|
|
 |
Scientific news from division 1 |
Phase Calibration of Accelerometers with Laser-Interferometric Methods
|
|
The measurement and calibration capabilities of the working group "acceleration" have been substantially extended in recent times with respect to larger measurement range and lower uncertainties [1].
For the Amplitude of the complex sensitivity coefficient of accelerometers PTB has proven its unique capabilities only recently in the international key comparison for the unit of acceleration (relative deviation of 1·10-3 from the reference value in the frequency range from 40 Hz to 5 kHz) [2].
For the measurement of the phase delay between the excitation acceleration and the accelerometer signal with laser-interferometric methods international comparisons have been performed for the first time between PTB and the NMI of the Republic of South Africa (CSIR-NML) in the frequency range from 10 Hz to 10 kHz [3]. A representative result depicted in Fig. 1 confirms the measurement uncertainty of 0,5° to 1° (depending on the frequency) specified by PTB. The deviations of the PTB results from the according reference values are below 0,5° in all cases. Additionally it is apparent that accelerometers already show a significant phase delay far below their resonance frequency. The usual description with a second-order model (3 parameter system) appears insufficient for an accurate description of this behaviour (c. f. calculated curve).
|
|
 |
|
Fig.1: Results of the inter-comparison for phase delay of an accelerometer standard (the calculated curve represents an ideal second-order model)
|
| |
For the precise determination of the phase the sine-approximation method, introduced into international standards [4] by PTB, is available in three different implementations. All of them have been applied during the inter comparison:
- homodyne-interferometer with quadrature output signals (displacement measurement)
- heterodyne-interferometer with quadrature analysis (displacement measurement)
- heterodyne-interferometer with time-interval analyser (velocity measurement)
These advanced measurement techniques are utilized e. g. for the phase calibration of reference accelerometers and transfer standards of laboratories participating in the German Calibration Service (DKD), which have to be recalibrated periodically by PTB.
Several DKD laboratories have reacted to the increasing industrial need for high precision amplitude and phase calibration (e. g. for modal analysis of structures or motion control systems) by purchasing top of the art commercial calibration equipment. PTB, in return, took its part in providing traceability with high precision Measurement and calibration capabilities via adequate national standard devices.
|
|
|
|
| [1] |
v. Martens, H.-J., Link, A., Schlaak, H.-J., Täubner, A., Wabinski, W., Göbel, U.: Recent advances in vibration and shock measurements and calibrations using laser interferometry. SPIE Volume 5503 (2004), 1-19 |
| [2] |
v. Martens, H.-J., Elster, C., Link, A ., Täubner, A., Wabinski, W.: Final report on key comparison CCAUV.V-K1, Metrologia 40 (2003), Tech. Suppl. 9001 |
| [3] |
Veldman C.S., v. Martens H.-J.: Final report on supplementary comparison SADCMET.AUV.V-S1. Metrologia 41 (2004) Tech. Suppl. |
| [4] |
ISO 16063-11 Methods for the calibration of vibration and shock transducers - Primary vibration calibration by laser interferometry |
|
|
|
|
Contact person: |
|
Thomas Bruns, FB 1.3, AG 1.31, E-Mail: thomas.bruns@ptb.de
|
|
© Physikalisch-Technische Bundesanstalt
Page created: 14.11.2005, last update: 14.11.2005,
Dirk Röske
|
|
|
