methods of those examined by us for measuring small friction moments consist at present of the pendulum and calibrated spring methods for laboratory research, and of the self-braking method for industrial use. This difference is due to the fact that the self-braking method is speedier, but it can only determine the mean value of the friction moment over a given time interval, which is often insufficient for research work.The pendulum method possesses a theoretically high sensitivity; however, the measurement of small moments entails several technical difficulties, the most important of which is the impossibility of evaluating the moment due to the system's residual unbalance and to the error in determining arml. For measuring friction moments of 10^–3–10^–4g·cm preference should be given to the calibrated spring method with the rotation axis of the system beingplaced in the vertical position.An essential defect of mechanical methods for determining the instantaneous values of the friction moment consists in the limited range of the measured moments.By means of electromechanical methods it is possible to measure arbitrarily small friction moments. However, they have to be calibrated by means of mechanical instruments. Induction instruments are considerably simpler in design than those of the moving-coil type, but they are less sensitive and have a large relative error. The use of electromechanical instruments is most suitable for comparison measurements and for production testing, due to their high productive capacity.     

Estimating the error in measuring the brightness of a color-TV screen

Factors are considered that give rise to the main error in measuring the brightness of a color- TV screen. Formulas are given for the main relative and additional errors in brightness measurement due to temperature change.Translated from Izmeritel'naya Tekhnika, No. 9, pp. 32–34, September, 1993.     

Measurement of the Specific Enthalpy of Vaporization on 1,1,1,2-Tetrafluoroethane in the Temperature Range from 180 to 240 K

An apparatus is described which is capable of measuring the enthalpy of vaporization in the temperature range from 100 to 250 K. The sample (R134a; purity, at least 99.999%) is located in the measuring cell at the saturated vapor pressure, p = p _s. A control circuit allows p to be kept constant by opening a motor-operated valve to a weighing cylinder after having switched on the electrical measuring cell heater. During the experiment, the temperature is kept constant within a 10mK. In the range 180 to 230 K, the data for R134a are compared with calculated values from the fundamental equation given by Tillner-Roth and Baehr, which is recommended by Annex 18 of the International Energy Agency (IEA) as an international standard. Good agreement within a standard uncertainty of 1.6×10^–3 is obtained. At temperatures of only 10 K above the triple-point temperature, the enthalpy of vaporization calculated from the Clausius–Clapeyron equation shows considerable uncertainty due to the determination of the small vapor pressure. It is chiefly in this range that it is advantageous to have the new apparatus.     

Measurement of rapidly changing temperatures of conducting solid bodies by means of thermocouples

Conclusions A thermocouple with welded electrodes possesses a considerable thermal inertia. Thermocouples without junctions are virtually inertialess and are capable of measuring rapidly changing temperatures on the surfaces of solid conducting bodies.The contact resistance between the thermal electrodes and the body with which they make contact has the maximum effect on the precision of measurements in the case when current-measuring instruments are used. This error can be reduced by increasing the contact pressure up to 2–2.5 kg-wt/mm² (196.13·10⁵–245.17·10⁵ N/m²), cleaning the contact surfaces and preheating the contact.     

Microgravimetric base survey at the gravimetric station of the all-union scientific-research institute of metrology

The results are presented of a microgravimetric survey of two bases of the gravimetric station of the All-Union Scientific-Research Institute of Metrology (VNIIM) using an E-54 variometer. The measurements form part of preparations for performing comparisons of absolute ballistic gravimeters at the observatory.Translated from Izmeritel'naya Tekhnika, No. 10, pp. 3–5, October, 1995.     

Compression manometer error due to the nature of its scale

Conclusions A comparison of errors in measuring pressure with a McLeod gauge by means of the linear and square-law scale methods shows that over the entire measurement range the linear scale method is more precise than the square-law scale method, with the exception of one point at which the errors of the two methods are equal.Translated from Izmeritel'naya Tekhnika, No. 10, pp. 33–35, October, 1971.     

