EP3436787A1 - Method for monitoring an ultrasonic flow meter - Google Patents

Method for monitoring an ultrasonic flow meter

Info

Publication number
EP3436787A1
EP3436787A1 EP16711960.1A EP16711960A EP3436787A1 EP 3436787 A1 EP3436787 A1 EP 3436787A1 EP 16711960 A EP16711960 A EP 16711960A EP 3436787 A1 EP3436787 A1 EP 3436787A1
Authority
EP
European Patent Office
Prior art keywords
initial
flow meter
ultrasonic
digital sample
ultrasonic flow
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
EP16711960.1A
Other languages
German (de)
French (fr)
Inventor
Lars Jespersen
David Brisson ANDERSEN
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Danfoss AS
Original Assignee
Danfoss AS
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Danfoss AS filed Critical Danfoss AS
Publication of EP3436787A1 publication Critical patent/EP3436787A1/en
Ceased legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
    • G01F1/66—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by measuring frequency, phase shift or propagation time of electromagnetic or other waves, e.g. using ultrasonic flowmeters

Definitions

  • the present invention relates to a method for monitoring an ultrasonic flow meter, the method comprising the steps of generating a reference fingerprint comprising one or more initial system parameters of the ultrasonic flow meter and comparing the generated reference fingerprint to the same system parameters being currently measured when the ultrasonic flow meter is in use. Furthermore, the present invention relates to the ultrasonic flow meter adapted to perform the method for monitoring the ultrasonic flow meter.
  • a volume flow rate q through the flow meter is directly proportional to a time difference At between transit times of ultrasonic signals transmitted upstream and downstream between a first transducer and a second transducer placed oppositely in a flow tube, the speed of sound c, and an overall sensor geometry constant K: q ⁇ K ⁇ At ⁇ c 2
  • K, At, and c the quality of the flow measurement thus depends directly on the accuracy of the three factors K, At, and c.
  • K may be determined during production flow calibration and is as such only required to be constant over time.
  • K may comprise properties of the overall sensor geometry, preferably transducer positions, sound beam pattern from transducers, sound reflector angles, sound properties of liner and fixture materials or geometry of spool piece, flow liner and fixtures.
  • the speed of sound c is often measured indirectly via a known relation between c and the temperature of the flowing media. The accuracy of c is thus dependent on the temperature sensors of the ultrasonic flow meter, a temperature measurement circuit of the electronics of the ultrasonic flow meter and the media flowing through the ultrasonic flow meter.
  • the accuracy of the time difference measurement At is mainly dependent on a time measurement circuit in the electronic parts of the ultrasonic flow meter.
  • fingerprinting for the ultrasonic flow meter.
  • it is known to generate a reference fingerprint comprising one or more initial system parameters of the ultrasonic flow meter and compare the generated reference fingerprints to the same system parameters being currently measured when the ultrasonic flow meter is in use. This allows to provide a method by which it is possible to detect if K or any of the measurement circuits for measuring time difference and temperature have changed over time and thus be able to diagnose possible flow meter inaccuracies.
  • the object of the invention is solved according to the method described in the outset in that the method comprises the step of generating a reference digital sample of an initial ultrasonic signal in order to generate data for the reference fingerprint, the initial ultrasonic signal being sent and received by the ultrasonic flow meter and the sent (also known as Tx) and/or received (also known as Rx) initial ultrasonic signal being digitally sampled by the ultrasonic flow meter so as to obtain a Tx and/or Rx reference digital sample, respectively.
  • Tx and Rx means signals which are derived from the transducer signals and are not directly the Tx and Rx signals across the two transducers.
  • the method according to the invention allows making use of the ultrasonic flow meter for self-monitoring.
  • the method according to the invention allows to generate the reference fingerprint and to compare the reference fingerprint to current system parameters in order to monitor the ultrasonic flow meter function just by using the measurement circuits already included in the ultrasonic flow meter, thus without using any external devices.
  • the ultrasonic flow meter comprises a first ultrasonic transducer and a second ultrasonic transducer, the initial ultrasonic signal being sent between the first ultrasonic transducer and the second ultrasonic transducer and the Tx and/or the Rx initial ultrasonic signal being sampled by an analog- to-digital converter of the ultrasonic flow meter so as to obtain the Tx and/or the Rx reference digital sample, respectively.
  • the analog-to-digital converter is part of an electronic circuit used to extract transit time from the ultrasonic signal during use of the ultrasonic flow meter.
  • the same analog-to-digital converter can be used for multiple purposes, allowing easy monitoring of the ultrasonic flow meter at low cost.
  • a separate analog-to-digital converter is provided in the ultrasonic flow meter to obtain the Tx and/or the Rx reference digital sample in addition to the analog-to-digital converter used to extract the transit time.
  • the analog-to-digital converter for obtaining the reference digital sample is part of a microcontroller of the ultrasonic flow meter.
  • the initial ultrasonic signal is sampled in one or more series of digital samples, each series having a sampling frequency, preferably the same, with an individual starting time relative to the beginning of sending of the ultrasonic signal and/or each series having an individual sampling frequency.
  • the method comprises the step of using the reference digital sample of the Tx and/or Rx ultrasonic signal for monitoring changes of an ultrasonic flow meter geometry.
  • the ultrasonic flow meter has the flow meter geometry which is described by the constant K which affects the calculation of the volume flow rate q through the ultrasonic flow meter, as explained before.
  • K comprises system properties of the ultrasonic flow meter geometry, preferably transducer positions, sound beam pattern from transducers, sound reflector angles, sound properties of liner and fixture materials, geometry of spool piece, flow liner and fixtures and sometimes other system parameters.
  • Using the Tx and/or the Rx reference digital sample of the ultrasonic signal for monitoring the ultrasonic flow meter geometry thus allows to detect time dependent changes of the constant K which may be a sign of flow meter inaccuracies.
  • K may be a sign of flow meter inaccuracies.
  • indirectly monitoring the ultrasonic flow meter geometry changes over time using the Rx and/or the Tx reference digital sample may provide an easy way of detecting possible flow meter inaccuracies.
  • the method comprises the step of using the Tx and/or the Rx reference digital sample of the initial ultrasonic signal for monitoring a transit time measurement circuit and/or a temperature measurement circuit of the ultrasonic flow meter.
  • Both electronic circuits provide information for calculating the flow rate q, as explained earlier.
  • Monitoring of the complete temperature measurement can be done by comparing the transit time as calculated from temperature, flow meter geometry and a known relation between the speed of sound and temperature, wherein the transit time is, for example, calculated from a correlation between the Rx initial ultrasonic signal and the Rx current ultrasonic signal. Hence, this assumes that the speed of sound versus temperature relation is known.
