Public Health Laboratory Service Board

Barry C Blake-Coleman

David J Clarke

Apparatus for determining the amount of biological material in a fluid medium, typically the concentration of bacteria in a fermentation chamber, has a test cell through which a medium can be passed with bacteria or after bacteria have been removed by filtration. In the test cell a vibratory element is excited to a resonant frequency indicative of density and a comparison of medium density and medium plus bacteria density reveals the bacteria concentration.

Determining amount of biological material

Apparatus for use in measuring fluid density comprises a fluid carrying helical sample tube 50 made of a conductive material for passing current therethrough. A cylindrical coil fixing sleeve 58 form surrounds the helical sample tube and engages the tube to prevent relative movement of the turns. A high flux permanent magnet 60 is carried on one post 54 and is aligned along the axis of the tube. The magnetic field established by magnet 60 and the pole extension 64 will subject each current-carrying length element of the sample tube to an axial force, the sum of these forces resulting in a bodily axial movement of the sample tube. The sample tube is excited to spring resonance by passing current through the sample tube. The resonant frequency is measured and is indicative of the mass of the fluid contained in the coil and thereby of the fluid density.

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Wiltshire, United Kingdom

Barry C Blake-Coleman