A Novel Laser Ultrasound Source and its Implementation in the Drinks Canning Industry

Abstract

The majority of conventional liquid level monitors in the drinks canning industry operate using a gamma-ray absorption technique. Gamma-rays with energies utilised in these machines are strongly absorbed by water/liquids. In a gamma ray measurement a collimated beam is momentarily exposed to the can that is to be measured, with some of the beam below and some above the nominal liquid level. The gamma-rays are detected using a scintillation tube after passing through the can and its contents. This is shown in the schematic diagram of fig.1. Thus if more of the gamma-ray beam is absorbed by a higher liquid level, the counts drop, and vice-versa. The type of machine is in the main a pass/fail monitor — that is it passes a can if the liquid level is above a predetermined height, and rejects it if it is not. There are several problems associated with the use of gamma ray based systems, most notably environmental considerations, the fact they are potentially hazardous and the strict legislation required.