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
  • G01F1/667—Arrangements of transducers for ultrasonic flowmeters; Circuits for operating ultrasonic flowmeters
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
  • G01F25/00—Testing or calibration of apparatus for measuring volume, volume flow or liquid level or for metering by volume
  • G01F25/10—Testing or calibration of apparatus for measuring volume, volume flow or liquid level or for metering by volume of flowmeters
• • 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
  • G01F1/667—Arrangements of transducers for ultrasonic flowmeters; Circuits for operating ultrasonic flowmeters
  • G01F1/668—Compensating or correcting for variations in velocity of sound

Definitions

• the transit time difference ⁇ t depends on the average flow velocity VI on the sound path, the sound input angle ⁇ in the fluid and the sound propagation time tl in the fluid. The relationship is described by the following formula:
• a clamp-on measurement is calibrated by mounting the sensors on the measuring tube of a calibration system.
• the measuring tube preferably has a similar nominal diameter as the tube on which the device is to be installed later.
• the fluid mechanical conditions of the calibration so the flow profile and the tube geometry occur as an additional source of error. So you have to make sure that there is an ideal flow profile. That can, especially with big ones Diameter, very expensive.
• the geometry of the measuring tube must also be measured very accurately. It is therefore desirable to provide a calibration method that contains only the parts of the measuring arrangement that are used unchanged in the later measuring point.
• the known solutions require a delay generator.
• the resolution of the thus realizable signal propagation times is always limited by the basic clock of the oscillator.
• Another limitation of the known solutions is that the same signal shape is output in both transmission directions.
• the signals of an ultrasonic flowmeter in and against the flow direction are not exactly identical in shape. Especially at high flow velocities, the signal shape of the signals received in and against the flow direction differ considerably.
• an artificial replica of the measuring path which responds to the transmission signals, which the converter generates at the terminals for the two transducers, with received signals which are delayed from the transmission signals by a predetermined duration and their maturities differ from each other by a given transit time difference.
• the artificial measuring path contains two DA transducers which are each assigned to one connection of the measuring transducer and one of which generates the signal in the flow direction and the other the signal against the flow direction. This is done by storing the digital signals in a memory and sending the transmit signal from the transmitter to the output of the signals to the two outputs of the DA converter.
• a transmission signal at one of the two transducer connections generates a first reception signal which is delayed by a predetermined first delay compared to the transmission signal and a transmission signal at the other transducer connection a second reception signal which is delayed by a predetermined second delay time compared to the transmission signal.
• the two response signals to the transmission signals at the terminals T1 or T2 of the transmitter are independently generated by a respective DA converter and the associated digital images of the response signals are calculated independently of each other and stored respectively in the memory of the associated DA converter that one of Zero different amplitude of the response signal after the expiration of a respective independently predetermined transit time t1 or t2 relative to the associated transmission signal on the terminal T1 or T2 is output.
• the measurement error of the converter is generally determined by comparing the default values with the corresponding measured values.
• the default values for the transit times between the transmission signals on the terminals T1 and T2 and the associated response signals are calculated from a default value for the volume flow. From the comparison between the default value for the volume flow and the volume flow determined by the transmitter based on the response signals, the measuring error of the transmitter is determined.
• the two predetermined transit times between the transmission signal on terminal T1 or T2 and the associated response signal from the same measuring point parameters are calculated with which the transmitter is parameterized.
• a correction factor is calculated and stored in the transmitter.
• a flow calibration is avoided. Instead of a flow reference, a time reference is used. Time references can be implemented much more accurately than flow references. In addition, the cost is significantly lower than the cost associated with using a flow calibration facility.
• Fig. 2 Transmitter with the artificial measuring path, instead of the
• An ultrasonic flowmeter essentially consists of a transmitter and the transducers and the measuring tube.
• the transducers are either built into the measuring tube or in the case of the Clamp-on flow meter mounted on the outside of the measuring tube.
• the unit of sound transducers and measuring tube will be referred to below as the measuring path.
• Flowmeter is the error of measuring the transit time and the transit time difference.
