Method and apparatus for correcting temperature variations in ultrasonic flowmeters
First Claim
1. A method for correcting for the effect of temperature in a fluid flow measuring apparatus of the type including first and second sound transducers for transmitting and receiving acoustic pulses along a path through said fluid, each of said transducers serving to transmit an acoustic output signal when driven by a suitable electrical drive signal and to generate an AC output signal when driven by a suitable acoustic input signal, said apparatus having a first state in which said first transducer is a transmitting transducer and said second transducer is a receiving transducer, and a second state in which said second transducer is a transmitting transducer and said first transducer is a receiving transducer, including the steps of:
- a) providing transducers having a resonant frequency that varies as a function of temperature and has a nominal resonant frequency at a nominal temperature;
b) applying to the transmitting transducers bursts of drive pulses, said drive pulses having a frequency that is approximately independent of temperature and is substantially equal to said nominal resonant frequency;
c) generating a sampling signal having a frequency substantially equal to said nominal resonant frequency and a predetermined temporal position with respect to said bursts, said sampling signal including a plurality of sampling transitions for use in timing the zero crossings of the AC output signals of the receiving transducers;
d) calibrating said apparatus at said nominal temperature;
e) measuring, at an unknown temperature, sets of sample values, the sample values of said sets being indicative of the elapsed times between the transitions of said sampling signal and corresponding zero crossings of said AC output signal;
f) deriving, from said sets of sample values, a temperature correction signal indicative of how the magnitudes of said sample values change during said measuring step;
g) calculating a fluid flow parameter from said sets of sample values using said temperature correction signal.
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Abstract
A method for correcting the effect of transducer temperature variations in an ultrasonic flowmeter. The method includes the steps of providing ultrasonic transducers having resonant frequencies that are approximately linear functions of temperature, and applying to those transducers bursts of ultrasonic drive pulses having a frequency that is independent of temperature. The method further includes the steps of calibrating said apparatus at a temperature approximately equal to the nominal temperature if said transducers, and using sample measurements taken at an unknown temperature to define a linear representation of how sample measurements vary during the course of bursts. Finally, the method includes the step of using the linear representation to correct fluid flow values calculated from the sample measurements.
68 Citations
21 Claims
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1. A method for correcting for the effect of temperature in a fluid flow measuring apparatus of the type including first and second sound transducers for transmitting and receiving acoustic pulses along a path through said fluid, each of said transducers serving to transmit an acoustic output signal when driven by a suitable electrical drive signal and to generate an AC output signal when driven by a suitable acoustic input signal, said apparatus having a first state in which said first transducer is a transmitting transducer and said second transducer is a receiving transducer, and a second state in which said second transducer is a transmitting transducer and said first transducer is a receiving transducer, including the steps of:
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a) providing transducers having a resonant frequency that varies as a function of temperature and has a nominal resonant frequency at a nominal temperature; b) applying to the transmitting transducers bursts of drive pulses, said drive pulses having a frequency that is approximately independent of temperature and is substantially equal to said nominal resonant frequency; c) generating a sampling signal having a frequency substantially equal to said nominal resonant frequency and a predetermined temporal position with respect to said bursts, said sampling signal including a plurality of sampling transitions for use in timing the zero crossings of the AC output signals of the receiving transducers; d) calibrating said apparatus at said nominal temperature; e) measuring, at an unknown temperature, sets of sample values, the sample values of said sets being indicative of the elapsed times between the transitions of said sampling signal and corresponding zero crossings of said AC output signal; f) deriving, from said sets of sample values, a temperature correction signal indicative of how the magnitudes of said sample values change during said measuring step; g) calculating a fluid flow parameter from said sets of sample values using said temperature correction signal. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A method for correcting for the effect of transducer temperature in a fluid flow measuring apparatus of the type including first and second sound transducers for transmitting and receiving acoustic pulses along a path through said fluid, each of said transducers serving to transmit an acoustic output signal when driven by a suitable electrical drive signal and to generate an AC output signal when driven by a suitable acoustic input signal, said apparatus having a first state in which said first transducer is a transmitting transducer and said second transducer is a receiving transducer, and a second state in which said second transducer is a transmitting transducer and said first transducer is a receiving transducer, including the steps of:
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a) providing transducers having resonant frequencies that are approximately linear functions of temperature and that are resonant at a nominal resonant frequency when the temperatures thereof are at a nominal temperature; b) applying to the transducers bursts of drive pulses having a frequency that is approximately independent of temperature and has a frequency substantially equal to said nominal resonant frequency; c) generating sampling signals having frequencies substantially equal to said nominal resonant frequency and predetermined time displacements with respect to said bursts, said sampling signals including a plurality of sampling transitions for timing the zero crossings of the AC output signals of the receiving transducers; d) calibrating said apparatus at a temperature approximately equal to said nominal temperature; e) taking, at an unknown temperature, pluralities of sample measurements for the bursts of said first and second states; f) defining approximately linear representations of said pluralities of sample measurements, said linear representations having slopes which are indicative of variations in the magnitudes of said sample measurements during the course of respective bursts; g) utilizing said linear representations to correct fluid flow values calculated from said pluralities of sample measurements. - View Dependent Claims (9, 10, 11, 12, 13, 14)
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15. A method for correcting for the output of a fluid flow measuring apparatus of the type including first and second sound transducers for transmitting and receiving acoustic pulses along a path through said fluid, each of said transducers serving to transmit an acoustic output signal when driven by a suitable electrical drive signal and to generate an AC output signal when driven by a suitable acoustic input signal, including the steps of:
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a) providing transducers which have a resonant frequency that varies as a function of temperature and which have a nominal resonant frequency at a nominal temperature; b) applying to the transmitting transducers a drive signal having a frequency that is approximately constant and approximately equal to said nominal resonant frequency; c) generating a sampling signal having a frequency approximately equal to said nominal resonant frequency, said sampling signal being adapted for use in conjunction with said drive signal to provide sample data values from which a fluid flow parameter may be calculated; d) calibrating said apparatus at said nominal temperature; e) taking, at an unknown temperature, a sequence of sample data values; f) deriving, from changes in sample data values that occur during the course of said sequence, a temperature correction signal; and g) calculating said fluid flow parameter from said sample data values and said correction signal. - View Dependent Claims (16, 17, 18)
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19. A method for correcting for the output of a fluid flow measuring apparatus of the type including first and second sound transducers for transmitting and receiving acoustic pulses along a path through said fluid, each of said transducers serving to transmit an acoustic output signal when driven by a suitable electrical drive signal and to generate an AC output signal when driven by a suitable acoustic input signal, including the steps of:
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a) providing transducers which have a resonant frequency that varies as a function of temperature and which have a nominal resonant frequency at a nominal temperature; b) applying to the transmitting transducers a drive signal having a frequency that is approximately constant and approximately equal to said nominal resonant frequency; c) calibrating said apparatus at said nominal temperature; d) measuring, at an unknown temperature, pluralities of data values indicative of the relationship between said drive signal and the AC outputs of said transducers; e) producing, from changes in said data values that occur during said measuring step, a correction signal indicative of the temperature of said transducers; and f) using said correction signal to correct the output of said apparatus for variations in the temperature of said transducers. - View Dependent Claims (20, 21)
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Specification