Linear Voltage Differential Transformer Research Articles

Design and Validation of a Variable Reluctance Differential Solenoid Transducer

This paper presents a novel variable reluctance differential solenoid transducer (VRDST) that offers improved high-speed sensing performance over linear voltage differential transformers (LVDTs) and differential variable reluctance transformers (DVRTs). The VRDST has the unique ability to measure both position and velocity simultaneously using two independent measurements. This paper investigates a basic geometry for a VRDST. The position and velocity measurement methods are derived and implemented in a Simulink simulation. The simulated VRDST model is augmented with an FEA simulation to predict the magnetic characteristics of the investigated design. The results and predictions established by the simulation and analytical models are validated experimentally with a physical prototype. The similarity between the experimental and simulated results suggest the proposed FEA and Simulink simulations can be used to accurately predict the performance of a physical VRDST. The findings from the analytical modeling, simulation study and experimental validation all unanimously prove the position measurement performs well when measuring low-speed displacements, while the integrated-velocity measurement is useful for measuring high-speed displacements. The differing frequency ranges of these two independent measurements are found to complement each other and suggest the VRDST is superior compared to DVRTs or LVDTs for applications requiring wide bandwidth position measurements.

Measurement station for interim inspections of Lightbridge metallic fuel rods at the Halden Boiling Water Reactor

Lightbridge Corporation has developed a new Uranium-Zirconium based metallic fuel. The fuel rods aremanufactured via a co-extrusion process, and are characterized by their multi-lobed (cruciform-shaped) cross section. The fuel rods are also helically-twisted in the axial direction. Two experimental fuel assemblies, each containing four Lightbridge fuel rods, are scheduled to be irradiated in the Halden Boiling Water Reactor (HBWR) starting in 2018. In addition to on-line monitoring of fuel rod elongation and critical assembly conditions (e.g. power, flow rates, coolant temperatures, etc.) during the irradiation, several key parameters of the fuel will be measured out-of-core during interim inspections. An inspection measurement station for use in the irradiated fuel handling compartment at the HBWR has therefore been developed for this purpose. The multi-lobed cladding cross section combined with the spiral shape of the Lightbridge metallic fuel rods requires a high-precision guiding system to ensure good position repeatability combined with low-friction guiding. The measurement station is equipped with a combination of instruments and equipment supplied from third-party vendors and instruments and equipment developed at Institute for Energy Technology (IFE). Two sets of floating linear voltage differential transformer (LVDT) pairs are used to measure swelling and diameter changes between the lobes and the valleys over the length of the fuel rods. Eddy current probes are used to measure the thickness of oxide layers in the valleys and on the lobe tips and also to detect possible surface cracks/pores. The measurement station also accommodates gamma scans. Additionally, an eddy-current probe has been developed at IFE specifically to detect potential gaps or discontinuities in the bonding layer between the metallic fuel and the Zirconium alloy cladding. Potential gaps in the bonding layer will be hidden behind a 0.5-1.0 mm thick cladding wall. It has therefore been necessary to perform a careful design study of the probe geometry. For this, finite element analysis (FEA) has been performed in combination with practical validation tests on representative fuel dummies with machined flaws to find the probe geometry that best detects a hidden flaw. Tests performed thus far show that gaps down to 25 μm thickness can be detected with good repeatability and good discrimination from lift-off signals.

In-core corrosion monitoring in the Halden test reactor

AbstractThe experimental research programme at the Halden Reactor Project includes a wide range of materials testing, both of in-core structural materials and fuel claddings. An important aspect of the tests is the use of online instrumentation situated within the reactor core. The Halden test reactor is cooled and moderated by heavy water, with a normal operating temperature of 230°C. Representative light water reactor conditions are obtained using dedicated water loops, which include comprehensive online water chemistry analysis systems, including dissolved oxygen/hydrogen concentrations and coolant conductivity. Details are given of the techniques currently used to provide online, in-core corrosion monitoring data, and illustrative results are presented. The techniques include crack growth rate determination by means of direct current potential drop measurements, determination of crack initiation and stress relaxation/creep by means of linear voltage differential transformers, and measurements of elect...

