Calibration Of Force Transducers Research Articles

Static, continuous and dynamic calibration of force transducers: A comparative study on a low-force strain-gauge measuring device

Static, continuous and dynamic calibration of force transducers: A comparative study on a low-force strain-gauge measuring device

Extrapolation errors of force transducer curve fitting equations

Calibration laboratories often face the challenge of the impossibility to perform full capacity range calibration of their force transducers, particularly below 10 % of the force transducer’s capacity. Sometimes these laboratories use curve fitting extrapolation to estimate and predict force transducer behavior within uncalibrated capacity ranges. This work deals with the study of extrapolation errors in force transducers to know and estimate prediction accuracies when using extrapolation for force transducer calibration in ranges below 10 % and between 50 % and 100 % of the transducer’s capacity. The results of this study showed that the magnitude of the extrapolation error is very close to the magnitude of the reproducibility error within calibrated capacity ranges in the laboratory.

A Proposed Algorithm for Determining the Suitable Number of Significant Digits of Force Transducer Calibration Constants

Precision measurement is one of the important goals of measurement and calibration. Positive measures are designed to provide researches with the highest accuracy and precision levels. In force measurements, force measuring instrument manufacturers are striving to achieve the best force measurement resolution to accompany the high level of calibration measurement capabilities achieved by the primary deadweight machines. In the calibration of the force transducers, polynomial equations which correlate, the applied load on the transducer and its corresponding output signal in mV/V are deduced. These equations contain numerical constants A, B and C. This paper introduces a mechanism to determine the suitable number of significant digits for these constants. Error analysis procedure for the calibration polynomial equation is proposed. This proposed algorithm safeguards the most accurate and realistic method for rounding the calibration constants

Static and dynamic bridge amplifier calibration according to ISO 4965-2

Dynamic measurements to correctly adjust the magnitude in fatigue testing require a dynamic calibration of force transducers and conditioning electronics if the dynamic loads are to be measured correctly. International standard ISO 4965 describes a calibration method for these components. At PTB, such a calibration of bridge amplifiers has now been performed for the first time. The calibration includes tests with static and dynamic signals. The reference for the calibration is the dynamic bridge standard of PTB. It is particularly suitable for this application as it can generate static and dynamic signals, and thus all investigations can be performed with one reference and in a reasonably short time. The signal creation and the data analysis were carried out using the open source program GNU Octave. For the data analysis, a semi-automatic procedure was developed to simplify the process. Calibrations of two digital bridge amplifiers were carried out.

NMISA’s new 5 kN deadweight force standard machine

This paper describes NMISA’s new 5 kN deadweight force standard machine. The machine has the capability to generate force in the range 50 N to 5 kN. The machine uncertainty is conservatively estimated at 0.008 % across the entire measuring range. The weights are adjusted according to the gravity value measured in the laboratory. This machine is used for the calibration of force transducers in tension and compression.

Dynamic Force Transducer Calibration Based on Electrostatic Force

Measurements of micro/nano dynamic force transducers (DFTs) in the micro-Newton range are of significant importance in many fields. In this paper, the electrostatic force in the micro-Newton range was used to generate dynamic force to calibrate the DFT, which is traceable to the International System of Units (SI). The relationship between the force input and voltage output of a DFT was investigated. The performance of DFT, such as resolution and reproducibility had been tested by the proposed method. The uncertainties, such as eccentric loading position, electrostatic force, output voltage measurement, and stiffness measurement, were estimated. The results showed that relative standard uncertainty in the determination of the calibration of the transducer was approximately 2.2%. This showed that the proposed system was very stable and repeatable.

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 is a difficult operation due to its weight and dimension, and possible misalignments and the resulting effects are usually neglected. In this work the effect on force measurements due to a 3 mm misalignment of a 3 MN BUS was evaluated. Measurements were performed at INRiM and at LNE in hydraulic presses. It is shown that the relative measurement errors due to misalignment were lower than the declared CMC uncertainty, thus the shift of the BUS did not influence the measurements.

Comparison results between PTB and CIMM on the force transducer calibration under sinusoidal loading

Sinusoidal force is a typical kind of dynamic force applied widely in practice, and the sinusoidal force calibration systems are set up in Physikalisch-Technische Bundesanstalt(PTB) and Changcheng Institute of Metrology & Measurement(CIMM) respectively. To examine and compare the measurement methods for force transducer calibration, a comparison on sinusoidal force calibration is taken between PTB and CIMM. The experiment results show that the absolute value of the normalized error En between both sides is always less than 1, in the frequency range from 20Hz to 2000Hz, by using mass blocks A(nominal 1kg) and B(nominal 2kg). While the large deviation corresponding to the mass block C(nominal 4kg) at frequencies higher than 1000Hz may be contributed to some rocking effect at high frequency.

Multicomponent force transducer calibration procedure using tilted plates

The calibration of a multicomponent force transducers (MFTs) represents a challenge in the meganewton range. In fact, the generation of transversal forces and moments is complex 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 components are possible. Therefore, a calibration system that could simultaneously generate all force/moment components and could be suitable in every FSM is needed. For this purpose, a couple of 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 particular some spurious values due to the uncertainty in the vertical force application point influenced the moment components.

