Multicomponent force transducer calibration procedure using tilted plates

The calibration of a multicomponent force transducers (MFTs)represents a challenge in the meganewtonrange. In fact,the generation of transversal forces and moments iscomplex since a force standard machine (FSM) is only able to apply an uniaxial force. Furthermore since MFTs are composed of multi-transducers, each one dedicated to a particular component, correlations between force and moment componentsare possible. Therefore, acalibration systemthat could simultaneously generate all force/moment components and could be suitableinevery FSMis needed. For this purpose, a coupleof tilted plates was designed. Calibration measurements were performed on a 2 MN MFT at INRiM, LNE and PTB. Exploitation matrixes and performance indicators showed good results, unless small but not negligible correlations between MFT outputs. In particularsome spurious valuesdue to the uncertainty inthe vertical force application pointinfluencedthe moment components

Modelling the development and arrangement of the primary vascular structure in plants

Background and Aims The process of vascular development in plants results in the formation of a specific array of bundles that run throughout the plant in a characteristic spatial arrangement. Although much is known about the genes involved in the specification of procambium, phloem and xylem, the dynamic processes and interactions that define the development of the radial arrangement of such tissues remain elusive. Methods This study presents a spatially explicit reaction-diffusion model defining a set of logical and functional rules to simulate the differentiation of procambium, phloem and xylem and their spatial patterns, starting from a homogeneous group of undifferentiated cells. Key Results Simulation results showed that the model is capable of reproducing most vascular patterns observed in plants, from primitive and simple structures made up of a single strand of vascular bundles (protostele), to more complex and evolved structures, with separated vascular bundles arranged in an ordered pattern within the plant section (e.g. eustele). Conclusions The results presented demonstrate, as a proof of concept, that a common genetic-molecular machinery can be the basis of different spatial patterns of plant vascular development. Moreover, the model has the potential to become a useful tool to test different hypotheses of genetic and molecular interactions involved in the specification of vascular tissue

Dynamic calibration system for seismometers: Traceability from 0.03 Hz up to 30 Hz

Mechanical calibration and traceability of seismometers in operating conditions are still a technical challenge, since very low-frequency ranges (below 0.1 Hz) are involved, and sensors under investigation are generally heavy and bulky. Recently, within the vibration metrology field, some pioneering works proposed to evaluate the seismometers’ sensitivity by applying laboratory mechanical calibration procedures, against primary or secondary standards, according to the ISO 16063 methods. By following this path, at INRIM, it has been developed a suitable system for short period horizontal and vertical ground velocity calibration of 3-axis seismometers. The calibration system allows to directly evaluate the sensitivities of the 2 axes perpendicular to the gravity field, with respect to the horizontal ground velocity (S-waves), and to derive the sensitivity of the vertical axis, parallel to the gravity field, with respect to the vertical ground velocity (P-waves), in the frequency range between 0.03 Hz and 30 Hz

Calibration of tri-axial MEMS accelerometers in the low-frequency range – Part 1: comparison among methods

Abstract. Two alternative experimental procedures for the calibration of tri-axial accelerometers have been compared with traditional methods, performed according the procedures stated in the standard ISO 16063-21. Standard calibration is carried out by comparison with a laser Doppler vibrometer (LDV), used as a primary reference transducer. The main sensitivities have been investigated and, where applicable, also transverse ones. Many aspects have been evaluated: the hypotheses about transverse sensitivities, the simplicity of the procedure, the number of measurements needed, and the effect of typology of transducer, depending on electrical and geometrical contributions. Two different accelerometers have been tested, a piezo-electric accelerometer and a capacitive MEMS accelerometer. A low-frequency range of vibration has been investigated, 3 and 6 Hz, with amplitude of acceleration ranging from 2 to 20 ms−2. A satisfactory reproducibility of methods has been verified, with percentage differences less than 2.5 %. Anyway, pros and cons of each method are also discussed with reference to their possible use for easy and quick calibration of low-cost tri-axial accelerometers

Theoretical insights on the influence of the experimental plan in the calibration of multicomponent force and moment transducers

In recent years, the increasing demand of multicomponent force and moment transducers led the necessity to develop specific calibration procedures. Sensitivity and exploitation terms of these transducers are usually expressed in matrix form to evaluate cross-talks between the different components. According to the seminal work of Ronald Fisher in 1926, to provide accurate results, calibrations shall be performed with different combinations of forces and moments in order to minimize the correlation between them. In this work, a theoretical investigation, based on an ideal transducer, on the influence of the experimental plan in the evaluation of exploitation matrix terms and the associated uncertainties as function of the number of measurements and the correlation between the applied forces and moments is performed. It is found that at decreasing number of measurements and increasing correlations between the applied forces and moments, uncertainties increase, while exploitation matrix terms are poorly affected by the chosen experimental plan

Calibration of tri-axial MEMS accelerometers in the low-frequency range – Part 2: Uncertainty assessment

Abstract. A comparison among three methods for the calibration of tri-axial accelerometers, in particular MEMS, is presented in this paper, paying attention to the uncertainty assessment of each method. The first method is performed according to the ISO 16063 standards. Two innovative methods are analysed, both suitable for in-field application. The effects on the whole uncertainty of the following aspects have been evaluated: the test bench performances in realizing the reference motion, the vibration reference sensor, the geometrical parameters and the data processing techniques. The uncertainty contributions due to the offset and the transverse sensitivity are also studied, by calibrating two different types of accelerometers, a piezoelectric one and a capacitive one, to check their effect on the accuracy of the methods under comparison. The reproducibility of methods is demonstrated. Relative uncertainty of methods ranges from 3 to 5 %, depending on the complexity of the model and of the requested operations. The results appear promising for low-cost calibration of new tri-axial accelerometers of MEMS type

