JP2007024681A - Ultrasonic fluid measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To measure accurately a propagation time of an ultrasonic wave between a pair of transducers, in an ultrasonic fluid measuring device. <P>SOLUTION: The transducer 12a is stored in a case 112a provided in a measuring tube 11 for circulating a test fluid, and a heater 121e is provided on the surface on the opposite side of the surface where a diaphragm 121b of the transducer 12a is in contact with the test fluid. A supply current to the heater 121e is controlled by a temperature adjusting means 131m, and since the diaphragm 121b is adjusted at a prescribed temperature, a spring constant of the diaphragm 121b which is dependent on the temperature can be kept constant, and fluctuation of its characteristic frequency can be suppressed. Consequently, a reception frequency of the transducer can be kept constant, and the accuracy of a prescribed operation on the test fluid can be maintained with a simple constitution. In addition, condensation on the diaphragm 121b of the transducer can be prevented, to thereby avoid reception trouble of the ultrasonic wave. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an ultrasonic fluid measuring device, and more specifically, by controlling the frequency of received waves of ultrasonic waves emitted from a pair of transducers to a specified value, the ultrasonic wave serving as a basis for a predetermined calculation related to a test fluid The present invention relates to a technique for accurately measuring propagation time.

  Conventionally, a pair of transducers are arranged shifted in the flow direction, and an ultrasonic wave is emitted from an upstream transducer in a forward direction with respect to the flow. And measuring the second propagation time until the ultrasonic wave is emitted from the downstream transducer in the opposite direction to the flow and received by the upstream transducer, and the first and second propagation times are measured. 2. Description of the Related Art An ultrasonic fluid measurement device that calculates a flow rate of a test fluid based on time is known. In this ultrasonic fluid measuring device, when measuring the first and second propagation times, a point of time when the output voltage of the transducer passes a zero level, called a zero cross point, is specified, and from the point of time when the ultrasonic wave is emitted. The time until the zero cross point is measured as the elapsed time. The elapsed time from the time when the leading wave arrives at the receiving-side transducer to the zero cross point is set as a detection delay time, and this detection delay time is subtracted from the elapsed time to calculate the propagation time.

Here, the detection delay time is not always constant, and varies depending on various conditions such as manufacturing variations in the natural frequency of the diaphragm of the transducer and differences in use environment (for example, temperature). Even if the detection delay time has changed, maintaining a certain detection delay time results in a detection error of the propagation time, and consequently the flow rate of the test fluid cannot be accurately calculated.
The following is known as an ultrasonic fluid measuring device corresponding to such a change in detection delay time. That is, an ultrasonic wave is emitted from the transmission-side transducer, and the output signal of the transmission-side transducer (the transducer generates an output signal due to its own vibration even during transmission) is in the nth period. Identify the zero crossing point of the wave. In addition, the zero cross point of the corresponding wave of the nth period in the output signal of the transducer on the receiving side is specified, and the time between these two specified zero cross points is measured as the propagation time (patent) Reference 1).
JP 09-26341 A (paragraph numbers 0031 to 0035)

  However, this known ultrasonic fluid measuring device has the following practical problems. In other words, this device specifies the zero-cross point for each output signal of the transmitter and receiver transducers, and measures the time between these zero-crosses as the propagation time, thereby canceling the change in detection delay time. It is. For this reason, it is assumed that the same change occurs in both detection delay times, but in reality, the change in both is not always equal. Even within the same ultrasonic fluid measuring device, there are variations in manufacturing between the upstream and downstream transducers, and the natural frequency may be different. Also, depending on the use environment, characteristic changes may appear only in one of the transducers. As an example of the latter, there is a case where an ultrasonic fluid measuring device is employed for flow rate measurement in a steam pipe. In this case, in particular, condensation tends to occur on the diaphragm of the downstream transducer, and the characteristic change of the transducer tends to be more significant on the downstream side than on the upstream side. Also, the characteristic change due to aging deterioration is not always the same for both transducers, and the deterioration may rapidly proceed with one transducer. If there is a difference between the changes in both detection delay times, the above-described apparatus cannot cancel the change, resulting in an error in propagation time, flow rate, and the like.