Pressure Transducer Based on Tensosensitive Films of Bismuth–Antimony Telluride

A new design of a semiconductor pressure transducer based on tensosensitive films of bismuth–antimony telluride, which provides a temperature compensation for the entire device structure, is proposed. The technical data of the tensometric transducer proposed for measuring the pressure of liquids and gases are presented.     

Effects of strain rate and temperature on the stress–strain response of solder alloys

To ensure reliable design of soldered interconnections as electronic devices become smaller, requires greater knowledge and understanding of the relevant mechanical behavior of solder alloys than are presently available. The present paper reports the findings of an investigation into the monotonic tensile properties of bulk samples of three solder alloys; a lead–tin eutectic and two lead-free solders (tin–3.5 copper and a tin–3.5 silver alloy). Temperatures between–10 and 75°C and strain rates between 10^–1 and 10^–3 s^–1 have been studied. Both temperature and strain rate may have a substantial effect on strength, producing changes well in excess of 100%. Strength is reduced by lowering strain rate and increasing temperature, and Sn–37 Pb is usually most sensitive to the latter. Expressions for strain and strain rate hardening have been developed. The Sn–0.5 Cu alloy is usually the weakest and most ductile. Sn–37 Pb is strongest at room temperature but with increasing temperature and lower strain rates it becomes inferior to Sn–3.5 Ag. Ductility changes with temperature and strain rate for all three alloys are generally small with inconsistent trends. The role of such data in stress analysis and modeling is considered and the paramount importance of employing data for conditions appropriate to service, is emphasized.     

A measuring and computing method and device for determining arterial blood pressure parameters N humans

A measuring and computing method and device are proposed for determining the essential arterial blood pressure parameters in humans by a noninvasive method, not requiring an occlusion cuff. Consideration is given to the working principle of the primary transducer, as the chief unit in the device, and to a computing algorithm for calculating the essential arterial pressure parameters as a systole and diastole in a digital artery.Translated from Izmeritel'naya Tekhnika, No. 4, pp. 60–62, April, 1994.     

Vacuum membrane capacity meters with electrostatic compensation

We describe new features of vacuum membrane capacity meters with electrostatic compensation, which improves their performance and expands their functional applicability for measuring volumes with complex configurations and flow rates of small gas streams. The concept is based on introduction of an additional reservoir with mobile gas-impermeable gate. When connected to the chambers of pressure gauge converter, the unit reduces the chamber volume in the course of pressure measurement so as to modify the conversion ratio in the vacuum meter measurement equation.Translated from Izmeritel'naya Tekhnika, No. 6, pp. 9–10, June, 1993.     

The effects of fluid flow on secondary arm coarsening during dendritic solidification

Although dendrites are the result of diffusion limited growth it has long been appreciated that flow within the parent melt can have a dramatic effect on these structures. A free boundary model of dendritic solidification is used to assess the effects on the secondary arm coarsening processes of fluid flow within the parent melt. It is found that for solutally controlled coarsening realistic interdendritic flow velocities of the order 10^–3–10^–2 m s^–1 give rise to ripening rates which are comparable to diffusive transport. However, only flows with a component aligned from the secondary tip towards the root enhance the ripening rate. Oppositely aligned flows actually reduce the ripening rate. Thus, due to the four-fold symmetry of dendrites in cubic metals, the actual effect on the secondary arm spacing could be quite small. The results are shown to be in general agreement with recent microgravity experiments on dendritic coarsening.     

Investigation of leak detection method by means of measuring the pressure increment in vacuum

Leak detection by measuring the pressure increment in a vacuum has found wide application on pressure vessels, pipes and accessories. However, the reproducibility of the method and the effect of some secondary factors on the results of leak detection have not yet been satisfactorily studied and explained. In this paper, the leak detection method is discussed and the possibility of measuring small leakage rates outlined. Some factors influencing the results, especially the virtual leakage rate and test temperature, which may affect the accurate measurement of small leakage rates, are investigated in detail. In order to improve measurement accuracy, it is suggested that the evacuation time is prolonged and, if possible, the testing system is pre-heated, to eliminate the influence of the virtual leakage rate as far as possible. The research results indicate that both the variation of the ambient temperature and the inconsistency of the temperature of the testing system with that of the gas leaking into the system will introduce errors. Methods for correcting measured results are proposed.     

