DEVICE AND METHOD FOR MEASUREMENT OF ULTRASONIC TRANSIT TIMES
A device for measurement of ultrasonic wave transit times of an ultrasonic flow sensor consists of: 1) a synchronization signal generator, 2) a reference pulse generator, 3) a sine wave generator, 4) an analog signal amplifier, 5) a comparator, 6) a plurality of latch circuits, 7) a digital adder, 8) an integrator, 9) an A/D converter, 10) a master counter, 11) a plurality of edge counters, and 12) an arithmetic circuit. The device measures the ultrasonic wave transit times using a method of averaging the ultrasonic wave arriving times at different measuring points (triggering point). This method has less dependency on triggering threshold level and the ultrasonic signal amplitude, and thus has less dependency on threshold drift, threshold stability, system gain fluctuation, electronic noise and signal amplitude variations. As a result, the method can greatly improve the velocity measurement accuracy and system robustness of an ultrasonic flow sensor.
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FIELD OF THE INVENTIONThe present disclosure relates to a device for measuring ultrasonic wave transit times from the transmitter to the receiver of an ultrasonic flow sensor.
BACKGROUND OF THE INVENTIONThe statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
An ultrasonic flow sensor measures the average velocity of liquid or gaseous media by means of ultrasonic transducers based on the principle that the transit time of an ultrasonic wave from the transmitter of a transducer to the corresponding receiver is determined by the fluid velocity and the ultrasonic wave propagating direction. Normally, a pair of transducers is used, one is installed in upstream and the other is installed in downstream. Each transducer can be used as a transmitter or a receiver. One ultrasonic wave is transmitted from the upstream transducer to the downstream transducer. The second ultrasonic pulse is transmitted from the downstream transducer to the upstream transducer. The transit time in each direction is measured by an electronic device. The difference of the two transit-time data is proportional to flow velocity. It is then used to calculate the average flow velocity of the fluid.
In conventional electronic devices of an ultrasonic flow sensor, the ultrasonic wave transit time is measured by a time counter to count a reference clock using the following method. 1) Sending ultrasonic pulse wave to the transmitter, starting the timer counter. 2) Monitoring the ultrasonic signal received by the receiver, when the received signal becomes higher than the predefined threshold value, immediately stopping the time counter, and recording the arriving time. This arriving time is treated as the transmit time.
In the above approach, an analog integrator may be used to measure the residual time from the counter stopping moment to the rising edge of the next cycle of the reference clock. This residual time is then combined with the previous transit-time to obtain a transit-time with higher accuracy.
However, this measurement method is susceptible to electronic noise and condition variation. Both the strength of the received signal and the predefined threshold value are subject to electronic noise. In addition, the strength of the received signal varies with the fluid properties such as temperature, velocity, turbulence, solids concentration, etc. As a result, the measured transit time changes not only with flow velocity, but with the fluid properties and electronic noise level. This significantly reduces the velocity measurement accuracy and stability of an ultrasonic flow sensor.
BRIEF SUMMARY OF THE INVENTIONFurther areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.
The object of the present invention is to provide an electronic device which can accurately and reliably measure the transit times from the transmitter to the receiver and hence improving the velocity measurement accuracy of an ultrasonic flow sensor.
In more detail the present invention provides an electronic device for measurement of ultrasonic wave transit times of an ultrasonic flow sensor consists of: 1) a synchronization signal generator, 2) a reference pulse generator, 3) a sine wave generator, 4) an analog signal amplifier, 5) a comparator, 6) a plurality of latch circuits, 7) a digital adder, 8) an integrator, 9) an A/D converter, 10) a master counter, 11) a plurality of edge counters, and 12) an arithmetic circuit (microprocessor). The device measures the ultrasonic wave transit times using a threshold level to trigger both the rising edge and falling edge of the received ultrasonic signal, and using a method of averaging the ultrasonic wave arriving times at different measuring points. This method has less dependency on the threshold level and the ultrasonic signal amplitude, thus, has less dependency on threshold drift, threshold stability, system gain fluctuation, electronic noise and signal amplitude variations. As a result, this method can greatly improve the velocity measurement accuracy and system robustness of an ultrasonic flow sensor.
