Electricity: measuring and testing – Determining nonelectric properties by measuring electric... – Particle counting
Patent
1990-01-29
1991-08-13
Wieder, Kenneth A.
Electricity: measuring and testing
Determining nonelectric properties by measuring electric...
Particle counting
164 41, 266 99, G01N 2700, G01R 2722
Patent
active
050399357
ABSTRACT:
The invention relates to apparatus as disclosed for example in U.S. Pat. Nos. 4,555,662 and 4,600,880 for on-line particle determination in molten metals, wherein a sample of the molten metal is drawn by a vacuum through a calibrated passage in the side-wall of a heat-resistant tube while a current is established through the passage between two electrodes on either side thereof. The passage of non-conducting particles through the orifice produces pulses whose magnitude and rate indicate respectively their size and the number of particles per unit volume. The electrodes and their leads form an interference-receiving antenna so that the wanted test signal, whose signal
oise ratio is inherently low, is subject to interference from neighbouring sources, such as motors, fluorescent lamps and particularly induction furnaces. The invention provides for the production of a cancellation signal to reduce the unwanted interference component in the test signal by means of a cancellation antenna suficiently close to the detector electrodes to receive substantially the same signal, the antenna either feeding the cancellation signal to a differential amplifier also fed with the wanted signal, or being connected in series with the interference antenna. The cancellation antenna can comprise a loop mounted on the head that supports the two electrodes.
REFERENCES:
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patent: 4161690 (1979-07-01), Feier
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patent: 4447883 (1984-05-01), Farrell et al.
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patent: 4600880 (1986-07-01), Doutre et al.
patent: 4763065 (1988-08-01), Hachey
Deschenes Gaetan
Hachey Raynald
Alcan International Limited
Regan Maura K.
Wieder Kenneth A.
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