# US 2010/0164512 A1 · Process and device for differentiating objects influencing an electromagnetic alternating field, in particular metal objects > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2010/0164512 A1 - Document ID: US20100164512A1 - Status: Published application - Kind: A1 - Application number: 12/528,131 - Filed: 2008-02-22 - Published: 2010-07-01 - Earliest claimed: 2007-02-23 - Assignees: Evk Di Kerschhaggl GmbH - Inventors: Michael Kiss; Bemhard Kohla; Bemd Graze - Web page: https://patentgrep.com/patent/US20100164512A1 ## CPC - G01V 3/101: {by measuring the impedance of the search coil; by measuring features of a resonant circuit comprising the search coil (measuring impedance or characteristics derived therefrom G01R27/00, e.g. quality factor G01R27/26)} - B07C 5/344: according to electric or electromagnetic properties {(sorting according to size measured electrically or electronically B07C5/08; material testing by magnetic means G01N24/00, G01N27/00, by electrical means G01N27/00; electrical measuring devices in general G01R; coin testing G07D5/00)} - B07C 5/366: {during free fall of the articles} - G01R 33/12: Measuring magnetic properties of articles or specimens of solids or fluids (involving magnetic resonance G01R33/20) - G01V: GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS (means for indicating the location of accidentally buried, e.g. snow-buried, persons A63B29/02) - B07C: POSTAL SORTING; SORTING INDIVIDUAL ARTICLES, OR BULK MATERIAL FIT TO BE SORTED PIECE-MEAL, e.g. BY PICKING (specially adapted for a specific purpose covered by another class, see the relevant place, e.g. A43D33/06, B23Q7/12) - G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12) ## Abstract The invention relates to a method for differentiating conductive and/or ferromagnetic objects (O) in a material stream (2), comprising the generation of an electromagnetic alternating field by means of exciting a coil (S) having a sinusoidal voltage (ue(t)) of a constant frequency (fM), the detection of an impedance change of the coil caused by an object (O) by determining at least one pair of values from a peak value (ÎM) and a phase shift (ΦM) of the coil current (iM(t)) for the excitation voltage (ue(t)) of the coil, and the determination of the material by comparing the peak values (ÎM) and the phase shifts (ΦM) to reference values, wherein the peak values (ÎM) of the coil current (iM(t)) are calculated at least one measuring phase angle (ΦM) by means of a limit comparator at a constant limit width (Δi), wherein the time (ΔtM) between the limit entry point (p4) and the limit exit point (p6) of the coil current (iM(t)) is measured, and the increase of the current path (iM(t)) is calculated from the limit width (Δi) and the time measured (ΔtM), and the peak value (ÎIM) is calculated from the increase of the sinusoidal current path (iM(t) and the frequency (fM) thereof. ## Claims ### Claim 1 A process for differentiating objects (O) influencing an electromagnetic alternating field, having metal objects, using a coil (S) arranged on a conveying route on which a material stream is moved in one direction (x) at a predetermined speed (v), wherein the material stream comprises conductive and/or ferromagnetic objects (O), comprising the steps of: generating an electromagnetic alternating field by exciting the coil (S) with a sinusoidal voltage (ue(t)) of a constant frequency (fM), detecting an impedance change in the coil S, which has been caused by an object (O), by determining at least one pair of values from a peak value (ÎM) of a sinusoidal coil current (iM(t)) and a phase shift (φM) between the coil current (iM(t)) and the excitation potential (ue(t)), and determining the material (Mat1, Mat2) of the object (O) by comparing the at least one pair of values from a peak value (ÎM) and a phase shift (φM) of the sinusoidal coil current (iM(t)) with reference values, wherein the peak values (ÎM) of the sinusoidal coil current (iM(t)) are calculated at least one predetermined measuring phase angle (φM) with the aid of a window comparator having a constant, adjustable, window width (Δi), wherein the time (ΔtM) between the window inlet point and the window outlet point of the coil current (iM(t)) is measured and the gradient of the current profile (iM(t)) is calculated from the window width (Δi) of the window comparator and the measured time (ΔtM) and the peak value (ÎM) is calculated from the gradient of the sinusoidal current profile iM(t) and its known frequency (fM). ### Claim 2 (depends on 1) The process according to claim 1, wherein the values of the inlet point and the outlet point of the window of the