JPH053886B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of the Invention] This invention relates to a receiving wave balance method in an ultrasonic flowmeter, and in particular, the invention relates to a receiving wave balance method in an ultrasonic flowmeter, in particular, in which ultrasonic waves are incident obliquely to the flow, and the ultrasonic propagation time from the upstream side to the downstream side and the ultrasonic wave propagation time from the downstream side to the upstream side are The present invention relates to a receiving wave balance method of an ultrasonic propagation time measuring section in an ultrasonic propagation time difference measurement type ultrasonic flowmeter that measures a flow rate by measuring a propagation time difference between ultrasonic propagation times to the sides. [Prior art and problems] An ultrasonic flowmeter is an instrument that measures flow rate by measuring the time difference between the ultrasonic propagation time from upstream to downstream and the ultrasonic propagation time from downstream to upstream. Are known. Fig. 3 shows the measurement principle of an ultrasonic flowmeter, in which the fluid to be measured flows in a pipe 1, an ultrasonic transducer 2 is arranged on the upstream side, and an ultrasonic transducer on the downstream side. 3 are arranged, and ultrasonic waves 4 are transmitted between them and received by the opposing ultrasonic transducers. Since the electromechanical coupling coefficients of these ultrasonic transducers 2 and 3 are usually different, a difference occurs in the amplitude of the received wave 5. The amplitudes of the respective received waves 5 are made the same by the reception balance circuit 6, and when the second wave of the reception waves becomes equal to the threshold value 7, the trigger circuit 8 sends out the reception signal 9. The flow velocity is measured by measuring the ultrasonic propagation time from the upstream side to the downstream side and the ultrasonic propagation time from the downstream side to the upstream side while switching upstream and downstream transmission and reception. In order to keep the amplitudes of the received waves input to the trigger circuit 8 at the same level, conventionally, received wave balance was performed by changing only the amplitudes. To explain this reception balance circuit with reference to FIG. 4, a reception wave 5 is supplied to an AGC circuit 10, the gain is controlled, and an AGC converted binary reception wave 11 is sent out, and this reception wave 11 is supplied to a comparator 12. Here, it is compared with the set peak value 14 from the peak value setting circuit 13, and a binary signal 15 is output. This binary signal 15 is applied to a gate circuit 16, which sends out a gated binary signal 17 for a predetermined period of time. This gated binary signal 17 is integrated through an integrating circuit 18 to become an AGC voltage 19, and the gain of the AGC voltage amplifier 10 is feedback-controlled, so that the peak value of the wave triggered by the trigger circuit 6 matches the set peak value. let In this way, the balance between the received waves going from upstream to downstream and the received waves going from downstream to upstream is adjusted. However, in this method of balancing the received waves by changing the gain of the received waves, only one wave height can be matched, so the temporal change rate of the wave amplitude is different, and the time difference occurs even though no fluid is flowing. There was a problem in which the flow rate value did not show zero because it was incorrectly measured as if it were present. Furthermore, the waveforms of the transmitted waves propagating from upstream to downstream or from downstream to upstream are slightly different due to differences in the temperature characteristics of the ultrasonic transducers and the asymmetry of the wedge. For example, as shown in FIG.
and the second received wave 21 may be different between the case where the received wave goes from upstream to downstream and the case where the received wave goes from downstream to upstream. In such a case, the second received wave 2
If the amplification factor of the AGC circuit 10 is controlled so that the second term portion 24 of the first received wave 20 matches from upstream to downstream and from downstream to upstream, the first trough portion 23 of the first received wave 20 will not match. As a result, the temporal slope from the first trough to the second peak differs between upstream → downstream and downstream → upstream reception, and the time from transmission until the second reception wave 21 reaches the threshold 7 is determined by the upstream → downstream reception wave. In this case, T _{1 is} generated, and T ₂ is generated in the received wave from downstream to upstream, resulting in a propagation time difference Δt. This is measured as if it were caused by flowing fluid. By the way, when we examine the values of the first trough and second peak of the received wave when the temperature of the ultrasonic transducer is changed, we get the following table.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention was to solve the above-mentioned problems by reducing the propagation time difference between the ultrasonic propagation time from the upstream side to the downstream side and the ultrasonic propagation time from the downstream side to the upstream side. The object of the present invention is to provide a receiving wave balance method for an ultrasonic flowmeter that is necessary for accurate measurement. [Summary of the Invention] In order to achieve the above object, the present invention measures the wave height values in the positive and negative directions of the waveforms of the upstream side received wave and the downstream side received wave, and The wave height value immediately before and the wave height immediately after the waveform that becomes the threshold value are compared, and the difference in amplitude and offset of the waveform that becomes the predetermined threshold value is calculated at the beginning of the upstream and downstream received waves. The upstream and downstream received waves are amplified according to the difference in offset, and the level is increased or decreased according to the difference in offset. First, the peak value of the upstream received wave immediately before the waveform that becomes a predetermined threshold value is By matching the wave height value of the downstream side received wave and the wave height value of the immediately following upstream side received wave and the wave height value of the downstream side received wave, the wave height is determined at the beginning of the upstream side received wave and the downstream side received wave. The present invention is characterized in that the temporal rate of change in the level of the waveform serving as the determined threshold value is made to match. [Embodiments of the Invention] Hereinafter, embodiments of the receiving wave balance method in an ultrasonic flowmeter according to the present invention will be described with reference to FIGS. 1 and 2. In FIG. 1, received waves 5 from the upstream ultrasonic transducer 2 and the downstream ultrasonic transducer 3 are supplied to a received wave switching device 26. As shown in FIG. This received wave switching device 26 is selected by a switching signal 29 from a microcomputer 28, and its output signal 30 is input to the AGC amplifier 10, and sent out as a balanced received wave 32 through an operational amplifier 31. A part of the balanced reception wave 32 is guided to a first comparator 33, and a trough threshold value 35 corresponding to the first trough obtained from the microcomputer 28 through the D/A converter 34 is introduced.
are compared and a binary signal 36 is applied to the microcomputer 28. Similarly, the second top part is also balanced received wave 3.
