Abstract: An arrangement for detecting metallic particles carried by a fluid includes a metallic probe member which surrounds an elongated passage through which the fluid flows and which is constituted by a split tube having two marginal portions delimiting a gap which extends along said passage and completely separates the marginal portions from one another. Capacitors are arranged at the gap and alternating electric current is caused to flow in the probe member around the passage so that the probe member and the capacitors form a tank circuit having resonance characteristics that are influenced by any inclusion then present in the passage in a manner dependent on the electromagnetic properties of the inclusion. The character of any metallic particle then present in the passage is determined from variations in the alternating electric current that reflect the influence of such metallic particle on the resonance characteristics.

Abstract: An inductance coil serves as a displacement sensor arranged in connection with a tuned circuit of an oscillator. Liquid level displacement in an LEC crystal growth environment is sensed as a frequency change in the oscillator circuit as compared to a set point value. The sensor is protected from the environment by an outer protective sheath of non-conductive, non-contaminating material such as boron nitride.

Abstract: A magnetic sensor for the collection and measurement of ferrous particles through the use of an electronic tuned circuit is disclosed. The sensor contains an electrical inductance along with an integral magnet to attract ferrous particles suspended in the fluid. The ferrous particles collecting on the magnetic surface of the sensor causes a change in the inductance of the integral coil which is measured by an electronic circuit. The electronic circuit operating in conjunction with the sensor utilizes a parallel tuned resonant circuit and time variant frequency multiplying to eliminate undesired response changes of the tuned circuit due to the temperature change of the sensor. The sensor may be located in environmental conditions which include a large variation in ambient temperature. The disclosed invention provides for compensation of such undesired changes caused by temperature change so that the actual change of the inductance in the sensor can be monitored without interference.

Abstract: An improved gas sensor which optically senses a signal indication proportional to the concentration of a paramagnetic/diamagnetic gas in a gaseous mixture. In a preferred embodiment of the invention a chamber is adapted to contain a gaseous mixture to be measured for the concentration of a paramagnetic/diamagnetic gas in the mixture. An optical source provides light to a movable element coupled to the chamber. In response to the application of a magnetic field across the chamber, any paramagnetic/diamagnetic gas in the chamber causes the movable element to be displaced by a distance proportional to the concentration of the paramagnetic/diamagnetic gas in the gaseous mixture. A photodetector circuit receives light from the movable element having a characteristic indicative of the distance that the movable element was displaced. In response to such received light, the photodetector provides a signal output proportional to the concentration of the paramagnetic/diamagnetic gas in the gaseous mixture.

Abstract: A method of investigating the condition of biological particles, in particular the fraction of viable cells in a bacteria population involves applying a voltage and monitoring the voltage induced by magnetic induction in a detector coil. The applied voltage is of a variable frequency alternating voltage and is preferably induced in the medium through a drive coil.

Abstract: A closed loop-like measuring passage is provided with two openings at symmetrical positions, and a sample gas is introduced through on opening into the passage and discharged therefrom through the other opening. A bypass pipe is connected to the measuring passage midway therealong, and a stable purge gas of known composition is introduced into the pipe from the center thereof. A magnetic field is generated in one of the two connecting portions between the bypass pipe and the measuring passage, and the oxygen gas attracting action of the field results in a change in the ratio of the split of the purge gas stream introduced into the bypass pipe and split into two streams. This change is detected by a pair of purge gas stream detecting sensors provided inside the bypass pipe symmetrically with respect to the portion through which the purge gas is introduced, and the thus detected signals are processed to obtain the difference between them which gives the oxygen gas concentration in the sample gas.

