JP4858219B2 - Ultrasonic current meter - Google Patents

Description

  The present invention relates to an apparatus for measuring flow velocity or flow rate using ultrasonic waves, and more particularly to a timer apparatus for measuring ultrasonic propagation time.

  As shown in FIG. 4, the conventional ultrasonic velocimeter has ultrasonic transducers 2 and 3 installed in the flow path 1 so as to be opposed to the flow direction, and the control unit 4 starts a timer 5 and simultaneously drives a driving circuit. 6 is operated. The ultrasonic wave transmitted from the ultrasonic transducer 2 driven by the drive circuit 6 is received by the ultrasonic transducer 3 and received and detected by the reception detection circuit 7 that has received the output of the ultrasonic transducer 3. The timer 5 measures the propagation time from when the ultrasonic wave is transmitted until it is detected, and the calculation unit 8 obtains the flow velocity in the flow path 1 by calculation from the time measured by the timer 5.

  In some cases, the propagation time of ultrasonic waves is obtained in both the upstream and downstream directions, and the flow velocity is obtained from the reciprocal difference.

  In addition, in order to measure minute changes in the propagation time at low flow rates, a second timer with high time resolution is installed, and the basic clock timer and high resolution timer are combined to increase measurement accuracy at low flow rates. There was also an ultrasonic current meter as described above (for example, see Patent Document 1).

  As an example of a high-resolution timer, as shown in FIG. 5, there is a ring oscillator in which an odd number of inversion means and delay means are connected in a ring shape, which has the characteristics of simple configuration, short start-up time, and high-frequency oscillation. ing.

  The operation of the ring oscillator will be described with reference to FIG. 5. The inverting means 9 and 10 respectively output outputs obtained by inverting the input signal to the delay means 11. Each delay means 11 outputs the same signal to the inversion means 9 and delay means 11 of the next stage after the delay time has elapsed. In this way, since the odd number of inversion means are installed in one round of the path connected in the ring shape, the signal moves along the ring path and oscillates with time without being stabilized. The number of oscillations is counted by the counter 12 and time is measured.

Since the output delay time of the delay means is longer than the output delay time of the inversion means, the output period of the inversion means is about twice the total delay time of each delay means, and this period becomes the resolution of time measurement.
JP 2000-213971 A

  However, in recent years, gas appliances that require flow rate measurement have become more sophisticated and more precise in safety standards, and the need to measure even lower flow rates has arisen, realizing a flow meter that measures such low flow rates. In this case, in the conventional configuration, it is necessary to further increase the frequency of the high resolution timer. In this case, the current consumption increases in proportion to the increase in frequency, and there is a problem that the battery cannot be operated for a long time.

Further, if the delay time of the delay means 11 is shortened in order to increase the frequency of the ring oscillator in the conventional configuration, the output of the delay means is changed from Hi to Lo or Lo before the input voltage of the inverting means is stabilized at Hi or Lo. Since it changes to Hi, the input signal amplitude of the inverting means 9 fluctuates with a small width in the vicinity of the threshold level. In such a state, there has been a problem that the oscillation operation becomes unstable due to factors such as noise, circuit power supply voltage, and characteristics of the inverting means.

  Therefore, in the configuration using the conventional technology, there is a limit to realizing high resolution of time measurement stably and with low current consumption, and it is difficult to perform the required low flow rate measurement with sufficient accuracy. Had the problem of being.

  The present invention solves the above-described conventional problems, and an object of the present invention is to provide a flowmeter that accurately measures from a high flow rate to a low flow rate with low power consumption without being affected by noise or component characteristics.

  In order to solve the above-described conventional problems, an ultrasonic current meter according to the present invention includes a transmission unit that transmits an ultrasonic signal, a reception unit that receives the ultrasonic signal, and an ultrasonic signal from the transmission unit. A timer for measuring a propagation time until reception, a calculation means for obtaining a flow velocity by calculation from a measurement result of the timer, and a control unit for controlling driving of the timer and the transmission / reception means, the timer receiving an input A plurality of sets of signal generating means comprising an inverting means for outputting an inverted signal, a delay means for delaying and outputting an input signal from the inverting means, and a holding means for holding the output signal of the delay means. A ring oscillator connected in a ring shape to form an oscillating unit, a counter for counting the number of outputs from the signal generation means at the final stage of the ring oscillator, and the ring with a predetermined signal Oscillator composed of a latch means for holding the operation start or stopped state, which is constituted so as to enable, or disable the operation of the holding means by the output signal of the latch means.