2 is led to a second comparator 37, where it is compared with a threshold value 39 corresponding to the second peak obtained from the microcomputer 28 through the D/A converter 38, and a binarized signal 40 is applied to the microcomputer 28. . The microcomputer 28 changes the threshold values 35 and 39 according to the binary signals 36 and 40, and finally changes the threshold values 35 and 39 to the first received wave selected by the received wave selector 26.
The level of the trough and the level of the second peak of the second received wave are detected. The first trough level of the first received wave of the upstream side received wave balanced received wave 32 is set as A1, the second peak level of the second received wave is set as B1, and the first trough level of the downstream side received wave balanced received wave 32 is set as A1. Assuming that the level is A2 and the second peak level of the second received wave is B2, if the received waves are perfectly balanced, A1 = A2, B1 =
It becomes B2. When receiving waves are not balanced, (A2 − B2) − (A1 − B1) corresponds to the difference in amplitude,
A1-A2 (A1-B1)/A2-B2 corresponds to the difference in offset levels. Therefore, the microcomputer 28
The AGC voltage 42 is sent to the AGC amplifier 10 through the D/A converter 41 so that the gain on the downstream side of the AGC amplifier 10 is (A1-B1)/(A1-B2) times the gain on the upstream side. On the other hand, the signal from the microcomputer 28 is balanced by adding an offset voltage 44 to the operational amplifier 27 so that the signal is multiplied by A1-A2 (A1-B1)/A2-B2 through the D/A converter 43. By repeating such operations, the first trough level A1=A2 and the second peak B1 of the upstream balanced received wave 32 and the downstream balanced received wave 32.
=B2. As a result, the temporal rate of change from the first trough to the second peak of both received waves becomes the same, and the error in the propagation time difference is eliminated. FIG. 2 is a flowchart showing the above-mentioned signal flow. [Effects of the Invention] As described above, according to the present invention, receiving wave balance is performed by detecting the first trough level of the first received wave and the second peak level of the second received wave.
The rate of change in level over time from the first trough to the second peak of each received wave can be made the same, and false detection of propagation time differences can be completely eliminated.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing the receiving balance method in an ultrasonic flowmeter according to the present invention, Fig. 2 is an operation flowchart showing the receiving balance method, and Fig. 3
The figure is an explanatory diagram showing the measurement principle of an ultrasonic flowmeter, and Figure 4 is a circuit diagram showing the conventional receiving balance method.
FIG. 5 is a waveform diagram for explaining erroneous detection of time difference by the conventional method. 2, 3... Ultrasonic transducer, 10... AGC amplifier, 26... Reception wave switching device, 27... Operational amplifier, 33... First comparator, 34... D/
A converter, 28...microcomputer, 38...D/
A converter.

Claims (1)

[Claims] 1. Measure the wave height values in the positive and negative directions of the waveforms of the upstream side received wave and the downstream side received wave, and measure the wave height immediately before the waveform that becomes the first predetermined threshold among the received waveforms. The high value and the immediately following wave height value are compared, and the difference in waveform amplitude and offset that is the first predetermined threshold value of the upstream and downstream received waves is calculated, and the difference in waveform amplitude and offset is calculated based on the difference in amplitude. The downstream received wave is amplified, and the level is raised or lowered depending on the difference in offset, and the peak value of the upstream received wave and the peak value of the downstream received wave are first determined immediately before the waveform that becomes a predetermined threshold value. By matching the wave height value of the upstream side received wave and the wave height value of the downstream side received wave immediately after, the waveform level that becomes the initially determined threshold of the upstream side received wave and the downstream side received wave is determined. A receiving wave balance method in an ultrasonic flowmeter characterized by matching the temporal rate of change of . 2. In the received wave balance method as set forth in claim 1, the wave height values of the peak immediately before and the peak immediately after the waveform that becomes the threshold value initially determined for the upstream and downstream received waves are measured. A receiving wave balance method characterized by: 3. In the received wave balance method described in claim 1, the predetermined threshold value is a positive value, the peak immediately before the waveform that becomes the initially determined threshold value of the received wave is a negative value, and the peak immediately before the waveform that becomes the initially determined threshold value is a negative value. A receiving wave balance method characterized by setting the peak of the value as a positive value. 4. In the received wave balance method described in claim 1, the predetermined threshold value is a negative value, the peak immediately before the waveform that becomes the initially determined threshold value of the received wave is a positive value, and A receiving wave balance method characterized by setting the peak of the value to a negative value. 5. In the received wave balance method described in claim 2, the predetermined threshold value is a positive value, the peak immediately before the waveform that becomes the initially determined threshold value of the received wave is a negative value, and the peak immediately before the waveform that is the first determined threshold value of the received wave is a negative value. A receiving wave balance method characterized by setting the peak of the value as a positive value. 6. In the received wave balance method described in claim 2, the predetermined threshold value is a negative value, the peak immediately before the waveform that becomes the initially determined threshold value of the received wave is a positive value, and the peak immediately before the waveform that becomes the initially determined threshold value is a positive value. A receiving wave balance method characterized by setting the peak of the value to a negative value.