Residual stress measurements in metal objects using four coils
US5898302A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Nov 25, 1997 |
| Grant date | Apr 27, 1999 |
| Priority date | — |
| Expiry date | Nov 25, 2017 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG01N27/72
- WIPO fieldMeasurement
- WIPO sectorInstruments
Abstract
A device for measuring residual stress in ferromagnetic and non-ferromagnetic metal objects. The device having four electrically identical induction coils which form a four terminal alternating current bridge circuit. There is a fine wire shield formed of fingers for shielding the coils from stray capacitance. The bridge having four coil terminals. Two diagonally opposite coil terminals are connected to a variable frequency constant voltage generator. The other two diagonally opposite coil terminals are connected to a low noise broad band preamplifier. The preamplifier amplifies any unbalance in the bridge. There is a double pole double throw switch connected to two coil terminals which are diagonally opposite each other. Connected to the preamplifier is an amplifier. The amplifier is connected to a phase detector which is connected to a computer. The phase detector detects in phase and quadrature component signals. The computer has software for determining changes in differential resistivity as a function of frequency, and for converting resistivity differences into residual stress using an algorithm.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.