  • the temperature measurement circuit in itself can be checked by comparing calibration reference
  • monitoring one or both of the electronic circuits for time dependent changes by using the Tx and/or the Rx reference digital sample of the initial ultrasonic signal and comparing properties of the initial ultrasonic signal to properties of a current ultrasonic signal may allow for easy detection of malfunction of each of the electronic circuits.
  • the method comprises the step of including the Tx and/or the Rx reference digital sample as an initial system parameter in the reference fingerprint and /or deriving an initial system parameter from the Tx and/or the Rx reference digital sample so as to include the derived initial system parameter in the reference fingerprint.
  • the Tx and/or the Rx reference digital sample in the reference fingerprint it can be decided at a later time which characteristics of the Tx and/or the Rx initial ultrasonic signal, respectively, shall be compared to characteristics of a current ultrasonic signal, thus allowing great flexibility for monitoring the ultrasonic flow meter.
  • the amount of data to be stored can be reduced, thus allowing reduced complexity and cost of a fingerprint storage device of the ultrasonic flow meter.
  • the Tx and/or the Rx reference digital sample is included as an initial system parameter in the reference fingerprint and an initial system parameter is derived from the Tx and/or the Rx reference digital sample and also included as an initial system parameter in the reference fingerprint. This allows great flexibility and furthermore restoring frequently used system parameters derived from the Tx and/or the Rx reference digital sample so as to reduce an amount of calculation necessary when comparing the reference fingerprint to a current ultrasonic signal.
  • the initial system parameters included in the reference fingerprint are not derived from the Tx and/or the Rx reference digital sample. They may for example be added manually or being derived from other sources than the reference digital samples. It is preferred that the reference fingerprint includes one or more of measurement clock calibration data, temperature measurement circuit calibration data, time measurement circuit calibration data, measurement statistics, an initial ultrasonic signal amplitude, or initial zero crossing patterns as initial system parameters. Such information may give detailed information about time dependent changes of the ultrasonic flow meter. It is preferred that the initial system parameters are derived from the reference digital sample, most preferably ultrasonic system parameters. Preferably, other parameters are derived from other parts of the circuit.
  • the method comprises the steps of deriving an initial zero crossing pattern from the Tx and/or the Rx reference digital sample and comparing the initial zero crossing pattern to a current zero crossing pattern of a current ultrasonic signal during use of the flow meter.
  • the initial zero crossing pattern itself may be stored as an initial system parameter in the reference fingerprint after being derived from the Tx and/or the Rx reference digital samples in form of number values or the Tx and/or the Rx reference digital sample may be stored in the reference fingerprint and the initial zero crossing pattern of the initial ultrasonic signal may be derived from the stored Tx and/or Rx reference digital sample at a later time when the initial zero crossing pattern shall be compared to the current zero crossing pattern of the current ultrasonic signal.
  • Tx and/or Rx signal slopes through the zero crossings may be derived, stored and compared as explained above, mutatis mutandis.
  • the method comprises the step of deriving an initial signal amplitude from the Tx and/or the Rx reference digital sample and comparing the initial signal amplitude to a current signal amplitude of a current ultrasonic signal during the use of the flow meter.
  • the initial ultrasonic signal amplitude may itself be stored as an initial system
  • the Tx and/or the Rx reference digital sample in form of a number value or the Tx and/or the Rx reference digital sample may be stored in the reference fingerprint and the Tx and/or the Rx initial ultrasonic amplitude may be derived from the stored Tx and/or the Rx reference digital sample at a later time when the initial ultrasonic signal amplitude shall be compared to a current ultrasonic signal amplitude.
  • a time dependent change in the ultrasonic signal amplitude therefore can be detected and maintenance of the ultrasonic flow meter could possibly be initiated accordingly.
  • a preferred method according to the invention comprises the step of deriving an initial envelope function from the Tx and/or the Rx reference digital sample and comparing the initial envelope function to a current envelope function of a current ultrasonic signal during use of the flow meter.
  • the Tx and/or the Rx initial envelope function itself may be stored as an initial system parameter in the reference fingerprint after being derived from the Tx and/or the Rx reference digital sample in form of a number value or the Tx and/or the Rx reference digital signal may be stored in the reference fingerprint and the initial envelope function of the Tx and/or the Rx initial ultrasonic signal may be derived from the stored Tx and/or Rx reference digital sample at a later time when the initial envelope function shall be compared to a current envelope function of a current ultrasonic signal.
  • a time dependent change in the ultrasonic signal envelope function can be detected and maintenance of the ultrasonic flow meter could possibly be initiated accordingly.
  • the method comprises the step of deriving initial frequency content from the Tx and/or the Rx reference digital sample and comparing the initial frequency content to a current frequency content of a current ultrasonic signal during use of the flow meter.
  • the frequency content comprises the frequency of the received signal in form of number values.
  • Frequency content here may e.g. refer to an FFT or DTFT of the signal, possibly a data reduced version of this.
  • the initial frequency content itself may be stored in the reference fingerprint as an initial system parameter after being derived from the Tx and/or Rx reference digital sample or the Tx and/or the Rx reference digital sample may be stored in the reference fingerprint and the initial frequency content may be derived from the stored Tx and/or Rx reference digital sample at a later time when the initial frequency content shall be compared to a current frequency content of a current ultrasonic signal.
  • a time dependent change in the frequency content can be detected and maintenance of the ultrasonic flow meter could possibly be initiated accordingly.
  • a preferred method according to the invention comprises the step of comparing the initial system parameter to the currently measured system parameter by one or more of correlation based comparison, difference calculation and ratio calculation. This allows easy comparison. All of the initial system parameters stored in the fingerprint may be compared to the corresponding current system parameter in the same way. However, in some embodiments different comparison methods are used for comparing different system parameters to each other.
  • the comparison is preferably performed by a microprocessor of the ultrasonic flow meter.
  • the microprocessor has also the function to calculate the fluid flow through the flow meter. This allows to reduce complexity of the ultrasonic flow meter by using just a single microprocessor and thus allows easy implementation of the method.
  • the fluid flow is calculated by an analog-to- digital converter of the ultrasonic flow meter being separate from the microprocessor.
  • the analog-digital-converter is a high speed analog-to-digital converter for oversampling the ultrasonic signal.
  • the method comprises the step of storing the reference fingerprint in a local flow meter memory and/or via a network connection in a remote data storage.
