JP2011180076A - Device for determining zero-cross time, and ultrasonic flowmeter equipped with the device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device for determining zero-cross time which can measure the zero-cross time accurately and appropriately, even when the amplitude of an input signal varies or when the input signal is affected by noise. <P>SOLUTION: The device for determining zero-cross time includes a maximum absolute value update determining part 100, which can determine that a maximum absolute value is updated, when a positive or negative absolute value in the input signal 210 is larger than the positive or negative maximum absolute value in the past, a maximum absolute value time determining part 400, which can output a maximum absolute value time signal 350 indicating the maximum absolute value time at which the positive or negative absolute value in the input signal 210 becomes maximum, based on the result of determination, a temporary zero-cross time latch part 410 which latches the temporary zero-cross time of the input signal 210; and a zero-cross time determining part 170 which determines the zero cross time, based on the maximum absolute value time signal 350 and the temporary zero-cross time. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  One embodiment of the present invention is a zero-crossing time determination device that can determine the zero-crossing time of an input signal that periodically changes and whose absolute value of amplitude changes.

  As one of the flow meters, there is an ultrasonic flow meter that utilizes a propagation time difference that occurs when ultrasonic waves propagate through a medium. In the ultrasonic flowmeter, as shown in FIG. 9, ultrasonic transmitters / receivers 10 and 11 are arranged in the flow path, the propagation time of the received signal 12 transmitted from the upstream and received downstream, and the ultrasonic wave Is transmitted from the downstream and the flow velocity of the medium such as gas or liquid flowing in the flow path is measured based on the propagation time of the reception signal 13 received upstream.

  The measurement of the propagation time may require a resolution of several ns or sub ns, but the ultrasonic wave used in the ultrasonic flowmeter has a frequency of about several tens of kHz to several MHz. When this frequency is used, a highly accurate resolution such as 1/10000 or more of one cycle is required. On the other hand, the amplitude of the ultrasonic wave is affected by the flow velocity of the medium flowing through the flow path and the fluid state. Therefore, when the method of determining the arrival of the ultrasonic wave by setting a threshold value for the received signal is used, the arrival time measured when the amplitude of the received signal changes. That is, as shown in FIG. 10, the time when the reception signal S1 having the normal amplitude reaches the threshold value th1 is T1, whereas the reception signal S2 having the reduced amplitude reaches the threshold value th1. The time spent is T2.

  Therefore, there is a zero cross method as a measurement method that is not affected by the change in the amplitude of the received signal. The zero cross method is a method of measuring the time at the zero cross point, which is the timing at which the received signal changes from positive to negative or from negative to positive. As shown in FIG. 10, the time T3 at the zero cross point does not change in any of the received signals S1 and S2. Thus, according to the zero cross method, the time at the zero cross point does not change even if the amplitude of the received signal changes.

  However, since the ultrasonic signal includes a plurality of zero cross points, it is important to surely select an appropriate zero cross point as a basis for measuring the propagation time difference. For example, there is a case in which a predetermined threshold value is provided and a method of selecting a zero cross point observed at the next timing when the ultrasonic signal exceeds the threshold value may be applied.

  However, this method does not take into account that the amplitude of the ultrasonic signal changes due to changes in the flow rate of the medium flowing through the flow path or changes in the ultrasonic device characteristics over time, and the zero cross point at the intended timing cannot be selected. was there. For example, when the threshold value th2 is provided as shown in FIG. 11, p1 is determined to be the zero cross point in the received signal S1 having a normal amplitude, whereas p2 is set to the zero cross point in the received signal S2 having a small amplitude. It will be judged. On the other hand, for example, there has been a conventional technique in which the differential of the peak hold signal of the received ultrasonic signal is shaped into a pulse and the next zero cross point of the Nth pulse is selected (Patent Document 1).

Republished patent WO2004 / 048902

  However, even in the conventional technique described in Patent Document 1, a predetermined threshold value is used for waveform shaping, and if the amplitude of the input signal changes, an appropriate zero cross point may not be detected.

  Therefore, an object of one embodiment of the present invention is to provide an ultrasonic flow meter that can solve the above-described problems. Another object of one embodiment of the present invention is to accurately and appropriately measure the flow rate of a measurement target medium.

