Wheatstone Bridge Arrangement Research Articles

An updated technique to obtain explosive kinetics data on microsecond timescales.

There are few techniques available for chemists to obtain time-to-explosion data with known temperature inputs at the early stages of the design and synthesis of new explosives. In the 1960s, a technique was developed to rapidly heat milligram-quantities of confined explosives to ∼1000K on microsecond timescales. Wenograd [Trans. Faraday Soc. 57, 1612 (1961)] loaded explosives inside stainless steel hypodermic needles, connected them to a fireset and rapidly discharged a capacitor through the steel. He obtained the temperature by measuring the needle resistance in a Wheatstone bridge arrangement and the time to explosion from a needle rupture. However, owing to the narrow-gauge needles used in the original research, the experiment was only possible with melt-castable explosives; it was never replicated, and modern diagnostics are now available with advances beyond the 1960s. Here, we report the development of the High Explosives Initiation Time (HEIT) test, which utilizes a 250J pulsed power system to heat the needles. This work extends the Wenograd approach by using optical diagnostics, computational modeling, and advanced techniques to measure needle resistance and needle rupture. Preliminary rate information for pentaerythritol tetranitrate (PETN) will be presented.

Design, fabrication and experimental analysis of piezoresistive bidirectional acoustic sensor

PurposeIdentification of the direction of the sound source is very important for human–machine interfacing in the applications such as target detection on military applications and wildlife conservation. Considering its vast applications, this study aims to design, simulate, fabricate and test a bidirectional acoustic sensor having two cantilever structures coated with piezoresistive material for sensing has been designed, simulated, fabricated and tested.Design/methodology/approachThe structure is a piezoresistive acoustic pressure sensor, which consists of two Kapton diaphragms with four piezoresistors arranged in Wheatstone bridge arrangement. The applied acoustic pressure causes diaphragm deflection and stress in diaphragm hinge, which is sensed by the piezoresistors positioned on the diaphragm. The piezoresistive material such as carbon or graphene is deposited at maximum stress area. Furthermore, the Wheatstone bridge arrangement has been formed to sense the change in resistance resulting into imbalanced bridge and two cantilever structures add directional properties to the acoustic sensor. The structure is designed, fabricated and tested and the dimensions of the structure are chosen to enable ease of fabrication without clean room facilities. This structure is tested with static and dynamic calibration for variation in resistance leading to bridge output voltage variation and directional properties.FindingsThis paper provides the experimental results that indicate sensor output variation in terms of a Wheatstone bridge output voltage from 0.45 V to 1.618 V for a variation in pressure from 0.59 mbar to 100 mbar. The device is also tested for directionality using vibration source and was found to respond as per the design.Research limitations/implicationsThe fabricated devices could not be tested for practical acoustic sources due to lack of facilities. They have been tested for a vibration source in place of acoustic source.Practical implicationsThe piezoresistive bidirectional sensor can be used for detection of direction of the sound source.Social implicationsIn defense applications, it is important to detect the direction of the acoustic signal. This sensor is suited for such applications.Originality/valueThe present paper discusses a novel yet simple design of a cantilever beam-based bidirectional acoustic pressure sensor. This sensor fabrication does not require sophisticated cleanroom for fabrication and characterization facility for testing. The fabricated device has good repeatability and is able to detect the direction of the acoustic source in external environment.

Design, construction and performance analysis of dynamic torque transducer

Most of the dynamic torque measurement devices present are not easy to afford and accurate for higher shaft speed, at the same time, especially in the case of Micro-hydropower stations where dynamic torque fluctuates and requires constant monitoring. To fulfill the lack of standard devices, this project concentrated on fabricating non-contact torque transducer devices using easily accessible materials. The project primarily focuses on developing electronics and mechanical systems required to measure dynamic torque. The hollow Aluminum shaft is taken as a torque transducer specimen with a coupling facility. A strain gauge is attached with the specimen shaft in the Wheatstone bridge arrangement such that the strain gauge produces an electrical signal while the shaft experiences strain. Arduino NANO as an I/O device, HX711 ADC module as a signal amplifier, HC05 as a Bluetooth module for wirelessly measured data communication. For calibration, torque is applied to the specimen by coupling it with motor-generator dynamic torque measurement apparatus (DL 10055ETM) which is manufactured by DE LORENZO. Linear regression is used to predict the value of applied torque. The experimental data obtained using the proposed torque transducer prototype has made it clear that it is possible to measure and analyze real-time digital data of dynamic torque produced on specimen shaft rotating at high speed, wirelessly, using locally available resources.

