(19)

(11)

EP 0 505 422 A1

(12)

(43) Date of publication: 30.09.1992 Bulletin 1992/40 (21) Application number: 91900865.0 (22) Date of filing: 11.12.1990

(51) International Patent Classification (IPC):  G01B 7/ 00( . ) G01V 3/ 10( . ) G01D 5/ 20( . ) (86) International application number: PCT/GB1990/001928 (87) International publication number: WO 1991/009277 (27.06.1991 Gazette 1991/14)

(84) Designated Contracting States: AT BE CH DK ES FR GB IT LI NL SE (30) Priority: 11.12.1989 DE 19893940894 (71) Applicant: BRITISH TECHNOLOGY GROUP LTD London SE1 6BU (GB)	(72) Inventor: CRAIGIE, Neil Stuart W-5063 Overath (DE) (74) Representative: Gaskin, John Shield  Patents Department British Technology Group Ltd 101 Newington Causeway London SE1 6BU London SE1 6BU (GB)