  In order to solve such a problem, a zero-crossing time determination device according to an aspect of the present invention provides a positive or negative absolute value in an input signal that changes periodically and whose absolute value of amplitude changes. A maximum absolute value update determination unit configured to be able to determine that the maximum absolute value has been updated when the maximum absolute value is greater than the maximum absolute value of the input signal, based on a determination result in the maximum absolute value update determination unit A maximum absolute value time determination unit configured to be able to output a maximum absolute value time signal indicating a maximum absolute value time at which the positive or negative absolute value is maximized, and a state in which the input signal is smaller than a predetermined value and larger A temporary zero-crossing time loop that is configured to periodically latch at least one of a change from a large state to a small state as a temporary zero-crossing time. Comprising a switch unit, and a zero-crossing time determining unit determines the zero crossing time on the basis of the maximum absolute value time signal and the provisional zero-cross time.

  According to the zero cross time determination apparatus having such a configuration, it is possible to reliably select a zero cross point at an intended timing in an input signal that changes periodically and whose absolute value of amplitude changes. As a result, for example, it is possible to accurately measure the ultrasonic propagation time difference, and to appropriately measure the flow rate of the measurement target medium.

  In addition, the maximum absolute value update determination unit used as the configuration of the apparatus can be configured with an analog circuit. In this case, the configuration can be simplified compared to a configuration in which an input signal is converted into a digital signal and digital signal processing is performed.

  The temporary zero-crossing time latch unit includes a counter unit that counts a change in a clock signal having a predetermined frequency, and when the input signal changes from a state smaller than the predetermined value to a larger state and smaller from the larger state. A counter latch configured to latch the output signal of the counter unit and output the provisional zero-crossing time at least when the state is changed to a state.

  The zero-crossing time determination device according to one aspect of the present invention is such that when a positive absolute value in an input signal that periodically changes and an amplitude absolute value changes is greater than the positive maximum absolute value in the past. A maximum absolute value update determination unit configured to be able to determine that the maximum absolute value has been updated, and a time at which the positive absolute value in the input signal is maximized based on a determination result in the maximum absolute value update determination unit A maximum absolute value time determination unit configured to be able to output a maximum absolute value time signal indicating the output, and a time when the input signal changes from a state larger than a predetermined value to a small state is output as a temporary zero cross time A provisional zero cross time latch unit, and a zero cross time determination unit that determines a zero cross time based on the maximum absolute value time signal and the provisional zero cross time. It may be.

  Alternatively, the zero-crossing time determination device according to one aspect of the present invention is such that the negative absolute value in the input signal that periodically changes and the absolute value of the amplitude changes is larger than the negative maximum absolute value in the past. A maximum absolute value update determination unit configured to be able to determine that the maximum absolute value has been updated, and a time at which the negative absolute value in the input signal is maximized based on a determination result in the maximum absolute value update determination unit And a maximum absolute value time determination unit configured to be able to output a maximum absolute value time signal indicating that a time when the input signal changes from a state smaller than a predetermined value to a larger state is output as a temporary zero cross time. A provisional zero-crossing time latch unit, and a zero-crossing time determination unit that determines a zero-crossing time based on the maximum absolute value time signal and the provisional zero-crossing time. It may be formed.

  The zero cross time determination unit preferably determines that the temporary zero cross time latched when the maximum absolute value time signal is output is a zero cross time.

  Since the zero cross point immediately after the timing when the maximum absolute value is updated in the input signal is the zero cross point in the state where the amplitude of the input signal is maximum, compared with the zero cross point in the state where the amplitude of the input signal is small, Difficult to be affected by noise.

  According to the above configuration, it is possible to measure the zero cross time at the zero cross point immediately after the timing when the maximum absolute value is updated in the input signal. Therefore, it is possible to measure a more accurate zero cross time that is not affected by noise or the like. As a result, the propagation time difference can be measured with high accuracy.

  The zero cross time determination unit may determine that the temporary zero cross time latched a predetermined time before the time when the maximum absolute value time signal is output is the zero cross time.

  The zero cross time determination unit may determine that the temporary zero cross time latched after a predetermined time from the time when the maximum absolute value time signal is output is the zero cross time.

  With the above configuration, it is possible to measure the zero cross time at the zero cross point at an arbitrary timing. For example, when it is predicted in advance that the amplitude of the input signal is maximized before the time when the maximum absolute value time signal is output, the zero crossing point at the zero crossing point in the state where the input signal is maximized It is possible to measure time.

