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1.
Summary A method is described for the measurements of small forces (10−5 – 10−3 newton) on a sample weighing a few grams. This sample is placed on a bar which is fixed on the turning coil of an ordinary
switchboard current meter. The force on the sample can be compensated by the Lorentz force on the current through the coil.
This method avoids a great many of the usual constructional difficulties of such apparatus and leads to a robust instrument
which is easy to handle and to. automatize, thus being of interest for use outside the laboratory. Especially this possibility
has induced us to choose as an example a magnetic susceptibility balance. For magnets of field strength up to 20 000 oerstedt
the precision obtained for the measured susceptibility amounts to one tenth of a percent. 相似文献
2.
J. M. W. Milatz H. J. J. van Boort J. van Laar C. T. J. Alkemade 《Applied Scientific Research》1955,4(1):447-456
Summary A device is described, which can be used for amplifying and measuring the a.c. output of slow responding detectors (e.g. bolometers),
receiving signals of constant but low frequency (∼1 Hz). This device, based on frequency conversion, which in principle is
insensitive to drift-effects, consists of a primary galvanometer, a rotating disk, chopping the lightbeam reflected by the
moving mirror of this galvanometer, and a phototube which receives the chopped lightbeam and which is coupled to an a.c. amplifier
with an a.c. galvanometer as indicating instrument. The sensitivity of the instrument described, which had a response frequency
of 1 2/3 Hz, proved to be limited by the Johnson noise of the input circuit only; drift effects proved to be greatly reduced. 相似文献
3.
R. E. de Haan 《Flow, Turbulence and Combustion》1971,24(1):1-20
A harmonic pressure generator is developed based on the principle of plane sound waves. The pressure is generated in a cylindrical enclosure by a piston with a flat bottom; the piston is driven by a coil situated in a radial magnetic field. The coil is supplied with an alternating current; the corresponding amplitudes of the piston are measured by a precision accelerometer mounted inside the hollow piston. The apparatus was designed to calibrate the probe microphone described in [1] over a frequency range from 50 to 4000 Hz, with an accuracy of a few percent. 相似文献
4.
Design of a pistonphone 总被引:1,自引:0,他引:1
R. E. de Haan 《Applied Scientific Research》1971,24(1):1-20
A harmonic pressure generator is developed based on the principle of plane sound waves. The pressure is generated in a cylindrical
enclosure by a piston with a flat bottom; the piston is driven by a coil situated in a radial magnetic field. The coil is
supplied with an alternating current; the corresponding amplitudes of the piston are measured by a precision accelerometer
mounted inside the hollow piston.
The apparatus was designed to calibrate the probe microphone described in [1] over a frequency range from 50 to 4000 Hz, with
an accuracy of a few percent. 相似文献
5.
A computerized apparatus for the measurement of low shear rate viscosity on polymer solutions at elevated pressure and temperature is described. The pressure is variable from 1 bar to 400 bar with an accuracy of ±5 bar. The temperature is variable from 0° to 100°C with an accuracy of ±0.3 K. The instrument is operated in a free-relaxation mode in which the decay of oscillation of the torsion pendulum after an initial displacement is recorded and used to compute the viscosity of the sample. The measurements are performed according to the contents of a user-specified control file, and the oscillation data are stored digitally and later analyzed for parameter estimation. The instrument operates in the very-low frequency range (0.03 to 0.25 Hz) and the accuracy of the measured viscosity is ±0.03 x 10–3 Ns/m2. 相似文献
6.
G. Harrison 《Rheologica Acta》1974,13(1):28-32
Summary An instrument has been developed for measuring the viscoelastic behaviour of polymer melts at low frequencies, in the range 10–3 to 50 Hz. The sample is contained between a cone and a fixed plate, or between parallel plates. The moving member is driven in torsional oscillation through a torsion wire. The amplitude of the resulting oscillation is compared in amplitude and phase with the driven end of the torsion wire. The amplitudes are measured digitally using optical diffraction gratings, and either an oscilloscope or a high-speed ultra-violet recorder is used to determine the phase angle between the two signals. The moving member is supported on an air bearing, which provides a very low friction support with a high degree of positional control thus giving a well defined sample geometry. The torsion wire is driven using a vibrator with a d.c. drive amplifier fed from a very low frequency oscillator. The sample temperature is controlled to better than 0.01 °C, with temperature gradients across the sample of a similar order of magnitude. The temperature range of the instrument is from –50 °C to +200 °C.The angular resolution of the measuring system is 3 × 10–5 radius, so that an accuracy of better than ±1% in the amplitude measurements can be obtained with the amplitude of shear in the sample kept sufficiently low that a linear stress-strain relation is maintained.With 3 figures 相似文献
7.