Abstract: A slag detector apparatus for detecting onset of 5% or less slag entrainment in a stream of molten metal employs a detection coil having an axial length at least equal to the length of a globule of molten metal in the stream being composed of a continuous succession of recurring cyclical globules of molten metal, and an impedance detector for periodic sampling and smoothing of the fluctuations of the terminal impedance of the detector coil corresponding to the fluctuating cross-sectional dimension of the stream. The detector coil is part of a signal sensitivity enhancement circuit in the apparatus which also includes a tunable capacitor connected with the detector coil. The capacitor is used for tuning the circuit to its resonance frequency so that the capacitive reactance of the circuit due to the presence of the capacitor cancels the inductive reactance of the circuit due to the presence of the coil so as to leave only an impedance that is due to resistance of the coil.

Abstract: A detector for producing an electrical signal proportional to the concentration of ferromagnetic particulate material in a fluid stream includes a sensing coil arranged to form the inductance coil of a radio frequency oscillator arranged to produce an electrical signal at a base frequency, a magnetic trap for producing a magnetic field and a support for supporting the sensing coil and the magnetic trap in juxtaposition to one another such that, when the coil is disposed within or proximate the fluid stream and electrically connected to the oscillator, energization of the magnetic trap causes ferromagnetic particulate material proximate the coil to be attracted toward the coil resulting in a deviation of the frequency of the signal from the base frequency proportional to the concentration of ferromagnetic particulate material in the fluid stream.

Abstract: The detection and identification of metal items is effected by a marginal oscillator the resonant circuit of which has an inductor surrounding a path along which any metal items are caused to travel. The frequency and amplitude changes in the oscillation produced by the oscillator due to the presence of a metal item in the inductor are compared with the changes caused by items of known metals and the identity of the metal of the item is derived from the comparison. Continuous or periodic drift correction of the frequency and amplidude values may be effected using a reference coil. Among other examples the invention may be used to monitor metallic particles in a lubricant or to identify larger items such as coins.

Abstract: A diagnostic debris sensor operating on the inductive pulse is triggered by ferrous particles floating by or attracted to a permanent magnet within a pulse-sensing coil and the entire sensor at that, the pulse-sensing coil is equipped with a second winding for either continuous monitoring or an occasional push-to-test checking of the pulse-sensing coil.

Abstract: The buildup of slag or ash on the interior surface of a furnace wall is monitored by disposing two coils to form a transformer which is secured adjacent to the inside surface of the furnace wall. The inductive coupling between the two coils of the transformer is affected by the presence of oxides of iron in the slag or ash which is adjacent to the transformer, and the application of a voltage to one winding produces a voltage at the other winding that is related to the thickness of the slag or ash buildup on the inside surface of the furnace wall. The output of the other winding is an electrical signal which can be used to control an alarm or the like or provide an indication of the thickness of the slag or ash buildup at a remote location.

Abstract: A method and an apparatus for the detection of slag co-flowing within a sam of molten steel being poured from metallurgical vessel, more particularly during continuous casting, makes it possible to detect even a small quantity of slag in the emerging flow of molten metal without requiring the removal of the shielding for the pouring stream, or without interfering with the pouring, by measuring changes in the electrical conductivity of the pouring system by means of electromagnetic fields. To this end, one or more transmitter coils and receiver coils are mounted fixedly around the pouring stream. The transmitter coils are fed with a current containing several frequencies, and the magnitude and phase position of the voltage induced in the receiver coils are evaluated frequency-selectively so as to increase the sensitivity, the measuring transducer being operated in a bridge circuit.

Abstract: A method of investigating the condition of biological particles, in particular the fraction of viable cells in a bacteria population involves applying a voltage and monitoring the voltage induced by magnetic induction in a detector coil. The applied voltage is of a variable frequency alternating voltage and is preferably induced in the medium through a drive coil.

Abstract: Paramagnetic gas analyzer comprising an electromagnet with an almost closed ferromagnetic circuit and a gap, including a measuring chamber with inlet and outlet lines for the gas to be analyzed as well as a gas of known magnetic susceptibility where devices are provided which measure the differential gas pressures in the respective lines by supplying an AC current to the electromagnetic. According to the present invention it is shown, how the power consumption can be considerably reduced. This object is achieved by superimposing a DC magnetic field generated by means of a permanent magnet onto the AC magnetic field. The amplitude of the measuring result depends on the product of the AC field and the DC field. If the DC field is strong enough, the AC field and thus the supplied power can be reduced accordingly. The latter also facilitates the filtering off of predetermined, undesirable signals.

