Method and apparatus for the non-destructive and contactless detection of faults in a test piece which is moved relative to a probe

US7423424B2 · kind B2 · utility

Assignee

• Prüftechnik Dieter Busch GmbH · DE

Inventors

• Roland Hoelzl · Munich, DE
• Michael Hermann · Tacherting, DE

Key dates

• Filing date: Jul 18, 2005
• Grant date: Sep 9, 2008
• Expiry date: May 14, 2026

Classification

• Technology area (CPC G): Physics
• CPC primary: G01N29/449
• WIPO field: Measurement
• WIPO sector: Instruments

Abstract

Method for nondestructive and contact-free detection of faults in a test specimen which is moved relative to a probe that detects a periodic electrical signal having a carrier oscillation whose amplitude and/or phase is/are modulated by any fault in the test specimen. The probe signal is filtered and sampled by a triggerable A/D converter stage to obtain a demodulated digital measurement signal which is filtered using a digital frequency-selective adjustable second filter unit to obtain a useful signal which is evaluated to detect a fault in the test specimen. The A/D converter stage is triggered at a fraction of the frequency of the carrier oscillation selected as a function of the fault frequency obtained as the quotient of the relative speed between the test specimen and the probe and the effective width of the probe, and the frequency-selective second filter unit is adjusted as a function of the fault frequency.