A. Kaye 《Rheologica Acta》1969,8(2):244-244
An apparatus designed to measure the dynamic viscoelastic response of polymer melts is described. Dynamic elasticity (G) and viscosity () can be measured over a frequency range 10–2-10–3 Hz and at temperatures up to 350 °C. The sample under test is held in a cone and plate assembly. A small strain is introduced by driving the plate with a variable speed synchronous motor and off-centre cam at low frequencies and by an electromagnetic vibrator at high frequencies. The amplitudes of the cone and plate are detected using the optical lever principle and photocell strips. The phase difference between the cone and plate is measured from a recorder trace at low frequencies and by direct reading on a meter at high frequencies.Results are described of measurements on silicone fluids, and on commercial grades of polyethylene with different molecular weight distributions and degrees of branching.A discussion is given of the correlation between the dynamic viscosity measurements and those taken under steady-flow conditions.Paper presented at the Conference on Experimental Rheology, University of Bradford, April 17–19, 1968. — Original paper published in J. Sci. Instruments Series 2,1, 1102–1112 (1968). 相似文献
8.
Measurement apparatus designed and constructed according to conceptions of the authors, enabled a more precise calculation of the heat transfer coefficient with the balance and gradient methods. Construction and use of the apparatus and devices are described below, results of experimental investigations for horizontal and vertical, isothermal, flat plates obtained independently with the balance and gradient methods, are also presented. The following equations were found:Nu=0.612 · (Ra)1/4 104 ≦Ra ≦ 108 for vertical platesNu=0.766 · (Ra)1/5 104 ≦Ra ≦ 107 Nu=0.173 · (Ra)1/3 105 ≦Ra≦ 108 for horizontal plates. On the basis of the results obtained from both these methods, differences of natural convection acting from vertical and horizontal plates are discussed. The usefulness of the balance and gradient methods have been considered for qualitative and quantitative investigations of heat transfer by natural convection. 相似文献
9.
María Soledad Barral Isabel Lizaso María Eugenia Muñoz Antonio Santamaría 《Rheologica Acta》2001,40(2):193-195
In this work we investigate the gel formation of EVA/recycled motor oil systems as a route to obtain synthetic binders which
could be used instead of natural bitumen, as well as mixed with natural bitumen to modify adequately its viscoelastic response.
The EVA copolymer studied in this work has a vinyl acetate content of 18 wt% and solutions of EVA/motor oil have been prepared
up to a concentration of 50 wt%. Dynamic viscoelastic frequency sweeps between 10−2 Hz and 102 Hz have shown that above 3 wt%, at 25 °C, EVA/motor oil systems form gels. It has been possible to define an elastic equilibrium
modulus, Ge, for each gel. The dependence of Ge on concentration has been compared with that of PVC/DOP and SBS/oil gels on the basis of the De Gennes model. Thermal stability
of EVA/motor oil gels has also been analyzed, indicating that for the highest polymer concentrations gel point is above 80 °C.
Received: 23 December 1999 Accepted: 13 June 2000 相似文献
10.
For active materials such as piezoelectric stacks, which produce large force and small displacement, motion amplification
mechanisms are often necessary – not simply to trade force for displacement, but to increase the output work transferred through
a compliant structure. Here, a new concept for obtaining large rotations from small linear displacements produced by a piezoelectric
stack is proposed and analyzed. The concept uses elastic (buckling) and dynamic instabilities of an axially driven buckling
beam. The optimal design of the buckling beam end conditions was determined from a static analysis of the system using Euler's
elastica theory. This analysis was verified experimentally. A stack-driven, buckling beam prototype actuator consisting of
a pre-compressed PZT stack (140 mm long, 10 mm diameter) and a thin steel beam (60 mm× 12 mm× 0.508 mm) was constructed. The
buckling beam served as the motion amplifier, while the PZT stack provided the actuation. The experimental setup, measuring
instrumentation and method, the beam pre-loading condition, and the excitation are fully described in the paper. Frequency
responses of the system for three pre-loading levels and three stack driving amplitudes were obtained. A maximum 16∘ peak-to-peak rotation was measured when the stack was driven at an amplitude of 325 V and frequency of 39 Hz. The effects
of beam pre-load were also studied. 相似文献
11.