Abstract: According to the present invention an oxygen measuring cell (10) is suggested comprising inlet conduit means (28) and outlet conduit means (30) for gas to be analyzed, further comprising two nitrogen-filled gas balloons (60, 62) arranged at respective ends of a dumbbell (58) which is secured, in its middle section, to a torsion part (54) arranged in transverse relationship to said dumbbell (58) for forming a torsion balance, further comprising magnet means for producing an inhomogeneous magnetic field in the region of said torsion balance, and comprising a measuring chamber (22) surrounding said torsion balance, said measuring chamber being, at least partially, of rotationally symmetric shape, said torsion part (54) extending along the longitudinal axis of said measuring chamber (22).

Abstract: A device for the determination of the concentration of substances with paramagnetic properties, particularly oxygen, in substance mixtures comprises a cell assembly divided into several chambers, which is arranged to revolve with relation to a service for producing a magnetic field penetrating the cell assembly, and a coil assembly associated with this assembly for the conversion of the magnetic induction produced in it by the paramagnetic substance into an electrical signal. The assembly of devices producing magnetic fields and their associated measuring field coils is unaffected by external interferences such as transfer of mechanical vibrations or influences of external magnetic fields.

Abstract: Gas testing apparatus comprises a gas chamber wherein a test body surrounded by a single turn electrical conductor is suspended by a metal strip in a non-uniform and non-symmetrical magnetic field which is formulated by especially shaped pole pieces which could, in one form, by permanent magnets. The test body is deflected from the initial position it takes when a reference gas is in the cell, by the admittance of a gas mixture of which is paramagnetic gas is one constituent. The deflection is sensed by an optical system comprising a light source, a mirror on the test body and a pair of photocells. The output of the photocells feeds an amplifier system, which in turn feeds the single turn coil by a current of an adequate value such that it stops the test body from moving from its initial position and hence is proportional to the partial pressure of the paramagnetic gas in the sample.

Abstract: The thickness of the layer of remaining molten metal at the bottom of a container is measured on tapping molten metal from the container. An alternating magnetic field is generated with a frequency such that the penetration depth (.delta.) in the metal is of the same order of magnitude as the residue thickness of the melt layer of interest for measurement. The alternating magnetic field is generated such that to begin with field components are reflected at a horizontal surface of the melt layer and towards an alternating magnetic field detection position. When the thickness of the melt layer decreases and approaches the residue thickness, less and less field components will be reflected at the surface of the melt and pass instead through the remaining melt layer. The resulting change in detected alternating magnetic field is utilized, e.g. for triggering an alarm or breaking off tapping in some other way.

Abstract: A method and apparatus is provided for characterizing magnetic coating compositions that contain magnetic particles dispersed in a solvent resin matrix. The coating composition, as it passes through a tube, is subjected to an alternating magnetic field and perpendicular thereto a constant magnetic field of appropriate field strength and duration. Via a measuring coil surrounding the tube the induced signal in the composition is monitored and the degree of dispersion, is measured by measuring the magnetic susceptibility of the coating material. By applying a constant magnetic field the degree of dispersion cna be changed at least for a certain time. The method and apparatus of the present invention can be incorporated into a coating apparatus to monitor and improve the magnetic characteristics of the coating material being applied to a substrate.

