Determination of Uncertainty in Calibration of Acoustic Emission Sensors

conference paper

English

The paper reviews the background, the methodology and the standardization of the primary calibration of acoustic emission sensors. There are discussed the aims and the purpose of the primary calibration. Two basic calibration methods, which were practically realized on our test stand, are closely described and explained. It is the method of reciprocity calibration according to NDIS 2109-91 and the step function calibration according to ASTM 1106. The reciprocity method makes use of three reversible sensors. Each time must be measured three measurements. One of the sensors works as a transmitter and the others as receivers. The absolute frequency characteristic is calculated from measured data and known transmission function of the test block. Matrix channel switch was developed to automate of the whole process. It allows to increase count of measurement and to decrease the possibility of error made by change of cables. The step function method of the calibration takes advantage of the knowledge of time behaviour of the displacement of the surface of the test block during the step release of force point wise acting on the surface of the test block. Requested frequency characteristic corresponds to a ratio of image of the output voltage from the sensor and the calculated surface displacement in the frequency area. For the realization of step function calibration the holding metal construction was manufactured and suitable capillary had to be obtained. The construction holds the capillary breaker. Laser interefometer Polytec OFV-5000 with optical head OFV-505 and computing module DD-300 for AE was used for validation of shape of signal generated by capillary break. As a transfer medium for wave propagation a large steel block was used. For controlling of the whole experiment PC was used. Software was programmed in LabVIEW 8.0 and controls measurement by all of the methods. The comparison of the results of the both method is presented. Uncertainty of measurement by reciprocity calibration is determined and presented in the paper. Parasitic effect and consequential restriction of each method are presented. Also the main problems, that were solved and have to be solved, are presented in the part of the practise realization description.

acoustic emission, sensor calibration, uncertainty

KEPRT, J.; BENEŠ, P.

2007

14. 10. 2007

Hellenic Society of NDT

Athens

105

110

322