Summary The accuracy of a visual photometric meter is limited by the luminance discrimination ratio ΔB/B of the eye, which, in the present case, is about 2 per cent. The unit, utilizing polarizers, measures optical paths to within
0.003 λ. The efficiency is compared with that of the photoelectric receiver, and accuracy values for some applications, including
analyses of the isotope mixtures D2O16/H2O16 and H2O18/H2O16, are given. 相似文献
12.
Summary On each side of a thin diaphragm, separating two chambers, a condenser plate is mounted at a small distance. The two capacities
thus formed are part of a bridge circuit which is fed by a high frequency oscillator. An amplifier with a narrow band width
and a phase — dependent rectifier give a voltage which is fed back to the manometer. At one side of the diaphragm a pressure
prevails, much lower than the one to be measured, at the other side the gas is admitted, the pressure of which is to be measured.
The displacement of the membrane by the gas pressure is almost completely compensated electrostatically by the feedback voltage.
By virtue of a differential way of feedback the reading is proportional to the pressure. The range is from 10−5-0.5 mm of mercury pressure difference at any absolute value. The apparatus is made of chemically fairly resistant materials,
and as its indication is in principle independent of the nature of the gas, it can be used for almost every gas. The apparatus
can also be used as a non-direct reading instrument in which case the upper limit of the range is 1 mm of mercury. 相似文献
13.
This article describes a pseudo-heterodyne demodulation technique for interferometric fiber optic sensors that has a larger
measurement range than is currently possible with pseudo-heterodyne demodulation. This sensor demodulation technique has a
bandwidth of 30 Hz to 2.5 kHz, is capable of resolving optical phase angles as small as 5×10−4 rad, and has a maximum measurement range of tens of radians in a bandwidth of 30–500 Hz. A comparison between the response
obtained from a resistance strain gage and a fiber optic sensor using this demodulation is favorable. 相似文献
14.
A particle image velocimetry system for microfluidics 总被引:20,自引:0,他引:20
J. G. Santiago S. T. Wereley C. D. Meinhart D. J. Beebe R. J. Adrian 《Experiments in fluids》1998,25(4):316-319
A micron-resolution particle image velocimetry (micro-PIV) system has been developed to measure instantaneous and ensemble-averaged
flow fields in micron-scale fluidic devices. The system utilizes an epifluorescent microscope, 100–300 nm diameter seed particles,
and an intensified CCD camera to record high-resolution particle-image fields. Velocity vector fields can be measured with
spatial resolutions down to 6.9×6.9×1.5 μm. The vector fields are analyzed using a double-frame cross-correlation algorithm.
In this technique, the spatial resolution and the accuracy of the velocity measurements is limited by the diffraction limit
of the recording optics, noise in the particle image field, and the interaction of the fluid with the finite-sized seed particles.
The stochastic influence of Brownian motion plays a significant role in the accuracy of instantaneous velocity measurements.
The micro-PIV technique is applied to measure velocities in a Hele–Shaw flow around a 30 μm (major diameter) elliptical cylinder,
with a bulk velocity of approximately 50 μm s-1.
Received: 26 November 1997/Accepted: 26 February 1998 相似文献
15.
This paper presents the results of new microtensile tests conducted to investigate the mechanical properties of submicron-thick
freestanding copper films. The method, used in this study, allows the observation of materials response under uniaxial tensile
loads with measurements of stress at strain rates up to 5.5 × 10−4/s. It also facilitates tension–tension fatigue experiments under a variety of mean stress conditions at cyclic loading frequencies
to 20 Hz. The sample processes involve fabrication of a supporting frame with springs and alignment beams all made of electroplated
nickel. Electroplating took place on top of a previously deposited sample rather than creating a structure by subtractive
fabrication. Tensile sample loading is applied using a piezoelectric actuator. Load was measured using a capacitance gap sensor
with a novel mechanical coupling to the sample. Tension–tension fatigue experiments were carried out with feedback to give
load control. Fatigue tests were conducted on sputter-deposited 500 and 900 nm copper films with grain sizes ∼50 nm. Fatigue
life reached 105 cycles at low mean load, which decreased with an increase in the mean load. The results indicate decreasing plasticity with
increasing mean load. 相似文献
16.