Abstract: A paramagnetic measuring instrument comprises a magnetic circuit, formed from ferromagnetic material and having pole ends defining a discontinuity, and a gas measuring chamber disposed in the discontinuity between the pole ends. The measuring chamber includes a frame shaped outer part formed from nonmagnetic material and having a central opening extending between the pole ends; two ferromagnetic pole shoes each respectively disposed adjacent a separate one of the pole ends and extending into the opening of the outer part; two distribution channels disposed in the outer part on opposite sides of the measuring gap for supplying a measuring gas and a comparison gas, respectively, to the measuring gap; and inlet and outlet gas lines for supplying the measuring gas and the comparison gas, respectively, and removing the mixture formed from the measuring and comparison gases.

Abstract: The specification describes a method and an apparatus for detecting and quantitatively assessing wear of a machine having ferromagnetic components subjected to wear during operation resulting in the production of ferromagnetic particulate wear debris, and a lubrication system utilizing a lubricating fluid, in which the wear debris becomes entrained, for lubricating the components. The method comprises the steps of passing a sample stream of the lubricating fluid at a predetermined rate of flow axially through the core of an inductance coil of a sample oscillator for producing a time varying signal which deviates from a predetermined value in proportion to the mass of ferromagnetic material contained in the fluid passing through the core, monitoring the rate of change of signal and activating an indicator when the rate of change of the signal exceeds a predetermined level.

Abstract: A device for the determination of the concentration of substances with paramagnetic properties, particularly oxygen, in substance mixtures comprises a cell assembly and devices to produce a magnetic field as well as to measure changes in the magnetic induction. Great mechanical accuracy and stability in the measuring of a change in the magnetic induction uninfluenced by external disturbing fields or by mechanical changes due to external temperature fluctuations or vibrations with a coil assembly for producing a magnetic field and for measuring the induction signal comprising self-contained coil carriers, which, surrounding a cell assembly and are arranged respectively at a distance from the axis of rotation of the cell assembly.

Abstract: This invention relates to a device for detecting electrically inductive particles in a fluid medium and is of particular use for detecting ferrous particles in the lubricant of an engine or mechanical transmissions thereby giving warning of malfunction of the engine or the transmission. The invention is of particular importance for the operation of an internal combustion engine, especially highly stressed helicopter and aircraft engines wherein prior warning of a malfunction permits corrective action prior to a catastrophic failure.

Abstract: An apparatus for indicating by electromagnetic means the level in metallurgical vessels means with transmitting and receiving coils which combined into a measuring unit having a transmitting coil which extends in the direction of the fill height and at least two receiving coils assigned thereto and staggered vertically. This simplifies and facilitates the assembly work.

Abstract: A method for testing electrostatic developer toners which comprises applying the toner to a stationary non-magnetic sleeve (4), moving the toner along the surface of the sleeve by an array of field lines generally normal to the surface produced by a multiple magnetic roll (1) rotating within the sleeve and determining the characteristics of the toner from the pattern (15) of the spread toner by reference to a calibrated scale (9) and a stop line (5) on the surface of the sleeve.

Abstract: An improved method and device for measuring magnetic particles in a liquid wherein a known amount of liquid is contacted with a bed of ferromagnetic fibers maintained in the magnetic field of a magnet with sufficient strength to substantially completely magnetize said particles for a time long enough for said particles to migrate to and be substantially completely captured by said fibers and having a magnetic flux sensor positioned between a pole face of said magnet and said bed wherein the distance from said sensor to the fibers farthest from said sensor is not greater than about 6 millimeters.

Abstract: A method and device for measuring the amount of magnetic particles in a fluid such as ferrous wear particles in the lubricant of a machine. The particles are entraped by contacting a volume of the fluid with a means to entrap the particles and magnetized by subjecting the entraped particles to a magnetic field. The amount of magnetic particles entraped is measured by measuring the magnetization of the entraped and magnetized particles.

Abstract: Process and apparatus for measuring the difference in the concentration of paramagnetic components between an unknown gas and a standard gas by periodically alternate entry of both gases into the gap chamber (2) of a magnetic circuit (1) and by detecting the periodical variations of the magnetic flux caused by the gases in the magnetic circuit.In this process,(a) the two gases are brought into the gap chamber (2) from opposite directions through gas lines (5, 6),(b) the boundary zone between the two gases perpendicular to the magnetic lines of force is moved back and forth in the gap chamber periodically by an alternating flow generator (7), and(c) constantly a portion of the gas mixture is made to escape through an exhaust line (9) from the region of the gap chamber (2) by the inflowing of at least one of the two gases.