  Therefore, the present invention keeps the natural frequency of the diaphragm of the transducer constant with a simple configuration, thereby accurately measuring the propagation time of the ultrasonic wave between the pair of transducers, and determining the flow rate of the test fluid in the measurement tube. It is an object of the present invention to provide an ultrasonic fluid measuring device capable of calculating accurately.

  An ultrasonic fluid measuring device according to the present invention is installed on a measurement tube that circulates a test fluid and an ultrasonic propagation line that is set across the measurement tube, and emits ultrasonic waves in a forward direction with respect to a flow. A first transducer, a second transducer installed downstream of the first transducer on the ultrasonic propagation line, and emitting ultrasonic waves in a direction opposite to the flow, and the first or second transducer. Among them, a temperature adjusting means for adjusting at least one of the diaphragms to a predetermined temperature is included. The diaphragms of the first and second transducers are adjusted to a predetermined temperature by the temperature adjusting means, and the time point at which the ultrasonic waves emitted from the first and second transducers are received by the receiving transducer is specified. Then, based on the specified reception time point, the time from when the first or second transducer emits the ultrasonic wave to the propagation to the transducer on the receiving side is measured, and based on the measured propagation time, Then, a predetermined calculation (for example, calculation of the flow rate) related to the test fluid is performed.

  According to the present invention, since the diaphragms of the first and second transducers are adjusted to a predetermined temperature by the temperature adjusting means, the spring constant of the diaphragm depending on the temperature can be kept constant. Therefore, since fluctuations in the natural frequency of the diaphragm are suppressed, the received wave frequency of the transducer can be kept constant, and it has actually propagated in the test fluid from the detected time between ultrasonic transmission and reception. An operation and a correction coefficient for correcting a change in frequency when calculating the propagation time are not required. Therefore, it is possible to maintain the accuracy of the predetermined calculation related to the test fluid with a simple configuration, and to reduce the size and cost of the device. In addition, measurement errors due to correction calculation errors can be improved. Furthermore, by adjusting the diaphragm of the transducer to a predetermined temperature, it is possible to obtain a secondary effect that condensation of the diaphragm can be prevented and an obstacle to receiving ultrasonic waves can be avoided.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 shows the configuration of an ultrasonic fluid measurement device (hereinafter referred to as “measurement device”) 1 according to an embodiment of the present invention. In this embodiment, hydrogen gas is employed as the test fluid. By installing the measuring device 1 in the anode piping of the fuel cell, the flow rate of hydrogen gas as the fuel gas can be detected. Note that the measuring object of the measuring device 1 according to the present invention is not limited to hydrogen gas in the anode pipe, and can be applied to all fluid compositions including air in the cathode pipe.

  The measuring tube 11 forms a passage for measuring the flow rate of the test fluid and the like, and is connected to the adjacent pipes 2 and 2 via flanges 111a and 111b formed at respective ends in the axial direction. A direction switching valve 3 is interposed in the upstream pipe 2, and the measurement pipe 11 is configured to be selectively connected to the pipe 2 and the other pipe 4 by the direction switching valve 3. ing. A tank 5 filled with nitrogen gas as a calibration fluid is connected to the other pipe 4, and the nitrogen gas in the tank 5 can be circulated through the measurement pipe 11. The pipe 2 is connected to an anode pipe of a fuel cell (not shown), and hydrogen gas can be circulated through the measurement pipe 11 through the pipe 2. Note that the calibration fluid (that is, nitrogen gas) is supplied to the measuring device 1 in a calibration process of the detection delay time tr described later (the received wave frequency fr at the time of calibration is detected simultaneously). When the amount of change in the composition (density) of the test fluid is small, or in applications where the long-term stability of the required measurement accuracy is satisfied, calibration is performed by connecting the tank 5 filled with the calibration fluid only during manufacturing or periodic inspection. You may make it work.