Integrated Monitoring System for Carbon Composite Strands in Cable-Stayed Bridge, Penobscot Narrows, Maine

An integrated monitoring system for carbon fiber composite cable (CFCC) strands recently implemented in the Penobscot Narrows Bridge in Maine is presented. This cable-stayed bridge features a cradle-stay system in the pylons that provides a continuous cable stay between the main span bridge deck anchorage and the back span bridge deck anchorage. The cradle-stay system allowed for replacing epoxy-coated steel strands with CFCC strands. The monitoring system installed in the bridge is composed of a set of sensors and devices that provide complementary structural information: (a) load cells supported on steel anchorage chairs, (b) linear voltage differential transformers (LVDTs) mounted on the steel anchorage chairs, (c) fiber-optic strain (FOS) sensors embedded in composite sleeves, and (d) temperature sensors. The monitoring system was designed to detect variations over time in individual carbon fiber strand force and strains at the anchorage locations and to correlate the measurements with ambient temperature. Laboratory tests were conducted to proof-load the steel anchorage chairs and to calibrate the LVDTs and embedded FOS strain measurement systems. The baseline response of the CFCC strands that was based on load cell, FOS sensors, and LVDTs measurements after the strand stressing operation is presented. The CFCC strands experienced changes in tensile force between +3% and −5% over the first 4 months in service, which were consistent with ambient temperature fluctuations. The FOS measured strand strains and the LVDT deflections of the anchored chair exhibited trends consistent with the variations in CFCC strand force.

Arabidopsis thaliana floral stem elongation: Evidence for an endogenous circadian rhythm

The floral stem elongation of Arabidopsis thaliana, Landsberg erecta ecotype, was studied with a plant growth-measuring apparatus using linear voltage differential transformers as sensors. Elongation rate displayed a clear rhythm which could be synchronized by a L:D (12:12) or L:D (7:7) photoperiod. The rhythm persisted afterwards in continuous constant conditions (CL). When pre-synchronization was L:D (12:12), the period in CL was 23.5 h. After L:D (7:7) synchronization (equal light/dark photoperiod which was not in phase with the 24 h daily period) a period of 21.4 h was measured in CL. Moreover, this later treatment triggered a significant increase in the first internode length. Thus, these results showed clearly that the floral stem growth was under the control of an endogenous circadian rhythm.

The role of creep damage in glass bead filled high density polyethylene

The effect of filled-in rigid particles on the strength, modulus and toughness of polymers has been investigated previously, as has creep damage in short fibre reinforced polyprolylene [1-5]. Rigid filler produces a large turbulence of stress field in matrix, and induces microdamage. It therefore significantly affects the mechanical properties of filled materials. In this letter, the influences of bead fraction and interfacial adhesion on creep behaviour are reported. The testing results show that creep damage plays an important role in the high stress level tests. Commercial high density polyethylene (HDPE), J3, supplied by Beijing Second Chemical Factory was used as the matrix material. The neat HDPE has a melting flow index (MFI) of 1.5 g 10 min -1 for series A and 1.9 g 10 rain -1 for series B. The diameter of the glass beads was 30-40 pro. In the manufacturing process, the glass beads and coupling agents were mixed in the chamber of a high speed mixer, then HDPE powder and treated glass beads were blended in a twin-screw extruder, and the pelleted extmdate was injection moulded into tensile bars. Annealing was carried out to relieve the residual stress in the specimens. The materials of series A are the filled HDPE with different volume fractions of glass beads (Table I). For material series B, glass beads were treated by three kinds of coupling agent to make filled HDPE with different interfacial adhesion. Details of these materials are shown in Table II. It has been indicated previously that excellent interfacial adhesion was obtained in Js [1]. J6 has weak bonding and J4 is intermediate in its bond strength. The geometry of the creep specimens refers to ASTM 638 type A. The dimensions of the gauge length area were 50 m m × 10 mm × 3 mm. Creep tests were carried out on a specially designed creep test machine. Linear voltage differential transformer (LVDT) was used to measure the extension of

Fiber‐Optic Bragg Grating Sensor for Nondestructive Evaluation of Composite Beams

Extensive testing of control specimens and large‐scale models of high‐strength concrete composite beams, 3,048‐mm (10‐ft) length, reinforced with pre‐stressed prisms, have resulted in deformation readings that are consistent with those obtained from classical measuring methods such as electric strain gauges and linear voltage differential transformers. The present paper provides the research findings of fiber‐optic Bragg gratings as strain/stress sensors for monitoring the critical sections of a series of this type of composite beams. The optical fibers used in this study had a numerical aperture of approximately 0.22 and a V‐value (reduced frequency) of 2.2 at 1,300‐nm operating wavelength. The theoretical strain coefficient of the optical fiber had a typical value of 0.762, which agreed quite well with the calibration test performed. A successful packaging of the fiber‐optic Bragg grating was used and modeled. Good bonding of sensor to the structure was shown to be imperative for maximum transfer of loa...