A Method of Measuring Current–Voltage Characteristics Based on the Hammerstein–Chebyshev Model

A method of measuring the current–voltage characteristics of nonlinear components is proposed, which involves applying a sinusoidal voltage to the object being measured, finding the Fourier spectrum to read out the output current, and a calculation using the spectrum of the coefficients of the expansion of the measured characteristic in Chebyshev polynomials. The properties of the Hammerstein–Chebyshev model are considered, a block diagram of a measuring instrument is presented, and recommendations are made for minimizing the systematic errors due to approximating their characteristics by Chebyshev polynomials.     

Strength and Failure Modes of Hoop Wound CFRP Tubes Under Compressive High Rates of Loading

A study was undertaken to investigate the response of hoop wound carbon fibre reinforced plastic (CFRP) tubes to dynamic compressive loading at strain rates in the range of 5–200/sec. An experimental rig was designed and built to test short tubular specimens under external radial pressure with minimum end constraints. The load was applied by detonating a small explosive charge inside a water filled, steel, cylindrical chamber enclosing the test specimen. For each test the external pressure and the strains, in both circumferential and longitudinal directions, were recorded on suitable digital processing equipment. Two distinct modes of failure were identified; material and structural (buckling). The mode of failure was dependent on the rate of loading and the tube diameter/thickness ratio. For 100 mm diameter tubes with diameter/thickness=40, buckling failure dominated at strain rates below 10/s. However, at higher strain rates, material failure and a considerable enhancement in burst strength was observed. For 100 mm diameter tubes, with diameter/thickness=80, a buckling mode of failure was in evidence in all the tests, irrespective of the rate of loading.R. Ahmad: Presently at School of Mechanical Engineering, University Sains Malaysia, Pulau Pinang, Malaysia.     

Electron tube Amplifiers

Conclusions Up-to-date electrometer tube amplifiers are a perfect equipment for measuring currents and voltages from sources with a large internal resistance, and they can be used for solving a wide range of problems related to electrometric measurements. The current sensitivity of mass-produced tube electrometers amounts to 10^–15–10^–14 A. Several problems, such as obtaining a logarithmic scale and high-speed systems for measuring very small currents are best solved by means of tube electrometers. It is true that in recent years tube electrometers have acquired an important rival consisting of electrometers with field-effect transducers; however, the latter are as yet in the development stage and one can expect that tube electrometers will for a long time occupy the leading position among other systems used for similar purposes.Translated from Izmeritel'naya Tekhnika, No. 12, pp. 39–44, December, 1966.     

Measurement of deviations from cylindricity

Conclusions It is suggested to measure spearately the diameter and the shape in the longitudinal and cross sections and to carry out a combined processing of the measurement result in order to obtain the radii of the surface points with respect to a given axis.The availability of the required instruments, the simple processing of results, and the small errors in determining the radii make it possible to recommend this technique for measuring high-precision components with lengths up to 1000 mm and diameters up to 200–300 mm. For components of a samller size it is advantageous to use instruments with two precise movements, consisting of a rotational and a longitudinal movement.Translated from Izmeritel'naya Tekhnika, No. 10, pp. 64–65, October, 1969.     

Apparatus for Measuring Ultralow-Frequency Noise in Semiconductor Gas-Sensitive Structures

Laboratory equipment for measuring ultralow-frequency current noise of semiconductor gas-sensitive layers in the 10^–6–1 Hz frequency band in the 20–450°C temperature range for different contents of the gaseous phase and various bias voltages (transport currents) is described. A procedure for making the measurements and for estimating their errors is presented.