Abstract: An oxygen sensor utilizes the paramagnetic property of oxygen to determing the relative concentration of oxygen in a test gas. The test gas is supplied to the core of an electromagnet or the gap of a permanent magnet. A known magnetic flux density for the electromagnet or permanent magnet are utilized in conjunction with a Hall effect sensor to determine a change in flux which is primarily due to the oxygen component of the test gas.

Abstract: For characterizing coating compositions with magnetic particles the coating composition is subjected to an alternating magnetic field of variable frequency. The field induced by the coating composition after energization is recorded, and thus the susceptibility of the coating composition is measured. Depending on the variable frequency, conclusions can be made regarding the degree of dispersion, particle density, and viscosity of the coating composition. The variable frequency is between 1 and 100 cps, and the field intensity of the energizing field should be lower than 10 Oerstedt. The coating composition is fluid or stagnant in a pipe *1, 11 which is surrounded by field coil and measuring coil.

Abstract: The specification describes a method and an apparatus for detecting and quantitatively assessing wear of a machine having ferromagnetic components subjected to wear during operation resulting in the production of ferromagnetic particulate wear debris, and a lubrication system utilizing a lubricating fluid, in which the wear debris becomes entrained, for lubricating the components. The method comprises the steps of passing a sample stream of the lubricating fluid at a predetermined rate of flow axially through the core of an inductance coil of a sample oscillator for producing a time varying signal which deviates from a predetermined value in proportion to the mass of ferromagnetic material contained in the fluid passing through the core, monitoring the rate of change of signal and activating an indicator when the rate of change of the signal exceeds a predetermined level.

Abstract: A large number of equally spaced Hall-sensors form a column. They are mounted in a tube with a closed bottom. Each sensor is a packaged integrated circuit with a Hall-cell connected to a Schmitt Trigger circuit. An annular float being fitted slidably about the tube carries a compound magnet that generates a pattern of regularly spaced apart magnetic field regions each having the same dimensions and each capable of switching an immediately adjacent Hall-sensor. The Hall-sensors are energized sequentially and one at one time. By counting the number of Hall-sensors scanned, from the beginning end of the column to the first Hall-sensor that is switched, a rough measure of the liquid level is obtained. The magnetic field regions are spaced apart by a distance that is not equal to the Hall-sensor spacing so that the pattern of Hall-sensor output voltages provides a unique vernier measure of the liquid level that is appropriately added to the afore-said rough measure.

Abstract: A detector of ion concentration in a liquid is composed of a detection cell comprising a tubular piece formed from an electrically insulating material with a central passage which is fed with a liquid whose ion concentration is to be measured. A conducting coil is placed around the tubular piece, and is part of a first resonant circuit. A second reference resonant circuit is also provided, and signals of fixed frequency are applied in parallel to the two resonant circuits, and a comparator delivers a signal having a magnitude representative of the difference between the output signals from the two resonant circuits. Such a detector finds a use for example in liquid chromatography.

Abstract: Disclosed is an inductance detector for detecting boundaries between and characteristics of at least two adjoining substances having different characteristics, such as impedance, wherein a coil assembly, which is energized by an alternating current, is electrically coupled to a detector for detecting at least changes in impedance of the coil assembly caused by the boundary proceeding into and through the coil assembly.