  • the ultrasonic flow meter preferably has the local flow meter memory such as for example a flash memory, an EEPROM, or any type of non-volatile memory.
  • the ultrasonic flow meter comprises additionally or in the alternative the network connection in order to remotely store the reference fingerprint data in the remote data storage, preferably the cloud or a server.
  • the method comprises the step of storing the reference fingerprint in the local flow meter memory and storing a backup of the reference fingerprint via the network connection in the remote data storage. This may allow for providing an easy remote storage or backup solution for the reference fingerprint.
  • the data may be retrieved from the local flow meter memory via a connected device, such as PC or a mobile phone.
  • the PC or mobile device may retrieve the reference fingerprint from a remote storage device via the PC's or mobile device's network connection, so that it can be compared to a current fingerprint retrieved from the device by the PC/mobile device.
  • the reference fingerprint is generated during production and/or calibration of the ultrasonic flow meter. This may allow for storing the reference fingerprint and monitoring the ultrasonic flow meter already at the production stage and/or calibration stage of the ultrasonic flow meter. Easy long term monitoring thus becomes possible on the basis of an early generated reference fingerprint. Furthermore, the problem of the invention is solved by the ultrasonic flow meter adapter to perform the method according to the invention. Having such an ultrasonic flow meter allows easy monitoring of system parameters based on the reference fingerprint comprising initial system parameters generated from the Tx and/or the Rx reference digital sample of the Tx and/or the Rx initial ultrasonic signal, respectively.
  • a preferred ultrasonic flow meter comprises an analog-to-digital converter being adapted to repeatedly generate series of Tx and/or Rx digital samples of the initial ultrasonic signal at a preferably same sampling frequency with an individual starting time relative to the beginning of sending of the signal for each digital sample and/or at an individual sampling frequency for each digital sample.
  • the Tx and/or the Rx initial ultrasonic signal may be multi sampled and thus even oversampled.
  • Generating two or more series of digital samples and combining them for generating fingerprint data may allow for using an undersampling analog-to- digital converter but none the less establishing an even oversampled reference digital reproduction of the Tx and/or the Rx initial ultrasonic signal.
  • a high-speed analog-to-digital converter may be provided by the ultrasonic flow meter. This may allow oversampled sampling directly without multisampling.
  • Fig. 1 shows an ultrasonic flow meter according to the invention
  • Fig. 2 shows a flow chart depicting an embodiment of the method according to the invention.
  • the use of fingerprinting for ultrasonic flow meters is known within industrial flow meters which often comprise multiple sound paths.
  • the fingerprint for these types of meters are often application dependent parameters and comprise various types of measurement statistics such as: 1 ) flow profile (derived from multipath measurements)
  • Fig.1 shows an exemplary embodiment of an ultrasonic flow meter according to the invention.
  • the ultrasonic flow meter 1 comprises a spool piece 2 in which a flow liner 3 is housed.
  • the flow liner 3 is arranged between a flow inlet 4 and flow outlet 5 of the spool piece 2.
  • the ultrasonic flow meter 1 furthermore comprises a reflector fixture for sound reflectors 6, 7.
  • the sound reflectors 6, 7 establish a sound path (dashed line) between a first transducer 8 and a second transducer 9 which are ultrasonic transducers.
  • Ultrasonic signals may be sent between the first ultrasonic transducer 8 and the second ultrasonic transducer 9.
  • the sent (Tx) and received (Rx) ultrasonic signal may be sampled by an analog-to-digital converter (not shown) housed in the enclosure 10 which houses an electronic PCB 1 1 .
  • the analog-to-digital converter is adapted to generate a Rx and Tx reference digital sample of a Rx and a Tx initial ultrasonic signal in order to generate data for a reference fingerprint of the ultrasonic flow meter 1 , the initial ultrasonic signal being sent and received by the first transducer 8 and the second transducer 9 and the Rx initial ultrasonic signal being digitally sampled by the analog-to-digital converter so as to obtain the Rx reference digital sample and the Tx initial ultrasonic signal being digitally sampled by the analog-to-digital so as to obtain the Tx reference digital sample.
  • the ultrasonic flow meter 1 is therefore adapted to be self-monitoring as no external devices need to be used in order to calibrate various electronic circuits of the ultrasonic flow meter 1 or the monitoring could also be upon request from a connected device. While time dependent changes of system parameters of the ultrasonic flow meter 1 may affect the accuracy of the flow measurements of a fluid flow passing from the flow inlet 4 to the flow outlet 5, the ultrasonic flow meter 1 is adapted to indirectly monitor a change of an ultrasonic flow meter geometry, a transit time measurement circuit (not shown), which is stored in the enclosure 10, and a temperature measurement circuit of the ultrasonic flow meter 1 of which the temperature sensor 12 is shown in Fig. 1 . Therefore, changes in K can be monitored indirectly by monitoring the Rx and/or Tx current ultrasonic signals. The indirect measurement of C via temperature can be monitored as described earlier and the quality of the At measurement can be monitored by monitoring a calibration of the time measurement circuit and clock calibration.
  • Fig. 2 now schematically shows a preferred method according to the invention.
  • a first step (S21 ) an initial ultrasonic signal is sent. More specifically, in this embodiment the first ultrasonic transducer 8 sends the Tx initial ultrasonic signal to the second ultrasonic transducer 9.
  • the second transducer 9 receives the Rx initial ultrasonic signal.
  • a Rx reference digital sample of the received Rx initial ultrasonic signal is generated using the ultrasonic flow meter 1 . More specifically, the analog-to-digital converter of the ultrasonic flow meter 1 generates the Rx reference digital sample from the Rx initial ultrasonic signal.
  • the analog-to-digital converter generates two series of digital samples of the initial ultrasonic signal, each series of samples having an individual sampling frequency and an individual starting time relative to the beginning of sending the initial ultrasonic signal.
  • a detailed Rx reference digital sample is generated.
  • a high speed analog-to-digital converter is used which allows oversampling of the Rx initial ultrasonic signal.
  • the Rx reference digital sample may be generated with a single series of digital samples which are placed so close to each other in time that they allow to digitally reconstruct the Rx initial ultrasonic signal.
  • S24 fourth step from the Rx reference digital sample, data is generated for the reference fingerprint of the ultrasonic flow meter 1 .
  • the Rx reference digital sample is included as an initial system parameter in the reference fingerprint.
  • an initial zero crossing pattern is derived from the Rx reference digital sample and the initial zero crossing pattern is included in the reference fingerprint as a further initial system parameter.
