Strain Gauge Bridge Research Articles

High‐temperature magnetostriction of magnetite and titanomagnetites

Magnetostriction of synthetic polycrystalline magnetite and titanium‐rich titanomagnetites has been measured from 25°C to their Curie temperatures. These are the first reported measurements of magnetostriction above room temperature for titanomagnetites. The magnetostriction constants are measured with a recording rotating field magnetostrictometer, which uses a strain gage bridge technique and two rotating SmCo5 permanent magnets. Magnetostriction is recorded continuously as the sample is slowly heated and cooled in a fixed magnetic field. Measurements were made on sintered polycrystalline samples of magnetite, titanomagnetite (Fe3‐xTixO4, x=0.0, 0.4, and 0.6), and an aluminum‐magnesium substituted titanium‐rich titanomagnetite (AMTM60). The thermal dependence of the polycrystalline magnetostriction constant λs(T) varies as (1‐T/Tc)1.3 for titanium‐rich titanomagnetites and as (1‐T/Tc)0.9 for pure magnetite. the polycrystalline magnetostriction constant is well approximated by a power law equation in terms of the saturation magnetization, λs(T)αMs(T) n, where n=2.31 (TM0), 3.47 (TM40), 2.75 (TM60), and 2.80 (AMTM60). The magnetostriction results for AMTM60 are in excellent agreement with previous predictions based on domain observations.

A circuit for lead resistance compensation and complex balancing of the strain-gauge bridge

In some specific applications, the strain-gauge bridge branches are separated and remote. Lead resistances between bridge branches and the measuring instrument introduce significant measurement error. The well-known error compensating circuits do not suit all applications, or they cannot be added to the already existing instrumentation without modification of its internal circuits. A circuit for lead resistance compensation and complex balancing of the 1/4 and 1/2, AC or DC excited bridges is described. It is possible to add this circuit in front of the instrumentation already in use with no modification of the instrumentation itself.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A photo-optical technique for measuring flow-induced vibrations in cantilevered tube bundles

A photo-optical technique has been developed for monitoring the dynamic displacement of cantilevered tubes in fluid flow. The technique employs an optical fiber to transmit light through the tube and a phototransistor array to measure the motion of the light beam that is projected from the end of the tube. The device is simple, inexpensive, and very sensitive to small displacements. Details are given for the development of the technique, analysis of performance, and static calibration. The device was tested by monitoring the dynamic response of a bundle of cantilevered tubes in both single-phase and two-phase Freon 11 flows. The results are compared with those of a standard strain gauge bridge.

A Comparison between Fibreoptic and Catheter‐Tip Bridge Strain Gauge Transducers for Measurement of Intrauterine Pressure in Labour

A new fibreoptic pressure transducer was used to measure uterine activity in labour, and the results were compared with those obtained with the catheter-tip bridge strain gauge transducer. Readings were obtained from 8 patients in spontaneous labour, and a total of 565 contractions were analysed. When all contractions were analysed the coefficient of variation ranged from 11.24 to 42.74. In 2 patients with vast difference in pressure readings one of the catheters had slipped into the lower uterine segment, when these 2 cases were not considered the coefficient of variation ranged from 11.24 to 21.18. Even in the others there were transient periods lasting 5 to 15 minutes when the pressure difference was greater than 10 mmHg between the 2 catheters. When they were excluded from analysis, along with the 2 cases where one of the catheters was displaced, the coefficient of variation ranged from 9.30 to 16.05. The fibreoptic pressure transducer appears to be a safe, convenient and fairly accurate means of assessing uterine activity. But one must be aware that a catheter giving low readings compared with the initial period soon after insertion may be due to displacement of the transducer tip to the uterine lower segment.

Compensation for error in high-temperature pressure measuring device

Autoclave type industrial equipment are being increasingly used nowadays for production processes at high pressures (up to 25.0 MPa) and temperatures (of the order of 400~ Highly reliable pressure control of in the equipment is very important keeping in view the grave hazards involved in these processes. This problem is solved by a traditional method using pressure transducers usually located in supply lines. However, control of pressure of viscous or condensed media using transducers installed in supply lines becomes unreliable. Adhesion or condensation of processed products on the sensitive elements of transducers, and internal surfaces of supply lines, leads to reduction in sensitivity and, in a series of cases, to instrument failure and loss of data on the pressure due to "choking" of supply lines. Under these conditions, pressure control based on deformation of the body of the equipment itself by having the sensitive element of the measuring device built into the equipment body is a very promising method. In this case, the effect of adhesion or condensation of treated substances on accuracy in measuring pressure in the equipment can be successfully avoided. However, since the sensitive part of the device has to be located in the zone of high and non-steady temperatures (between heater and body of equipment), the designer has to solve the problem of compensating for sharply increasing temperature errors which substantially distort the instrument readings. Various methods and circuits are available for temperature error compensation in resistance strain-gauge pressure transducers [1-5]. A major part of these is applicable for transducers with linear temperature characteristics and cannot be successfully used for compensating for temperature errors in resistance strain-gauge transducers with significant nonlinearity in their temperature dependence. A circuit was developed which facilitates adequate suppression of the noise signal due to the effect of temperature over a wide range of its variation with sharply defined nonlinearity in temperature characteristics of the transducers. The circuit is based on breaking up the entire temperature range into intervals in which temperature dependences are sufficiently linear. The noise signal suppressing circuit is provided with differing sensitivity to temperature variations for each temperature interval. This approach made it possible to achieve adequate temperature error compensation in the high-temperature pressure measuring device (HMD) in the 20-400~ temperature range at 0-25 MPa pressures. The proposed circuit of the the HMD (Fig. I) consists of a strain-gauge bridge of tensoresistors RA and RK and resistors RI and R2 and thermobridge of thermoresistor RT and resistors R4, RS, and R6. The group of resistors R31 R3 n with controlled contacts is connected to the supply circuit. Resistor R9 and the set of resistors RI01 -RI0 n with contacts are connected to the thermobridge outlet. The group of resistors R72 - R7 n and R82 - R8, with corresponding contacts is connected in parallel to resistors R5 and R6 of the thermobridge.

