Extended range ADC flow meter
A method of calculating a time difference is disclosed. The method includes sampling a first ultrasonic signal (r 21 ) to produce a first sampled signal (y 1 ( i )) and sampling a second ultrasonic signal (r 12 ) to produce a second sampled signal (y 2 ( i )). A first time (LEAD_LAG) is determined between a time the first sampled signal crosses a threshold (θ 1 ) and a time the second sampled signal crosses the threshold. The first sampled signal is cross correlated with the second sampled signal to produce a second time (SAMP_OFFSET). The time difference is calculated in response to the first and second times.
1. A method comprising:
receiving, at an ultrasonic measurement circuit, a first ultrasonic signal from a first transducer through a material;
receiving, at the ultrasonic measurement circuit, a second ultrasonic signal from a second transducer through the material;
sampling, by the ultrasonic measurement circuit, the first ultrasonic signal to produce a first sampled signal;
determining, by the ultrasonic measurement circuit, a first envelope of the first sampled signal;
sampling, by the ultrasonic measurement circuit, the second ultrasonic signal to produce a second sampled signal;
determining, by the ultrasonic measurement circuit, a second envelope of the second sampled signal;
determining, by the ultrasonic measurement circuit, a first time between the first envelope crossing a threshold and the second envelope crossing the threshold;
determining, by the ultrasonic measurement circuit, an in-phase signal from the first ultrasonic signal;
determining, by the ultrasonic measurement circuit, a quadrature signal from the second ultrasonic signal;
determining, by the ultrasonic measurement circuit, a second time between the first and second sampled signals using the in-phase signal and the quadrature signal; and
determining, by the ultrasonic measurement circuit, a velocity of the material based in part on an angle from the first transducer and the second transducer to a pipe wall, distance between the first transducer and the second transducer, the first time, and the second time.
2. The method of claim 1 , wherein determining a second time using the in-phase signal and the quadrature signal further comprises cross correlating the first and second sampled signals.
3. The method of claim 2 , wherein cross correlating comprises:
multiplying, by the ultrasonic measurement circuit, the first sampled signal by the second sampled signal; and
adding, by the ultrasonic measurement circuit, products from the step of multiplying to produce cross correlation values.
4. The method of claim 2 , comprising producing the second time by one of parabolic function and cosine function interpolation.
5. The method of claim 1 , comprising:
sampling, by the ultrasonic measurement circuit, the in phase signal;
sampling, by the ultrasonic measurement circuit, the quadrature signal; and
wherein determining a second time using the in-phase signal and the quadrature signal further comprises determining a second time using the sampled in phase signal and the sampled quadrature signal.
6. The method of claim 1 , wherein:
the first ultrasonic signal originated from the second transducer; and
the second ultrasonic signal originated from the first transducer.
7. The method of claim 1 , comprising:
determining, by the ultrasonic measurement circuit, a first maximum value of the first sampled signal;
determining, by the ultrasonic measurement circuit, a second maximum value of the second sampled signal;
normalizing, by the ultrasonic measurement circuit, the first sampled signal with the first maximum value; and
normalizing, by the ultrasonic measurement circuit, the second sampled signal with the second maximum value.
8. A method comprising:
receiving, at an ultrasonic measurement circuit, a first ultrasonic signal from a first transducer through a material;
receiving, at the ultrasonic measurement circuit, a second ultrasonic signal from a second transducer through the material;
sampling, by the ultrasonic measurement circuit, the first ultrasonic signal to produce a first sampled signal;
determining, by the ultrasonic measurement circuit, a first envelope of the first sampled signal;
sampling, by the ultrasonic measurement circuit, the second ultrasonic signal to produce a second sampled signal;
determining, by the ultrasonic measurement circuit, a second envelope of the second sampled signal;
determining, by the ultrasonic measurement circuit, a first time between the first envelope crossing a threshold and the second envelope crossing the threshold;
determining, by the ultrasonic measurement circuit, an in-phase signal from the first ultrasonic signal;
determining, by the ultrasonic measurement circuit, a quadrature signal from the second ultrasonic signal;
determining, by the ultrasonic measurement circuit, a second time between the first sampled signal and the second sampled signal using the in-phase signal and the quadrature signal; and
determining, by the ultrasonic measurement circuit, a velocity of the material based in part on an angle from the first transducer and the second transducer to a pipe wall, distance between the first transducer and the second transducer, and the first time and the second time.
9. The method of claim 8 , wherein determining a second time using the in-phase signal and the quadrature signal further comprises cross correlating the first and second sampled signals further comprises:
multiplying, by the ultrasonic measurement circuit, the first sampled signal by the second sampled signal; and
adding, by the ultrasonic measurement circuit, products from the step of multiplying to produce cross correlation values.
10. The method of claim 9 , wherein determining the second time uses a parabolic function interpolation.
11. The method of claim 9 , wherein determining the second time uses a cosine function interpolation.
12. The method of claim 1 , wherein each of the first and second ultrasonic signals are transmitted in response to an excitation frequency.
13. The method of claim 12 , wherein the steps of sampling comprise sampling at a frequency at least four times the excitation frequency.
14. The method of claim 8 , comprising:
determining, by the ultrasonic measurement circuit, a first maximum value of the first sampled signal;
determining, by the ultrasonic measurement circuit, a second maximum value of the second sampled signal;
normalizing, by the ultrasonic measurement circuit, the first sampled signal with the first maximum value; and
normalizing, by the ultrasonic measurement circuit, the second sampled signal with the second maximum value.
15. A system comprising:
a first transducer arranged to transmit a first signal having a first frequency at a first time and receive a second signal at a second time;
a second transducer spaced apart from the first transducer and arranged to receive the first signal and transmit the second signal having the first frequency;
an analog-to-digital converter (ADC), coupled to the first transducer and the second transducer, to:
receive, from the first transducer, a second signal through a material;
receive, from the second transducer, a first signal through the material;
sample the received first signal at a second frequency to produce a first sampled signal; and
sample the received second signal at the second frequency to produce a second sampled signal; and
a processing circuit to:
determine a first envelope of the first sampled signal;
determine a second envelope of the second sampled signal;
determine a first time between the first envelope crossing a threshold and the second envelope crossing the threshold;
determine an in-phase signal from the first ultrasonic signal;
determine a quadrature signal from the second ultrasonic signal;
determine a second time between the first and second envelopes using the in-phase signal and the quadrature signal; and
determine a velocity of the material based in part on an angle from the first transducer and the second transducer to a pipe wall, distance between the first transducer and the second transducer, the first time, and the second time.