  Further, the maximum absolute value time determination unit is configured such that when the maximum absolute value is not further updated in a predetermined period from when the maximum absolute value update determination unit determines that the maximum absolute value has been updated, the maximum absolute value is determined. It may be configured to output a time signal.

  Here, it is preferable that the predetermined period used in the maximum absolute value time determination unit is arbitrarily selected from periods between one cycle and 1.25 cycles of the input signal.

  According to this, the zero cross time at the zero cross point immediately after the timing when the maximum absolute value is updated in the input signal can be reliably measured with good timing.

  Moreover, this invention includes the ultrasonic flowmeter provided with one of the said zero crossing time determination apparatuses. According to this, the ultrasonic flowmeter which can measure a flow volume with sufficient accuracy can be provided.

  According to one aspect of the present invention, for example, it is possible to reliably select a zero-cross point at an intended timing in an input signal, which is a basis for measuring a propagation time difference of an ultrasonic wave, and a highly accurate zero-cross time determination device is provided. Can be provided.

The figure which shows the 1st structural example of a zero crossing time determination apparatus. The figure which shows the structural example of the largest absolute value update determination part. The wave form diagram at the time of operation | movement of a zero crossing time determination apparatus. The figure which shows the 2nd structural example of a zero crossing time determination apparatus. The figure which shows the 3rd structural example of a zero crossing time determination apparatus. The wave form diagram at the time of operation | movement of the 3rd structural example of a zero crossing time determination apparatus. The figure which shows the 4th structural example of a zero crossing time determination apparatus. The wave form diagram at the time of operation | movement of the 4th structural example of a zero crossing time determination apparatus. The figure which shows the structural example of an ultrasonic flowmeter. The 1st waveform diagram which shows the conventional operation | movement of an ultrasonic flowmeter. The 2nd waveform diagram which shows the conventional operation | movement of an ultrasonic flowmeter.

An embodiment according to the present invention will be specifically described according to the following configuration with reference to the drawings. However, the embodiment described below is merely an example of the present invention, and does not limit the technical scope of the present invention. In addition, in each drawing, the same code | symbol is attached | subjected to the same component and the description may be abbreviate | omitted.
1. Definition 2. Embodiment 1
(1) First configuration example of zero-cross time determination device (2) Operation of zero-cross time determination device (3) Summary Embodiment 2
4). Embodiment 3
5. Embodiment 4
6). Supplement

<1. Definition>
First, terms used in this specification are defined as follows.
“Zero cross point”: A point at which the waveform of the input signal crosses a predetermined potential. The predetermined voltage is often a zero potential, but is not limited to this, and the predetermined potential can be arbitrarily determined.
“Hi” and “Lo”: Binary values in the binarized signal are referred to as “Hi” and “Lo”, respectively. “Hi” indicates a state in which the binarized signal indicates a high potential, and “Lo” indicates a state in which the binarized signal indicates a low potential.

<2. Embodiment 1>
One embodiment of the present invention is a zero cross time determination device used in a flow meter such as an ultrasonic flow meter, which uses a signal that periodically changes and whose amplitude has an absolute value change as an input signal. . As already described, this zero-crossing time determination device can be used as a part of the configuration of the ultrasonic transceivers 10 and 11 in the flow meter shown in FIG. Hereinafter, Embodiment 1 will be described with reference to FIGS. 1 to 3.

<(1) First Configuration Example of Zero Cross Time Determination Device>
FIG. 1 is a diagram illustrating a first configuration example of a zero-crossing time determination device. As shown in FIG. 1, the zero-cross time determination device according to the first embodiment includes a maximum absolute value update determination unit 100, a maximum absolute value time determination unit 400, a provisional zero-cross time latch unit 410, and an output latch 170. The

(Maximum absolute value update determination unit 100)
The maximum absolute value update determination unit 100 is configured to receive the input signal 210 and the reset signal 200 and to output the maximum absolute value update signal 320 and the maximum absolute value signal 310.

  FIG. 2 is a diagram illustrating a specific configuration example of the maximum absolute value update determination unit 100. As shown in FIG. 2, the maximum absolute value update determination unit 100 includes a comparator 500, a current source 510, a switch 520, a diode 530, a capacitor 540, a discharger 550, and an impedance converter 560.