Bridge-to-computer data acquisition system with feedback nulling

A system is presented with which a computer can be used to provide electronic feedback nulling of a Wheatstone bridge measurement system used for data acquisition. This system provides compensation for drifts away from null resulting from the measurement setup or amplifier drifts with time or temperature. An example of the system in the case of a strain gauge bridge used with a cantilever beam is described. >

Errors due to axisymmetric non-uniform loading of column load cells

An analysis of the relationship between the sensitivity of a column load cell to end-loading conditions and the aspect ratio of the column is described for the particular case of axisymmetric non-uniform loading. The relationship between the sensitivity of strain gauge bridges to axisymmetric non-uniform loading and their distance from the loaded end was calculated using both finite element analysis and superimposed homogeneous solutions. In order to verify the computed results, a steel cylinder was loaded through each of six pads of various profiles. Strain gauges bonded to the cylinder were used to record the strains at various distances from the end. Although the computer solution did not take into account shear forces present on the load cell ends, reasonable agreement was found between the computed and experimental results. The results confirmed previous experience that the sensitivity to axisymmetric non-uniform loading rises rapidly as the aspect ratio is reduced below 3.5. The results also indicate that a strain gauge bridge at a distance from the end of 1.25 times the radius will have a low sensitivity to axisymmetric non-uniform loading. It is therefore suggested that it may be possible to develop a load cell of aspect ratio 1.25 that has a low sensitivity to axisymmetric non-uniform loading, although further work is required to investigate the effects of shear forces.

ハーモニックドライブを利用したロボットの関節トルク測定

In the present paper we propose a joint torque sensing technique using elasticity of the harmonic drive. The technique is based on the constraction of the strain gauge bridges on the flexspline in harmonic drives, by which the modulation in the sensor output due to the wave generator rotation is eliminated. By utilizing the present technique, the torque exerted on robotic joints is measured very easily without spoiling stiffness of the robots.

Dc amplifier with auto-zeroing of thermal drift

A dc strain-gauge bridge amplifier configuration with automatic compensation of thermal drift using common operational amplifiers is presented. The amplifier operation is divided into two steps: one of auto-zeroing and other of amplification of the input signal. The zeroing of the input signal is achieved by switching the bridge excitation to zero periodically at a frequency of about 100 Hz, thus limiting the maximum frequency of the input signal to about 8 Hz. With a gain of 5000, the output voltage drift of the amplifier is measured to be about 1 mV for a temperature change of 40 °C.

X-ray Diffraction Studies of the Axial Tensile Modulus of Rigid-Rod Polymer Fibers

ABSTRACTWe report the design and use of a device to measure the axial tensile modulus of high modulus fibers by following the change in the meridional X-ray spacings as a function of applied tension. The device, which mounts on a Picker 4-circle automated diffractometer, applies tension to the fiber sample by a cantilever arrangement. Tension is measured by a strain gauge bridge on the cantilever arm. The tension is adjusted and read by the control computer, a VAX 11/730. Measurements made on PBZT and PBO fibers before and after heat treatment are reported. For PBZT fibers (as spun, and heat treated at 525° C and 650° C) with tensile moduli of 186, 283 and 290 GPa, the X-ray determined moduli are 348, 385 and 395 GPa. For PBO fibers (as spun and heat treated at 600° C and 665° C) with tensile moduli of 166, 318 and 290 GPa, the X-ray determined moduli are 387, 477 and 433 GPa. These modulus values are to be compared with theoretical values presented by Wierschke in the previous paper and sonic modulus values discussed by Jiang et al in the following paper.

Force Sensing in Magnitude, Direction, and Position

A sensing device is described which measures the magnitude, direction, and position of force in the plane of the sensor. The basic sensing method is by strain gauge bridges, the outputs of which are amplified and fed via Analogue to Digital (A/D) converters to a microcomputer for calculation of the force characteristics. The transducer system is shown to be capable of measuring quasi static forces; experimental measurements confirming the feasibility of the device. Further research work is planned to improve the accuracy of the system and to ascertain and improve its capability of measuring dynamic forces.