  The measuring tube 11 swells in a cylindrical shape at two locations that are displaced in the tube axis direction, with an axis forming an angle θ with respect to the tube axis Ap (corresponding to the ultrasonic wave propagation line At) as a center. The pair of transducer cases 112a and 112b formed in this way includes an upstream transducer (corresponding to a “first transducer”) 12a and a downstream transducer (corresponding to a “second transducer”) 12b. , Are stored respectively.

  These transducers 12 a and 12 b are configured to include a diaphragm that generates ultrasonic waves Wt for measurement, and are connected to the control unit 13. The control unit 13 includes a propagation time measurement unit 131 and a flow rate / concentration calculation unit 132. The control unit 13 generates a drive signal for causing the transducers 12a and 12b to emit the ultrasonic wave Wt, and the emitted super The reception signals Wr1 and Wr2 output from the transducers that have received the sound wave Wt are input. Each transducer 12a, 12b receives a drive signal from the control unit 13 and emits an ultrasonic wave Wt along the ultrasonic propagation line At. The control unit 13 calculates and outputs the flow rate Q and density (indicating the concentration) ρ of the hydrogen gas flowing through the measurement tube 11 based on the received reception signals Wr1 and Wr2. The output flow rate Q and the like are displayed on a monitor (not shown).

Here, the detection principle of the flow rate Q and the density ρ by the measuring device 1 will be described with reference to FIG.
FIG. 2 shows waveforms of ultrasonic transmission waves Wt and reception waves Wr1 and Wr2. When the ultrasonic wave Wt is emitted from the upstream transducer 12a in the forward direction with respect to the flow, the received wave obtained by the downstream transducer 12b is Wr1, and the ultrasonic wave Wt from the downstream transducer 12b is reverse to the flow. The received wave obtained by the upstream transducer 12a when launched is Wr2. After the ultrasonic wave Wt is emitted, a reception time point tdi (i = i = i = a zero-crossing point of the first fall) after the reception signal (indicated by voltage V) reaches a predetermined level Vth. 1, 2). That is, the received waves Wr1 and Wr2 contain noise, and the ultrasonic wave that first reaches the transducer on the receiving side (hereinafter referred to as “first wave”) has a small amplitude. It is difficult to measure accurately, and the point where the amplitude is more than a certain value is specified as the reception time point. Also, the time from when the receiving-side transducer receives the leading wave until the reception time tdi is specified is the detection delay time tri, and the leading wave reaches the receiving-side transducer after the ultrasonic wave Wt is emitted. Is the propagation time ti. Here, as shown in FIG. 1, when the sound velocity in hydrogen gas is Cg, the flow velocity of hydrogen gas is Vg, and the propagation distance of the ultrasonic wave Wt is Lm, when the ultrasonic wave Wt is emitted in the forward direction, The relationship of the following formulas (1) and (2) is established between the time tdi and the times tri and ti when fired in the reverse direction.

td1 = t1 + tr1
= Lm / (Cg + Vg × cos θ) + tr1 (1)
td2 = t2 + tr2
= Lm / (Cg−Vg × cos θ) + tr2 (2)
When detecting the flow rate Q, the sound velocity Cg is eliminated from the equations (1) and (2), and the following equation (3) relating to the flow velocity Vg is obtained.

Vg = {Lm / (2 × cos θ)} × {1 / (td1-tr1) −1 / (td2-tr2)} (3)
Substituting the flow velocity Vg calculated by the equation (3) into the following equation (4), the flow rate Q is calculated. The cross-sectional area of the measuring tube 11 is A, and the flow velocity distribution coefficient in the measuring tube 11 is K.
Q = Vg × A × K (4)
On the other hand, when detecting the density ρ, the flow velocity Vg is eliminated from the equations (1) and (2), and the following equation (5) relating to the sound velocity Cg is obtained.