  The comparator 500 compares the amplitudes of the input signal 210 and the maximum absolute value signal 310, and when the amplitude of the input signal 210 is larger, Hi, and when the amplitude of the input signal 210 is smaller, Lo. The maximum absolute value update signal 320 is output. The switch 520 is turned on when the signal input from the comparator 500 is Hi, and is turned off when the signal is Lo. When the switch 520 is in the ON state, the current flowing from the current source 510 is charged to the capacitor 540 via the diode 530 and the maximum absolute value signal 310 is updated via the impedance converter 560. When the reset signal 200 instructs to reset the circuit, the discharger 550 discharges the electric charge charged in the capacitor 540.

  In the first embodiment, the operation is performed based on the maximum positive value of the input signal 210, but this may be performed based on the minimum value that is a negative maximum absolute value. In other words, the maximum absolute value signal 310 and the maximum absolute value update signal 320 can also be referred to as a maximum value signal and a maximum value update signal, or a minimum value signal and a minimum value update signal, respectively. Similarly, the “maximum absolute value XX” can be called “maximum XX” or “minimum XX” in some cases.

  That is, the maximum absolute value update determination unit 100 is configured to be able to determine that the maximum absolute value has been updated when the input signal 210 is larger than the positive maximum absolute value in the past.

(Maximum absolute value time determination unit 400)
The maximum absolute value time determination unit 400 includes a retriggerable one-shot multivibrator 110 and a reset set flip-flop 120.

  The retriggerable one-shot multivibrator 110 is configured to change the retriggerable one-shot multivibrator output signal 340 from Lo to Hi when the maximum absolute value update signal 320 detected first falls. The retriggerable one-shot multivibrator 110 outputs a retriggerable one-shot multivibrator output signal 340 when the rising edge of the maximum absolute value update signal 320 is not detected within a predetermined period from the falling edge of the detected maximum absolute value update signal 320. It is configured to change from Hi to Lo.

  The reset set flip-flop 120 is configured to change the output latch timing signal 350, which is an output signal, from Lo to Hi when detecting the fall of the retriggerable one-shot multivibrator output signal 340. The reset set flip-flop 120 is configured to be reset by a reset signal 240.

  That is, the maximum absolute value time determination unit 400 can output the output latch timing signal 350 indicating the maximum absolute value time at which the positive absolute value in the input signal 210 becomes maximum based on the determination result in the maximum absolute value update determination unit 100. It is configured. More specifically, the maximum absolute value time determination unit 400 determines that the maximum positive absolute value is obtained in a predetermined period (T) from when the maximum absolute value update determination unit 100 determines that the positive maximum absolute value has been updated. Further, when not updated, the output latch timing signal 350 is output. The output latch timing signal 350 is also called a maximum absolute value time signal, and may be configured to output a time when the negative absolute value becomes maximum as will be described later.

(Temporary zero cross time latch unit 410)
The provisional zero cross time latch unit 410 includes a comparator 130, a counter 140, a clock generation unit 150, and a counter latch 160.

  The comparator 130 is configured to compare the input signal 210 with a zero potential, and output Hi as a binarized signal 330 if the input signal 210 is higher than the zero potential, and Lo if it is lower.

  The clock generation unit 150 supplies a clock signal having a predetermined frequency to the counter 140.

  The counter 140 is configured to continuously count up the clock signal according to the instruction of the start / stop signal 220 and output the count signal. The counter 140 is configured to be reset by a reset signal 230.

  The counter latch 160 is configured to latch the count signal at the falling edge of the binarized signal 330 and output it as a temporary zero cross time signal 360. Here, the count signal, which is a signal obtained by continuously counting up the clock signal by the counter 140, indicates time information, and the falling edge of the binarized signal 330 is a zero cross in which the input signal 210 changes from positive to negative. Indicates a point. Therefore, it can be said that the temporary zero cross time signal 360 is a signal indicating the time at the zero cross point at which the input signal 210 changes from positive to negative.

  That is, the provisional zero cross time latch unit 410 is configured to periodically latch the time when the input signal 210 changes from a state larger than a predetermined value to a small state as a provisional zero cross time and output the provisional zero cross time signal 360. It is what.