A New Method of Measurement and Analysis of the Stem Extension Growth Rate to Demonstrate Complete Synchronisation of Chenopodium rubrum Plants by Environmental Conditions

Summary Linear voltage differential transformers (LVDTs) are among the most appropriate devices for measuring plant organ growth. They are characterized by high resolution, low cost, and easy handling. As a novum we have developed a computerized LVDT based measuring system that permits numerical and graphical analysis of stem elongation while the corresponding measurement process itself (i.e. data acquisition) concurrently takes place in the background. Using these methods an adequate interpretation of the growth behavior of the plants under investigation is already possible during the course of the experiment. This is usually referred to as on-line analysis. Since data sets of up to six different experiments can be handled in the main memory of the computer at the same time, even the comparison of the running experiment with earlier ones is feasible. Ten individual plants as well as environmental variables like light fluence rate and temperature can be measured simultaneously. The precision of the growth measurement amounts to ± 0.002 mm. Longterm measurement is possible by a software controlled self adjusting circuit that constantly maintains the LVDTs within their measuring range. Moreover, our software provides an easy-to-use menu oriented user interface to facilitate handling the system. The presented measuring system visualizes the ongoing plant growth process, thereby allowing one to apply chemical or physical treatments to the individual plants of a perfectly synchronized experimental population at specific, well-defined developmental stages. In this article we give detailed information about the set-up of the measuring system, the employed soft- and hardware and the checks needed to ensure their proper functioning, and demonstrate the perfect synchronization of the stem extension rate of a population of plants.

In vitro effects of external fixation on intact and osteotomized tibiae. A biomechanical study.

In order to study the in vitro mechanical effects of external fixation on intact and osteotomized bone, human and rabbit tibiae were tested in three-point bending in an Instron testing machine. Intact tibiae were loaded in the elastic range before and after application of an external fixation device. In the human specimens the Vidal-Adrey double frame was used, and in the rabbit specimens the external mini-fixation. The bone deformation in the anteroposterior direction was measured with a linear voltage differential transformer. After application of external fixation a median bone elastic stiffness of 110.2 per cent in human tibiae and of 106.1 per cent in rabbit tibiae was found, in relation to the stiffness of intact tibiae without external fixation. The stiffness increase was significant in human specimens, but not significant in rabbit specimens. In osteotomized human tibiae fixed with the Vidal-Adrey double frame a median stiffness of 8.5 per cent of the stiffness of intact bones was found when compression was not applied, compared to 19.9 per cent when compression was applied. In rabbit tibiae a median stiffness of osteotomized bones with external mini-fixation was 8.9 per cent of the stiffness of intact bones. There was a good agreement between the results in rabbit tibiae with the mini-fixation and human tibiae with external fixation without compression. The external mini-fixation thus seems to be a suitable model for the study of bone healing in rabbit tibiae.

Mechanical effects of metal plate fixation. In vitro investigation on intact and osteotomized human and rabbit tibiae.

In order to study the in vitro stress-protecting effect on intact bone, and the rigidity of plate fixation on osteotomized bone, human and rabbit tibiae were tested in three-point bending in an Instron testing machine. Intact tibiae were loaded in the elastic range before and after metal plate application. The deformation was measured with a linear voltage differential transformer. In the human specimens a median stiffness increase of 31 per cent was obtained in the plated bone segment after application of a tibial plate (140 x 12 x 4 mm) and of 43.8 per cent after application of a femoral plate (140 x 16 x 5 mm). In the rabbit specimens a median stiffness increase of 31.9 per cent was obtained after application of a thin plate (45 x 5 x 1 mm). In osteotomized human tibiae with tibial plate fixation, a median elastic stiffness of 51.4 per cent of the intact bone was found, compared to 40.4 per cent in osteotomized rabbit tibiae plated with the thin plate. There was good agreement between the results in human tibiae plated with a tibial plate, and rabbit tibiae with the small plate. In previous studies of the stress-protecting effect of internal plate fixation on rabbit tibiae more rigid plates have been used. These plates seem to have been overdimensioned. In further studies in rabbits plates of similar size as the one tested in this study should be applied.

