| 摘要 |
In apparatus for on-line particle determination in molten metals a sample of molten metal is drawn through a calibrated passage (22) while a steady current is established through the passage between two electrodes (12, 14) on opposite sides thereof. Particles moving through the passage produce voltage pulses whose magnitude and rate indicate respectively their size and number per unit volume. The wanted test signal can be obtained between the two current carrying electrodes (12, 14), or between two other electrodes (15, 54) disposed on opposite sides of the passage. The electrodes (12, 14 or 15, 48) form an interference-receiving antenna so that the wanted low signal/noise ratio test signal is overlaid with interference from neighbouring sources. This interference is reduced by a cancellation signal produced by a cancellation antenna constituted by a similar pair of electrodes (12, 15 or 48, 54), either separate from the main current-carrying electrodes or having one of them in common. A four electrode configuration permits the diameter of the passage to be monitored continuously. A five electrode configuration has three electrodes (15, 48, 54) separate from the current-carrying electrodes (12, 14) forming the two antennae and connected differentially. A further electrode (60) if provided is used to minimize ground loops in the signal path. A head member (70) carrying the tube (16) and electrode cluster (12, 14, 15, 48, 54, 60) is mounted to move between operative and storage positions relative to a main body (72) member carrying the power supply (66); these are made symmetrical about a longitudinal axis so that interference signals are in anti-phase and cancel. |