(Output latch 170)
The output latch 170 is configured to latch the temporary zero cross time signal 360 at the rising edge of the output latch timing signal 350 and output the latched temporary zero cross time signal 360 as the zero cross time signal 250.

  However, the timing for latching the temporary zero cross time signal 360 in the output latch 170 can be changed as necessary. In other words, the output latch 170 may latch the provisional zero cross time signal 360 at an arbitrary timing determined based on the output latch timing signal 350 and output it as the zero cross time signal 250.

<(2) Example of Operation of Zero Cross Time Determination Device>
FIG. 3 is a waveform diagram of each signal during the operation of the zero-crossing time determination device. Each signal is output from each component of the zero cross time determination device as described above.

  The maximum absolute value signal 310 indicates the maximum value of the input signal 210 up to that time. The maximum absolute value update signal 320 indicates that the maximum absolute value signal 310 has been updated, and becomes Hi when the input signal 210 is larger than the immediately preceding maximum absolute value signal 310. The binarized signal 330 is a signal obtained by binarizing the input signal 210 with a zero potential. The retriggerable one-shot multivibrator output signal 340 is generated based on the maximum absolute value update signal 320 and is used to generate the output latch timing signal 350. The output latch timing signal 350 is used when the temporary zero cross signal 360 is latched to determine the zero cross time signal 250. The provisional zero-cross signal 360 indicates the time when the input signal 210 changes from positive to negative, and is generated based on the count signal (not shown) and the binarized signal 330. Hereinafter, characteristic signals will be described more specifically.

  The retriggerable one-shot multivibrator output signal 340 changes from Lo to Hi at the fall of the first detected maximum absolute value update signal 320 (T10), and the detected fall of the maximum absolute value update signal 320 When the rising edge of the maximum absolute value update signal 320 is not detected during a predetermined period (T) from T to T, the level changes from Hi to Lo. Here, in this embodiment, when the rising edge of the maximum absolute value update signal 320 is not detected in a period of 1 to 1.25 times the cycle of the input signal 210 from the falling edge of the detected maximum absolute value update signal 320, Hi. Changes from Lo to Lo. If this predetermined period (T) is shorter than one cycle of the input signal 210, the maximum absolute value is actually updated later, and the intended zero-cross point is detected even though the maximum absolute value update signal 320 changes. There are cases where it is not possible. If the predetermined period (T) is longer than the 1.25 period of the input signal 210, the temporary zero cross time signal 360 is latched after the temporary zero cross time signal 360 has changed to the next value. Become. That is, not the time of the zero cross point Z immediately after the amplitude of the input signal 210 becomes maximum, but the time of the next zero cross point is measured. Therefore, it is preferable that the predetermined period (T) used in the maximum absolute value time determination unit 400 is designed to be arbitrarily selected from a period between 1 and 1.25 times the period of the input signal 210.

The provisional zero cross time signal 360 is a signal obtained by latching the count signal output from the counter at the falling edge of the binarized signal 330. As described above, the count signal is a signal indicating time information, and the falling edge of the binarized signal 330 is a signal indicating a zero cross point at which the input signal 210 has changed from positive to negative. Therefore, the provisional zero cross time signal 360 is This is a signal indicating the time at the zero crossing point at which the input signal 210 changes from positive to negative. As shown in FIG. 3, the temporary zero cross time signal 360 is synchronized with the falling edge of the binarized signal 330, N _n−5 , N _n−4 , N _n−3 , N _n−2 , N _n−1. , N _n and N _{n + 1} .

  As described above, the output latch timing signal 350 changes from Lo to Hi in synchronization with the fall of the retriggerable one-shot multivibrator output signal 340 (T20).

The zero cross time signal 250 is a signal obtained by latching the temporary zero cross time signal 360 at the rising timing (T20) of the output latch timing signal 350. As shown in FIG. 3, the N _n in the present embodiment. That is, it can be seen that the zero cross time signal 250 indicates N _n as the zero cross time corresponding to the next zero cross point at which the amplitude of the input signal 210 is maximized.

