PTB News 1/2004 (111 kB) PTB News 1/2004, English edition Issue May 2004PTB has developed and constructed a new impact-force-standard measuring device. For the first time force transducers subjected to shock can now be calibrated dynamically with the new equipment. The acceleration of two masses striking each other is determined by means of a laser-Doppler-interferometer.
Although dynamical force measurements are becoming increasingly important in industry (e.g.: in crash tests) it is still general practice to carry out static calibrations on force transducers even if they are to be used for dynamic measurements. In consequence, the actual measurement uncertainties are not precisely known.
In addition to the established static calibration PTB has developed an impact-force-standard mea-suring device, which describes the measurand “force” by principle of inertial mass. The force is traced backed to the SI units through measurements of mass and acceleration.
The apparatus utilises two cuboid-shaped mass-bodies of roughly 10 kg, guided on air-bearings for low friction. A force transducer is connected between them and they are brought to collision. The velocity of the mass-bodies is measured without contact by a laser-Doppler-interferometer (vibro-meter). Numerical differentiation yields the desired time-dependent acceleration.
The new calibrating facility for shock forces of up to 20 kN is now in commissioning. First tests demonstrated a force amplitude reproducibility better than 0.1%. It is now for the first time possible to investigate the dynamic behaviour of force transducers under well-characterized shock loading.