(19)

(11)

EP 0 507 813 A1

(12)

(43) Date of publication: 14.10.1992 Bulletin 1992/42 (21) Application number: 91901456.0 (22) Date of filing: 28.12.1990

(51) International Patent Classification (IPC):  G01L 9/ 00( . ) (86) International application number: PCT/GB1990/002035 (87) International publication number: WO 1991/010120 (11.07.1991 Gazette 1991/15)

(84) Designated Contracting States: DE FR GB (30) Priority: 28.12.1989 GB 19890029276 29.12.1989 GB 19890029307 (71) Applicant: BRITISH TECHNOLOGY GROUP LTD London SE1 6BU (GB)	(72) Inventor: ROGERS, Tony, William, James Reading Berkshire RG3 2EU (GB) (74) Representative: Gaskin, John Shield  Patents Department British Technology Group Ltd 101 Newington Causeway London SE1 6BU London SE1 6BU (GB)