Two-wire bridge-to-frequency converter

An integrated two-wire bridge-to-frequency converter is presented for use as a remote-signal conditioner for sensor bridges such as strain-gauge bridges of platinum-wire temperature-sensing bridges. The converter has a sensitivity on the order of 1 Hz per 1-/spl mu/V/V relative bridge output. A center frequency of 10 kHz allows the application of an untrimmed bridge with an imbalance up to /spl plusmn/10000 /spl mu/V/V. The instability is less than 10/SUP -4/ per Kelvin and per 1-V supply-voltage variation. The untrimmed transfer inaccuracy is lower than 1%. The linearity error is lower than 0.01%. Different bridge readout functions can be chosen by different circuit configurations. The converter can be connected to a single supply voltage. The frequency output is modulated on the supply current. The supply voltage is 12-24 V.

Miniature pressure sensors and their temperature compensation

A signal-conditioning IC was designed for a family of miniature pressure sensors. It converts the small output signal of the strain gauge bridges to a single-ended and amplified signal. In addition, it provides the possibility of laser trimming to align each individual specimen in the course of production. Furthermore, all linear temperature drifts over a wide range of temperatures are compensated by the temperature-dependent thin films.

Output signal simulators of strain gauge bridges

Output signal simulators of strain gauge bridges

Measurement of vibrations by strain gauges, part I: Theoretical basis

A principle is formulated in which relationships between inertial and elastic properties of structures are utilized for the detection of structural vibrations by means of surface strain measurements. The strain gauge bridges are described, and the bridge sensitivity factors evaluated for measurements of in-plane and flexural vibrations on (arbitrary) plates and beams. Simplified measurement procedures are developed for measurement in far field vibration regions.

A stimulator for moving textured surfaces sinusoidally across the skin

The stimulator allows textured surfaces to be moved sinusoidally across the skin of the fingerpad. Sinusoidal motion is produced by a “scotch yolk” driven by a DC motor. The amplitude of movement is adjustable up to a maximum of 80 mm peak to peak and the frequency is continuously adjustable from 0.1 Hz to 2.0 Hz. Movement of the surface is monitored by an optical transducer and contact force between the finger and the surface is monitored by a strain gauge bridge. The stimulator is simple and robust and is suitable for both neurophysiological and psychophysical experiments in animals and humans.

Draft Measurements with a Three-Point Hitch Dynamometer

ABSTRACT Athree-point dynamometer* suitable for use with either Catagory I or II tractors, was designed and constructed. Signals from a strain gage bridge were conditioned and were originally recorded on a simple strip chart recorder. At the present time, data are stored in a micro-computer located in the tractor cab. Data are then transferred to a cassette tape in the field for later analysis. The dynamometer has been used in replicated tests and field trials for several years, while the micro-computer data collection system has been used for two years as part of the instrumentation used in a study of tillage energy.

A two-dimensional force transducer

A two-dimensional force transducer is described which is capable of measuring the magnitude, direction and position of a force acting in the plane of the transducer. The basic sensing method is by strain gauge bridges, the outputs of which are amplified and fed to a microcomputer for calculation of the force characteristics. A working model has confirmed by feasibility of the transducer. The latter has been designed to measure quasi-static forces and it has been shown experimentally to do this relatively well. Further research work is required to improved the accuracy of the device and its capability of measuring dynamic forces.

Friction tester for the lubrication properties of ophthalmic solutions

A novel and useful device is described to measure the coefficient of sliding friction and the scuff load of ophthalmic solutions for polymeric surfaces. Instead of the conventional electric continuity method, a strain gauge bridge is employed to measure the stability. Vertical forces in the range of 1–10 g are applied to a spherical stylus which runs in a track of lubricating solution applied to a rotating plate of the same or different material as the stylus. The plate rotates at constant speed with respect to the stylus. The horizontal force resulting from friction has been of the order of 0.01–0.10 g. The device is capable of resolving small differences in the lubricating quality of ophthalmic solutions having a low coefficient of friction. The usefulness of the device has been demonstrated by measuring the lower coefficients of friction of an ophthalmic solution in the above-mentioned range of small vertical forces. Reproducible data have been obtained for the ophthalmic test solution.

Use of Mixer-Torque Measurements as an Aid to Optimizing Wet Granulation Process

AbstractInstrumentation designed for monitoring the wet granulation process is described. A Hobart mixer was instrumented with a slip ring torque sensor using a voltage of 5 volts D.C. to excite a strain gauge bridge. An amplifier was used to magnify the low signal levels produced by the strain gauge bridge and the gain was set at 179.6 so that 2 volts equals 200 inch ounce. The output was recorded using a Bascom-Turner recorder. The relative dynamic torque, was measured in millivolts as a function of granulating fluid added and time to optimize the granulation process using the planetary mixer. The instrumentation described in this paper has considerable potential for optimization and validation studies for wet granulation procedures.