Set-ups of measuring devices to determine the deformation of force transducers

On static and dynamic force measuring devices, set-ups have been realised and investigated which allow the deformation of force transducers under load to be measured by means of a differential laser vibrometer. Especially in the range of dynamic measurements, it is often necessary to know the deformation path in addition to the force.

Fig. 1 shows these set-ups at a 10 kN shaker system (on the left) and at the 20 kN force standard machine (on the right). In the case of the dynamic application, the complete set-up is situated on a vibration absorption table by which the influence of vibrations caused by the shaker is minimised. The two laser heads are applied to a cantilever and can be positioned directly above the installed force transducer.

Figure 1: Vibrometer devices for the measurement of the deformation of force transducers under load. On the left: Set-up at the 10 kN shaker; on the right: Set-up at the 20 kN force standard machine.

The deformation measurement is performed in such a way that one laser beam is reflected on the base plate of the shaker and the other on the surface of the force transducer. By means of this differential measurement, the deformation of the force transducer is determined. The static measurement is carried out in accordance with the same principle. Here, a frame has been constructed and integrated into the machine which serves to mount the laser heads. In addition, a reflection plate has been mounted on the transducer to make the surface of the transducer accessible for the laser beam.

First measurements carried out on the two set-ups showed relative uncertainties of < 1% whereby, in the case of dynamic measurements, the resonance behaviour of the force transducer must be taken into account: in the case of frequencies at which cross resonances occur, the purely vertical movement of the force transducer is superposed by cross movements which may cause strong falsifications of the measurement results. In such cases, the relative repeatability can assume values above 10%. Outside these frequency ranges, the repeatability was less than 0.5% [1, also at www.imeko.org].

[1] A. Buß: Static and dynamic measurement of force transducer’s deformation under load, Proceedings of the XIX IMEKO World Congress, Lisbon, Portugal, Sept. 6-11, 2009

Contact person:

Andre Buß, Department 1.2, WG 1.23, E-mail: andre.buss@ptb.de