window comparator are arranged symmetrically to a signal centre line, in particular zero line, of the coil current. ### Claim 3 (depends on 1) The process according to claim 1, wherein at least one peak value (ÎM) determined in a discrete measuring phase (φM) is compared to corresponding peak values of reference samples for determining the material of the object (O). ### Claim 4 (depends on 1) The process according to claim 1, wherein at least one measuring phase (φM) near a maximum angle of phase difference (φmax), which occurs when the object (O) comes closest to the coil (S), is selected, wherein, the distance between the measuring phase angle (φM) and the maximum angle of phase difference (φmax) is chosen to be at least so large that it is achieved also with the smallest objects (O) occurring in the material stream. ### Claim 5 (depends on 1) The process according to claim 1, wherein the moment of achieving the measuring phase angle (φM) with a known speed (v) of the material stream is used as a reference moment for discharging the object (O) from the material stream. ### Claim 6 (depends on 1) The process according to claim 1, wherein the maximum angle of phase difference (φmax) is determined. ### Claim 7 (depends on 1) The process according to claim 1, wherein the moment of achieving the maximum angle of phase difference (φmax) with a known speed (v) of the material stream is used as a reference moment for discharging the object (O) from the material stream. ### Claim 8 (depends on 1) The process according to claim 1 wherein by periodically detecting pairs of values from the peak value and phase shift of the current profiles (i0(t), iM(t)), the respective locus curve (A1, A2) is received point by point for different phase angles φ(x) and used for evaluation via comparison with reference locus curves. ### Claim 9 (depends on 1) The process according to claim 1, wherein the offset phase (φos) is determined from the excitation potential distribution ue(t) and the current profile i0(t) of the coil S in a condition which is unaffected by objects (O) and subsequently the measuring phase angles (φM) of the current profiles (iM(t)) are related to the offset phase (φos). ### Claim 10 (depends on 1) The process according to claim 1, wherein the excitation or measuring frequency fM, respectively, is adjusted to a value ranging between 1 kHz and 1 MHz, between 5 and 100 kHz and between 10 and 50 kHz. ### Claim 11 (depends on 1) The process according to claim 1, wherein the coil diameter (d) is chosen to be smaller than an average diameter (D) of the objects (O) to be differentiated. ### Claim 12 A device for differentiating objects (O) influencing an electromagnetic alternating field, comprising: a voltage source for generating a sinusoidal excitation potential (ue(t)) of a constant frequency (fM), a coil (S) which is supplied with the excitation potential (ue(t)) for generating an electromagnetic alternating field, calculating means for detecting an impedance change in the coil (S), which has been caused by an object (O), by determining at least one pair of values from a peak value (ÎM) of a sinusoidal coil current (iM(t)) flowing through the coil (S) and a phase shift (φM) between the coil current (iM(t)) and the excitation potential (ue(t)), and means for determining the material (Mat1, Mat2) of the object (O) by comparing the at least one pair of values from a peak value (ÎM) and a phase shift (φM) of the sinusoidal coil current (iM(t)) with reference values, wherein a window comparator has a constant, adjustable, window width (Δi) which is supplied with the coil current (iM(t)) and, respectively, a voltage signal uM(t) proportional thereto, time recording means for measuring the length of time (ΔtM) which the coil current (iM(t)) needs in order to pass through the comparator window (Δi), with the calculating means being designed for calculating the gradient of the current profile (iM(t)) from the length of time (ΔtM) and the window width (Δi) of the window comparator at least one predetermined measuring phase angle (φM) as well as for calculating the peak value (ÎM) from the gradient of the sinusoidal coil current iM(t) and its known frequency (fM). ### Claim 13 (depends on 12) The device according to claim 12, wherein a current/voltage transformer, for converting the coil current (iM(t)) into a proportional voltage signal UM(t). ### Claim 14 (depends on 12) The device according to claim 12, wherein the coil (S) is connected with a capacitance (C) into an oscillating circuit. ### Claim 15 (depends on 12) The device according to claim 12, wherein the values of the inlet point (−Vref) and the outlet point (+Vref) of the window of the window comparator are arranged symmetrically to a signal center line, in particular zero line, of the coil current. ### Claim 16 (depends on 12) The device according to claim 12, wherein a comparator for detecting the zero crossing (NL) of the excitation potential (ue(t)). ### Claim 17 (depends on 12) The device according to claim 12, wherein the time recording means are designed as digital counters with a constant counting frequency. ### Claim 18 (depends on 17) The device according to claim 17, wherein the output signal (K1) of the zero-crossing comparator starts the counters and the window comparator stops a counter when the coil current (im(t)) enters into the comparator window and stops a further counter when the coil current (iM(t)) leaves the comparator window. ### Claim 19 (depends on 18) The device according to claim 18, wherein, from the difference of the two counts, the length of time (ΔtM) is derived which the coil current (iM(t)) needs in order to pass through the comparator window (Δi). ### Claim 20 (depends on 17) The device according to claim 17, wherein the window comparator starts a counter when the coil current (iM(t)) enters into the comparator window and stops the counter when the coil current (iM(t)) leaves the comparator window. ### Claim 21 (depends on 12) The device according to claim 12, wherein the calculating means are designed for comparing at least one peak value (ÎM) determined in a discrete measuring phase (φM) to corresponding peak values of reference samples for determining the material of the object (O). ### Claim 22 (depends on 18) The device according to claim 18, wherein the calculating means are designed for using the counted measurand of the second counter as an index of a reference value table and for reading out, for each index value (Ref—1-Ref—5), a reference threshold value (Lim—1-Lim—5) associated therewith and for comparing it to the counted measurand of the first counter and for inferring the material of the object (O) from exceeding or falling below the reference threshold value (Lim—1-Lim—5) used in each case. ### Claim 23 (depends on 12) The device according to claim 12, wherein the excitation potential (ue(t)) is adjusted to a value ranging between 1 kHz and 1 MHz, between 5 and 100 kHz and between 10 and 50 kHz. ### Claim 24 (depends on 12) The device according to claim 12, wherein a measuring cycle is performed in each period of the excitation potential (ue(t)). ### Claim 25 A sorting plant comprising a conveying means on which a material stream is movable at a constant speed v in which objects O are contained which are supposed to be identified based on their conductivity and/or ferromagnetic properties and sorted out by means of an object discharging unit, at least one device for differentiating objects (O) influencing an electromagnetic alternating field, having a voltage source for generating a sinusoidal excitation potential (ue(t)) of a constant frequency (fM), a coil (S) which is supplied with the excitation potential (ue(t)) for generating an electromagnetic alternating field, calculating means for detecting an impedance change in the coil (S), which has been caused ban object (O), by determining at least one pair of values from a peak value (ÎM) of a sinusoidal coil current (iM(t)) flowing through the coil (S) and a phase shift (φM) between the coil current (iM(t)) and the excitation potential (ue(t)), and means for determining the material (Mat1, Mat2) of the object (O) by comparing the at least one pair of values from a peak value (ÎM) and a phase shift (φM) of the sinusoidal coil current (iM(t)) with reference values, having a window comparator having a constant, adjustable, window width (Δi) which is supplied with the coil current (iM(t)) and, respectively, a voltage signal uM(t) proportional thereto, time recording means for measuring the of time (ΔtM) which the coil current (iM(t)) needs in order to pass through the comparator window (Δi), with the calculating means being designed for calculating the gradient of the current profile (iM(t)) from the length of time (ΔtM) and the window width (Δi) of the window comparator at least one predetermined measuring phase angle (φM) as well as for calculating the peak value (ÎM) from the gradient of the sinusoidal coil current iM(t) and its known frequency (fM), wherein the coil (S) is arranged close to the conveying means so that objects (O) moving in the conveying direction (x-direction) of the material stream will cause a material characteristic impedance change in the coil (S), which is detected by the device, with the device activating the object discharging unit.