  According to the invention, the holding means for holding the output of the signal generating means constituted by the inverting means and the delay means is provided, and a plurality of signal generating means are connected in a ring shape with the holding means interposed to constitute a ring oscillator However, since the operation of the holding means becomes effective when the operation of the ring oscillator is stopped by the latch means operated by the measurement stop signal, the operation of the holding means causes the signal generating means connected in a ring shape to When the measurement is stopped halfway, it is possible to hold the oscillation phase information of the ring oscillator, which is the time not counted in the counter that counts the output of the signal generator at the final stage, without losing it, and the next measurement start signal Can be reflected as the oscillation start condition of the ring oscillator that starts the operation.

  Thus, when all the holding means are used as valid when the ring oscillator is stopped, the next measurement can be started using the oscillation phase information of the ring oscillator at the time of measurement stop, so the time resolution is the inversion means. The delay time is one stage, and a high time resolution can be obtained without increasing the oscillation frequency of the ring oscillator.

  In addition, as another form of enabling the holding means, there is a form that uses only the holding means determined in advance when the ring oscillator is stopped, and in this case, the signal of the holding means at the time of measurement stop can be fixed, If only the holding means connected to the signal generation circuit in the final stage is used as valid, the oscillation start condition of the ring oscillator that starts the operation with the next measurement start signal can be made constant, and one measurement is performed under the same conditions. Accurate measurement is possible.

As described above, by changing the mode in which the holding unit is made effective, it is possible to select an appropriate time measuring unit according to the application. For example, when time measurement is performed at a predetermined interval, in the method of calculating the average value by performing measurement per time multiple times, the form in which all the holding means are effectively used when the ring oscillator is stopped is high resolution. If the measurement is performed only once at a predetermined interval, a form that uses a specific holding means when the ring oscillator is stopped enables high-precision measurement with constant measurement conditions. can do.

  The ultrasonic anemometer of the present invention can realize high-resolution measurement without increasing the oscillation frequency and can select an appropriate time measurement means according to the application. It is possible to provide a high-accuracy and stable ultrasonic velocimeter with low current consumption up to an area.

A first invention is an ultrasonic anemometer that propagates ultrasonic waves between an upstream side and a downstream side of a fluid flowing in a flow path and measures a propagation time thereof to obtain a flow velocity, and transmits an ultrasonic signal Transmitting means, receiving means for receiving an ultrasonic signal, receiving detection circuit for detecting reception with a signal from the receiving means and outputting a measurement stop signal, and receiving the ultrasonic signal from the transmitting means to the receiving means Comprises a timer for measuring a propagation time until reception, a calculation means for obtaining a flow velocity by calculation from a measurement result of the timer, and a control unit for controlling driving of the timer and the transmission / reception means, A set of signal generating means comprising an inverting means for outputting a signal obtained by inverting the signal, a delay means for outputting the input signal from the inverting means with a predetermined time delay, and a holding means for holding the output signal of the delay means. Multiple A ring oscillator connected in a ring shape to form an oscillating unit, a counter for counting the number of outputs from the signal generation means at the final stage of the ring oscillator, and the ring oscillator in an operation start state with a signal from the control unit or Latch means for holding in a stopped state, the latch means holds the ring oscillator in an operating state by a measurement start signal from the control unit and invalidates the operation of the holding means, from the reception detection circuit The ring oscillator is held in a stopped state by the measurement stop signal, and the operation of the holding means is made effective .

  Then, a holding means for holding the output of the signal generating means constituted by the inverting means and the delay means is provided, and a plurality of signal generating means are connected in a ring shape with the holding means interposed to form a ring oscillator, and the measurement is stopped. Since the operation of the holding means becomes effective when the operation of the ring oscillator is stopped by the latch means operated by a signal, the measurement is stopped in the middle of the signal generating means connected in a ring shape by the operation of the holding means. When this happens, it is possible to retain the oscillation phase information of the ring oscillator, which is a time not counted in the counter that counts the output of the signal generator at the final stage, without losing it, and the operation starts with the next measurement start signal This can be reflected as the oscillation start condition of the ring oscillator.

  Thus, when all the holding means are used as valid when the ring oscillator is stopped, the next measurement can be started using the oscillation phase information of the ring oscillator at the time of measurement stop, so the time resolution is the inversion means. The delay time is one stage, and a high time resolution can be obtained without increasing the oscillation frequency of the ring oscillator.

  In addition, as another form of enabling the holding means, there is a form that uses only the holding means determined in advance when the ring oscillator is stopped, and in this case, the signal of the holding means at the time of measurement stop can be fixed, If only the holding means connected to the signal generation circuit in the final stage is used as valid, the oscillation start condition of the ring oscillator that starts the operation with the next measurement start signal can be made constant, and one measurement is performed under the same conditions. Accurate measurement is possible.