Cg = (Lm / 2) × {1 / (td1-tr1) + 1 / (td2-tr2)} (5)
The sound velocity Cg calculated by the equation (5) is substituted into the following equation (6) to calculate the density ρ. Note that the specific heat ratio of the test fluid is γ, the gas constant is R, and the absolute temperature is T.
ρ = γ × {R × T / (22.4 × Cg ² )} (6)
In the embodiment shown in FIG. 1, the ultrasonic propagation line At is set linearly, and the pair of transducers 12a and 12b are arranged on the opposite side wall of the measuring tube 11 with the tube axis Ap as the center. ing. However, according to the present invention, the present invention is not limited to such an arrangement, and both transducers can be arranged only on one side of the measurement tube 11 by setting the ultrasonic propagation line At to bend on the tube wall. .

In the above description, the zero-crossing point of the first falling after the reception signal reaches the predetermined level Vth is specified as the reception time tdi, but the time when the output of the transducer reaches the predetermined level Vth is directly received. You may specify as a time.
Here, the basic measurement principle (including correction of the detection delay time tr) of the propagation time of the ultrasonic wave Wt in the present embodiment will be described in detail with reference to FIGS.

  In the measuring device 1, in the calculation of the flow velocity Vg and the flow rate Q of the test fluid, the difference between the propagation times t1 and t2 of the ultrasonic wave Wt is taken (see the above formula (3)). For this reason, it is necessary to accurately measure the propagation times t1 and t2 in order to ensure the accuracy of the predetermined calculation relating to the test fluid. When using a test fluid with a low sound velocity such as air or when the propagation time t is sufficiently long with respect to the detection delay time tr, a gas with a high sound velocity such as hydrogen gas is tested as in this embodiment. When employed as a fluid or when the propagation distance Lm of the ultrasonic wave Wt is short, the influence of the change in the detection delay time tr cannot be ignored when measuring the propagation time t. For example, when a foreign substance adheres to the diaphragm of the transducer and the natural frequency of the diaphragm changes and the detection delay time tr changes, the detection delay time tr is corrected according to the change of the natural frequency. is required.

  FIG. 3 shows waveforms of the transmission wave Wt and the reception wave Wr. FIG. 4 shows the frequency characteristics of the transducers 12a and 12b. Here, as shown in FIG. 5, the transducers 12a and 12b are housed in a transducer case 112a bulging out from the measuring tube 11 and sealed with a sealing material 121c, and a diaphragm 121b for transmitting and receiving ultrasonic waves. It is comprised including. The natural frequency fr of the diaphragm 121b is calculated by the following equation (7), where k is the spring constant of the diaphragm 121b and m is the equivalent mass.

fr = (1 / 2π) × √ (k / m) (7)
Here, when foreign matter (for example, condensation of humidified water vapor contained in the fuel gas or adhesion of dust) adheres to the diaphragm 121b, the equivalent mass m of the diaphragm 121b is increased by an amount corresponding to the mass of the foreign matter. Since it increases apparently, as shown in FIG. 4, the natural frequency fr decreases to a smaller value fr ′. When the natural frequency fr of the diaphragm 121b changes, as shown in FIG. 3, the period tp of the received wave Wr is extended, and changes from Wr indicated by a solid line to Wr ′ indicated by a dotted line.

  In FIG. 3, the specified reception time td is specified as the time when a predetermined detection delay time tr has elapsed from the arrival time of the leading wave S1, and this detection delay time tr is the diaphragm 121b of the receiving-side transducer. Changes with the change in the natural frequency fr or the period tp of the received wave Wr. The reception time td ′ when the natural frequency fr decreases due to foreign matter adhering to the diaphragm 121b is a time corresponding to a change in the natural frequency fr than the original reception time td (hereinafter referred to as “error time”). It is specified as a time point delayed by δt. This error time δt is calculated by the following equation (8) according to the number of waves that have reached until the reception time point td ′ is specified (hereinafter referred to as “the number of alternatings at the time of detection”) Nr.