The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.
The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features.
Referring to
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C0=NTr.
Where N is the output of the mater counter 120, Tr is the period of the reference clock. The master counter 120 can only count complete clock cycles, its output N is a positive integer number, any time less than one clock cycle will not be counted.
Referring to
C1=N1Tr.
Where N1 is the output of the first counter 121. Similar to the master counter, the edge counter 121 can only count complete clock cycles, its output N1 is a positive integer number, any time less than one clock cycle will not be counted.
Referring to
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T1=C0−t1=NTr−t1
Referring to
T2=C0+C1−t2=(N+N1)Tr−t2.
Referring to
Tm=(T1+T2)/2=NTr+N1Tr/2−(t1+t2)/2.
Referring to
Tm=NTr−t1.
-
- Obviously, the transit-time Tm obtained by prior art differs from the one obtained by the first embodiment of the present disclosure by N1Tr/2. This difference does not have any impact on the flow measurement, because the flow rate is calculated based on transit-time difference between upstream Tm and downstream Tm. In addition, the difference can be calibrated so to have accurate transit-time measurement.
ΔTm=|Δt1|.
ΔTm=|Δt1|.
ΔTm=|Δt1+Δt2|/2.
ΔTm=|Δt1+Δt2|/2.
It is noted from the
Δt1≈−Δt2
As a result, their average, ΔTm, is always smaller than |Δt1|. In effect,
ΔTm≈0.
This indicates that the transit-time obtained by the present invention does not change with threshold drifting or signal amplitude variation. By contract, the transit-time obtained by prior art is sensitive to threshold drifting and signal amplitude variation. As a result of this, the transit time measurement accuracy and reliability are greatly improved by using the method of the present disclosure compared to the method of prior art.
Referring to
Referring to
Referring to
Referring to
Referring to
Referring to
C0=NTr,
where N is the output of the mater counter 120, Tr is the period of the reference clock. The master counter 120 can only count complete clock cycles, its output N is a positive integer number, any time less than one clock cycle will not be counted.
Referring to
C1=N1Tr,
where N1 is the output of the counter 121. Similar to the master counter 120, the edge counter 121 can only count complete clock cycles, its output N1 is a positive integer number, any time less than one clock cycle will not be counted.
Referring to
C2=N2Tr,
where N2 is the output of the counter 122. Similar to the master counter 120, the edge counter 122 can only count complete clock cycles, its output N2 is a positive integer number, any time less than one cycle pulse will not be counted.
Referring to
C3=N3Tr,
where N3 is the output of the counter 123. Similar to the master counter 120, the edge counter 123 can only count complete clock cycles, its output N3 is a positive integer number, any time less than one clock cycle will not be counted.
Referring to
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Referring to
Referring to
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Referring to
Referring to
T1=C0−t1=NTr−t1.
Referring to
T2=C0+C1−t2=(N+N1)Tr−t2.
Referring to
Referring to
Referring to
-
- Here Tx is the period of the received ultrasonic signal. The center of T3 and T4 is always one period away from the center of T1 and T2. T—123 is expressed as following,
T—123=(3N1+2N2+N3)Tr/4−Tx/2.
ΔTm=|Δt1+Δt2+Δt3+Δt4|/4.
Since (Δt1, Δt2) and (Δt3, Δt4) change in opposite directions, their average is always smaller than |t1|. This indicates that the ultrasonic wave transit time measurement accuracy is greatly improved using the method of the present disclosure compared to the method of prior art.
Referring to
Referring to
Referring to
Referring to
Referring to
Referring to
C0=NTr,
where N is the output of the mater counter 120, Tr is the period of the reference clock. The master counter 120 can only count complete clock cycles, its output N is a positive integer number, any time less than one clock cycle will not be counted.