As described above, by changing the mode in which the holding unit is made effective, it is possible to select an appropriate time measuring unit according to the application. For example, when time measurement is performed at a predetermined interval, in the method of calculating the average value by performing measurement per time multiple times, the form in which all the holding means are effectively used when the ring oscillator is stopped is high resolution. If the measurement is performed only once at a predetermined interval, a form that uses a specific holding means when the ring oscillator is stopped enables high-precision measurement with constant measurement conditions. can do.

According to a second aspect of the present invention, in a ring oscillator configured by connecting a plurality of sets of signal generation means in a ring shape, the delay time characteristics of the respective signal generation means are configured to have substantially the same characteristics. Is.

  And since the time interval of one set of signal generating means is constant per inversion means, it is possible to measure an accurate time and it is not necessary to verify the time interval.

The third invention is characterized in that the delay means constituting the signal generation means is configured to set a predetermined delay time by connecting an even number of inversion means.

  And since the structure of the inversion means and the delay means is the same, the speed of the moving signal in the ring oscillator becomes constant, and the interval of the signals detected by the detection means becomes equal, so an accurate time can be measured, Time interval testing is also unnecessary.

4th invention is equipped with the holding | maintenance selection means which selects only the holding | maintenance means predetermined among several holding | maintenance means, or all the holding | maintenance means are validated, and a holding | maintenance selection means is a control part. The effective form of the holding means is selected on the basis of the signal from.

  Then, by changing the mode in which the holding unit is enabled by the holding selection unit, it is possible to select an appropriate time measuring unit according to the application. For example, when all the holding means are used effectively when the ring oscillator is stopped, the next measurement can be started using the oscillation phase information of the ring oscillator at the time of measurement stop, so the time resolution is equivalent to one stage of the inverting means. Thus, a high time resolution can be obtained without increasing the oscillation frequency of the ring oscillator.

  In addition, when only the predetermined holding means is used as valid when the ring oscillator is stopped, the signal of the specific holding means at the time of measurement stop can be fixed, and only the holding means connected to the signal generation circuit at the final stage is effective. As a result, the oscillation start condition of the ring oscillator that starts the operation with the next measurement start signal can be made constant, and one measurement can be performed under the same condition, thereby enabling accurate measurement.

In other words, in the method of obtaining the average value by performing a plurality of measurements per time, a configuration using all the holding means as effective when the ring oscillator is stopped can realize high-resolution measurement, and a predetermined interval. In the case where the measurement is performed only once, a mode in which a specific holding unit is used effectively when the ring oscillator is stopped can realize high-precision measurement with a constant measurement condition.

According to a fifth aspect of the present invention, when the holding selection means receives a time selection signal from the control unit that is output when the propagation time at the previous measurement is greater than or equal to a predetermined value, only the predetermined holding means is enabled. It is characterized by this.

  Since the resolution of the flow velocity is determined by the ratio between the propagation time and the time resolution, the measurement resolution increases as the propagation time increases. Therefore, when the measurement resolution required for the propagation time is greater than or equal to a value that can be obtained, only a predetermined holding means is valid and one measurement result is accurately obtained.

In a sixth aspect of the invention, the holding selection means is made effective only for a predetermined holding means when receiving a flow velocity selection signal from the control unit that is output when the flow velocity at the previous measurement is equal to or greater than a predetermined value. It is characterized by.

  If the measurement accuracy of the required flow rate is constant with respect to the measurement value, the resolution of the flow rate increases as the measurement flow rate increases, and the required time resolution increases. Therefore, when the resolution required for the flow velocity measurement is greater than or equal to a value obtained, only a predetermined holding means is valid and one measurement result is accurately obtained.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the present embodiment.

(Embodiment 1)
FIG. 1 is a block diagram of an ultrasonic current meter according to the first embodiment of the present invention.

  In FIG. 1, ultrasonic vibrators 2 and 3 constituting ultrasonic transmission means and reception means are installed in a flow path 1 through which a fluid flows, in the flow direction, and between the ultrasonic vibrators 2 and 3. The ultrasonic wave is transmitted from one side and received by the other side, and the propagation time is measured. The drive circuit 6 is operated by a signal from the control unit 4 to start transmission of ultrasonic waves from the ultrasonic transducer 2 or 3, and at the same time, the timer 5 is operated to start time measurement from the start of transmission.

  The ultrasonic wave transmitted from one of the ultrasonic transducers 2 or 3 is received by the other ultrasonic transducer, and when this reception signal is sent to the reception detection circuit 7 and a reception signal of a predetermined level or more is detected, the reception is completed. The operation of the timer 5 is stopped and the measurement of the propagation time is ended.