δt = Nr × (1 / fr′−1 / fr) (8)
From the above, when the actual detection delay time tr changes due to the change in the natural frequency fr after the previous calibration, the reception time td ′ has the relationship of the following equation (9).
td ′ = td + δt
= (T + tr) + δt (9)
Therefore, in order to avoid a measurement error due to a change in the natural frequency fr of the diaphragm 121b, the actual frequency (hereinafter referred to as “received wave frequency”) fr ′ from the received wave Wr is measured when the propagation time t is measured. Detection is required to calculate the error time δt, and a correction operation is required to add the calculated error time δt to the detection delay time tr. The detection alternating number Nr that is a correction coefficient is set together with the detection delay time tr at the time of calibration, and is calculated by the following equation (10), with the received wave frequency obtained at the time of calibration being fr.

Nr = tr × fr (10)
In the present invention, the correction coefficient storage as described above, the correction calculation executed at high speed for each measurement sampling, and the calibration work for absorbing the manufacturing variation of the transducer are omitted, with a simple configuration. The same effect as the correction calculation can be obtained. This will be described below.

FIG. 6 is a block diagram showing the configuration of the propagation time measurement unit 131 and the flow rate / concentration calculation unit 132 in the control unit 13 shown in FIG. The configuration of the control unit 13 will be described with reference to the time chart shown in FIG.
In this embodiment, a function of controlling the reception wave frequency of the ultrasonic wave Wt emitted from the pair of transducers 12a and 12b to a specified value is provided, and the propagation of the ultrasonic wave serving as a basis for a predetermined calculation relating to the test fluid with a simple configuration. The time is to be measured accurately. In addition, the control unit 13 is provided with a function for prohibiting specification of the reception time until the predetermined prohibition period tg elapses after the ultrasonic wave Wt is emitted, and erroneous reception due to noise superimposed on the reception wave Wr. It is supposed to prevent the time point from being specified. In addition, a function for correcting a shift in the reception time point td (or the detection alternating number Nr) due to a change in the sound velocity or the like of the test fluid is provided, and this return is performed when a “return” described later occurs in the change in the elapsed time td. The measurement error of the propagation time t due to is avoided.

The direction switch 131a shown in FIG. 6 selects one transducer (for example, the upstream transducer 12a) for transmission, and selects the other downstream transducer 12b for reception.
The transmission drive unit 131b generates a drive signal for the transmission transducer 12a. The generated drive signal is output to the transducer 12a via the direction switch 131a, and the ultrasonic wave Wt is emitted. The emission time of this ultrasonic wave Wt is set to t0 (refer FIG. 7). At the same time as generating the drive signal, the transmission drive unit 131b outputs a time measurement start signal start to the prohibition period setting unit 131c and the elapsed time measurement unit 131f.

  Upon receiving the measurement start signal start, the prohibition period setting unit 131c outputs a reception control signal Sg to the reception detection unit 131d. As shown in FIG. 7, this reception control signal Sg is a signal that prohibits specification of the reception time point over a predetermined prohibition period tg. The prohibition period tg is set to Lo level, and after the elapse of the prohibition period tg, Hi Switch to level. While the reception control signal Sg is set at the Lo level, specification of the reception time point by the reception detection unit 131d is prohibited or substantially prohibited, and the reception control signal Sg is switched to the Hi level, so that Identification is allowed.

In the case of the present embodiment, the reception time point td is specified as the first falling zero-cross point A after the reception control signal Sg becomes Hi level and the specification of the reception time point is permitted. The prohibition period tg is stored in the prohibition period storage unit 131e shown in FIG. 6, and is read into the prohibition period setting unit 131c. As an example of the prohibition period tg, a period until the reception wave Wr becomes steady can be used. In this case, it is assumed that the received wave Wr is steady when the amplitude of the received wave Wr reaches the maximum value. As another example of the prohibition period tg, as shown in FIG. 7, the amplitude fluctuation amount ΔVs (= Vs _n −Vs _n−1 ) for each period of the received wave Wr is sufficiently larger than the amplitude of the noise component Wn. A period up to (for example, twice as large) may be adopted. Further, as another example, if the reception signal reaches a predetermined level Vth (see FIG. 2) after the ultrasonic wave Wt is emitted, the reception time tdi is specified as the prohibition period tg. (At this time, the time charts in FIGS. 2 and 7 can be regarded as equivalent).