Referring to
C1=N1Tr,
where N1 is the output of the counter 121. Similar to the master counter 120, the edge counter 121 can only count complete clock cycles, its output N1 is a positive integer number, any time less than one clock cycle will not be counted.
Referring to
C2=N2Tr,
where N2 is the output of the counter 122. Similar to the master counter 120, the edge counter 122 can only count complete clock cycles, its output N2 is a positive integer number, any time less than one clock cycle will not be counted.
Referring to
C3=N3Tr,
where N3 is the output of the counter 123. Similar to the master counter 120, the edge counter 123 can only count complete clock cycles, its output N3 is a positive integer number, any time less than one clock cycle will not be counted.
Referring to
C4=N4Tr,
where N4 is the output of the counter 124. Similar to the master counter 120, the edge counter 124 can only count complete clock cycles, its output N4 is a positive integer number, any time less than one clock cycle will not be counted.
Referring to
C5=N5Tr,
where N5 is the output of the counter 125. Similar to the master counter 120, the edge counter 125 can only count complete clock cycles, its output N5 is a positive integer number, any time less than one clock cycle will not be counted.
Referring to
C6=N6Tr,
where N6 is the output of the counter 126. Similar to the master counter 120, the edge counter 126 can only count complete clock cycles, its output N6 is a positive integer number, any time less than one clock cycle will not be counted.
Referring to
C7=N7Tr,
where N7 is the output of the counter 127. Similar to the master counter 120, the edge counter 127 can only count complete clock cycles, its output N7 is a positive integer number, any time less than one clock cycle will not be counted.
Referring to
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T1=C0−t1=NTr−t1.
Referring to
T2=C0+C1−t2=(N+N1)Tr−t2.
Referring to
T3=C0+C1+C2−t3=(N+N1+N2)Tr−t3.
Referring to
T4=C0+C1+C2+C3−t4=(N+N1+N2+N3)Tr−t4.
Referring to
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Referring to
Here Tx is the period of the received ultrasonic signal. The center of T3 and T4 is always one period away from the center of T1 and T2. Similarly, the center of T5 and T6 is always one period away from the center of T3 and T4, and etc. The term T—1—8 can be expressed as follows,
T—1—8=(7N1+6N2+5N3+4N4+3N5+2N6+N7)Tr/8−1.5Tx.
ΔTm=|Δt1+Δt2+Δt3+Δt4+Δt5+Δt6+Δt7+Δt8|/8.
(Δt1, Δt2), (Δt3, Δt4), (Δt5, Δt6), and (Δt7, Δt8) change in opposite directions. As a result, their average is always smaller than |Δt1|. In effect, ΔTm≈0. This indicates that the ultrasonic wave transit time measurement accuracy is greatly improved using the method of the present disclosure compared to the method of prior art.
Noise in the received signal could cause threshold triggering error, thus, cause transit time measurement error. However, with multiple triggering mechanisms as illustrated in
Claims
1. A device for measurement of ultrasonic wave transit times of an ultrasonic flow sensor consists of:
- a synchronization signal generator,
- a reference pulse generator,
- a sine wave generator,
- an analog signal amplifier,
- a comparator,
- a plurality of latch circuits,
- a digital adder,
- an integrator,
- an A/D converter,
- a master counter,
- a plurality of edge counters, and
- an arithmetic circuit.
2. The device for measurement of ultrasonic wave transit times of claim 1, wherein the synchronization signal generator performs the following functions: 1) initiating the measurement cycle, 2) triggering the sine wave generator to start sending sine wave signal to the transmitter of the ultrasonic flow sensor, 3) triggering the reference pulse generator to start generating high frequency clock signal, and 4) commanding the master counter to start counting the reference clock.
3. The device for measurement of ultrasonic wave transit times of claim 1, wherein the reference pulse generator sends high frequency clock signal to: 1) the master counter, 2) the edge counters, and 3) the latch circuits. These clocks are used to measure the arriving time of the ultrasonic wave at different measuring points.