  • an initial signal amplitude is derived from the Rx reference digital sample and the initial signal amplitude is included in the reference fingerprint as a yet further initial system parameter.
  • measurement clock calibration data is included in the reference fingerprint as a yet further initial system parameter.
  • an initial envelope function is derived from the Rx reference digital sample and included in the reference fingerprint as a yet further initial system parameter.
  • an initial frequency content which comprises the frequency of the initial ultrasonic signal is derived from the Rx reference digital sample and included in the reference fingerprint as a yet further initial system parameter. Deriving the initial system parameters is done by the same microprocessor which calculates the flow rate.
  • the generated reference fingerprint is compared to the same Rx system parameters being currently measured when the ultrasonic flow meter is in use (S26).
  • each of the previously mentioned initial system parameters is compared to a
  • the ultrasonic flow meter 1 comprises a local flow meter memory (not shown) in the enclosure 10.
  • the local flow meter memory is a flash memory (or any other type of non-volatile memory) storing the reference fingerprint locally.
  • the reference fingerprint is stored permanently in production stage of the ultrasonic flow meter 1 .
  • An alternative embodiment of the ultrasonic flow meter 1 (not shown) comprises a network connection, for example a wireless network connection, for storing the reference fingerprint in a remote data storage, instead.
  • the present invention provides a method for monitoring the ultrasonic flow meter 1 , the method comprising the steps of generating the reference fingerprint comprising one or more initial system parameters of the ultrasonic flow meter 1 and comparing the generated reference fingerprint to the same system parameters being currently measured when the ultrasonic flow meter 1 is in use.
  • Tx and/or the Rx reference digital sample of the Tx and/or Rx initial ultrasonic signal, respectively in order to generate data for the reference fingerprint monitoring of the ultrasonic flow meter is very easy since the initial ultrasonic signal is sent and received by the ultrasonic flow meter itself and the sent (Tx) and/or received (Rx) initial ultrasonic signal is digitally sampled by the ultrasonic flow meter itself so as to obtain the Tx and/or Rx reference digital sample, respectively. No external devices for monitoring are thus necessary.
  • a Tx reference digital sample from a Tx initial ultrasonic signal may be generated.
  • the reference digital sample may be generated from an initial ultrasonic signal running from the first ultrasonic transducer to the second ultrasonic transducer or vice versa.
  • a person skilled in the art will understand that the present invention is not limited to the exemplary embodiment described.
  • a Tx reference digital sample from a Tx initial ultrasonic signal may be generated.
  • the reference digital sample may be generated from an initial ultrasonic signal running from the first ultrasonic transducer to the second ultrasonic transducer or vice versa.
  • at least 4 samples are generated initially: Tx samples for both transducers and Rx samples from both transducers.
  • At least 4 samples are normally sampled under zero flow conditions, but additional series of the samples may also be sampled at a high flow rate for later reference.
  • Each of these at least 4 series of sampled signals may be generated by one or more of the 2 different undersampling/interleaving methods or by direct oversampling via a high speed analog - to - digital converter.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Fluid Mechanics (AREA)
  • General Physics & Mathematics (AREA)
  • Measuring Volume Flow (AREA)

Abstract

The current invention relates to a method for monitoring an ultrasonic flow meter (1) comprising the steps of generating a reference fingerprint comprising one or more initial system parameters of the ultrasonic flow meter (1) and comparing the generated reference fingerprint to the same system parameters being currently measured when the ultrasonic flow meter (1) is in use. According to the invention, a reference digital sample of an initial ultrasonic signal is generated in order to generate data for the reference fingerprint, the initial ultrasonic signal being sent and received by the ultrasonic flow meter (1) and the sent (Tx) and/or the received (Rx) initial ultrasonic signal being digitally sampled by the ultrasonic flow meter (1) so as to obtain a Tx and/or Rx reference digital sample, respectively. This allows easy monitoring of the ultrasonic flow meter (1).

Description

Method for monitoring an ultrasonic flow meter
The present invention relates to a method for monitoring an ultrasonic flow meter, the method comprising the steps of generating a reference fingerprint comprising one or more initial system parameters of the ultrasonic flow meter and comparing the generated reference fingerprint to the same system parameters being currently measured when the ultrasonic flow meter is in use. Furthermore, the present invention relates to the ultrasonic flow meter adapted to perform the method for monitoring the ultrasonic flow meter.
In ultrasonic flow meters based on the transit time difference principle, a volume flow rate q through the flow meter is directly proportional to a time difference At between transit times of ultrasonic signals transmitted upstream and downstream between a first transducer and a second transducer placed oppositely in a flow tube, the speed of sound c, and an overall sensor geometry constant K: q≡ K■ At■ c2 The quality of the flow measurement thus depends directly on the accuracy of the three factors K, At, and c.
The constant K may be determined during production flow calibration and is as such only required to be constant over time. K may comprise properties of the overall sensor geometry, preferably transducer positions, sound beam pattern from transducers, sound reflector angles, sound properties of liner and fixture materials or geometry of spool piece, flow liner and fixtures. The speed of sound c is often measured indirectly via a known relation between c and the temperature of the flowing media. The accuracy of c is thus dependent on the temperature sensors of the ultrasonic flow meter, a temperature measurement circuit of the electronics of the ultrasonic flow meter and the media flowing through the ultrasonic flow meter.
The accuracy of the time difference measurement At is mainly dependent on a time measurement circuit in the electronic parts of the ultrasonic flow meter. In order to detect changes which affect K, At, and c which may require recalibration or maintenance of the ultrasonic flow meter, it is known to use fingerprinting for the ultrasonic flow meter. Accordingly, it is known to generate a reference fingerprint comprising one or more initial system parameters of the ultrasonic flow meter and compare the generated reference fingerprints to the same system parameters being currently measured when the ultrasonic flow meter is in use. This allows to provide a method by which it is possible to detect if K or any of the measurement circuits for measuring time difference and temperature have changed over time and thus be able to diagnose possible flow meter inaccuracies. It is an object of the present invention to come to a method for monitoring an ultrasonic flow meter which allows easy fingerprinting and monitoring of the ultrasonic flow meter. The object of the invention is solved according to the method described in the outset in that the method comprises the step of generating a reference digital sample of an initial ultrasonic signal in order to generate data for the reference fingerprint, the initial ultrasonic signal being sent and received by the ultrasonic flow meter and the sent (also known as Tx) and/or received (also known as Rx) initial ultrasonic signal being digitally sampled by the ultrasonic flow meter so as to obtain a Tx and/or Rx reference digital sample, respectively.