Traceable dynamic calibration of force transducers by primary means

We describe an apparatus for traceable, dynamic calibration of force transducers using harmonic excitation, and report calibration measurements of force transducers using this apparatus. In this system, the force applied to the transducer is produced by the acceleration of an attached mass, and is determined according to Newton’s second law, F = ma. The acceleration is measured by primary means, using laser interferometry. The capabilities of this system are demonstrated by performing dynamic calibrations of two shear-web-type force transducers up to a frequency of 2 kHz, with an expanded uncertainty below 1.2%. We give an account of all significant sources of uncertainty, including a detailed consideration of the effects of dynamic tilting (rocking), which is a leading source of uncertainty in such harmonic force calibration systems.

Investigations for the model-based dynamic calibration of force transducers by using shock excitation

Within the scope of the joint research project EMRP IND09 "Traceable dynamic measurements of mechanical quantities", numerous measurements were performed at PTB's 20 kN primary shock force calibration device to investigate and validate the approach of a model-based dynamic calibration of force transducers by using shock excitations. The tests included several strain gauge force transducers of greatly differing structural design, size, weight and mechanical coupling. By looking at a few examples, investigated physical models of the measurement set-up and developed data analysis procedures for parameter identification based on measured shock data are presented and discussed. The models reproduce the dynamic response including the observed modal oscillations of various origins that limit the usable measurement bandwidth. Moreover, these modal oscillations may have an important role for the parameter identification process, which is further discussed. This paper is an extended version of the original contribution to the IMEKO 2014 conference in Cape Town, South Africa.

A metrological approach for the calibration of force transducers with interferometric readout

We introduce an experimental calibration method for force transducers with interferometric readout. The head of the transducer is compressed on the pan of a weighing scale until the first maximum of interference is reached. An optomechanical feedback loop makes sure that the force applied remains constant during the integration time of the weighing scale. At the end of the integration time, the transducer is forced to move to the next maximum of interference, where it is again locked into position to allow the user to read the corresponding increase in weight on the scale. Repeating a similar procedure for a series of consecutive maximum-to-maximum steps, one can finally plot the weight indicated by the scale as a function of the displacement of the head of the transducer, and, from there, extract its spring constant. The method relies only on measurements of weights and laser wavelengths, both of which can be, in principle, referred to metrological standards.

Analysis of Force Transducer Calibration Accuracy Based on Different Influence Factors

The actual use conditions of force transducer is differences between the factory verification conditions, so based on the structure and working principles, this article is aimed at accurate calibration and proper use of force transducer. Through the CAE simulations and calibration experiments in actual working conditions which are the installation pre-tightening force, structure of fittings and pedestal’s hardness, analyses the output signals of force transducer. Force standard machine was carried out on the calibration experiment to verify the correctness of the numerical simulation. And then the outcomes obtained by numerical simulations and the calibration experiments, it studies the differences of every output performance index of force transducers in different working conditions above-mentioned.

From oscillation to impact: the design of a new force calibration device at PTB

This article describes the design of a new facility which is under construction at the Physikalisch-Technische Bundesanstalt for the calibration of force transducers with impulse forces. Force pulses of 1 ms duration and less are generated by the impact of two bodies of known mass, having their acceleration derived from velocity data taken with laser-Doppler interferometry. To minimize the influence of friction, linear air bearings are used as guideways for these bodies. Numerical simulations based on a non-linear mass-spring model are performed to obtain a prediction of the expected signals under the influence of hertz-like contacts as well as of the pulse duration and the amplitude. Finally, the major sources of measurement uncertainty are discussed.

Investigation of the comparison method for the dynamic calibration of force transducers

The method of the dynamic calibration of force measuring devices using a force exciter and standard force transducer is discussed, which will also be referred to as the comparison method. To ensure traceability to the definition of force according to Newton's law, the standard force transducer must be calibrated by a direct method. For this purpose, defined inertial forces are generated at the PTB with a shaker and a load mass.

Measurement Uncertainty Analysis of a Transfer Standard Force Calibration System

Abstract Force transducer calibration may be performed by means of dead weights or by comparison with a transfer standard. Directly applied dead weights with traceability to the National Institute of Standards and Technology (NIST) are primary force standards. Low-capacity force transducers are generally calibrated by primary standards, but for force transducer calibrations above 1000 lb (453.6 kg), many force transducers are calibrated by means of secondary force standards used as transfer standards. The purpose of this paper is to provide a measurement uncertainty analysis of transfer standard force calibration at one test facility. Significant error sources are identified and quantified. The methodology presented is generally applicable; however, the error evaluations are specific to the measurement process and test equipment used.

An absolute impulsive method for the calibration of force transducers

A simple, absolute method is described for calibrating force transducers. It is based on the momentum transferred in the impact of a pendulum against the transducer. The force range used in the measurements described was from approximately 10-5 N to approximately 10-3 N, but extension to much higher forces is straightforward. The duration of the impulses was in the range of 100 mu s-2 ms. The method is particularly appropriate for piezoelectric transducers.