Abstract: A device for detecting metallic objects in a material flow, comprising as sensing member a scanning coil consisting of a primary coil and, for example, two oppositely connected secondary windings arranged symmetrically around the primary winding so that the voltage induced in the secondary winding becomes zero as long as no conducting objects appear in the scanning area. To eliminate irrelevant signals from conducting objects in the vicinity of the scanning coil but not in the material flow or from weakly conducting objects in the material flow, the primary winding is fed with at least two alternating currents having different frequencies. The corresponding secondary voltages are rectified in phase-controlled rectifiers, and in a calculating circuit the difference is derived between the output of one rectifier voltage and the output of another rectifier multiplied by a constant factor which includes the relation between the frequencies of the corresponding alternating voltages.

Abstract: A high permeability ferrite core, which includes a gap between adjacent ends thereof, is combined with a magnetic coil encircling the core, and is located in a sub positioned in the drill string just above the drill bit of a borehole drilling rig. The core is positioned so that the gap thereof lies across a recess region formed in the outer wall of the sub. Drilling fluids flow along the outer surface of the sub on the return path from the drill bit to the mud pits located at the surface of the borehole. A constant current, or voltage, at a frequency within the range of 20 KHz-20 MHz is applied to the terminals of the coil encircling the core and the eddy currents developed in the gap region produce a measurable back emf at the coil terminals. The current produced by this emf voltage is indicative of the resistivity of the drilling fluid within the recess region in the wall of the sub and the fluctuations of the voltage accurately follow the variations in drilling fluid resistivity.

Abstract: A method for determining the size of metal particles which includes the positioning of an inductive circuit within a particle flow path to establish an oscillatory signal, varying the signal frequency to determine at which amplitude a signal is substantially constant, and then recording changes in signal amplitude which correlate to changes in particle size.

Abstract: Method and apparatus to monitor the quantity of magnetically permeable particles in admixture with a fluid carrier in which the mixture is placed in a magnetic field having flux lines which change in direction or position. The mixture is out of physical contact with a source of the field and with a movable member the degree of movement of which is influenced by the strength of the field. The degree of movement of the member is monitored and this corresponds to the quantity of particles in the mixture.

Abstract: A xerographic copying apparatus including a device for monitoring the concentration of toner in a xerographic developer mixture of ferromagnetic particles and non-ferromagnetic toner, said device comprising a measuring induction coil that is mounted close to the developer supply so that its magnetic field traverses a portion of the mass of the developer, and a reference induction coil that is mounted close to the measuring coil, but with its magnetic field prevented from traversing the developer mixture, and suitably closely on a wall of the hopper for the toner supply.

Abstract: An improved method and apparatus of producing Ferrograms in which centrifugal force is used to facilitate the spread of a deposit of magnetically or electrically polarized or polarizable particles onto a substrate to facilitate subsequent analysis of the particles.

Abstract: A predetermined quantity of the fluid to be analyzed is made to pass through magnetized filtering packing, and the content of the solid fraction is measured after the exit of the fluid from the packing, before its re-entry into it. Recirculation is continued until a permanent, unvarying residual content of the solid phase in the fluid is attained. The fluid subjected to the recirculation is periodically acted upon by an alternating magnetic field, outside the packing.

Abstract: A debris detection system for detecting debris in a fluid flow in which both a primary and a secondary fluid flow from a fluid reservoir are maintained. The fluid reservoir is situated downstream of the system being served and receives the debris from the system being served. Within the reservoir the primary fluid flow is shielded from all but the colloidal debris received. All non-colloidal as well as colloidal debris is diverted to the secondary fluid flow where the amount and rate of debris accumulation is detected.

Abstract: A sensor for sensing the presence of oxygen in a test gas mixture comprises either first or second tubes for the separate flow of a measured gas and a gas to be tested for a single tubular arrangement for the successive flow of these two gases in association with a plurality of radio-frequency coils which are connected in an electrical bridge circuit to that they can be balanced in any variation of the inductance measure. Since oxygen in the gas produces a paramagnetism which provides induction variations in the coils of the balancing circuit, the variations of the balancing circuit may be used to sense the proportion of the oxygen content in the gases. With the inventive method the gases are passed into association with the balancing circuit and variations of the test gas from the measured gas are sensed by the circuit balance which is produced by the oxygen which is present in the gas mixtures. Such a sensor may be used for breath protection, diving and medical fields.

