Development and metrological characterisation of the new LNE 500 N·m deadweight torque standard machine ACTA IMEKO | www.imeko.org December 2020 | Volume 9 | Number 5 | 168 ACTA IMEKO ISSN: 2221-870X December 2020, Volume 9, Number 5, 168 - 172 DEVELOPMENT AND METROLOGICAL CHARACTERISATION OF THE NEW LNE 500 Nm DEADWEIGHT TORQUE STANDARD MACHINE C. Duflon1, P. Averlant2 LNE, Paris, France, 1 carole.duflon@lne.fr, 2 philippe.averlant@lne.fr Abstract: This paper describes the development and metrological characterisation of the new LNE 500 Nm deadweight torque standard machine. This machine is integrated into the LNE 5 kNm deadweight torque standard machine. New masses and a mass change platform have been developed and added to the 5 kNm machine. After this, LNE realised the metrological characterisation of the 500 Nm machine. The determination of the uncertainties of this torque standard machine and the comparison measurements with the LNE 50 Nm deadweight torque standard machine and with CEM, the National Metrology Institute of Spain, are described in this paper. The results show that the estimated uncertainties are satisfactory because they are a factor of about four times smaller than those of the old standard machines. Keywords: torque standard machine 1 INTRODUCTION The development of the torque standard machine of 500 Nm is part of a wider scheme which aims at updating French metrological references in torque metrology. The Laboratoire national de métrologie et d’essais (LNE) is conducting this project which involves the development of several machines: 5 Nm; 50 Nm; 500 Nm; and 5000 Nm. The development and the metrological characterisation of the 5 Nm, 50 Nm and 5000 Nm torque deadweight standard machine have already been made and presented in articles [1][2][3][4]. The next sections introduce, for the 500 Nm torque standard machine, the development of the deadweights, the principle of the mass change platform (see Figure 1), the determination of the uncertainties and the comparison measurements carried out with the LNE 50 Nm deadweight torque standard machine and with the National Metrology Institute of Spain (CEM) 1 kNm deadweight torque standard machine. After this comparison a Euramet comparison will be done. This Euramet comparison will be used to support our BIPM Calibration and Measurement Capabilities change. Figure 1: 500 Nm and 5 kNm machines Mass change platform Weightstacks: 5 kN and 500 N http://www.imeko.org/ mailto:carole.duflon@lne.fr file:///C:/Users/ajk1/AppData/Local/Microsoft/Windows/INetCache/Content.Outlook/ZR5YRJ3G/philippe.averlant@lne.fr ACTA IMEKO | www.imeko.org December 2020 | Volume 9 | Number 5 | 169 2 DEVELOPMENT OF THE 500 Nm MACHINE The 500 Nm deadweight torque standard machine is integrated into the LNE 5 kNm deadweight torque standard machine. New masses and a mass change platform have been developed and added to the 5 kNm machine (see Figure 1). The next sections describe these new parts. The lever arm and the air bearing are described in detail in the article [2]. 2.1 The weightstack Figure 2: 500 Nm weightstack Two weightstacks (see Figure 2) were manufactured to be placed on both extremities of the lever arm to apply torques either on the left or the right side. These stacks have a height and an arm interface identical to the weightstack of the 5 kNm machine so that the machine can operate in the same way. They are made of a series of non-magnetic stainless steel disks that are sequentially hung from each other depending on the height of the weight carrier. Each stack is composed of the same series of the following 22 discs: - 10 discs each creating 10 N; - 2 discs each creating 20 N; - 2 discs each creating 10 N; - 2 discs each creating 20 N; - 6 discs each creating 50 N. This particular layout enables loadings to be conducted with intervals of 10 Nm, 20 Nm or 50 Nm, by increasing or decreasing load values over ten steps with only one motorisation. This allows us to respect the international practices regarding calibration of torque transducers with a capacity of 100 Nm, 200 Nm and 500 Nm. 2.2 The mass change platform The mechanism for carrying out the mass chain change consists of a change platform (see