Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
  • G01F15/00—Details of, or accessories for, apparatus of groups G01F1/00 - G01F13/00 insofar as such details or appliances are not adapted to particular types of such apparatus
  • G01F15/02—Compensating or correcting for variations in pressure, density or temperature
  • G01F15/04—Compensating or correcting for variations in pressure, density or temperature of gases to be measured
  • G01F15/043—Compensating or correcting for variations in pressure, density or temperature of gases to be measured using electrical means
• • 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
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
  • G01F15/00—Details of, or accessories for, apparatus of groups G01F1/00 - G01F13/00 insofar as such details or appliances are not adapted to particular types of such apparatus
  • G01F15/02—Compensating or correcting for variations in pressure, density or temperature
  • G01F15/022—Compensating or correcting for variations in pressure, density or temperature using electrical means
• • 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

Definitions

• the invention relates to acoustic flowmeters including ultrasonic flowmeters used to measure flowing exhaust gas velocity.
• Transmitting pulses of acoustic energy through a fluid is useful for measuring the state and properties of the fluid, specifically the velocity and temperature.
• Piezoceramic elements are commonly used in acoustic transducers to generate ultrasonic acoustic pulses or continuous wave fields.
• the ultrasonic flowmeter measures the flowing exhaust gas velocity using the relation
• Tl ultrasonic pulse transit time upstream
• T2 ultrasonic pulse transit time downstream
• V velocity of the gas through the pipe
• ⁇ angle between the ultrasonic beam and the pipe
• L path length of the ultrasonic beam between the transmitter and receiver transducers.
• the transit time (i.e. Tl and T2 ) is measured by sending a pulse of ultrasound across the pipe, and measuring the time differential (i.e. transit time ) for the pulse to be detected at the receiving transducer.
• a typical transit time is about 220/xs with a 3.1 inch path length.
• the gas velocity is about 150 ft/s, with a resulting upstream transit time measuring about 256 ⁇ s, and a downstream transit time measuring about 34 ⁇ s.
• the measured transit times are affected by the temperature of the gas.
• the speed of sound in air changes with temperature using the relation:
• T gas is 298 K and C equals 345 m/s, or 1135 ft/s. With a high gas temperature of 425 0 C, T gas is 698 K and C equals 529 m/s, or 1736 ft/s.
• V ( 1/Tl - 1/T2 ) * L / (2* cos ⁇ ).
• the ultrasonic pulse typically requires about 12 ⁇ s to propagate through the transducer and associated measurement electronic amplifiers and coaxial cables in a tested arrangement at 298 K.
• the invention recognizes that this delay time changes with temperature.
• the invention involves aspects of calibrating the ultrasonic flowmeter. In a broad sense, these aspects address the variations in the delay time with changes in temperature. In one aspect, calibration of the path length between the sending and receiving transducers and calibration of the transducer delay time over a wide temperature range are optimized. In another aspect, the flowmeter output is temperature compensated based on the flowmeter gas temperature (beyond the typical 1/T density compensation). These two mentioned aspects may be embodied in an ultrasonic flowmeter individually or in combination in accordance with the invention. Comprehended methods may be used in various applications involving an acoustic flowmeter, for example, in a sampling system for exhaust gas.
• FIGURE 1 illustrates a bag mini-diluter sampling system made in accordance with the invention
• FIGURE 2 illustrates the flowmeter in the system of Figure 1 ;
• FIGURE 3 is a graph depicting speed of sound error with optimized calibration of the path length and transducer delay time according to one aspect of the invention.
• FIGURE 4 is a graph depicting measured volume error, this error is corrected by temperature compensation according to another aspect of the invention.
• FIG. 1 illustrates a bag mini-diluter sampling system at 10.
• Sampling system 10 includes a main conduit having an inlet 12 for receiving exhaust.
• Flowmeter 14 measures the flow of fluid through the main conduit, and total exhaust volume is accumulated.
• Flowmeter 14 provides a direct exhaust flow measurement signal, and is calibrated according to the invention.
• a blower 16 may assist fluid flow through the conduit.
• a sample line 18 samples exhaust from the main conduit.
• a dilution inlet 20 receives a dilution gas.
• Fixed flow control 22 and fixed flow control 24 (mass flow controllers or critical flow Venturis) control the flow of dilution gas and sampled exhaust gas, respectively, to provide a generally fixed ratio at the mixing section.
• Pump 26 pumps the mixture of the dilution gas and the exhaust gas sample for eventual collection in bags 32.
• Proportional flow device 28 provides a flow to sample collecting bags 32 that is proportional to the flow through the main conduit. Accordingly, bypass 30 is provided to allow some of the mixture to bypass the collections.
• Figure 2 illustrates flowmeter 14 in greater detail showing a pair of acoustic transducers 40 arranged in an opposed fashion across the conduit.
• the flowmeter 14 may be made in any suitable way.
• the transducers 40 may be made in any suitable way. That is, the invention relates to aspects of calibrating an acoustic flowmeter, and is exemplified in the calibration of a pair of ultrasonic flowmeters in a sampling system.
• the calibration of the path length between the sending and receiving transducers and the calibration of the transducer delay time over a wide temperature range are optimized.
• the flowmeter output is temperature compensated based on the exhaust flowmeter gas temperature (beyond the typical 1/T density compensation).
• the ultrasonic flowmeter in the working example was calibrated by flowing air at 298 K, and the path length was measured using calipers as 3.260 inches. The transit times were adjusted for correct measurement of gas velocity, with the resulting transducer delay times:
• Figure 4 shows a consistent error in measured volume with temperature in the working example.
• the working example uses a second aspect of the invention to correct this error.
• this correction is included in the ultrasonic flowmeter user functions with the following results: FTP75 within 0.8% of CVS for weighted fuel economy, HWFE within .6% , and US06 within .6% .
• the preferred embodiment of the invention incorporates two separate aspects of the invention in combination into a calibration method to address time delay variations with temperature.
• the preferred approaches for these two separate aspects are described in the working example. It is to be appreciated that other approaches could be taken to calibrate path length and calibrate transducer delay time over a wide temperature range, and to temperature compensate flowmeter output.
• Embodiments of the invention employing one or both aspects of the invention may provide acceptable operation over a wide temperature range.
• ultrasonic flowmeters are only operable in a very limited temperature range, and a large heat exchanger is used to assure that gas temperature is in the range.

Landscapes

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

Priority Applications (3)

Applications Claiming Priority (2)

Publications (2)

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ID=35655709

Family Applications (1)

Country Status (5)

Cited By (4)

Families Citing this family (21)

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• 2004
  • 2004-07-21 US US10/895,625 patent/US7124621B2/en not_active Expired - Lifetime
• 2005
  • 2005-06-17 JP JP2007522508A patent/JP4724714B2/ja not_active Expired - Lifetime
  • 2005-06-17 WO PCT/US2005/021548 patent/WO2006019487A2/en not_active Ceased
  • 2005-06-17 DE DE112005001773.7T patent/DE112005001773B4/de not_active Expired - Fee Related
• 2007
  • 2007-01-16 GB GB0700762A patent/GB2430261B/en not_active Expired - Fee Related

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