Fully suspended, five-axis, three-magnetic-bearing dynamic spin rig with forced excitation 总被引:2,自引:0,他引:2
C. R. Morrison A. Provenza A. Kurkov G. Montague K. Duffy O. Mehmed D. Johnson R. Jansen 《Experimental Mechanics》2005,45(3):226-237
A significant advancement in the dynamic spin rig (DSR), i.e., the five-axis, three-magnetic-bearing DSR, is used to perform
vibration tests of turbomachinery blades and components under rotating and non-rotating conditions in a vacuum. The rig has
three magnetic bearings as its critical components: two heteropolar radial active magnetic bearings and a magnetic thrust
bearing. The bearing configuration allows full vertical rotor magnetic suspension along with a feedforward control feature,
which enables the excitation of various modes of vibration in the bladed disk test articles. The theoretical, mechanical,
electrical, and electronic aspects of the rig are discussed. Also presented are the forced-excitation results of a fully levitated,
rotating and non-rotating, unbladed rotor and a fully levitated, rotating and non-rotating, bladed rotor in which a pair of
blades were arranged 180° apart from each other. These tests include the “bounce” mode excitation of the rotor in which the
rotor was excited at the blade natural frequency of 144 Hz. The rotor natural mode frequency of 355 Hz was discerned from
the plot of acceleration versus frequency. For non-rotating blades, a blade-tip excitation amplitude of approximately 100
g A−1 was achieved at the first-bending critical (≈144 Hz) and at the first-torsional and second-bending blade modes. A blade-tip
displacement of 1.778×10−3m (70 mils) was achieved at the first-bending critical by exciting the blades at a forced-excitation phase angle of 90° relative
to the vertical plane containing the blades while simultaneously rotating the shaft at 3000 rpm. 相似文献
17.
Summary An apparatus permitting to record the heart-beats of working persons is described. The input signal is obtained from a barrier layer photocell and a lamp at the ear-lobe. The signal is amplified by a differential amplifier with symmetrical input and feed-back. 相似文献
18.
Liping Yao Zhong Zeng Yi Zhang Zhouhua Qiu Huan Mei Liangqi Zhang Yongxiang Zhang 《Heat and Mass Transfer》2012,48(12):2103-2111
The effects of rotating magnetic field (RMF) on the three-dimensional thermocapillary flow of semiconductor melt (Pr?=?0.01) in a floating half-zone model under microgravity are investigated numerically by the finite volume method. The results indicate that the thermocapillary flow without magnetic field is a steady three-dimensional convection for Ma?=?40 in a floating half-zone model with As?=?1, and the convection evolves to an oscillatory three-dimensional flow by applying 1–6?mT RMF with 50?Hz rotating frequency. Based on the fast Fourier transform spectrum, the convection is confirmed to be a periodically oscillating flow, the oscillatory main frequency, 1.59?×?10?3?Hz for 1?mT RMF and 5.84?×?10?2?Hz for 6?mT RMF, increases with the magnetic strength. However, with increasing the magnetic field strength up to 7?mT, the three-dimensional thermocapillary flow is effectively controlled and the convection turns into a steady axisymmetrical one. 相似文献
19.
H. J. E. Smits D. van den Ende G. J. Beukema E. G. Altena P. H. J. Spitteler 《Rheologica Acta》1992,31(5):471-480
A dynamic viscometer is described, with which the dynamic moduli in the frequency range from 2 × 10–3 to 10 Hz can be determined for liquids with 10–3 Pa< |G
* | <102 Pa. Due to the application of an air bearing and inductive transducers for the detection of the angular displacement of both the drive and the measuring cylinder a sensitive apparatus has been made. Very small strains (0 10–3) can be applied and only a small amount of sample (4 ml) is needed. The operation of the apparatus is fully computer-controlled, thus, long runs at various frequencies and temperatures are possible without operator intervention. The theoretical background, calibration procedure, and operation window are described. A presentation of some measurements on two polyisoprene/polystyrene triblock copolymer solutions concludes the work. 相似文献
20.
Aerodynamic force measurement using 3-component accelerometer force balance system in a hypersonic shock tunnel 总被引:1,自引:0,他引:1
A new three-component accelerometer force balance has been designed, calibrated and tested in hypersonic shock tunnel (HST2)
of Indian Institute of Science. The newly designed balance is able to measure aerodynamic forces (within test time of one
millisecond) on test models at angles of attack from 0 to 12°. Two models, a blunt cone with after body and a blunt cone with
after body and frustum are used to establish the accuracy of the force balance. The tests were conducted for the above two
configurations with a constant Mach number of 8 and total enthalpy of 2.0 MJ/kg. The effectiveness of the balance is demonstrated
by comparing the forces and moments of measured data with AGARD models. The flow fields around the test model are simulated
using a 3D axisymmetric Navier–Stokes solver and the simulated results were compared with the measured values. Measured and
computed force data are matched within ±10% for two different models tested here. The accuracy of the force balance is also
estimated with the Newtonian theory and the values are approximately ±10% for the axial component and ±8% for the normal and
pitching moment components.
相似文献