GTM has gone one further on the way to the precise measuring of torque and efficiency in wind power plant test rigs:
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The use of modern materials and designs allows larger and larger loads. In many areas of modern mechanical engineering, aerospace, construction and testing and safety engineering, forces of up to 10 MN are measured.
GTM, known around the world for precision force transducers, even in the MN range, is the first manufacturer to start operating a Force Standard Machine (FSM) for tensile and compressive forces up to 10 MN. The FSM was inaugurated to mark the company’s 25th anniversary in March of last year.
The FSM, which has a total weight of approximately 45 tonnes and a construction height of 6.5 metres, is housed fully to guarantee exact tempering. There are special lifting and transportation facilities to aid the placement of calibration objects. Compressive force transducers may have a diameter of up to 500 mm and a construction height of 700 mm. The tensile force range allows tensile bars up to 1800 mm in length with a connecting thread up to M200 in accordance with ISO 376.
The construction height and the unit’s own weight required a special foundation. The FSM stands in a pit 2 metres deep and anchored into the ground on four pillar foundations each 16 metres long. A total of approximately 35 tonnes of steel reinforced concrete were added. You can view a short film about the whole construction and assembly phase in "Calibrate / 10 MN Video" (spanish - french - italian - russian page).
Periodical inspection of the GTM calibration laboratory by the Deutsche Akkreditierungsstelle (DAkkS) (Germany’s accreditation body) took place a few weeks ago in September. The FSM is now listed as a force reference standard (K-BNME) among the services offered by the calibration laboratory; calibrations are offered for force transducers and tensile bars of between 2 MN and 10 MN. The maximum possible measuring range of the K-BNME crosses three orders of magnitude between 50 kN and 11 MN.
Up to 10 MN, the accredited uncertainty of measurement is 0.03% and between 200 kN and 5 MN it is only 0.02%. The lesser uncertainty of measurement in the lower force range seems unusual, as uncertainties generally increase as loads decrease. This is easily explained by infrastructural conditions, however, and is in line with the state of the art: the K-BNME is traced to the official standards at the PTB in Braunschweig. The varying uncertainties of measurement of these standards in different force ranges have been taken into account. We are happy to be able to say that these are among the lowest uncertainties of measurement in a worldwide comparison.
Within the scope of the DAkkS, the GTM calibration laboratory in Bickenbach with the smallest measuring unit (100N K-BNME) now also covers the force measuring range between 0.5 N and 10 MN with the largest measuring unit, placing it at the top of privately owned calibration laboratories around the world.