Measurement system of ferromagnetic particles
First Claim
1. An arrangement for quantifying the proportion of ferromagnetic particles in a medium, which arrangement comprises:
- a flow channel for the medium;
a low frequency source, which is a sine wave generator or a triangle wave generator, to generate a feed for basic magnetization of the ferromagnetic particles;
a high frequency source to generate an excitation for additional magnetization of the ferromagnetic particles, said high frequency source being connected to a carrier input of a modulator, in which case an output signal of the modulator is the excitation;
a magnetizing winding round said flow channel, connected to the low frequency source, to generate a magnetic field in the medium;
an excitating winding to be fed by the excitation round said flow channel to generate an additional magnetic field in the medium;
a secondary winding functioning as a sensor of the magnetic field to measure change in the magnetic flux density of the medium, or to generate a response; and
means for separating, a part from the response which is due to the magnetic non-linearity of the medium,wherein the arrangement further comprises means for generating the excitation from numerous frequency components so that a spectrum of the arrangement is wide in respect of spectra of typical interferences and at least nearly continuous, said means for generating the excitation comprising a third source, the output signal of which is a random signal and the third source being, connected to a modulation input of the modulator, and said means for separating from the response the part due to the magnetic non-linearity of the medium comprise after the secondary winding in order;
a high-pass filter to remove low frequency parts from the response;
a multiplier, to one input of which is connected through a delay unit a circuit feeding the excitating/magnetizing winding, and a bandpass filter to generate an actual signal; and
a detector, to carrier input of which is connected the low/high frequency source through a frequency multiplier and phase shifter, to generate an output signal.
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Abstract
A system by which the proportion of ferromagnetic particles in a dielectric medium is measured. A magnetic field is generated by two signals in the medium: a low frequency feed and a relatively high frequency excitation. The feed magnetizes the ferromagnetic particles in the medium to the nonlinear range of the magnetization curve. The excitation is generated so that its spectrum is relatively wide and it is dense with frequency components. The level of the excitation is so high that the magnetic flux density in the medium corresponding to the excitation fluctuates nonlinearly, when the feed is at its peak value or near this. The magnetic field of the medium is measured by a secondary winding, and from the response signal produced by the sensor is detected the part resulting from the magnetic non-linearity, which part is the output signal. In the detection the response is multiplied by the signal, which arises magnetic field and includes the same random fluctuation as the response. The higher the proportion of the ferromagnetic particles in the medium is, the higher the level of the output signal. The secondary winding comprises several portions so that the parasitic voltages caused by the stray capacitances compensate each other. The measurement is real-time and accuracy, because the excitation is a random signal by nature, in which case its spectrum includes, instead of one frequency component, densely frequency components in a certain band. The result is a 20-30 dB higher signal-to-noise ratio in the response and output signal compared with the known technique. A device according to the method is suitable for use in an industrial plant and moving vehicles, in which there are interfering fields and the temperature can be high.
8 Citations
21 Claims
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1. An arrangement for quantifying the proportion of ferromagnetic particles in a medium, which arrangement comprises:
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a flow channel for the medium; a low frequency source, which is a sine wave generator or a triangle wave generator, to generate a feed for basic magnetization of the ferromagnetic particles; a high frequency source to generate an excitation for additional magnetization of the ferromagnetic particles, said high frequency source being connected to a carrier input of a modulator, in which case an output signal of the modulator is the excitation; a magnetizing winding round said flow channel, connected to the low frequency source, to generate a magnetic field in the medium; an excitating winding to be fed by the excitation round said flow channel to generate an additional magnetic field in the medium; a secondary winding functioning as a sensor of the magnetic field to measure change in the magnetic flux density of the medium, or to generate a response; and means for separating, a part from the response which is due to the magnetic non-linearity of the medium, wherein the arrangement further comprises means for generating the excitation from numerous frequency components so that a spectrum of the arrangement is wide in respect of spectra of typical interferences and at least nearly continuous, said means for generating the excitation comprising a third source, the output signal of which is a random signal and the third source being, connected to a modulation input of the modulator, and said means for separating from the response the part due to the magnetic non-linearity of the medium comprise after the secondary winding in order; a high-pass filter to remove low frequency parts from the response; a multiplier, to one input of which is connected through a delay unit a circuit feeding the excitating/magnetizing winding, and a bandpass filter to generate an actual signal; and a detector, to carrier input of which is connected the low/high frequency source through a frequency multiplier and phase shifter, to generate an output signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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16. A method for quantifying the proportion of ferromagnetic particles in a medium, in which method comprises:
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a low frequency sinusoidal or triangular signal, or feed, is generated, by which a magnetic field is arisen in a medium to magnetize ferromagnetic particles in the medium to nonlinear range of the magnetization curve; a high frequency signal compared with the feed, or an excitation, is generated by which an additional magnetic field is arisen in the medium, said excitation being produced by modulating a carrier generated by a high frequency source by a random signal; changes in the magnetic flux density are measured; and a part due to the magnetic non-linearity of the medium is separated from a signal, or response (RE), produced by measuring, wherein the excitation is generated from numerous frequency components so that a spectrum of the excitation is at least nearly continuous and wide in respect of spectra of typical interferences, and for separating from the response the part due to the magnetic non-linearity of the medium; low frequency parts are removed from the response through filtering; the filtered response is multiplied by a delayed excitation signal that has ails the magnet field, which signal includes the same random fluctuation as the response; the part due to said non-linearity is detected from the signal obtained above, or the multiplication signal, to produce an actual output signal by removing from said multiplication signal by filtering the frequency components apart from frequency components in a certain range round the frequency 2f1, where f1 is the fundamental frequency of the feed. - View Dependent Claims (17, 18, 19, 20, 21)
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Specification