  Further, the output of the drive circuit 6 is input to the direction switching means 13, the ultrasonic transmission / reception direction is determined according to the direction switching output of the control unit 4, and the ultrasonic transducers 2, 3 are determined based on the determined transmission / reception direction. And the drive circuit 6 and the reception detection circuit 7 are connected to perform the transmission / reception operation of the ultrasonic wave, and the connection between the ultrasonic transducers 2 and 3 and the drive circuit 6 and the reception detection circuit 7 is changed by the next direction switching output. Switches the propagation direction of sound waves. For example, first, the drive circuit 6 and the ultrasonic transducer 2 are connected, and the reception detection circuit 7 and the ultrasonic transducer 3 are connected. The ultrasonic wave transmitted by driving the ultrasonic vibrator 2 by the output of the drive circuit 6 is received by the ultrasonic vibrator 3. The reception detection circuit 7 that has received the output of the ultrasonic transducer 3 detects the reception. The reception detection circuit 7 stops the operation of the timer 5 when reception is detected.

  In this way, first, the propagation time of the ultrasonic wave transmitted in the fluid flow direction from the ultrasonic vibrator 2 installed on the upstream side is one of the two timers provided in the timer 5. It is measured using. The two timers provided in the timer 5 are selected by a direction switching signal output from the control unit 4, and the ultrasonic propagation time is measured by the selected one timer.

  Next, the control unit 4 changes the direction switching output, and connects the drive circuit 6 and the ultrasonic transducer 3, and the reception detection circuit 7 and the ultrasonic transducer 2. Similarly, the other of the two timers provided in the timer 5 is used as the propagation time of the ultrasonic wave transmitted from the ultrasonic transducer 3 installed on the downstream side against the fluid flow direction. Is measured.

  As described above, two timers in which the propagation time of the ultrasonic wave transmitted from the upstream side and the propagation time of the ultrasonic wave transmitted from the downstream side are provided in the timer 5 by the direction switching signal output from the control unit 4 are set. Each is measured.

  And the calculating part 8 calculates | requires the flow velocity in the flow path 1 by the propagation time reciprocal difference method from the propagation time which the timer 5 measured.

  Next, a specific configuration of the timer 5 will be described with reference to the block diagram of FIG.

  The timer 5 is provided with two timers, a ring timer A16 and a ring timer B17, for measuring the propagation time of the ultrasonic wave transmitted from the upstream side and the propagation time of the ultrasonic wave transmitted from the downstream side. 4 is provided with a selector 18 for selecting which timer to measure time in accordance with a direction switching signal from 4.

  The selector 18 switches between the ring timer A16 and the ring timer B17 according to the direction switching signal output from the control unit 4, and measures the propagation time with a different timer for each direction.

  The detailed configurations of the ring timer A16 and the ring timer B17 are configured as shown in FIG.

  The inverting means 10 for judging and outputting the input signal, the delay means 11 for delaying the output from the inverting means 10 for a predetermined time, and outputting the output of the delay means 11 as it is to the next stage or changing to Hi A set of signal generating means 5a composed of holding means 19 capable of selecting whether or not to hold the output at the time is connected in a ring shape to form an oscillating portion to constitute a ring oscillator.

  An odd number of inversion means 10 are installed in one round of the path connected in a ring shape, and the signal moves along the ring path and oscillates with time without being stabilized while the input of the holding means 19 is Lo. It is composed. That is, when the measurement start signal is input, the first-stage signal generation means 5a starts operating, and after a predetermined delay time elapses, it is output to the next-stage signal generation means 5b. Similarly, the signal generation means 5b outputs the signal to the next-stage signal generation means 5c after a predetermined delay time has elapsed. Similarly, the output of the delay means 11 of the last signal generation means 5g is counted by the counter 20 via the signal generation means 5d, 5e, 5f, and is input again to the first signal generation means 5a to perform the above operation. By repeating, the output of the signal generation unit 5g at the final stage generates a Hi / Lo clock signal regulated by the total delay time set by the plurality of signal generation units 5a to 5g. Time measurement can be performed by detecting and counting the rise or fall of the clock signal.

  Further, the output state is held at Hi or Lo by the measurement start signal from the control unit 4 and the measurement stop signal from the reception detection circuit 7, and the ring oscillators of the ring timer A16 and the ring timer B17 are held in the operating state or the stopped state. As a latch means, the timer 5 is provided with an RS latch circuit 21, the measurement start signal from the control unit 4 is connected to the reset terminal (R), and the measurement stop signal from the reception detection circuit 7 is set. It is connected to the terminal (S). The output (Q) of the RS latch circuit 21 is connected to the control terminal of the holding means 19 and is input via the holding means 19 to the signal generation circuit 5a at the first stage of the ring oscillator.