4. The device for measurement of ultrasonic wave transit times of claim 1, wherein the sine wave generator sends sine waves to the transmitter of the ultrasonic flow sensor. After certain period of time delay, the sine wave signal arrives at the receiver of the ultrasonic flow sensor with modulated amplitudes.
5. The device for measurement of ultrasonic wave transit times of claim 1, wherein the analog signal amplifier is AC-coupled. It amplifies the output signal from the receiver of the ultrasonic flow sensor.
6. The device for measurement of ultrasonic wave transit times of claim 1, wherein the comparator compares the signal received from the analog signal amplifier with the predefined threshold value. When the received signal becomes higher than the threshold value, it outputs a positive pulse. On the other hand, when the received signal becomes lower than the threshold value, it outputs a negative pulse.
7. The device for measurement of ultrasonic wave transit times of claim 1, wherein the latch circuits are employed to measure the time intervals which are less than one reference clock cycle and cannot be counted by the master counter and the edge counters.
8. The device for measurement of ultrasonic wave transit times of claim 1, wherein the digital adder is used to add the outputs of all the latch circuits together and then output the summed signal to the integrator.
9. The device for measurement of ultrasonic wave transit times of claim 1, wherein the integrator converts the short pulse from the adder to an analog exponential signal.
10. The device for measurement of ultrasonic wave transit times of claim 1, wherein the A/D converter converts the analog output of the integrator to a digital value.
11. The device for measurement of ultrasonic wave transit times of claim 1, wherein the master counter is used to measure the arriving time of ultrasonic wave at the first measuring point.
12. The device for measurement of ultrasonic wave transit times of claim 1, wherein the edge counters are used to measure the arriving time of ultrasonic wave at the subsequent measuring points after the first measuring point.
13. The device for measurement of ultrasonic wave transit times of claim 1, wherein the arithmetic circuit calculates the ultrasonic wave transit times from the inputs of the master counter, the edge counters and the A/D converter, by averaging the arriving times at different measuring points. This time measurement method has less dependency on triggering threshold level and ultrasonic signal amplitudes, and thus has less dependency on threshold drift, threshold stability, system gain fluctuation and signal amplitude variations. With multi-point triggering and multiple transit-time averaging as explained in previous section, this time measurement method is also more robust again noise interference than prior art. As a result, the method can greatly improve the velocity measurement accuracy of an ultrasonic flow sensor.
14. The device for measurement of ultrasonic wave transit times of claim 1, wherein an even number of latch circuits are employed. And the number of edge counters is always one less than the total number of the latch circuits. For example, if the total number of latch circuits is eight, the total number of the edge counters is seven.
15. The device for measurement of ultrasonic wave transit times of claim 14, wherein two latch circuits and one edge counter are employed. The ultrasonic wave transit time is calculated based on the average of the arriving times at the first and second measuring points.
16. The device for measurement of ultrasonic wave transit times of claim 14, wherein four latch circuits and three edge counters are employed. The ultrasonic wave transit time is calculated based on the average of arriving times at the 1-4 measuring points.
17. The device for measurement of ultrasonic wave transit times of claim 16, wherein the ultrasonic wave transit time is calculated based on the average of arriving times at the third and fourth measuring points.
18. The device for measurement of ultrasonic wave transit times of claim 14, wherein eight latch circuits and seven edge counters are employed. The ultrasonic wave transit time is calculated based on the average of arriving times at the 1-8 measuring points.
19. The device for measurement of ultrasonic wave transit times of claim 18, the ultrasonic wave transit time is calculated based on the average of arriving times at the fifth and sixth measuring points.
20. The device for measurement of ultrasonic wave transit times of claim 18, the ultrasonic wave transit time is calculated based on the average of arriving times at the seventh and eighth measuring points.
Type: Application
Filed: Oct 6, 2012
Publication Date: Apr 10, 2014
Applicant: Spire Metering Technology LLC (Acton, MA)
Inventor: Chang Shen (Acton, MA)
Application Number: 13/646,665