Figure 3), on each side of the arm, placed on the rear of the machine The mass change platform is equipped with a slide and a pivot for translation and rotation. Movements are motorised. The translational plate, allowing the approach of the masses in position 5 kN or 500 N, is comb-shaped and must be inserted in the basket support plate. Then the existing basket motors are used to lift the masses. Figure 3: Mass change platform and weightstacks Mass change platform Weightstack 5 kN Weightstack 500 N Basket support plate http://www.imeko.org/ ACTA IMEKO | www.imeko.org December 2020 | Volume 9 | Number 5 | 170 3 EVALUATION OF UNCERTAINTY The uncertainty of the torque T applied by the 500 Nm machine has been estimated including the uncertainty contribution of the deadweight force, of the length and due to sensitivity mobility of the lever (see Table 1). Concerning the deadweight force, the uncertainties have been estimated as usual and same components than for the 5 kNm range of the machine (see [4]) have been taken into account. As there is only one lever used for both the 5 kNm and 500 Nm ranges, we use the same calibration results obtained on a three-dimensional measuring machine. So components link to length are exactly the same as for 5 kNm range (see [4]). The sensitivity and mobility of the lever arm associated with the air bearing have been estimated in the same way as for the 5 kNm range: lever imbalances have been measured using a small capacity torque transducer with a very small resolution. Additional to all those components, a last uncertainty contribution is taken into account. Doing interlaboratory comparison, deviations could be observed between two torque calibration machines. In force and torque field, sometimes, Table 1: Uncertainty budget of the LNE 500 Nm torque standard machine Uncertainty component Standard uncertainty / Nm FORCE MASS Calibration Measurement truenessa Drift (based on calibration uncertainty) EARTH’S GRAVITATIONAL FIELD AIR BUOYANCY 2.7 × 10-6 × T 1.0 × 10-6 × T 1.5 × 10-6 × T 1.0 × 10-6 × T 3.1 × 10-7 × T 1.7 × 10-6 × T LENGTH Calibration Measurement truenessa Temperature Drift (based on calibration uncertainty) Force position Deformation and inclination 2.0 × 10-5 × T 1.2 × 10-5 × T 6.1 × 10-6 × T 4.9 × 10-6 × T 1.2 × 10-5 × T 6.7 × 10-6 × T 2.9 × 10-7 × T SENSITIVITY and MOBILITY 7.1 × 10-4 + 9.4 × 10-7 × T TORQUE TRANSMISSION 1.6 × 10-3 + 1.9 × 10-5 × T a Due to the use of nominal value instead of measured value those deviations are bigger than the combined uncertainty, means that there are significant, or that the uncertainties have been underestimated. To avoid this, we enlarge the uncertainty, adding a component based on comparison results. We call this component “torque transmission” because the mechanical way to apply the torque to the device could explain the deviation results. For the 500 Nm range, this component is estimated using the deviation between the measurements obtained by transducers calibrated by the LNE 500 Nm, LNE 50 Nm and CEM machines. The comparison of measurements is presented in the next chapter. The expanded (k = 2) uncertainty 𝑈𝑇 of the torque (𝑇 , in Nm) applied by the LNE 500 Nm machine is obtained by combining these components: 𝑈𝑇 = 3 mN∙m + (5.0 × 10 −5 × 𝑇) N∙m (1) 4 COMPARISON MEASUREMENTS The comparison has been made with transducers calibrated by LNE and CEM. CEM used their 1 kNm torque standard machine. The expanded uncertainty (k = 2) on the applied torque T (in Nm) is equal to (2.0 × 10−5 × T) Nm. Each torquemeter was calibrated twice in LNE’s 500 Nm torque standard machine, firstly before sending it to CEM and secondly after receiving it back, thereby establishing the drift. For torque from 10 N·m to 50 Nm an internal LNE comparison with the 50 Nm torque standard machine has been made. The expanded uncertainty (k = 2) on the applied torque T (in Nm) is equal to 0.5 mNm + (5.0 × 10-5 × T) Nm. The comparison took place over a few days so only one calibration was made on the 500 Nm machine. For these comparisons we used five transfer torquemeters. Table 2 shows the measuring bridges used and the measuring steps realised with the set of torquemeters. Table 2: Measuring ranges