Balanced Drive and Sense CMOS Thermal Piezoresistive Resonators and Oscillators

In this work, we report a novel fully balanced drive and sense thermal-piezoresistive resonator (TPR) in 2P-4M 0.35μm CMOS technology with maskless post-release process. Through the use of the Wheatstone bridge arrangement for both the thermal drive heater resistors and sense piezoresistors, the proposed design greatly simplifies the overall system by removing the need for bias-tee or noisy and power consuming current sink/source. This ensures that the differential terminals of drive and sense ports are at the same DC potential, thus allowing the use of standard differential amplifiers as interface circuits. In addition, this design utilizes bimorph like actuation which enables in-plane motion. An in-plane clamped-clamped beam (CCB) TPR was fabricated, demonstrating a quality factor (Q) of 1,600 at 2 MHz with transconductance (gm) of 46.8 μS for a dc-power of 1.7 mW in a vacuum (1 mTorr). To go one step further, a double-ended tuning fork (DETF) TPR was designed, featuring a transconductance of 62.7 μS with Q of 4,400 at 1.9 MHz under the same conditions as CCB. The CCB thermal-piezoresistive oscillator (TPO) implemented using a discrete interface circuit had phase noise of -89 dBc/Hz and -100 dBc/Hz at 1 kHz and 1 MHz respectively while that for DETF TPO was -100 dBc/Hz at 1 kHz and -100 dBc/Hz at 1 MHz in air. Frequency stability was found to be 180 ppb and 125 ppb for CCB and DETF TPOs respectively in air.

Performance analysis of embossed diaphragm based MEMS piezo resistive pressure sensor for flood level measurement

This paper focuses on the performance of an embossed or simply bossed diaphragm to measure the flood level in the range of 1cm to 100cm which is proportional to a pressure in the range of 98Pa to 9.8kPa approximately 10kPa. This diaphragm is a special type of design which is used to construct very thin diaphragms to sense low pressure ranges. The diaphragms are designed using Intellisuite MEMS CAD tool. The performance of embossed diaphragm with respect to different shapes such as square, rectangle and circle is investigated. The square dimension of 500μm×500μm with emboss dimension 300 μm×300μm with thickness of 3μm is satisfying the small scale deflection.The diaphragm yields maximum displacement of 0.95µm. The diaphragm is analysed for maximum stress regions. The longitudinal stressSxx54.63 MPa, the transverse stress Syysis 54.63MPa and the bending stress Szz is 19.19 MPa. The electrical output is estimated by placing four piezo resistors in the maximum stress region using wheatstone bridge arrangement is 7.964 mV

Design and Development of a Pressure Transducer for High Hydrostatic Pressure Measurements up to 200 MPa

A number of pressure transducers, based on strain gauge, capacitance/inductance type, frequency resonators, are commercially available and are being used for sensing and producing an electrical output proportional to applied pressure. These sensors have their own advantages and limitations due to operational ease, measurement uncertainty and the costs. Strain gauge type transducers are now well established devices for accurate and precise measurement of pressure within measurement uncertainty up to 0.1 % of full scale. In the present research work, an indigenous strain gauge pressure transducer has been designed, developed, tested and calibrated for pressure measurement up to 200 MPa. The measurement uncertainty estimated using the pressure transducer was found better than 0.1 % of full scale. This transducer was developed using four foil type strain gauges, bonded, two in axial direction while other two in radial direction, to the controlled stress zones of a tubular maraging steel active cylinder working also as diaphragm. The strain gages were then connected to a Wheatstone bridge arrangement to measure stress generated strains. The pressure was applied through matching connector designed in the same tubular transducer active element. The threaded unique design in a single piece through collar, ferule and tubing arrangement provides leak proof pressure connections with external devices without using additional seals. The calibration and performance checking of the pressure transducer was carried out using dead weight type national pressure standard using the internationally accepted calibration procedure.

Knitted strain sensors: impact of design parameters on sensing properties.