  Here, the holding means 19 outputs the input as it is when the output (Q) of the RS latch circuit 21 is Lo, and the delay means 11 of each signal generation circuit is changed to Hi when the output (Q) is Hi. Hold the output when. The input of the RS latch circuit 21 is a measurement start signal that is an output of the control unit 4 and a measurement stop signal that is an output of the reception detection circuit 7. The RS latch circuit 21 is reset by the measurement start signal, the output (Q) becomes Lo, the output holding function of the holding means 19 is disabled, and the operation of the ring timer A16 or the ring timer B17 is started.

  Next, when the reception detection circuit 7 detects reception, a reception detection signal is generated, the RS latch circuit 21 is set, the output (Q) becomes Hi state, the output holding function of the holding means 19 is enabled, and the first stage signal of the ring oscillator The input of the generation circuit 5a is held in the Hi state, and the operation of the ring timer A16 or the ring timer B17 is stopped.

  In addition, as a method for enabling the output holding function of the holding means 19, there are a method in which only a specific holding means 19 in the ring oscillator is activated and a method in which all the holding means 19 in the ring oscillator are activated. Yes, holding selection means 22 is provided as this method selection means, and based on a selection signal instructed from the control unit 4, whether only a specific holding means 19 is valid or all the holding means 19 are valid. I am trying to select it. When either one is selected and the measurement stop signal is input and the output (Q) of the RS latch circuit 21 is in the Hi state, the Hi signal is supplied to the control terminal of the holding means 19 according to the selected output holding function. Is supplied.

  When the method of enabling all the holding means 19 is selected by the holding selection means 22, when the signal movement is stopped in the middle of the ring oscillator without being counted by the counter 20 by the measurement stop signal, the signal at the time of the stop The moving state can be held as the signal position information by the holding means 19, and the measurement can be started subsequently from the signal position information held at the time of stopping at the next measurement of the propagation time in the same direction without losing the intermediate state. In the measurement method in which the time measurement is performed a plurality of times and the propagation time is obtained from the average value, the measurement error can be almost eliminated, and the measurement resolution can be increased. That is, time resolution higher than the oscillation frequency can be obtained without increasing the oscillation frequency of the ring oscillator.

  When the method for enabling only the specific holding means 19 is selected by the holding selection means 22, the specific holding means 19 is always stopped in the Hi state when the measurement stop signal is input. Oscillation is always started under the same conditions at the start. For example, if the holding means 19 of the signal generating means 5g is held in the Hi state by the measurement stop signal in FIG. 3, the next measurement start signal is input. When this is done, the input of the first-stage signal generation means 5a always starts from the Hi state, and the measurement conditions at the start of measurement can be made the same.

  In this method, when measuring the time only once in a predetermined cycle and obtaining the value as the propagation time, the measurement conditions at the start of measurement are made constant, so that highly accurate measurement with reduced measurement variation is achieved. Can be realized.

  Further, in the ring oscillator configured by connecting a plurality of sets of signal generating means 5a to 5g in a ring shape, each of the signal generating means 5a to 5g is configured to have substantially the same characteristics. Since the time interval of one stage of the inverting means 10, that is, the time interval between the pair of signal generating means 5a to 5g is constant, it is possible to measure an accurate time, and the time interval is not required to be verified.

Further, the delay means 11 constituting the signal generation means 5a to 5g is configured to set a predetermined delay time by connecting an even number of inversion means 23, and by this configuration, the inversion means 10 is set.
And the delay unit 11 have the same configuration, the speed of the moving signal in the ring oscillator is constant between the holding units 19, and the holding time interval is constant, so that an accurate time can be measured. The interval test is also unnecessary.

  Moreover, according to the measurement mode which the control part 4 judges, the mode which makes the output holding function of the holding means 19 effective via the holding selection means 22 is changed, and an appropriate time measuring means is selected according to the application. can do.

  For example, in the high-resolution measurement mode in which all the holding means 19 are used when the ring oscillator is stopped, the next measurement can be started using the oscillation phase information of the ring oscillator at the time of measurement stop, so the time resolution is A delay time corresponding to one stage of the inverting means 10 is obtained, and high time resolution can be obtained without increasing the oscillation frequency of the ring oscillator.

  In addition, the high-accuracy measurement mode that is used only when the holding means 19 determined in advance when the ring oscillator is stopped can fix the signal of the specific holding means 19 at the time of the measurement stop, and the signal generation circuit 5g in the final stage When only the holding means 19 connected is used as valid, the oscillation start condition of the ring oscillator that starts the operation with the next measurement start signal can be made constant, and one measurement can be performed under the same condition, so that the accurate measurement is possible. Measurement is possible.