In this context Tx and Rx means signals which are derived from the transducer signals and are not directly the Tx and Rx signals across the two transducers.
The method according to the invention allows making use of the ultrasonic flow meter for self-monitoring. The method according to the invention allows to generate the reference fingerprint and to compare the reference fingerprint to current system parameters in order to monitor the ultrasonic flow meter function just by using the measurement circuits already included in the ultrasonic flow meter, thus without using any external devices. Preferably, the ultrasonic flow meter comprises a first ultrasonic transducer and a second ultrasonic transducer, the initial ultrasonic signal being sent between the first ultrasonic transducer and the second ultrasonic transducer and the Tx and/or the Rx initial ultrasonic signal being sampled by an analog- to-digital converter of the ultrasonic flow meter so as to obtain the Tx and/or the Rx reference digital sample, respectively. Preferably, the analog-to-digital converter is part of an electronic circuit used to extract transit time from the ultrasonic signal during use of the ultrasonic flow meter. Thus, the same analog-to-digital converter can be used for multiple purposes, allowing easy monitoring of the ultrasonic flow meter at low cost. However, in some embodiments of the invention, a separate analog-to-digital converter is provided in the ultrasonic flow meter to obtain the Tx and/or the Rx reference digital sample in addition to the analog-to-digital converter used to extract the transit time. It is preferred that the analog-to-digital converter for obtaining the reference digital sample is part of a microcontroller of the ultrasonic flow meter. Preferably, the initial ultrasonic signal is sampled in one or more series of digital samples, each series having a sampling frequency, preferably the same, with an individual starting time relative to the beginning of sending of the ultrasonic signal and/or each series having an individual sampling frequency. This allows using an undersampling analog-to-digital- converter to come to oversampled resolution information extracted from the initial ultrasonic signal, under the condition that the ultrasonic signal is constant. Preferably, multiple series of digital samples are combined to digitally reconstruct properties of the initial ultrasonic signal which shall be stored in the reference fingerprint. Preferably, both the sent initial ultrasonic signal and the received initial ultrasonic signal are digitally sampled and initial digital samples are generated for each of them.
It is preferred that the method comprises the step of using the reference digital sample of the Tx and/or Rx ultrasonic signal for monitoring changes of an ultrasonic flow meter geometry. The ultrasonic flow meter has the flow meter geometry which is described by the constant K which affects the calculation of the volume flow rate q through the ultrasonic flow meter, as explained before. K comprises system properties of the ultrasonic flow meter geometry, preferably transducer positions, sound beam pattern from transducers, sound reflector angles, sound properties of liner and fixture materials, geometry of spool piece, flow liner and fixtures and sometimes other system parameters. Using the Tx and/or the Rx reference digital sample of the ultrasonic signal for monitoring the ultrasonic flow meter geometry thus allows to detect time dependent changes of the constant K which may be a sign of flow meter inaccuracies. Thus, a change in ultrasonic flow meter geometry and thus K may give rise to recalibration or repair of the ultrasonic flow meter. Therefore, indirectly monitoring the ultrasonic flow meter geometry changes over time using the Rx and/or the Tx reference digital sample may provide an easy way of detecting possible flow meter inaccuracies. In a preferred method, the method comprises the step of using the Tx and/or the Rx reference digital sample of the initial ultrasonic signal for monitoring a transit time measurement circuit and/or a temperature measurement circuit of the ultrasonic flow meter. Both electronic circuits provide information for calculating the flow rate q, as explained earlier. Monitoring of the complete temperature measurement can be done by comparing the transit time as calculated from temperature, flow meter geometry and a known relation between the speed of sound and temperature, wherein the transit time is, for example, calculated from a correlation between the Rx initial ultrasonic signal and the Rx current ultrasonic signal. Hence, this assumes that the speed of sound versus temperature relation is known. The temperature measurement circuit in itself can be checked by comparing calibration reference
measurements for the temperature measurement circuit with a current calibration measurement. Thus, monitoring one or both of the electronic circuits for time dependent changes by using the Tx and/or the Rx reference digital sample of the initial ultrasonic signal and comparing properties of the initial ultrasonic signal to properties of a current ultrasonic signal may allow for easy detection of malfunction of each of the electronic circuits.
It is preferred that the method comprises the step of including the Tx and/or the Rx reference digital sample as an initial system parameter in the reference fingerprint and /or deriving an initial system parameter from the Tx and/or the Rx reference digital sample so as to include the derived initial system parameter in the reference fingerprint. When including the Tx and/or the Rx reference digital sample in the reference fingerprint it can be decided at a later time which characteristics of the Tx and/or the Rx initial ultrasonic signal, respectively, shall be compared to characteristics of a current ultrasonic signal, thus allowing great flexibility for monitoring the ultrasonic flow meter. When deriving an initial system parameter from the Tx and/or the Rx reference digital sample so as to include the derived initial system parameter in the reference fingerprint, the amount of data to be stored can be reduced, thus allowing reduced complexity and cost of a fingerprint storage device of the ultrasonic flow meter. In some embodiments, the Tx and/or the Rx reference digital sample is included as an initial system parameter in the reference fingerprint and an initial system parameter is derived from the Tx and/or the Rx reference digital sample and also included as an initial system parameter in the reference fingerprint. This allows great flexibility and furthermore restoring frequently used system parameters derived from the Tx and/or the Rx reference digital sample so as to reduce an amount of calculation necessary when comparing the reference fingerprint to a current ultrasonic signal. However, some of the initial system parameters included in the reference fingerprint in some embodiments are not derived from the Tx and/or the Rx reference digital sample. They may for example be added manually or being derived from other sources than the reference digital samples. It is preferred that the reference fingerprint includes one or more of measurement clock calibration data, temperature measurement circuit calibration data, time measurement circuit calibration data, measurement statistics, an initial ultrasonic signal amplitude, or initial zero crossing patterns as initial system parameters. Such information may give detailed information about time dependent changes of the ultrasonic flow meter. It is preferred that the initial system parameters are derived from the reference digital sample, most preferably ultrasonic system parameters. Preferably, other parameters are derived from other parts of the circuit.