<(3) Summary>
As described above, according to the zero-crossing time determination apparatus in the present embodiment, the input signal 210 that periodically changes and the absolute value of the amplitude changes without being affected by the change in the amplitude of the input signal 210, etc. It becomes possible to select the zero cross point at the intended timing with certainty. Thereby, it is possible to accurately measure the propagation time difference of the ultrasonic wave including the zero cross time determination device, and to appropriately measure the flow rate of the measurement target medium. In particular, according to the configuration of the present embodiment, it is possible to output the zero cross time signal 250 as the time at the zero cross point immediately after the amplitude of the input signal 210 becomes maximum.

  In the present embodiment, the time at the next zero cross point at which the amplitude of the input signal 210 has shown a positive maximum value is measured. However, the present invention is not limited to this, and is understood by those skilled in the art from this embodiment. This invention is included in the present application. For example, a configuration in which the time at the next zero cross point at which the amplitude of the input signal 210 shows a negative minimum value can be considered. A configuration is also conceivable in which time is measured at about N zero cross points at which the amplitude of the input signal 210 is maximum.

  Further, if the provisional zero cross time before and after a predetermined time from the time when the amplitude of the input signal 210 shows the maximum value is determined as the zero cross time, the zero cross time at the zero cross point can be measured at an arbitrary timing.

  However, the zero cross point immediately after the timing when the amplitude of the input signal 210 becomes maximum has a large amount of change in the signal (differential value of the signal), and therefore, compared with the zero cross point at the timing when the amplitude of the input signal 210 is small. It is hard to be affected by noise. That is, according to the configuration of the present embodiment, the zero cross time is measured using the zero cross point immediately after the timing when the amplitude of the input signal 210 becomes maximum, so that it is more accurate and not affected by noise or the like. It becomes possible to measure the zero crossing time. As a result, the propagation time difference can be measured with high accuracy.

  In the present embodiment, the predetermined period used to generate the output latch timing signal 350 in the maximum absolute value time determination unit 400 is arbitrarily selected from a period between 1 and 1.25 times the cycle of the input signal 210. It is designed to be This is preferable because the zero cross time at the zero cross point immediately after the timing when the maximum absolute value is updated in the input signal 210 can be reliably measured with good timing.

<3. Second Embodiment>
Next, Embodiment 2 will be described with reference to FIG. Compared with the first embodiment, the second embodiment is the same as the first embodiment except that the second embodiment further includes an inverter 180 immediately after the input signal 210 is input to the zero-crossing time determination device.

  The inverter 180 is configured to be able to invert the polarity of the input signal 210. Here, the inverter 180 may have a signal amplification function.

  As described above, in the zero cross time determination apparatus including the inverter 180, the polarity of the inverted input signal 211 input to the maximum absolute value update determination unit 100 and the comparator 130 is opposite to that of the input signal 210. For this reason, in the zero-crossing time determination device of the second embodiment, the input signal 210 operates based on the minimum value instead of the maximum value, and the input signal 210 instead of the zero-cross point where the input signal 210 changes from positive to negative. 210 operates based on the zero cross point at which the value changes from negative to positive.

  According to the zero cross time determination apparatus of the second embodiment, it is possible to output the zero cross time signal 251 as the time at the next zero cross point where the amplitude of the input signal 210 is minimized.

<4. Embodiment 3>
Next, Embodiment 3 will be described with reference to FIGS. Compared to the first embodiment, the third embodiment is different in that the D-FF (D-flip flop) 180 is provided between the maximum absolute value time determination unit 400 and the output latch 170. The configuration is the same as that of the first embodiment.

  The D-FF 190 is configured to operate at the rising edge of the binarized signal 330 with the output latch timing signal 350 as an input, and to output the delayed output latch timing signal 380 to the output latch 170. That is, the D-FF 190 has a function of delaying the output latch timing signal 350 until the next rising timing of the binarized signal 330.

  The output latch 170 is configured to latch the temporary zero cross time signal 360 at the rising edge of the delayed output latch timing signal 380 and output the latched temporary zero cross time signal 360 as the zero cross time signal 252.

  FIG. 6 is a diagram illustrating waveforms of respective units during operation of the zero-crossing time determination device according to the third embodiment. As shown in FIG. 6, the delayed output latch timing signal 380 output from the D-FF 190 is a signal obtained by delaying the output latch timing signal 350 until the next rising timing of the binarized signal 330. Further, since the output latch 170 latches the provisional zero cross time signal 360 at the rising edge of the delayed output latch timing signal 380, the input signal 210 is not the zero cross point Z immediately after the timing when the input signal 210 becomes maximum, but the input signal 210 is next. The time at the zero cross point that changes from negative to positive is output as a zero cross time signal 252.