  That is, in the method of obtaining the average value by performing the measurement per time multiple times, the high resolution measurement mode in which all the holding means 19 are used effectively when the ring oscillator is stopped realizes the high resolution measurement. High-precision measurement mode that uses the specific holding means 19 when the ring oscillator is stopped can be used when the ring oscillator is stopped. can do.

  And as a measurement mode which the control part 4 judges, when the propagation time at the time of last measurement is more than the predetermined value defined beforehand, it has the mode which outputs a time selection signal so that a high precision measurement mode may be selected, and a control part When a time selection signal is output from 4, a time holding selection means 14 for controlling the control terminal of the holding means 19 is provided so that only a predetermined holding means 19 is effective.

  According to the above configuration, since the resolution of the flow velocity is determined by the ratio between the propagation time and the time resolution, the measurement resolution increases as the propagation time increases. Therefore, when the measurement resolution that requires the propagation time is greater than or equal to a value that can be obtained, only the predetermined holding means 19 is valid, and a single measurement result is accurately obtained.

  In addition, as another measurement mode, there is a mode for outputting a flow rate selection signal so that the high-precision measurement mode is selected when the flow rate at the previous measurement is equal to or higher than a predetermined value. Is output, the flow rate holding selection means 15 for controlling the control terminal of the holding means 19 is provided so that only the predetermined holding means 19 is effective.

  Also in the above configuration, if the measurement accuracy of the required flow rate is constant with respect to the measurement value, the resolution of the flow rate increases as the measurement flow rate increases, and the required time resolution increases. Therefore, when the resolution required for the flow velocity measurement is greater than or equal to a value, only the predetermined holding means 19 is valid and one measurement result is accurately obtained.

  The operation of the ultrasonic anemometer configured as described above will be briefly described. First, when a measurement start signal is output from the control unit 4, the drive circuit 6 starts to operate and the direction switching unit 13 performs the operation. An ultrasonic wave is transmitted from the ultrasonic vibrator 2 installed on the upstream side, propagates through the fluid in the flow path 1 and is received by the ultrasonic vibrator 3 installed on the downstream side.

The measurement start signal from the control unit 4 is simultaneously sent to the timer 5, the selector 18 selects the ring timer A16 by the direction switching signal, and is input to the reset terminal (R) of the RS latch circuit 21 of the ring timer A16. The output (Q) is held in the Lo state by the measurement start signal, the output holding function of the holding means 19 becomes invalid, and the signal generating means 5a to 5g constituted by the inverting means 10, the delay means 11 and the holding means 19 After a predetermined delay time has elapsed, signal movement starts in a ring shape, and a Hi / Lo signal having a predetermined width is generated as a clock signal. The time can be measured by counting the output of the last-stage signal generation means 5g generated as the clock signal by the counter 20.

  Then, when the signal received by the ultrasonic transducer 3 detects a signal of a predetermined level or higher by the reception detection means 7, it is determined that the reception is completed, and a measurement stop signal is output.

  The measurement stop signal from the reception detection means 7 is input to the set terminal (S) of the RS latch circuit 21 of the ring timer A16, the output (Q) is held in the Hi state, and the control terminal of the holding means 19 is fixed to Hi. Thus, the output holding function is effectively operated, and the signal movement in the signal generation means 5a to 5g formed in a ring shape is stopped.

  The time from the measurement start signal of the control unit 4 to the measurement stop signal of the reception detection means 7 is counted by the counter 20 and obtained as the propagation time by the calculation unit 8.

  At this time, when the propagation time or flow velocity at the time of the previous measurement is equal to or greater than a predetermined value, the control unit 4 determines that it is not necessary to perform time measurement in the high resolution measurement mode, and the holding means connected in a ring shape 19, the holding selection unit 22 such as the time holding selection unit 14 or the flow rate holding selection unit 15 is operated so that only the holding unit 19 forming the final stage signal generation unit 5g is effective. Select the accuracy measurement mode.

  In this case, the oscillation of the ring oscillator is started by the measurement start signal, and the oscillation is stopped when the measurement stop signal is input. The counter 20 counts the number of oscillations during that time.

  When the oscillation is stopped, the output of a specific holding unit 19, for example, the output of the holding unit 19 of the signal generating unit 5g is fixed to Hi and stopped. Thereby, when the next measurement is started, the signal movement of the ring oscillator can always be started from the signal generation means 5a at the same position, and when the time is obtained by one measurement, the measurement condition is kept constant. High time measurement can be performed.

  In the present embodiment, the propagation time and the flow velocity have been described as the conditions for selecting the high-accuracy measurement mode. However, the present invention is not limited to this, and the measurement mode is selected such as battery voltage, leak detection, temperature, etc. Needless to say, it can be applied to all conditions that are considered effective.