Preferably, the method comprises the steps of deriving an initial zero crossing pattern from the Tx and/or the Rx reference digital sample and comparing the initial zero crossing pattern to a current zero crossing pattern of a current ultrasonic signal during use of the flow meter. As explained before, the initial zero crossing pattern itself may be stored as an initial system parameter in the reference fingerprint after being derived from the Tx and/or the Rx reference digital samples in form of number values or the Tx and/or the Rx reference digital sample may be stored in the reference fingerprint and the initial zero crossing pattern of the initial ultrasonic signal may be derived from the stored Tx and/or Rx reference digital sample at a later time when the initial zero crossing pattern shall be compared to the current zero crossing pattern of the current ultrasonic signal. Thus, a time dependent change in the zero crossing pattern therefore can be detected and maintenance of the ultrasonic flow meter could possibly be initiated accordingly upon request. As another initial system parameter, Tx and/or Rx signal slopes through the zero crossings may be derived, stored and compared as explained above, mutatis mutandis.
It is preferred that the method comprises the step of deriving an initial signal amplitude from the Tx and/or the Rx reference digital sample and comparing the initial signal amplitude to a current signal amplitude of a current ultrasonic signal during the use of the flow meter. As explained before, the initial ultrasonic signal amplitude may itself be stored as an initial system
parameter in the reference fingerprint after being derived from the Tx and/or the Rx reference digital sample in form of a number value or the Tx and/or the Rx reference digital sample may be stored in the reference fingerprint and the Tx and/or the Rx initial ultrasonic amplitude may be derived from the stored Tx and/or the Rx reference digital sample at a later time when the initial ultrasonic signal amplitude shall be compared to a current ultrasonic signal amplitude. Thus, a time dependent change in the ultrasonic signal amplitude therefore can be detected and maintenance of the ultrasonic flow meter could possibly be initiated accordingly.
A preferred method according to the invention comprises the step of deriving an initial envelope function from the Tx and/or the Rx reference digital sample and comparing the initial envelope function to a current envelope function of a current ultrasonic signal during use of the flow meter. In some embodiments the Tx and/or the Rx initial envelope function itself may be stored as an initial system parameter in the reference fingerprint after being derived from the Tx and/or the Rx reference digital sample in form of a number value or the Tx and/or the Rx reference digital signal may be stored in the reference fingerprint and the initial envelope function of the Tx and/or the Rx initial ultrasonic signal may be derived from the stored Tx and/or Rx reference digital sample at a later time when the initial envelope function shall be compared to a current envelope function of a current ultrasonic signal. Thus, a time dependent change in the ultrasonic signal envelope function can be detected and maintenance of the ultrasonic flow meter could possibly be initiated accordingly.
It is preferred that the method comprises the step of deriving initial frequency content from the Tx and/or the Rx reference digital sample and comparing the initial frequency content to a current frequency content of a current ultrasonic signal during use of the flow meter. Preferably, the frequency content comprises the frequency of the received signal in form of number values. Frequency content here may e.g. refer to an FFT or DTFT of the signal, possibly a data reduced version of this. The initial frequency content itself may be stored in the reference fingerprint as an initial system parameter after being derived from the Tx and/or Rx reference digital sample or the Tx and/or the Rx reference digital sample may be stored in the reference fingerprint and the initial frequency content may be derived from the stored Tx and/or Rx reference digital sample at a later time when the initial frequency content shall be compared to a current frequency content of a current ultrasonic signal. Thus, a time dependent change in the frequency content can be detected and maintenance of the ultrasonic flow meter could possibly be initiated accordingly.
A preferred method according to the invention comprises the step of comparing the initial system parameter to the currently measured system parameter by one or more of correlation based comparison, difference calculation and ratio calculation. This allows easy comparison. All of the initial system parameters stored in the fingerprint may be compared to the corresponding current system parameter in the same way. However, in some embodiments different comparison methods are used for comparing different system parameters to each other. The comparison is preferably performed by a microprocessor of the ultrasonic flow meter. Preferably, the microprocessor has also the function to calculate the fluid flow through the flow meter. This allows to reduce complexity of the ultrasonic flow meter by using just a single microprocessor and thus allows easy implementation of the method.
However, in some embodiments the fluid flow is calculated by an analog-to- digital converter of the ultrasonic flow meter being separate from the microprocessor. This is preferred when the analog-digital-converter is a high speed analog-to-digital converter for oversampling the ultrasonic signal. It is preferred that the method comprises the step of storing the reference fingerprint in a local flow meter memory and/or via a network connection in a remote data storage. The ultrasonic flow meter preferably has the local flow meter memory such as for example a flash memory, an EEPROM, or any type of non-volatile memory. However, in some embodiments the ultrasonic flow meter comprises additionally or in the alternative the network connection in order to remotely store the reference fingerprint data in the remote data storage, preferably the cloud or a server. In some embodiments, the method comprises the step of storing the reference fingerprint in the local flow meter memory and storing a backup of the reference fingerprint via the network connection in the remote data storage. This may allow for providing an easy remote storage or backup solution for the reference fingerprint. In some embodiments the data may be retrieved from the local flow meter memory via a connected device, such as PC or a mobile phone. Also, the PC or mobile device may retrieve the reference fingerprint from a remote storage device via the PC's or mobile device's network connection, so that it can be compared to a current fingerprint retrieved from the device by the PC/mobile device.
It is preferred that the reference fingerprint is generated during production and/or calibration of the ultrasonic flow meter. This may allow for storing the reference fingerprint and monitoring the ultrasonic flow meter already at the production stage and/or calibration stage of the ultrasonic flow meter. Easy long term monitoring thus becomes possible on the basis of an early generated reference fingerprint. Furthermore, the problem of the invention is solved by the ultrasonic flow meter adapter to perform the method according to the invention. Having such an ultrasonic flow meter allows easy monitoring of system parameters based on the reference fingerprint comprising initial system parameters generated from the Tx and/or the Rx reference digital sample of the Tx and/or the Rx initial ultrasonic signal, respectively.
A preferred ultrasonic flow meter according to the invention comprises an analog-to-digital converter being adapted to repeatedly generate series of Tx and/or Rx digital samples of the initial ultrasonic signal at a preferably same sampling frequency with an individual starting time relative to the beginning of sending of the signal for each digital sample and/or at an individual sampling frequency for each digital sample. Thus, the Tx and/or the Rx initial ultrasonic signal may be multi sampled and thus even oversampled.
Generating two or more series of digital samples and combining them for generating fingerprint data may allow for using an undersampling analog-to- digital converter but none the less establishing an even oversampled reference digital reproduction of the Tx and/or the Rx initial ultrasonic signal. However, also a high-speed analog-to-digital converter may be provided by the ultrasonic flow meter. This may allow oversampled sampling directly without multisampling.
