24.09.2014
As part of the European Metrology Research Programme EMRP, new methods for the dynamic calibration of torque transducers have been investigated within the scope of the joint research project IND09 "Traceable Dynamic Measurement of Mechanical Quantities" [1]. For this purpose, a model-based description of the torque transducer to be calibrated has been developed which requires modelling of the measuring device. To describe the damping parameter of the dynamic torque measuring device, the damping of torsional vibration has been investigated [2].
For the investigations, a measurement set-up has been developed (see Figure 1) which allows the device under test to be excited by a negative torque step. This has been realised by test specimens made of brittle ceramics, which break when the load is too high.
Figure 1: Measuring set-up for damping measurements
The breaking test specimen reacts with sinusoidal torsional vibrations q(t) whose amplitude decay is analysed, as shown in Figure 2.
The amplitude of the vibration decreases exponentially with time according to
with the starting amplitude q0, the damping constant δ, the angular frequency ω and the phase φ.
An alternative procedure analyses the decay of the vibration amplitude from a starting value qk over n vibrations, and the logarithmic decrement Λ is given by
Rotational vibrometers provide non-contact measurements of the torsional vibrations at the top and at the bottom of the measurement object (see Figure 1).
The difference between these two measured torsional angles is the torsion of the measurement object, whose damping properties are to be determined. The voltage signals of the vibrometers are recorded by a fast data acquisition system. The decay of the recorded vibration amplitude is analysed in the time domain by means of a sine fit. Detailed information about the procedure can be found under [3].
Literature:
[1] C. Bartoli et al., "Traceable Dynamic Measurement of Mechanical Quantities: Objectives and First Results of this European Project" in International Journal of Metrology and Quality Engineering; 3, 127–135 (2012)
DOI: 10.1051/ijmqe/2012020
[2] L. Klaus, Th. Bruns, M. Kobusch, "Modelling of a Dynamic Torque Calibration Device and Determination of Model Parameters" in ACTA IMEKO Vol. 3, No. 2 (2014), pp. 14-18, online at:http://acta.imeko.org/index.php/acta-imeko/article/view/IMEKO-ACTA-03%20%282014%29-02-05/253
[3] L. Klaus, M. Kobusch, "Experimental Method for the Non-Contact Measurement of Rotational Damping" in Proc. of Joint IMEKO International TC3, TC5 and TC22 Conference, 2014, Cape Town, South Africa, online at:http://www.imeko.org/publications/tc22-2014/IMEKO-TC3-TC22-2014-003.pdf
Contact persons:
Leonard Klaus, Department 1.7, WG 1.73, e-mail: 
leonard.klaus(at)ptb.de
Michael Kobusch, Department 1.7, WG 1.73, e-mail: michael.kobusch(at)ptb.de