# US 2017/0131131 A1 · Method and apparatus for electrode impedance measurement > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2017/0131131 A1 - Document ID: US20170131131A1 - Status: Published application - Kind: A1 - Application number: 15/348,689 - Filed: 2016-11-10 - Published: 2017-05-11 - Earliest claimed: 2015-11-10 - Assignees: ABB AB - Applicants: ABB Limited - Inventors: Ray KEECH - Web page: https://patentgrep.com/patent/US20170131131A1 ## CPC - G01F 25/10: of flowmeters - G01F 1/584: {constructions of electrodes, accessories therefor} - G01F 1/586: {constructions of coils, magnetic circuits, accessories therefor (G01F1/582 takes precedence; magnet; inductances; transformers; selection of materials for their magnetic properties per se H01F)} - G01F 1/588: {combined constructions of electrodes, coils or magnetic circuits, accessories therefor} - G01F 1/60: Circuits therefor - G01R 27/26: Measuring inductance or capacitance; Measuring quality factor, e.g. by using the resonance method; Measuring loss factor; Measuring dielectric constants {; Measuring impedance or related variables} - G01F: MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME - G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12) ## Abstract A method measures electrical impedance of electromagnetic flowmeter sensing electrodes includes intermittently injecting an impedance measurement signal to at least one sensing electrode while a coil excitation drive signal is applied to flowmeter field generating coils. During a first interval, when the coil excitation drive signal is applied to the coils and the impedance measurement signal is injected to a sensing electrode, a first measurement signal is obtained. The first measurement signal includes an electromagnetically induced flow measurement signal and an electrode impedance measurement signal. During a second interval, when the coil excitation drive signal is applied to the coils but the impedance measurement signal is not injected to the sensing electrodes, a second measurement signal is obtained that includes an electromagnetically induced flow measurement signal. The first and second measurement signals combine into an output signal including the electrode impedance measurement signal without the electromagnetically induced flow measurement signal. ## Claims ### Claim 1 A method of obtaining a measure of electrical impedance in respect of one or more sensing electrodes of an electromagnetic flowmeter, the method comprising: intermittently injecting an impedance measurement signal to at least one of the sensing electrodes whilst a coil excitation drive signal is applied to field generating coils of the flowmeter; during a first interval, when the coil excitation drive signal is applied to the coils and the impedance measurement signal is injected to at least one of the sensing electrodes, obtaining a first measurement signal from the sensing electrodes, the first measurement signal comprising an electromagnetically induced flow measurement signal and an electrode impedance measurement signal; during a second interval, when the coil excitation drive signal is applied to the coils but the impedance measurement signal is not injected to at least one of the sensing electrodes, obtaining a second measurement signal from the sensing electrodes, the second measurement signal comprising an electromagnetically induced flow measurement signal; and combining the first measurement signal and the second measurement signal to obtain an output signal comprising the electrode impedance measurement signal without the electromagnetically induced flow measurement signal. ### Claim 2 (depends on 1) The method according to claim 1, wherein the coil excitation drive signal has a recurring waveform, and wherein the intermittent impedance measurement signal is not injected during every recurrence of the coil excitation drive signal. ### Claim 3 (depends on 1) The method according to claim 1, wherein the coil excitation drive signal has a cyclically varying waveform having a drive period; optionally wherein the cyclically varying waveform of the coil excitation drive signal has symmetrically-alternating half cycles. ### Claim 4 (depends on 1) The method according to claim 1, wherein the combining involves the use of a delay line having a delay period. ### Claim 5 (depends on 4) The method according to claim 4, wherein the delay line is implemented by a comb filter, the comb filter having the delay period. ### Claim 6 (depends on 4) The method according to claim 4, wherein the coil excitation drive signal has a cyclically varying waveform having a drive period; and wherein the delay period is an integer number of cycles of the drive period of the coil excitation drive signal. ### Claim 7 (depends on 4) The method according to claim 4, wherein the coil excitation drive signal has a cyclically varying waveform having a drive period; wherein the cyclically varying waveform of the coil excitation drive signal has symmetrically-alternating half cycles; and wherein the delay period is an integer number of half cycles of the drive period of the coil excitation drive signal. ### Claim 8 (depends on 1) The method according to claim 1, wherein the coil excitation drive signal has a form selected from a group comprising: a square wave, a pulsed form, a non 50:50 pulsed form, a sine wave, a triangular wave, a saw-tooth wave; and/or wherein the impedance measurement signal is injected to at least one of the sensing electrodes in a manner selected from a group comprising: constant current, constant voltage from a resistive source, voltage injection from a capacitive source. ### Claim 9 (depends on 1) The method according to claim 1, wherein the injection of the