Abstract: A device for measuring local electric conductivity of plasma, comprising a probe, which is kinematically coupled to a drive mechanism and has a series circuit including an inductive sensor, a measuring oscillator, and a detector having one output coupled, via an optoelectronic converter, to a differential stage having a switch and a memory member. An output of the differential stage is coupled to one input of a measurement recording unit having another input coupled to a unit for feeding commands which is electrically coupled to an electropneumatic control unit accommodating air valves of drive mechanisms of the probe and calibration crystal, the air valve being coupled to pneumatic cylinders of the drive mechanisms by means of flexible bases made of an insulating material.

Abstract: An oxygen detection system including two equal and symmetrically constructed major DC magnetic circuits each having an air gap which is alternatively filled with a sample and a reference gas. A magnetic bridge arm connects the major magnetic circuits in series opposition to derive a null response when the flux carried in the magnetic circuits is equal and a component of varying flux when the sample and reference gases are interchanged to cause an unequal flux to be developed in the circuits caused by a change in the reluctance across the gaps. An encircling inductance coil senses the flux in the null bridge arm which is electronically sampled in sychronism with the sample and reference gas interchange to develop a difference signal directly derived and proportional to the difference in magnetic susceptibility of the sample and reference gases. An active magnetic shield cancels stray fields from affecting the sensor.

Abstract: A paraffin monitor includes a pair of probes which are immersed in a medium having paraffin contained therein. A circuit is connected to the probes which provides an output voltage. The characteristics of the electric circuit changes over a period of time, causing a corresponding change in the voltage output, in accordance with a change in the amount of paraffin on the probes.

Abstract: The invention relates to a method permitting the magnetic properties of ferromagnetic powders which are used for the preparation of heavy media for the float-sink dressing of minerals, to be tested. To this end, the invention provides for the ferromagnetic powder to be magnetized in a magnetic steady field at a field strength within the range 600 to 1000 amperes per cm and the magnetized ferromagnetic powder to be demagnetized in a cyclicly decreasing magnetic alternating field at a field strength within the range 1000 to 1500 amperes per cm. Next, the ferromagnetic powder so pretreated is heaped up, in the center portion of a circular plate made from dielectric material and the circular plate is placed on an iron core-provided coil. An alternating current voltage of 180 to 260 volts is applied to the coil, thereby effecting the occurrence of alternating fields of 180 to 220 amperes per cm in the center portion of the circular plate.

Abstract: A paraffin monitor includes a pulse source periodically providing pulses. Apparatus, adapted to be immersed in a medium having paraffin, provides an output signal in response to each pulse in accordance with a paraffin film grown on said apparatus while the apparatus is immersed in the medium.

Abstract: A magnetic analyzer is provided for detecting the concentration of a paramagnetic gas, such as oxygen, in a gas being tested. This detection is based on detecting the surface-pressure generated between a gas being tested and a comparison gas. The surface-pressure is sensed by a condenser-microphone which is coupled to comparison gas passageways in two pairs of magnetic pole pieces which are inserted in a measuring chamber filled with the gas being tested and which alternately generate a magnetic field.

Abstract: Methods and apparatus for monitoring the condition of dielectric fluid used in EDM are described. A continuous sample of dielectric liquid is withdrawn from a tank containing the EDM electrode and workpiece and is passed between electrodes of a capacitance cell before being returned to the tank. The capacitance between the electrodes gives an indication of the amount of metal particles resulting from EDM in the dielectric liquid. In another arrangement a magnetic field is used to direct most ferrous particles through a capacitance cell or part of a capacitance cell while most non-ferrous particles pass through another cell or another part of the cell. Measurement of the capacities of the cells or parts of cells provides an indication of the relative amounts of ferrous and non-ferrous particles in the dielectric liquid.