This paper presents a study of the sensing properties exhibited by textile-based knitted strain sensors. Knitted sensors were manufactured using flat-bed knitting technology, and electro-mechanical tests were subsequently performed on the specimens using a tensile testing machine to apply strain whilst the sensor was incorporated into a Wheatstone bridge arrangement to allow electrical monitoring. The sensing fabrics were manufactured from silver-plated nylon and elastomeric yarns. The component yarns offered similar diameters, bending characteristics and surface friction, but their production parameters differed in respect of the required yarn input tension, the number of conductive courses in the sensing structure and the elastomeric yarn extension characteristics. Experimental results showed that these manufacturing controls significantly affected the sensing properties of the knitted structures such that the gauge factor values, the working range and the linearity of the sensors varied according to the knitted structure. These results confirm that production parameters play a fundamental role in determining the physical behavior and the sensing properties of knitted sensors. It is thus possible to manipulate the sensing properties of knitted sensors and the sensor response may be engineered by varying the production parameters applied to specific designs.

Explosion-proof monitoring of hydrocarbons by mechanically stabilised, integrable calorimetric microsensors

Safe detection of combustible gases is demonstrated by a new type of integrated micropellistor and heat conductivity sensor. The basic element in both types of calorimetric devices is a thermally isolated microhotplate with a Pt heater, embedded in non-stoichiometric silicon-nitride. The pellistors are formed from a pair of an active and a passive resistor element in a Wheatstone-bridge arrangement, and heated up to 200–600°C in the environment to be monitored with a power dissipation of 20–60mW. A novel, proprietary one-side porous silicon micromachining process was developed for the formation of the air gap around the devices, offering a thin single crystalline Si support for the membrane.1Patent pending.1 Owing to the better mechanical stability obtained, the relatively large mass of porous substance, containing the finely dispersed catalysts of Pt, Pd or Rh on one hand, and for forming the chemically inert reference device on the other hand, can be deposited on top of the microheaters without jeopardising the heater integrity. The sensors, utilising the heat conductivity principle, are composed of a pair of chemically passive elements, having different heat exchange properties due their dissimilar surface. Explosion-proof detection of hydrocarbons was demonstrated by measuring concentration levels between the lower and upper explosion limits (LEL, UEL) with no protective encapsulation, whatsoever.

A new approach to the third order calibration of internal strain gauge balances used for aerodynamic load measurement

Abstract With respect to wind tunnel aerodynamic load measurement, an internal strain gauge balance (often referred to as a sting balance) is essentially a compact load cell designed to fit within a cavity of the aerodynamic body and form a link between the model and a fixed ground point via a sting support system. The structure of an internal strain gauge balance is designed to incorporate a series of planar surfaces such that the deflection of each surface is predominantly induced by a unique aerodynamic load. Strain gauges, mounted on groups of surfaces in a Wheatstone bridge arrangement produce output signals proportional to the applied aerodynamic loads. A strain gauge balance is calibrated by applying known loads, measuring the bridge outputs and then formulating an equation which relates the two variables together. Although calibration techniques are well established, reservations have been recently expressed concerning the ability of the associated calibration equation to satisfactorily model the response of the balance when subjected to a six component aerodynamic loading. This generally accepted calibration equation (referred to here as the traditional equation) results in a quadratic approximation to the behaviour of the output signals with applied loads, whereas a more appropriate variation would be cubic. Other limitations of the traditional calibration equation are that the behaviour of the balance to two simultaneously applied loads is based upon limited combinations of the two applied loads, and that the acquisition of the required loads from the strain gauge signals is frequently based upon an approximate matrix inversion method. The proposed calibration equation, described within this paper, models the behaviour of the sting balance to the third order, takes account of all possible combinations of two simultaneously applied loads, and avoids the use of an approximate matrix inversion when deriving the desired aerodynamic loading from the signal outputs. It is also shown that the proposed method may be used to determine the interaction of all possible combinations of up to three simultaneously applied loads.

Atomic force microscopy probe with piezoresistive read-out and a highly symmetrical Wheatstone bridge arrangement

We have developed a new generic platform for the fabrication of multipurpose microprobes with integrated piezoresistive read-out, built-in background filter and silicon tip. The probe fabrication is based on SOI wafers with buried boron etch-stop layers, which allow us to realize probes with fully encapsulated resistors and integrated silicon tips. The dimensions of the resistors are well defined and leak-current is eliminated. Probes with a force constant in the range of 0.8–4 N/m and with resonant frequencies in the range of 40–80 kHz have been fabricated. The probes typically display a deflection sensitivity of (Δ R/ R)z −1=2.4×10 −7 Å −1, and a force sensitivity (Δ R/ R) F −1=2.7×10 −6 nN −1. The change in resistance of the piezoresistors is detected by a highly symmetrical on-chip Wheatstone bridge arrangement. The measured noise level in the Wheatstone bridge is in good agreement with the calculated noise limit and a minimum detectable cantilever deflection of 0.3 Å has been predicted for a measurement bandwidth of 10 Hz. The symmetrical bridge configuration has been compared with a nonsymmetrical setup, and it is concluded that the symmetrical Wheatstone bridge significantly decreases nonlinearities in the output response. Finally, the probe has successfully been used for atomic force microscopy (AFM) imaging.