  In the third embodiment, only one D-FF 190 is disposed, but a plurality of D-FFs 190 may be disposed in series. When a plurality of D-FFs 190 are arranged in series, the delay output latch timing signal 380 can be delayed by a desired period.

  When the D-FF 190 is arranged between the maximum absolute value time determination unit 400 and the output latch 170 in this way, the zero cross time at the zero cross point after a predetermined time from the time when the amplitude of the input signal 210 shows the maximum value is measured. It becomes possible to do.

<5. Embodiment 4>
Next, Embodiment 4 will be described with reference to FIGS. Compared to the first embodiment, the fourth embodiment is different in that a delay latch 191 is provided between the counter latch 160 and the output latch 170.

  The delay latch 191 is configured to operate at the falling edge of the binarized signal 330 with the provisional zero cross time signal 360 as an input, and to output the delay provisional zero cross time signal 390 to the output latch 170. In other words, the delay latch 191 has a function of delaying the provisional zero cross time signal 360 until the next falling timing of the binarized signal 330. As a result, when the temporary zero cross time signal 360 and the delayed temporary zero cross time signal 390 are compared, the output values are delayed one by one. The output latch 170 is configured to latch the delayed temporary zero cross time signal 390 at the rising edge of the output latch timing signal 350 and output the latched delayed temporary zero cross time signal 390 as the zero cross time signal 253.

  FIG. 8 is a diagram illustrating waveforms of respective units during operation of the zero-crossing time determination device according to the fourth embodiment. As shown in FIG. 8, it can be seen that the delayed temporary zero cross time signal 390 output from the delay latch 191 is delayed by one as compared with the temporary zero cross time signal 360. Further, since the output latch 170 latches the delayed temporary zero cross time signal 390 when the output latch timing signal 350 rises, the input signal 210 is not before the zero cross point Z immediately after the timing when the input signal 210 becomes maximum, but before that. The time at the zero cross point that changes from negative to positive is output as a zero cross time signal 253.

  In the fourth embodiment, only one delay latch 191 is arranged, but a plurality of delay latches 191 may be arranged in series. When a plurality of delay latches 191 are arranged in series, the delayed temporary zero cross time signal 390 can be delayed by a desired period.

  If the delay latch 191 is arranged between the counter latch 160 and the output latch 170 in this way, it is possible to measure the time at the zero cross point a predetermined time before the time when the amplitude of the input signal 210 shows the maximum value. Become.

<6. Supplement>
Although the embodiments of the present invention have been specifically described above, the present invention is not limited to these configuration examples, and includes various modes that can be considered by those skilled in the art from these configuration examples.

  For example, the configurations of the maximum absolute value update determination unit 100, the maximum absolute value time determination unit 400, and the provisional zero cross time latch unit 410 are not limited to the configurations described in the embodiments, and other configurations that can be considered by those skilled in the art. Of course. In addition, the operation timing of each component can be changed as appropriate.

  Moreover, the zero-crossing time determination device of the present invention can be applied to a flow meter such as an ultrasonic flow meter, and the present invention includes such a flow meter. According to such a flow meter, it is possible to accurately measure the propagation time difference in the ultrasonic transceiver arranged in the flow meter, and to measure the flow velocity of the measurement target medium appropriately and accurately.

  The zero cross time determination apparatus of the present invention can be applied to a flow meter represented by an ultrasonic flow meter. Moreover, it is applicable also to the electronic device which measures zero crossing time based on the input signal similar to a flowmeter.

10 · 11 ··· Ultrasonic transceiver 12 · 13 ··· Received signal 100 ··· Maximum absolute value update determination unit 110 ··· Retriggerable one-shot multivibrator 120 ··· Reset set flip-flop 130 ··· Comparator 140 ··· Counter 150 ...... Clock generation unit 160 ...... Counter latch 170 ...... Output latch (zero cross time determination unit)
180 …… Inverter 190 …… D-FF (D-flip-flop)
191 ... Delay latch 200 ... Reset signal 210 ... Input signal 211 ... Inverted input signal 220 ... Start / stop signal 230/240 ... Reset signal 250/251/252/253 ... Zero cross time signal 310 ... Maximum absolute value signal 320 ... Maximum absolute value update signal 330 ... Binarization signal 340 ... Retriggerable one-shot multivibrator output signal 350 ... Output latch timing signal (maximum absolute value time signal)
360... Temporary zero cross time signal 380... Delayed output latch timing signal 390... Delayed temporary zero cross time signal 400... Maximum absolute time determination unit 410. ... Switch 530 ... Diode 540 ... Capacitor 550 ... Discharger 560 ... Impedance converter