realised during the comparisons Transfer torquemeter Measuring bridges Steps (N·m) Raute TT1 50 N·m HBM DK38 10, 20, 30, 40, 50 GTM Dm-TN 50 N·m HBM DK38 10, 20, 30, 40, 50 Raute TT1 100 N·m HBM ML38 10, 20, 30, 40, 50, 100 Raute TT1 500 N·m HBM ML38 50, 100, 150, 200, 250, 300, 400, 500 GTM Dm-TN 500 N·m HBM ML38 50, 100, 150, 200, 250, 300, 400, 500 The calibrations were performed in both clockwise and anticlockwise modes. http://www.imeko.org/ ACTA IMEKO | www.imeko.org December 2020 | Volume 9 | Number 5 | 171 The calibration of each torquemeter has been realised by performing, in order, the following operations: • Application of three preloads at the nominal value of the torquemeter held for thirty seconds and with a rest period of thirty seconds between each preload. • Application of four series of increasing charges and three series of decreasing charges without return at zero charge between each step. The measurements are taken after about thirty seconds. • Rotation of the torquemeter around its axis (3 different angles). Preload at the maximum load of the sensor after each rotation Figure 4 shows, for each torque step, the weighted average of differences between the CEM and LNE 50 Nm and the LNE 500 Nm machines. The vertical bars represent the uncertainty (k = 2) of the LNE 500 Nm torque standard machine. Figure 4: Weighted average of difference = (results CEM and LNE 50 Nm - results LNE 500 Nm) ± ULNE500 For each step, the difference is less than the uncertainty, so it is not significant. Maximum differences are taken into account in the uncertainty budget as the torque transmission component. 5 CONCLUSION The metrological characterisation of the LNE torque standard machine of 500 Nm gave an expanded (k = 2) uncertainty equal to 3 mN·m + (5.0 × 10-5 × T) N·m. The comparison performed with the LNE 50 Nm machine and the CEM 1 kNm machine showed that this uncertainty is quite justified. The results show that the estimated uncertainties are satisfactory because they are a factor of about four times smaller than those of the old standard machines. A Euramet comparison will be done to support our BIPM Calibration and Measurement Capabilities change. 6 REFERENCES [1] P. Averlant, A. Gosset, “Development of the new LNE 50 N·m deadweight torque standard machine”, in Proc. of 20th IMEKO TC3 Int. Conf., Merida, Mexico, 27 – 30 November 2007. Online [accessed 20201126]: https://www.imeko.org/publications/tc3- 2007/IMEKO-TC3-2007-097u.pdf [2] P. Averlant, P. Lacipiere, J.-M. Davis, “Development of the new LNE 5 kN·m deadweight torque standard machine”, in Proc. of Joint IMEKO http://www.imeko.org/ https://www.imeko.org/publications/tc3-2007/IMEKO-TC3-2007-097u.pdf https://www.imeko.org/publications/tc3-2007/IMEKO-TC3-2007-097u.pdf ACTA IMEKO | www.imeko.org December 2020 | Volume 9 | Number 5 | 172 22nd TC3, 12th TC5 and 3rd TC 22 Int. Conf., Cape Town, South Africa, 3 - 5 February 2014. Online [accessed 20201126]: https://www.imeko.org/publications/tc3- 2014/IMEKO-TC3-2014-001.pdf [3] C. Duflon, P. Averlant, “Qualification métrologique des nouveaux bancs de référence de couple de 5 N·m et de 50 N·m du LNE”, Revue française de métrologie, vol. 2014-2, no. 34, DOI: 10.1051/rfm/2014007, 2014. Online [accessed 20201126]: https://metrologie- francaise.lne.fr/sites/default/files/media/document/ rfm34-1402-duflon.pdf [4] P. Averlant, C. Duflon, “Metrological characterisation of the 5 kN·m torque standard machine of LNE”, in Proc. of 12th IMEKO World Congress, Belfast, UK, 3 - 6 September 2018. Online [accessed 20201126]: https://iopscience.iop.org/article/10.1088/1742- 6596/1065/4/042044/pdf http://www.imeko.org/ https://www.imeko.org/publications/tc3-2014/IMEKO-TC3-2014-001.pdf https://www.imeko.org/publications/tc3-2014/IMEKO-TC3-2014-001.pdf https://metrologie-francaise.lne.fr/sites/default/files/media/document/rfm34-1402-duflon.pdf https://metrologie-francaise.lne.fr/sites/default/files/media/document/rfm34-1402-duflon.pdf https://metrologie-francaise.lne.fr/sites/default/files/media/document/rfm34-1402-duflon.pdf https://iopscience.iop.org/article/10.1088/1742-6596/1065/4/042044/pdf https://iopscience.iop.org/article/10.1088/1742-6596/1065/4/042044/pdf