Grain-boundary room-temperature low-field magnetoresistance in Sr2FeMoO6 films

Thin films of (001)-oriented Sr2FeMoO6 have been epitaxially deposited or LaAlO3 and SrTiO3 (001) substrates by pulsed laser deposition. The deposition conditions were optimized. Single-phase Sr2FeMoO6 was obtained in 100 mTorr 99.999% Ar gas at 825 °C. Transport and magnetic data showed a metallic temperature dependence and a saturation magnetization Ms at 10 K of 3.2μB/f.u. However, the Curie temperature TC≈380 K was reduced from 415 K found for tetragonal polycrystalline best ceramics, which lowers Ms at 300 K in the thin films to 1.5μB/f.u. compared to 2.2μB/f.u. in the ceramics. A low remanence was attributed to the presence of antiphase boundaries. A Wheatstone bridge arrangement straddling a bicrystal boundary was used to verify that spin-dependent electron transfer through a grain boundary and not an antiphase boundary is responsible for the low-field magnetoresistance found in polycrystalline samples below TC.

Intra- versus intergranular low-field magnetoresistance of Sr2FeMoO6 thin films

Thin films of (001)-oriented Sr2FeMoO6 have been epitaxially deposited on LaAlO3 and SrTiO3 (001) substrates. Comparison of their transport and magnetic properties with those of polycrystalline ceramic samples shows a metallic versus semiconductor temperature dependence and a saturation magnetization Ms at 10 K of 3.2 μB/f.u. in the film as against 3.0 for a tetragonal polycrystalline sample. However, the Curie temperature TC≈389 K is reduced from 415 K found for the tetragonal ceramic, which lowers Ms at 300 K in the thin films to 2.0 μB/f.u. compared to 2.2 μB/f.u. in the ceramics. A Wheatstone bridge arrangement straddling a bicrystal boundary has been used to verify that spin-dependent electron transfer through a grain boundary is responsible for the low-field magnetoresistance found in polycrystalline samples below TC.

Piezoresistive silicon V-AFM cantilevers for high-speed imaging

A low stiffness silicon V-AFM cantilever with integrated piezoresistive sensors on its root is applied to an atomic force microscope (AFM) for high-speed piezoresistive imaging. The images are presented from a sample with 1.0 μm high microfeatures in constant-height (variable force) mode with a tip scan rate of 1000 μm/s. The experiment is performed in a DC Wheatstone bridge arrangement with a 3.0 V battery supply. Electrical hum pickup, 1/f noise, and magnetic effect affecting the image will be discussed.

Fabrication of improved piezoresistive silicon cantilever probes for the atomic force microscope

This paper describes an improved design for a monolithic silicon atomic force microscope (AFM) probe using piezoresistive sensing. The probe is V shaped, with a sharp tip at the free end and two piezoresistors at the root, and is fabricated using silicon-on-insulator (SOI) starting material. The maximum sensitivity of the AFM probe is measured to be 4.0(± 0.1) × 10 −7 Å −1, which is larger than that of the previous parallel-arm piezoresistive AFM probe. The measured results are in reasonable agreement with the values predicted by theory. The minimum detectable force and minimum detectable deflection of the AFM probes are predicted to be 1.0 × 10 −10 N and 0.29 Å r.m.s., respectively, using a Wheatstone bridge arrangement biased at a voltage of ± 5 V and bandwidth of 10 Hz–1 kHz.

A new technique for the automatic measurement of high value resistors

The development of an automatic adapted Wheatstone bridge arrangement for the measurement of high value resistance standards between 109 and 1014 Omega at voltages up to 1 kV is described. This uses stable voltage reference supplies in place of the resistors in the reference arms of the bridge. The system has been implemented at the National Physical Laboratory to replace the previous manual system without impairing the uncertainty of the measurements.

Pressure Jump Apparatus for the Study of Fast Reactions

ABSTRACT Fabrication of a new pressure jump cell made entirely from Plexiglas is described. Chemical relaxation effects greater than 50 μsec can be measured when the pressure on a chemical system is suddenly released from 40 atm by means of a bursting phosphor-bronze diaphragm and the resulting conductance change is measured by a Wheatstone bridge arrangement.