Claims (10)

It is possible to determine that the maximum absolute value has been updated when the positive or negative absolute value in the input signal that changes periodically and the absolute value of the amplitude changes is larger than the positive or negative maximum absolute value in the past. A maximum absolute value update determination unit configured in
Maximum absolute value time configured to be able to output a maximum absolute value time signal indicating a maximum absolute value time at which the positive or negative absolute value in the input signal is maximized based on a determination result in the maximum absolute value update determination unit A determination unit;
Temporary zero cross time latch configured to periodically latch at least one of when the input signal changes from a smaller state to a larger state and when the input signal changes from a larger state to a smaller state as a provisional zero cross time And
A zero cross time determination unit that determines a zero cross time based on the maximum absolute value time signal and the provisional zero cross time;
A zero-crossing time determination device. The provisional zero cross time latch unit is
A counter unit for counting a change in a clock signal having a predetermined frequency;
At least one of when the input signal changes from a state smaller than the predetermined value to a larger state and when the input signal changes from a larger state to a smaller state, the output signal of the counter unit is latched and the provisional zero cross time is set. The zero cross time determination device according to claim 1, further comprising: a counter latch configured to output. It is configured to be able to determine that the maximum absolute value has been updated when the positive absolute value in the input signal that periodically changes and the absolute value of the amplitude changes is greater than the positive maximum absolute value in the past. A maximum absolute value update determination unit;
A maximum absolute value time determination unit configured to output a maximum absolute value time signal indicating a time at which the positive absolute value in the input signal is maximized based on a determination result in the maximum absolute value update determination unit;
A temporary zero-crossing time latch unit configured to output as a temporary zero-crossing time when the input signal changes from a state larger than a predetermined value to a small state;
A zero cross time determination unit that determines a zero cross time based on the maximum absolute value time signal and the provisional zero cross time;
A zero-crossing time determination device. It is configured to be able to determine that the maximum absolute value has been updated when the negative absolute value in the input signal that periodically changes and the absolute value of the amplitude changes is larger than the negative maximum absolute value in the past. A maximum absolute value update determination unit;
A maximum absolute value time determination unit configured to output a maximum absolute value time signal indicating a time at which the negative absolute value in the input signal is maximized based on a determination result in the maximum absolute value update determination unit;
A provisional zero-crossing time latch unit configured to output as a provisional zero-crossing time when the input signal changes from a state smaller than a predetermined value to a larger state;
A zero cross time determination unit that determines a zero cross time based on the maximum absolute value time signal and the provisional zero cross time;
A zero-crossing time determination device. The zero-crossing time determination unit determines that the temporary zero-crossing time latched when the maximum absolute value time signal is output is a zero-crossing time.
The zero cross time determination apparatus according to any one of claims 1 to 4. The zero cross time determination unit determines that the temporary zero cross time latched a predetermined time before the time when the maximum absolute value time signal is output is a zero cross time,
The zero cross time determination apparatus according to any one of claims 1 to 4. The zero cross time determination unit determines that the temporary zero cross time latched after a predetermined time from the time when the maximum absolute value time signal is output is a zero cross time,
The zero cross time determination apparatus according to any one of claims 1 to 4. The maximum absolute value time determination unit is configured to output the maximum absolute value time signal when the maximum absolute value is not further updated in a predetermined period from when the maximum absolute value update determination unit determines that the maximum absolute value has been updated. The zero cross time determination apparatus according to any one of claims 1 to 7, wherein the zero cross time determination apparatus is configured to output. The zero cross time determination device according to claim 8, wherein the predetermined period used in the maximum absolute value time determination unit is arbitrarily selected from a period between one cycle and 1.25 periods of the input signal.   The ultrasonic flowmeter provided with the zero crossing time determination apparatus of any one of Claims 1 thru | or 9.