Abstract: In an apparatus for on-line particle determination in molten metals, a sample of molten metal is drawn through a calibrated passage while a steady current is established through the passage between two electrodes 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, or between two other electrodes disposed on opposite sides of the passage. The electrodes form an interference-receiving antenna so that the wanted low signal/noise ratio test signal is overlaid with interference from neighboring sources. This interference is reduced by a cancellation signal produced by a cancellation antenna constituted by a similar pair of electrodes, either separate from the main current-carrying electrodes or having one of them in common.

Abstract: New methods and apparatus for the measurement of thermal conductivity of gases employ a single katharometer element comprising a thermistor. In one circuit the thermistor is part of a first potential divider whose output voltage is compared to that of a second reference potential divider by applying them to the inputs of a differential amplifier supplying heating current to the element. In another circuit, in which the katharometer element may be other than a thermistor, the element and a resistor are connected in series to a common reference point of the circuit and are supplied with current so that the voltages across them correspond to their respective resistances; the voltage cross the item not connected to the reference point is transferred to another circuit element that is connected to the reference point so that they can be compared directly.

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/noise ratio is inherently low, is subject to interference from neighbouring sources, such as motors, fluorescent lamps and particularly induction furnaces.

Abstract: A new method and apparatus for the measurement of thermal conductivity of gases employs a single katharometer element, which preferably is a thermistor, but may be a heated filament. In a preferred circuit the element is part of a first potential divider whose output voltage is compared to that of a second reference potential divider by applying them to the inputs of a differential amplifier supplying heating current to the element. If the temperature of the element changes, changing its resistance, the amplifier output changes the amount of power supplied to the katharometer element to restore it to the predetermined temperature. Passage of a gas with a different thermal characteristic over the element changes its temperature which is corrected by the circuit so that the element operates at a constant temperature. The output of the amplifier to maintain the constant temperature is therefore a measure of the gas thermal conductivity.

Abstract: An apparatus and method for the detection and measurement in a molten metal sample of suspended particulates comprises a container having a composite wall including concentric electrically conducting outer and inner walls (10) and (12) and a disc (14) of refractory material having a passage (16) of predetermined size therethrough providing communication between the inside and outside of the container. In use, molten metal is pumped through the passage (16) so as to establish a current path from the inner wall through the passage to the out wall. A current is passed along the current path, and voltage changes are measured as indicating passage of suspended particulates through the passage.