• the task of calibrating the converter is thus to determine the measurement error of the transit time and the transit time difference.
• the transmitter also carries out the calculation of the volume flow from the measured transit times. It therefore makes sense to include this calculation in the calibration by comparing the volumetric flow output from the transmitter with a specified volumetric flow and thus determining the measuring error of the volumetric flow.
• the transmitter is connected to an artificial measuring path.
• This artificial measuring path responds to the transmit signals of the transmitter with received signals, which are delayed with respect to the transmit signals by run times that exactly match the transit times of the signals of the equivalent true measuring path.
• a 2-channel generator for arbitrary signals can be used for the generation of the signals. Generators that can generate time-limited signals with adequate runtime accuracy for this task have been offered by several companies for several years.
• Fig. 3 shows an embodiment of the artificial measuring path consisting of signal generator, computer and signal shaping unit.
• the signals are calculated on a computer and downloaded to the signal generator.
• the DA converter is given this signal in the form of a time series. That is, it is digitized at discrete interpolation points.
• the digitized time series sd_i is:
• Ti i * Ta and DA_Max is the numerical value corresponding to the maximum amplitude that the DA converter can output.
• Ta is the sampling interval of the DA converter.
• Volume flow can be made with a given volume flow.
• the mean runtime and the runtime difference are on Basis of the measuring path model and the measuring point parameters such as the geometry of the real measuring path as well as the sound velocities of the measuring medium and the pipe wall as well as the running times in the sound transducers.
• the difference of the transit times of the two signals at the terminals T1 and T2 is calculated from the predetermined volume flow.
• the flow causes a difference .DELTA.t between the maturities tu and td opposite or in the flow direction.
• the relationship between the transit time tL in the fluid, the transit time difference ⁇ t and the transit times tu and td is:
• a typical volume flow Q for the selected pipe diameter is specified. From the volumetric flow, the time difference ⁇ t results after changing over the equation (4) to:
• the transit time t1 is calculated according to equation (10).
• the transit times tu and td of the signals which are loaded onto the signal generator are given by Eqs. (8) and (9).
• the transmitter now determines the transit time and the transit time difference on the signals generated by the artificial measuring path and from this according to GL (4) the volume flow. The comparison of this volume flow with the default value results in the measurement error of the volume flow to be determined.
• Measuring device made This can be done, for example, by calculating a correction factor from the calibration result and storing it in the transmitter. Since modern ultrasonic flowmeters are equipped with microprocessors, the calculation of the adjustment can also be done by the transmitter itself. For this, the transmitter must know the default value of the volume flow.
• An advantageous embodiment of the invention therefore provides that the transmitter retrieves or receives the default value of the volume flow from the artificial measuring path via an interface and from this default value and the measured value, the measurement error and the correction factor for the Adjustment calculated. Thus, the adjustment is integrated into the meter and no longer needs to be done in the laboratory.
• the parameterization of the artificial measuring path can be carried out by the transmitter itself.
• the transmitter thus takes over the tasks of the computer shown in FIG.
• the transmitter is connected to the artificial measuring path via a suitable interface.
• the transmitter calculates the signals on the basis of the measuring point parameters and the default value for the volume flow and loads the signals onto the artificial measuring path.
• the measuring point parameters are the above-mentioned parameters of the physical measuring path to be simulated by the artificial measuring path, such as e.g. Pipe diameter and speed of sound.
• the parameter sets for one or more measuring points to be used for calibrations can be stored on the transmitter.
• the calibration is done by disconnecting the transmitter from the transducers and instead connecting the artificial measuring path and connecting the parameterization interface between the artificial measuring path and the transmitter.
• the calibration process can be started via the control terminal of the transmitter. This embodiment of the invention is so safe to use that it can also be used in the field and is not limited to use in the calibration laboratory.

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

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• 2009
  • 2009-11-19 JP JP2011536867A patent/JP4979838B2/ja active Active
  • 2009-11-19 EP EP09817083.0A patent/EP2356408B1/de active Active
  • 2009-11-19 WO PCT/EP2009/065481 patent/WO2010057951A2/de active Application Filing
  • 2009-11-19 DE DE102009046871A patent/DE102009046871A1/de not_active Withdrawn
  • 2009-11-19 US US13/130,533 patent/US9086309B2/en active Active

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