impedance measurement signal is synchronised with the coil excitation drive signal; optionally wherein the impedance measurement signal comprises pulses of short duration, timed to occur just after polarity inversion of the coil excitation drive signal. ### Claim 10 (depends on 9) The method according to claim 9, wherein the impedance measurement signal is timed to occur within only the first 75% of a half-cycle of the coil excitation drive signal; or wherein the impedance measurement signal is timed to occur within only the first 50% of a half-cycle of the coil excitation drive signal; or wherein the impedance measurement signal is timed to occur within only the first 25% of a half-cycle of the coil excitation drive signal. ### Claim 11 (depends on 1) The method according to claim 1, wherein, for a pair of sensing electrodes, impedance measurement signals are injected in a staggered manner, such that one electrode of the pair receives an impedance measurement signal after the other electrode of the pair. ### Claim 12 (depends on 1) The method according to claim 1, wherein the first interval and the second interval are adjacent in time. ### Claim 13 (depends on 1) The method according to claim 1, wherein the first interval and the second interval are spaced apart in time. ### Claim 14 (depends on 1) The method according to claim 1, further comprising demodulating the electrode impedance measurement signal of the output signal to obtain a measure of electrical impedance in respect of at least one of the sensing electrodes. ### Claim 15 (depends on 14) The method according to claim 14, further comprising comparing the measure of electrode impedance to at least one threshold, and signalling at least one suspected fault condition in dependence on the results of the comparison. ### Claim 16 (depends on 14) The method according to claim 14, where measures of electrode impedance are obtained in respect of a plurality of sensing electrodes located around a cross-section of a conduit, at positions between a low point of the cross-section and a high point of the cross-section, in order to determine the filling level of the conduit from the electrode impedance of each of the sensing electrodes. ### Claim 17 (depends on 1) The method according to claim 1, further comprising, in parallel with the combining of the first measurement signal and the second measurement signal to obtain the output signal comprising the electrode impedance measurement signal without the electromagnetically induced flow measurement signal: processing the first and/or second measurement signals to obtain a second output signal comprising the electromagnetically induced flow measurement signal without the electrode impedance measurement signal. ### Claim 18 (depends on 17) The method according to claim 17, wherein processing the first measurement signal comprises subjecting the first measurement signal to a comb filter operation. ### Claim 19 (depends on 18) The method according to claim 18, wherein the coil excitation drive signal has a cyclically varying waveform having a drive period; wherein the cyclically varying waveform of the coil excitation drive signal has symmetrically-alternating half cycles; and wherein said comb filter operation uses a delay period corresponding to the half cycle period of the coil excitation drive signal. ### Claim 20 A sensing apparatus for obtaining a measure of electrical impedance in respect of one or more sensing electrodes of an electromagnetic flowmeter, the sensing apparatus comprising: one or more signal generators configured to intermittently inject an impedance measurement signal to at least one of the sensing electrodes whilst a coil excitation drive signal is applied to field generating coils of the flowmeter; circuitry for obtaining a first measurement signal from the sensing electrodes during a first interval when the coil excitation drive signal is applied to the coils and the impedance measurement signal is injected to at least one of the sensing electrodes, the first measurement signal comprising an electromagnetically induced flow measurement signal and an electrode impedance measurement signal; circuitry for obtaining a second measurement signal from the sensing electrodes during a second interval when the coil excitation drive signal is applied to the coils but the impedance measurement signal is not injected to at least one of the sensing electrodes, the second measurement signal comprising an electromagnetically induced flow measurement signal; and circuitry for combining the first measurement signal and the second measurement signal to obtain an output signal comprising the electrode impedance measurement signal without the electromagnetically induced flow measurement signal. ### Claim 21 (depends on 20) The sensing apparatus according to claim 20, wherein the or each signal generator is configured such that the intermittent impedance measurement signal is not injected during every recurrence of the coil excitation drive signal, the coil excitation drive signal having a recurring waveform. ### Claim 22 (depends on 20) The sensing apparatus according to claim 20, wherein the circuitry for combining comprises a delay line having a delay period. ### Claim 23 (depends on 22) The sensing apparatus according to claim 22, wherein the circuitry for combining further comprises a comb filter to provide the delay line, the comb filter having the delay period. ### Claim 24 (depends on 22) The sensing apparatus according to claim 22, wherein the coil excitation drive signal has a cyclically varying waveform having a drive period; and wherein the delay period is an integer number of cycles of the drive period of the coil excitation drive signal. ### Claim 25 (depends