Evaporated film strain gauges for high-temperature applications

A thin film strain gauge employing evaporated chromium or platinum resistance patterns sandwiched between silicon monoxide layers, and based on a ceramic coated molybdenum substrate, has been developed which possesses good stability at temperatures of up to 600°C in an atmosphere of carbon dioxide; to provide temperature compensation, the resistance pattern is deposited in the form of a Wheatstone bridge arrangement. This type of element would appear to have characteristics superior to those of the commercial nichrome foil gauges under these conditions, and to be suitable for both alternating and static strain measurements. Gauges with silicon monoxide protected chromium resistive films deposited on sapphire, have been shown to be stable up to temperatures in excess of 800°C, although the use of this substrate at elevated temperatures requires that the test piece to which the gauge is attached is closely matched in expansion coefficient.

Impedance Changes Induced in the Brain by Electric Stimulation

The extensive application of electric stimulation of the brain, not only experimentally but also for therapeutic purposes as in the so-called electric shock treatment of certain psychoses, makes it desirable to get a more intimate knowledge of the effects of electric stimuli and the subsequent excitation upon the state of the cells of the central nervous system. It is known that excitation of peripheral nerves is associated with decrease in D.C. resistance (Hermann, Ebbecke) and A.C. impedance (Lullies, Cole and Curtis) respectively. Since such changes may be able to throw some light upon the state of the cellular surface films (Gildemeister), it seemed of interest to ascertain whether similar effects are demonstrable in the central nervous system. For the measurement of the impedance a Wheatstone bridge arrangement energized with A.C. of from 500 to 6000 cycles was used as previously described. (Spiegel and Spiegel-Adolf). Quick determinations of the balance were facilitated by a 5-stage amplifier connected not only to a telephone receiver but also to an “electric eye” so that the minimum could be detected by visual as well as by acoustic observations. In the first series of experiments on cats under superficial ether anesthesia the electrodes were platinum wires coated with platinum black, inserted into the brain substance as in previous experiments (Spiegel and Spiegel-Adolf) ti or platinum-Ringer electrodes placed with the smallest possible pressure on the surface of the brain. The stimulating electrodes were placed on the motor cortex and the testing electrodes (connected to the Wheatstone bridge) on the parieto-occipital region of the same or of the opposite hemisphere.

ELECTRICAL ACTIVITY OF THE EXPOSED HUMAN BRAIN

The application of electrical methods to the study of cerebral function is still in an experimental stage. In 1923 Grant,1using a simple Wheatstone bridge arrangement, reported marked diminution in the electrical resistance of tumor tissue as compared with that of normal brain. Berger2amplified electric potentials set up in the brain and ascribed changes in potential to nervous activity. Foerster and Altenburger3succeeded in recording characteristic changes in potential in several cases of tumor of the brain. Subsequently, electroencephalographic methods have resulted in the accumulation of a considerable amount of data, especially with respect to the epileptic syndromes.4Recently, important contributions to the possibility of localization of tumors by electroencephalography5have been made. However, in only a few instances (notably, those of Foerster and Altenburger,3in Germany, and Walter, in England) have direct records from the cortex been demonstrated. We believed that studies

Studies in contact potentials the evaporation of sodium films

In this paper the contact potential method of Bosworth and Rideal has been applied to the study of films of sodium on tungsten at elevated temperatures. Since the filament on which the sodium film under observation was deposited was heated most conveniently by the passage of an electric current, it was important to ensure that no error was introduced in the measurement of the contact potential due to the potential drop along the filament caused by the heating current. This difficulty has been overcome by two methods, first by employing a rotary split commutator permitting alternate measurements of the contact potential and passage of the heating current, a device suitable for relatively slow changes in film properties, but unsuitable for rapid changes necessitating the employment of a string galvanometer. In the second method the system was so arranged that the electron-collecting portion of the filament was effectively at its geometrical centre, and the geometry of the filament system was unaffected by changes in the filament temperatures. Under these conditions a Wheatstone's Bridge arrangement enabled the potential difference down the filament to be eliminated and the correct position of the collecting area ensured by noting the position of no change in the recorded contact potential on reversal of the heating current through the filament. We may note that in reversible changes the surface potential changes on heating but returns immediately on cooling to its original value; such changes are assumed therefore to be unaccompanied by any change in the surface concentration ( θ ) and are intrinsic thermal properties of the film at a constant θ . The surface potential of the tungsten filament itself changes with varying temperature, and any irregularities due to maladjustment of the apparatus can be detected in this way.