  When the control unit 4 determines that the propagation time or flow velocity at the previous measurement is less than a predetermined value and the high resolution measurement mode is necessary, the output holding function of all holding means 19 connected in a ring shape is effective. The holding selection means 22 is operated so that the high resolution measurement mode is selected.

  In this case, the oscillation of the ring oscillator is started by the measurement start signal, and the oscillation is stopped when the measurement stop signal is input. The counter 20 counts the number of oscillations during that time.

When the signal movement is stopped in the middle of the ring oscillator formed in a ring shape when oscillation is stopped, for example, when the signal movement is stopped by the signal generation means 5c, the output of the holding means 19 of the signal generation means 5c is fixed to Hi. Stop. As a result, it can be held as oscillation phase information, and when the next measurement start signal is input, signal movement can be started continuously from the oscillation phase at the time of the previous stop, and multiple times are measured continuously. When the average value is obtained by performing the above, it is possible to perform time measurement with high resolution without being affected by the oscillation phase that changes every time the operation is stopped.

  That is, the width of the clock signal determined in one round of the ring-shaped path can be increased to the resolution determined by the number of signal generation means 5a to 5g, and high-resolution time measurement can be realized without increasing the oscillation frequency.

  Next, when a direction switching signal is output from the control unit 4, ultrasonic waves are transmitted against the fluid flow from the ultrasonic vibrator 3 installed on the downstream side, and propagates the fluid in the flow path 1. It is received by the ultrasonic transducer 2 installed on the upstream side.

  At the same time, the measurement start signal is sent to the timer 5, the selector 18 selects the ring timer B17 by the direction switching signal, and is output by the measurement start signal input to the reset terminal (R) of the RS latch circuit 21 of the ring timer B17 (Q ) Is held in the Lo state, the output holding function of the holding means 19 is disabled, and the signal generating means 5a to 5g constituted by the inverting means 10, the delay means 11, and the holding means 19 have passed a predetermined delay time. Then, signal movement starts in a ring shape, and a Hi / Lo signal having a predetermined width is generated as a clock signal. The time can be measured by counting the output of the last-stage signal generation means 5g generated as the clock signal by the counter 20.

  When the signal received by the ultrasonic transducer 2 detects a signal of a predetermined level or higher by the reception detection means 7, it is determined that the reception is completed, and a measurement stop signal is output.

  The measurement stop signal from the reception detection means 7 is input to the set terminal (S) of the RS latch circuit 21 of the ring timer B17, the output (Q) is held in the Hi state, and the control terminal of the holding means 19 is fixed to Hi. Thus, the output holding function is effectively operated, and the signal movement in the signal generation means 5a to 5g formed in a ring shape is stopped.

  The time from the measurement start signal of the control unit 4 to the measurement stop signal of the reception detection means 7 is counted by the counter 20 and obtained as the propagation time by the calculation unit 8.

  Hereinafter, the selection of the high-resolution measurement mode and the high-precision measurement mode can be performed under the same conditions as in the case of performing time measurement by propagating ultrasonic waves from the upstream side to the downstream side, and the operation is also the same. The description is omitted.

  And the calculating part 8 calculates | requires the flow velocity in the flow path 1 by the propagation time reciprocal difference method from the propagation time from the upstream to the downstream and the propagation time from the downstream to the upstream.

  As described above, the ultrasonic velocimeter in the present embodiment is provided with the holding means 19 that holds the outputs of the signal generating means 5a to 5g composed of the inverting means 10 and the delay means 11, and this holding means 19 is interposed. Thus, a plurality of sets of signal generating means 5a to 5g are connected in a ring shape to form a ring oscillator, and the operation of the holding means 19 becomes effective when the operation of the ring oscillator is stopped by the latch means 21 operated by the measurement stop signal. Therefore, the counter 20 that counts the output of the signal generation means 5g at the final stage when the measurement means is stopped in the middle of the signal generation means 5a to 5g connected in a ring shape by the operation of the holding means 19. It is possible to hold the oscillation phase information of the ring oscillator, which is a time not counted in the period, without losing it. It can be reflected as an oscillation start condition of regulator.

In this way, when all the holding means 19 are used as valid when the ring oscillator is stopped, the next measurement can be started using the oscillation phase information of the ring oscillator at the time of measurement stop, so the time resolution is reversed. The delay time is one stage, and high time resolution can be obtained without increasing the oscillation frequency of the ring oscillator.