Effect of the mode of action of an oscillating soil-working tool on draft and power requirements. A theoretical analysis and an experimental verification

Mathematical models for predicting the draft and power requirements of an oscillating soil-working tool executing ‘simple harmonic’, ‘quick-return’ or ‘quick-cutting’ motions were developed. An experimental soil-working tool was built to execute the three types of oscillating motion. An extended octagonal ring transducer was designed to sense the horizontal and vertical components of the force on the tool when it was working in a soil medium. The oscillating velocity of the tool was sensed by using a linear voltage differential transformer. The tool was tested in a soil bin containing artificial soil, and the draft, the vertical force on the tool and its velocity were measured. The experimental values of draft and power requirements were compared with the predicted values.

Evaluation of miniature rock prism test for determining the potential alkali-expansivity of aggregates

Expansion of miniature rock prisms sawn normal to the layering of the rock and stored in 2N NaOH was monitored with a Huggenberger gauge or a linear voltage differential transformer (LVDT). Owing to their thinness (3 mm) the samples become saturated quickly and expansion usually commences within the first week, compared with the long initiation period typical of the rock cylinder method ASTM C586. The miniature rock prism test was evaluated for alkali-carbonate, slowly expanding siliceous aggregates and classical alkali-silica reactive rocks. Rates of expansion generally correlated well with those of corresponding concrete prisms tested according to CSA A23.2 - 14A.

Force-Time Parameters and Physical Growth of Boys Ages 6 to 12 Years

Abstract Boys (N = 59) in the 6 to 12 yr age range served as subjects in a study to ascertain the influence of body size and composition on peak force and maximal rate of static strength exertion as measured from force-time (F-T) curves. Weight, fat free weight, standing height, sitting height, and sitting/standing height ratio were assessed as representative physical growth variables. Maximal exertion of static muscular force for elbow flexors and grip squeezing muscle groups were recorded using a Linear Voltage Differential Transformer (LVDT) with 1 millisec samples analyzed through a series of computer programs. The design included repeat testing of the growth measures and static force tasks for each subject on two different days 1 wk apart. High reliability coefficients were found for all variables. Dividing the subjects into 5 age groups yielded significant age-wise developmental trends for all variables. ANCOVA, using the physical growth variables as the covariates, yielded no significant age-wise trend for either peak force or maximal rate for the elbow flexion and grip squeezing tasks. The results indicated that rate of force production is somewhat independent of peak force, yet influenced by body size and composition as is peak force.

Low‐temperature thermal expansivities of polyethylene, polypropylene, mixtures of polyethylene and polypropylene, and polystyrene

AbstractLength‐temperature measurements on a series of polymer blends over the whole range of composition from pure polyethylene to pure polypropylene and one set of determinations on a 50:50 copolymer and on polystyrene are evaluated. The total crystallinity of the samples did not exceed 54%. The experimental procedure utilized a linear variable differential transformer without the use of a confining fluid, and the temperature ranged from about +20 to –185°C. A least‐square numerical differentiation procedure based on moving arcs is applied to yield directly the coefficients of thermal expansion as a function of temperature. The linear voltage differential transformer (LVDT) technique can detect transitions in which the change in thermal expansion coefficients is less than 10−5°C.−1. In polypropylene as well as the blends, the principal glass transition is clearly seen in the range observed by others, namely at about –9 to –14°C. Its location varies only slightly with composition at polyethylene contents less than 88 mole‐%. For polyethylene the transition region broadens noticeably. The results are suggestive of two transitions for 0 > T > –40°C. A second transition region is observed for either pure component around –126°C. Its location varies some what with composition. However, our results do not indicate the appearance of an additional transition region characteristic of the mixture. The copolymer exhibits a major transition at –61°C. in good agreement with earlier workers. The thermal expansion decreases again around –150°C. In general our observations concerning transitions below Tg are consistent with dynamic results.