Effects due to the misalignment of build-up systems for force measurements in the Meganewton range

Calibration of force transducers in the Meganewton range is typically performed by comparison with reference build-up systems (BUS) under hydraulic presses for high loads. The centring of a BUS isa difficultoperation due to itsweight and dimension, andpossible misalignmentsand the resultingeffects are usually neglected.In this work the effect on force measurements due toa 3 mmmisalignment of a 3 MN BUS wasevaluated.Measurements were performed at INRiM and at LNE in hydraulic presses.Itis shown that the relative measurement errorsdue to misalignment were lowerthan the declared CMC uncertainty,thus the shiftof the BUSdid not influence the measurements

Adult conspecific density affects Janzen-Connell patterns by modulating the recruitment exclusion zones

Plant-soil negative feedback (NF) is a well-established phenomenon that, by preventing the dominance of a single species, allows species coexistence and promotes the maintenance of biodiversity. At community scale, localized NF may cause the formation of exclusion zones under adult conspecifics leading to Janzen-Connell (JC) distribution. In this study, we explore the connection between adult density, either conspecifics or heterospecifics, on the probability of occurrence of JC distributions. Using an individual-based modelling approach, we simulated the formation of exclusion zones due to the build-up of NF in proximity of conspecific adult plants and assessed the frequency of JC distribution in relation to conspecifics and heterospecifics density ranging from isolated trees to closed forest stands. We found that JC recruitment distribution is very common in the case of an isolated tree when NF was strong and capable to form an exclusion zone under the parent tree. At very low NF intensity, a prevalence of the decreasing pattern was observed because, under such conditions, the inhibitory effect due to the presence of the mother tree was unable to overcome the clustering effect of the seed dispersal kernel. However, if NF is strong the JC frequency suddenly decreases in stands with a continuous conspecific cover likely as a result of progressive expansion of the exclusion zone surrounding all trees in closed forest stands. Finally, our simulations showed that JC distribution should not be frequent in the case of rare species immersed in a matrix of heterospecific adults. Overall, the model shows that a plant suffering from strong NF in monospecific stands can rarely exhibit a recruitment pattern fitting the JC model. Such counterintuitive results would provide the means to reconcile the well-established NF framework with part the forest ecologists’ community that is still skeptical towards the JC model.SynthesisOur model highlights the complex interconnection between NF intensity, stand density, and recruitment patterns explaining where and why the JC distribution occurs. Moreover, predicting the occurrence of JC in relation to stand density we clarify the relevance of this ecological phenomenon for future integration in plant community frameworks

Multicomponent force transducer calibration procedure using tilted plates

The calibration of a multicomponent force transducers (MFTs)represents a challenge in the meganewtonrange. In fact,the generation of transversal forces and moments iscomplex since a force standard machine (FSM) is only able to apply an uniaxial force. Furthermore since MFTs are composed of multi-transducers, each one dedicated to a particular component, correlations between force and moment componentsare possible. Therefore, acalibration systemthat could simultaneously generate all force/moment components and could be suitableinevery FSMis needed. For this purpose, a coupleof tilted plates was designed. Calibration measurements were performed on a 2 MN MFT at INRiM, LNE and PTB. Exploitation matrixes and performance indicators showed good results, unless small but not negligible correlations between MFT outputs. In particularsome spurious valuesdue to the uncertainty inthe vertical force application pointinfluencedthe moment components

Perspectives and limits on the use of commercial low-cost digital MEMS accelerometers in gravimetry

The value of the acceleration due to gravity is of interest in a wide range of fields, from geophysics, geodesy, water-floor monitoring, and hazard forecasting to oil, gas and mineral exploration. For this purpose, relative or absolute gravimeters have been developed and used for decades. While absolute gravimeters are mainly used in monitoring stations or as reference, relative gravimeters are those actually used to determine the relative variations of the local gravitational field given their smaller dimension, lighter weight, and better reading resolution, despite the high costs and the difficulty in being used under severe environmental conditions. In the last years, the advent of micro-electromechanical-systems (MEMS), in particular MEMS accelerometers, has opened up the doors to new measuring possibilities at very low-costs. As a consequence, different international research groups focused their efforts to develop relative MEMS gravimeters and showed that this technology might be really useful for monitoring the gravitational field. However, their current production is limited to a few specimens and prototypes that cannot be exploited on a large scale at the present day. For this reason, this work investigates the possibilities and the limits in the use of commercial digital MEMS accelerometers as relative gravimeters. The digital MEMS accelerometers investigated in this work are two commercial low-cost digital MEMS accelerometers (STM, model LSM6DSR, and Sequoia, model GEA). The first is composed of an accelerometer sensor, a charge amplifier, and an analog-to-digital converter and is connected by a serial cable to a separated external microcontroller (ST, model 32F769IDISCOVERY), in which other electronic components are integrated. The second is composed of the sensing element and the analog-to-digital converter. Both are connected to the computer via USB cable. The two devices are included in a thermally insulated case, in which a resistive heater and a resistance thermometer (PT1000), connected in loop, are placed in order to guarantee temperature stability during use. The system, installed on a tilting table to ensure higher accuracy in the evaluation of local g, is calibrated in static conditions by comparison to the absolute gravimeter IMGC-02 at a specific measurement location at INRIM. Calibration is repeated several times over a period of a few weeks in order to evaluate repeatability, reproducibility and stability over time. Despite the promising future prospects of this technology, at present, the levels of precisions are low compared to the ones required by most of geodynamics applications