In the following, the invention will be described in more detail by disclosing a preferred embodiment of the invention referring to the attached figures, in which: Fig. 1 shows an ultrasonic flow meter according to the invention; and
Fig. 2 shows a flow chart depicting an embodiment of the method according to the invention. The use of fingerprinting for ultrasonic flow meters is known within industrial flow meters which often comprise multiple sound paths. The fingerprint for these types of meters are often application dependent parameters and comprise various types of measurement statistics such as: 1 ) flow profile (derived from multipath measurements)
2) flow profile symmetry (derived from multipath measurements)
3) Speed of Sound variation
4) Turbulence pattern for various paths
5) Signal to noise ratio changes
6) Signal amplitude changes It is not known to use changes in various measurement circuit parameters and changes in transmit (Tx) and receive (Rx) signal characteristics.
Furthermore it is possible to also include various measurement statistics, such as signal amplitudes, signal to noise ratio and standard deviation of various measurements.
Fig.1 shows an exemplary embodiment of an ultrasonic flow meter according to the invention. The ultrasonic flow meter 1 comprises a spool piece 2 in which a flow liner 3 is housed. The flow liner 3 is arranged between a flow inlet 4 and flow outlet 5 of the spool piece 2. The ultrasonic flow meter 1 furthermore comprises a reflector fixture for sound reflectors 6, 7. The sound reflectors 6, 7 establish a sound path (dashed line) between a first transducer 8 and a second transducer 9 which are ultrasonic transducers. Ultrasonic signals may be sent between the first ultrasonic transducer 8 and the second ultrasonic transducer 9. The sent (Tx) and received (Rx) ultrasonic signal may be sampled by an analog-to-digital converter (not shown) housed in the enclosure 10 which houses an electronic PCB 1 1 . The analog-to-digital converter is adapted to generate a Rx and Tx reference digital sample of a Rx and a Tx initial ultrasonic signal in order to generate data for a reference fingerprint of the ultrasonic flow meter 1 , the initial ultrasonic signal being sent and received by the first transducer 8 and the second transducer 9 and the Rx initial ultrasonic signal being digitally sampled by the analog-to-digital converter so as to obtain the Rx reference digital sample and the Tx initial ultrasonic signal being digitally sampled by the analog-to-digital so as to obtain the Tx reference digital sample.
As explained before, the ultrasonic flow meter 1 is therefore adapted to be self-monitoring as no external devices need to be used in order to calibrate various electronic circuits of the ultrasonic flow meter 1 or the monitoring could also be upon request from a connected device. While time dependent changes of system parameters of the ultrasonic flow meter 1 may affect the accuracy of the flow measurements of a fluid flow passing from the flow inlet 4 to the flow outlet 5, the ultrasonic flow meter 1 is adapted to indirectly monitor a change of an ultrasonic flow meter geometry, a transit time measurement circuit (not shown), which is stored in the enclosure 10, and a temperature measurement circuit of the ultrasonic flow meter 1 of which the temperature sensor 12 is shown in Fig. 1 . Therefore, changes in K can be monitored indirectly by monitoring the Rx and/or Tx current ultrasonic signals. The indirect measurement of C via temperature can be monitored as described earlier and the quality of the At measurement can be monitored by monitoring a calibration of the time measurement circuit and clock calibration.
Fig. 2 now schematically shows a preferred method according to the invention. In a first step (S21 ) an initial ultrasonic signal is sent. More specifically, in this embodiment the first ultrasonic transducer 8 sends the Tx initial ultrasonic signal to the second ultrasonic transducer 9. Thus, in the second step (S22), the second transducer 9 receives the Rx initial ultrasonic signal. In a third step (S23) a Rx reference digital sample of the received Rx initial ultrasonic signal is generated using the ultrasonic flow meter 1 . More specifically, the analog-to-digital converter of the ultrasonic flow meter 1 generates the Rx reference digital sample from the Rx initial ultrasonic signal. In the present embodiment, the analog-to-digital converter generates two series of digital samples of the initial ultrasonic signal, each series of samples having an individual sampling frequency and an individual starting time relative to the beginning of sending the initial ultrasonic signal. Thus, a detailed Rx reference digital sample is generated. However, in other embodiments of the invention a high speed analog-to-digital converter is used which allows oversampling of the Rx initial ultrasonic signal. In these embodiments the Rx reference digital sample may be generated with a single series of digital samples which are placed so close to each other in time that they allow to digitally reconstruct the Rx initial ultrasonic signal. In a fourth step (S24,) from the Rx reference digital sample, data is generated for the reference fingerprint of the ultrasonic flow meter 1 . In a first substep not shown, the Rx reference digital sample is included as an initial system parameter in the reference fingerprint. In a second substep not shown, an initial zero crossing pattern is derived from the Rx reference digital sample and the initial zero crossing pattern is included in the reference fingerprint as a further initial system parameter. In a third substep not shown, an initial signal amplitude is derived from the Rx reference digital sample and the initial signal amplitude is included in the reference fingerprint as a yet further initial system parameter. In a fourth substep not shown, measurement clock calibration data is included in the reference fingerprint as a yet further initial system parameter. In a fifth substep not shown, an initial envelope function is derived from the Rx reference digital sample and included in the reference fingerprint as a yet further initial system parameter. In a sixth sub step not shown, an initial frequency content which comprises the frequency of the initial ultrasonic signal is derived from the Rx reference digital sample and included in the reference fingerprint as a yet further initial system parameter. Deriving the initial system parameters is done by the same microprocessor which calculates the flow rate. Thus, aforementioned initial system
parameters are included in the reference fingerprint of the ultrasonic flow meter in a fifth step of the inventive method (S25). In a sixth step of the method as shown in Fig. 2, the generated reference fingerprint is compared to the same Rx system parameters being currently measured when the ultrasonic flow meter is in use (S26). Thus, more specifically, each of the previously mentioned initial system parameters is compared to a
corresponding current system parameter of a Rx current ultrasonic signal being received by the second ultrasonic transducer 9. All of the initial system parameters included in the reference fingerprint are compared to the corresponding current system parameters by difference calculation. When the difference between a pair of an initial system parameter and a current system parameter passes a predetermined threshold an alarm is sent by the ultrasonic flow meter 1 via a network connection in order to initiate
maintenance upon request.
In the present embodiment of the ultrasonic flow meter 1 and the
implemented method the ultrasonic flow meter 1 comprises a local flow meter memory (not shown) in the enclosure 10. The local flow meter memory is a flash memory (or any other type of non-volatile memory) storing the reference fingerprint locally. The reference fingerprint is stored permanently in production stage of the ultrasonic flow meter 1 . An alternative embodiment of the ultrasonic flow meter 1 (not shown) comprises a network connection, for example a wireless network connection, for storing the reference fingerprint in a remote data storage, instead.