on 22) The sensing apparatus according to claim 22, wherein the coil excitation drive signal has a cyclically varying waveform having a drive period; wherein the cyclically varying waveform of the coil excitation drive signal has symmetrically-alternating half cycles; and wherein the delay period is an integer number of half cycles of the drive period of the coil excitation drive signal. ### Claim 26 (depends on 20) The sensing apparatus according to claim 20, further comprising a timer for synchronising the injection of the impedance measurement signal with the coil excitation drive signal; optionally configured such that the impedance measurement signal comprises pulses of short duration, timed to occur just after polarity inversion of the coil excitation drive signal; or configured such that the impedance measurement signal is timed to occur within only the first 75% of a half-cycle of the coil excitation drive signal; or configured such that the impedance measurement signal is timed to occur within only the first 50% of a half-cycle of the coil excitation drive signal; or configured such that the impedance measurement signal is timed to occur within only the first 25% of a half-cycle of the coil excitation drive signal. ### Claim 27 (depends on 20) The sensing apparatus according to claim 20, configured such that, for a pair of sensing electrodes, impedance measurement signals are injected in a staggered manner, such that one electrode of the pair receives an impedance measurement signal after the other electrode of the pair. ### Claim 28 (depends on 20) The sensing apparatus according to claim 20, configured such that the first interval and the second interval are adjacent in time. ### Claim 29 (depends on 20) The sensing apparatus according to claim 20, further comprising a demodulator for demodulating the electrode impedance measurement signal of the output signal to obtain a measure of electrical impedance in respect of at least one of the sensing electrodes. ### Claim 30 (depends on 29) The sensing apparatus according to claim 29, further comprising circuitry for comparing the measure of electrode impedance to at least one threshold, and signalling at least one suspected fault condition in dependence on the results of the comparison. ### Claim 31 (depends on 29) The sensing apparatus according to claim 29, wherein a plurality of sensing electrodes are located around a cross-section of a conduit; at positions between a low point of the cross-section and a high point of the cross-section, to enable the filling level of the conduit to be determined from the electrode impedance of each of the sensing electrodes. ### Claim 32 (depends on 20) The sensing apparatus according to claim 20, further comprising, in parallel with the circuitry for combining, circuitry for processing the first and/or second measurement signals to obtain a second output signal comprising the electromagnetically induced flow measurement signal without the electrode impedance measurement signal. ### Claim 33 (depends on 32) The sensing apparatus according to claim 32, wherein the circuitry for processing comprises a comb filter. ### Claim 34 (depends on 33) The sensing apparatus according to claim 33, wherein the coil excitation drive signal has a cyclically varying waveform having a drive period; wherein the cyclically varying waveform of the coil excitation drive signal has symmetrically-alternating half cycles; and wherein said comb filter uses a delay period corresponding to the half cycle period of the coil excitation drive signal. ### Claim 35 (depends on 20) The sensing apparatus according to claim 20 being an electromagnetic flowmeter, the electromagnetic flowmeter comprising said field generating coils, an excitation current generator for supplying said field generating coils with said coil excitation drive signal, and said sensing electrodes. ### Claim 36 A method of obtaining a measure of electrical impedance in respect of one or more sensing electrodes of an electromagnetic flowmeter, the method comprising: injecting intermittent impedance measurement pulses to at least one of the sensing electrodes whilst subjecting the sensing electrodes to a cyclically varying electromagnetic field, thereby causing the sensing electrodes to produce a composite signal comprising electromagnetically induced flow measurement signals and electrode impedance measurement signals; and subjecting the composite signal to a filter operation in which the composite signal is combined with a delayed portion of itself, the delay period being such as to cancel the electromagnetically induced flow measurement signals from the composite signal, thereby enabling the electrode impedance measurement signals to be extracted and used to obtain a measure of electrode impedance. ### Claim 37 A sensing apparatus for obtaining a measure of electrical impedance in respect of one or more sensing electrodes of an electromagnetic flowmeter, the sensing apparatus comprising: one or more signal generators configured to intermittently inject impedance measurement pulses to at least one of the sensing electrodes whilst the sensing electrodes are subjected to a cyclically varying electromagnetic field, thereby causing the sensing electrodes to produce a composite signal comprising electromagnetically induced flow measurement signals and electrode impedance measurement signals; and filter circuitry configured to combine the composite signal with a delayed portion of itself, the delay period being such as to cancel the electromagnetically induced flow measurement signals from the composite signal, thereby enabling the electrode impedance measurement signals to be extracted and used to obtain a measure of electrode impedance.