  As another form of enabling the holding means 19, there is a form in which only the predetermined holding means 19 is used as valid when the ring oscillator is stopped. In this case, the signal of the holding means 19 at the time of stopping the measurement is fixed. If only the holding means 19 connected to the last-stage signal generation circuit 5g is used as valid, the oscillation start condition of the ring oscillator that starts the operation with the next measurement start signal can be made constant, and one measurement can be performed. Can be performed under the same conditions, so accurate measurement is possible.

  As described above, by changing the mode in which the holding unit 19 is enabled, an appropriate time measuring unit can be selected according to the application. For example, in the case of measuring time at a predetermined interval, in a method of performing measurement per time a plurality of times and obtaining an average value thereof, a mode in which all the holding means 19 are effectively used when the ring oscillator is stopped is high. When the measurement of the resolution can be realized and the measurement is performed only once at a predetermined interval, the form in which the specific holding means 19 is used effectively when the ring oscillator is stopped is a highly accurate measurement with a constant measurement condition. Can be realized.

  Further, the output of the latch circuit 21 whose output is switched by the measurement start signal and the measurement stop signal is connected to a control terminal for changing the state of the holding means 19, and the operation of the ring oscillator is controlled via the holding means 19, and the holding means Since the operation of 19 is controlled to enable or disable the output holding function, the mode for enabling the holding means 19 can be changed with a simple configuration so that an appropriate time measuring means can be selected according to the application. It has become.

  As described above, the ultrasonic current meter of the present invention can increase the measurement resolution without increasing the oscillation frequency, enables high-accuracy flow rate measurement with low power consumption, and is driven by batteries such as gas meters and water meters. It can be applied to various measuring devices.

Whole block diagram of ultrasonic current meter in Embodiment 1 of the present invention Block diagram of the timer of the ultrasonic current meter Block diagram of a ring timer showing the detailed configuration of the timer of the ultrasonic current meter Overall block diagram of a conventional ultrasonic current meter The block diagram which shows the detailed constitution of the timer of the conventional ultrasonic current meter

Explanation of symbols

1 Flow path 2.3 Ultrasonic transducer (transmission / reception means)
4 Control Unit 5 Timer 5a to 5g Signal Generation Unit 8 Arithmetic Unit 10 Inversion Unit 11 Delay Unit 16 Ring Timer A (Timer)
17 Ring timer B (timer)
19 Holding means 20 Counter 21 RS latch circuit (latch means)
22 Holding selection means

Claims (6)

An ultrasonic anemometer that propagates ultrasonic waves between the upstream side and the downstream side of the fluid flowing in the flow path and measures the propagation time to obtain the flow velocity,
A transmission means for transmitting an ultrasonic signal; a reception means for receiving an ultrasonic signal; a reception detection circuit for detecting reception with a signal from the reception means and outputting a measurement stop signal;
A timer for measuring a propagation time until the reception means receives an ultrasonic signal from the transmission means, a calculation means for obtaining a flow velocity by calculation from a measurement result of the timer, and controlling driving of the timer and the transmission / reception means And a control unit that
The timer is composed of an inverting means for outputting a signal obtained by inverting the input, a delay means for outputting the input signal from the inverting means with a predetermined delay, and a holding means for holding the output signal of the delay means. A ring oscillator that forms an oscillating unit by connecting a plurality of signal generating means in a ring shape, a counter that counts the number of outputs from the signal generating means at the final stage of the ring oscillator, and the ring oscillator in an operation start state or Comprising latch means for holding in a stopped state,
Said latch means, and disabling the operation of said holding means holds said ring oscillator at the measurement start signal from the control unit to the operating state, the ring oscillator by measuring stop signal from the signal detection circuit in a stopped state ultra sound wave current meter configured so that the operation of the holding means is effective holds. The ultrasonic anemometer according to claim 1, wherein a delay time characteristic of each of the signal generating means is substantially equal in a ring oscillator configured by connecting a plurality of sets of signal generating means in a ring shape. The ultrasonic current meter according to claim 1 or 2 , wherein the delay means constituting the signal generation means is configured to set a predetermined delay time by connecting an even number of inversion means. Among the plurality of holding means, provided with a holding selection means for selecting whether to enable only a predetermined holding means or to enable all the holding means,
Holding selection means, ultrasonic flow rate meter according to any one of claims 1 to 3 which is adapted to select a valid form of holding means on the basis of a signal from the control unit. 5. The super-selection means according to claim 4, wherein when the time selection signal output from the control unit is output when the propagation time at the previous measurement is equal to or greater than a predetermined value, only the predetermined holding means is valid. Sonic anemometer. 5. The ultrasonic wave according to claim 4 , wherein the holding selection means is effective only for a predetermined holding means when receiving a flow velocity selection signal from the control unit that is output when the flow velocity at the previous measurement is equal to or greater than a predetermined value. An anemometer.

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