As can be seen, the present invention provides a method for monitoring the ultrasonic flow meter 1 , the method comprising the steps of generating the reference fingerprint comprising one or more initial system parameters of the ultrasonic flow meter 1 and comparing the generated reference fingerprint to the same system parameters being currently measured when the ultrasonic flow meter 1 is in use. By generating the Tx and/or the Rx reference digital sample of the Tx and/or Rx initial ultrasonic signal, respectively, in order to generate data for the reference fingerprint monitoring of the ultrasonic flow meter is very easy since the initial ultrasonic signal is sent and received by the ultrasonic flow meter itself and the sent (Tx) and/or received (Rx) initial ultrasonic signal is digitally sampled by the ultrasonic flow meter itself so as to obtain the Tx and/or Rx reference digital sample, respectively. No external devices for monitoring are thus necessary. For example, in addition to or instead of generating an Rx reference digital sample from an Rx initial ultrasonic signal, a Tx reference digital sample from a Tx initial ultrasonic signal may be generated. Furthermore, the reference digital sample may be generated from an initial ultrasonic signal running from the first ultrasonic transducer to the second ultrasonic transducer or vice versa. A person skilled in the art will understand that the present invention is not limited to the exemplary embodiment described. For example, in addition to or instead of generating an Rx reference digital sample from an Rx initial ultrasonic signal, a Tx reference digital sample from a Tx initial ultrasonic signal may be generated. Furthermore, the reference digital sample may be generated from an initial ultrasonic signal running from the first ultrasonic transducer to the second ultrasonic transducer or vice versa. Furthermore, in an embodiment not shown, at least 4 samples are generated initially: Tx samples for both transducers and Rx samples from both transducers.
These at least 4 samples are normally sampled under zero flow conditions, but additional series of the samples may also be sampled at a high flow rate for later reference. Each of these at least 4 series of sampled signals may be generated by one or more of the 2 different undersampling/interleaving methods or by direct oversampling via a high speed analog - to - digital converter.

Claims

Claims
A method for monitoring an ultrasonic flow meter (1 ) comprising the steps:
- Generating a reference fingerprint comprising on one or more initial system parameters of the ultrasonic flow meter (1 ); and
- Comparing the generated reference fingerprint to the same system parameters being currently measured when the ultrasonic flow meter (1 ) is in use, characterized in that the method comprises the step of:
- Generating a reference digital sample of an initial ultrasonic signal in order to generate data for the reference fingerprint, the initial ultrasonic signal being sent and received by the ultrasonic flow meter (1 ) and the sent (Tx) and/or (Rx) received initial ultrasonic signal being digitally sampled by the ultrasonic flow meter (1 ) so as to obtain a Tx and/or Rx reference digital sample, respectively.
The method according to claim 1 , characterized in that the ultrasonic flow meter (1 ) comprises a first ultrasonic transducer and a second ultrasonic transducer, the initial ultrasonic signal being sent between the first ultrasonic transducer and the second ultrasonic transducer and the Tx and/or Rx initial ultrasonic signal being sampled by an analog-to-digital-converter of the ultrasonic flow meter (1 ) so as to obtain the Tx and/or Rx reference digital sample, respectively.
The method according to claim 1 or 2, characterized in that the method comprises the step:
- Using the Tx and/or the Rx reference digital sample of the
ultrasonic signal for monitoring changes of an ultrasonic flow meter (1 ) geometry.
The method according to any of the claims 1 to 3, characterized in that the method comprises the step:
- Using the Tx and/or Rx reference digital sample of the initial ultrasonic signal for monitoring a transit time measurement circuit and/or a temperature measurement circuit of the ultrasonic flow meter (1 ).
The method according to any of the claims 1 to 4, characterized in that the method comprises the step: - Including the Tx and/or the Rx reference digital sample as an initial system parameter in the reference fingerprint and/or deriving an initial system parameter from the Tx and/or the Rx reference digital sample so as to include the derived initial system parameter in the reference fingerprint.
The method according to any of the claims 1 to 5, characterized in that the reference fingerprint includes one or more of measurement clock calibration data, temperature measurement circuit calibration data, time measurement circuit calibration data, measurement statistics, an initial ultrasonic signal amplitude, an initial zero crossing pattern, an initial envelope function or an initial frequency content as an initial system parameter.
The method according to any of the claims 1 to 6, characterized in that the method comprises the steps:
- Deriving an initial zero crossing pattern from the Tx and/or Rx reference digital sample; and
- Comparing the initial zero crossing pattern to a current zero crossing pattern of a current ultrasonic signal during use of the flow meter (1 ).
The method according to any of the claims 1 to 7, characterized in that the method comprises the step:
- Deriving an initial signal amplitude from the Tx and/or the Rx reference digital sample; and
- Comparing the initial signal amplitude to a current signal amplitude of a current ultrasonic signal during use of the flow meter (1 ).
9. The method according to any of the claims 1 to 8, characterized in that the method comprises the step: - Deriving an initial envelope function from the Tx and/or Rx reference digital sample; and
- Comparing the initial envelope function to a current envelope function of a current ultrasonic signal during use of the flow meter (1 ).
10. The method according to any of the claims 1 to 9, characterized in that the method comprises the step:
- Deriving initial frequency content from the Tx and/or the Rx reference digital sample; and
- Comparing the initial frequency content to a current frequency content of a current ultrasonic signal during use of the flow meter (1 ). 1 1 . The method according to any of the claims 1 to 10, characterized in that the method comprises the step:
- Comparing the initial system parameter to the currently measured system parameter by one or more of correlation based comparison, difference calculation and ratio calculation.
12. The method according to any of the claims 1 to 1 1 , characterized in that the method comprises the step:
Storing the reference fingerprint in a local flow meter memory and/or via a network connection in a remote data storage. The method according to any of the claims 1 to 12, characterized in that the reference fingerprint is generated during production and/or calibration of the ultrasonic flow meter (1 ).
An ultrasonic flow meter (1 ) adapted to perform the method according to any of the claims 1 to 13.
The ultrasonic flow meter (1 ) according to claim 14, characterized in that the ultrasonic flow meter (1 ) comprises an analog-to-digital- converter being adapted to repeatedly generate series of digital samples of the initial ultrasonic signal at a preferably same sampling frequency with an individual starting time relative to the beginning of sending of the signal for each digital sample and/or at an individual sampling frequency for each digital sample.
EP16711960.1A 2016-03-31 2016-03-31 Method for monitoring an ultrasonic flow meter Ceased EP3436787A1 (en)

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