  The reception detection unit 131d illustrated in FIG. 6 inputs the reception signal Wr from the transducer 12b selected for reception by the direction switch 131a. The reception detection unit 131d suspends specification of the reception time point while converting the reception signal Wr into a rectangular signal Sb until the reception control signal Sg input from the prohibition period setting unit 131c is switched to a Hi level indicating cancellation of prohibition. To do. In addition, the reception detection unit 131d receives the falling point (hereinafter referred to as “zero cross point”) of the rectangular signal Sb (= P6) obtained first after the reception control signal Sg is switched to the Hi level as the reception time point. ) B is specified, and at the specified zero cross point B, a time measurement end signal stop is output to the elapsed time measuring unit 131f.

The elapsed time measuring unit 131f operates the timer by inputting the timing start signal start and stops the timer by inputting the timing end signal stop, and the elapsed time from the input of the timing start signal start to the input of the timing end signal stop And the time measurement result td is output to the propagation time calculation unit 131h.
On the other hand, the reception wave frequency detection unit 131g serves as reception wave frequency detection means for detecting the frequency of the output waveform of the transducer on the reception side as the reception wave frequency, and is in parallel with the measurement of the elapsed time td in the elapsed time measurement unit 131f. Then, the rectangular signal Sb is input from the reception detector 131d, and the reception wave frequency fr is detected based on the input rectangular signal Sb. That is, the reception wave frequency detection unit 131g counts the number of rectangular signals Sb input per unit time or calculates the input period tp of the rectangular signal Sb and calculates the reciprocal thereof to determine the reception wave frequency fr. Is detected. Then, the reception wave frequency detection unit 131g outputs the detected reception wave frequency fr to the detection delay time setting unit 131i, the period transition correction unit 131j, and the activation determination unit 131k.

  At this time, the range in which the rectangular signal Sb is counted is that the propagation time t has elapsed from the time t0 when the ultrasonic wave Wt was emitted, with reference to the propagation time t calculated in the previous measurement, as shown in FIG. The period up to the point in time. The range for counting the rectangular signal Sb is a period from the elapse of the number of periods (for example, P2) in which the amplitude of the received wave Wr is larger than the amplitude of the noise component Wn to the reception specific time td. Also good. In addition, instead of the test fluid (hydrogen gas), a calibration fluid (nitrogen gas) having a known sound velocity is circulated from the tank 5 to the measurement tube 11 shown in FIG. 1 to obtain a predetermined detection delay time tr in advance. Alternatively, the frequency fr received during the detection delay time tr may be detected by the received wave frequency detector 131g.

With such a configuration, it is possible to prevent detection of the frequency of the noise component Wn irrelevant to detection of the flow rate Q and concentration ρ of the test fluid, and to minimize the frequency detection error.
Further, the propagation time calculation unit 131h illustrated in FIG. 6 calculates the propagation time t by the following equation (11) based on the input elapsed time td, the detection delay time tr, and the period transition correction amount tc described later. The propagation time t is output to the flow rate / concentration calculation unit 132.

t = td−tr−tc (11)
The detection delay time tr is set by a detection delay time setting unit 131i described later, and the period transition correction amount tc is set by a period transition correction unit 131j described later. Both the detection delay time tr and the period transition correction amount tc are read into the propagation time calculation unit 131h.
The detection delay time setting unit 131i holds a detection delay time tr updated according to a calibration process described later.

The period transition correction unit 131j calculates the period transition correction amount tc based on the input propagation time td, prohibition period tg, and received wave frequency fr.
Here, the operation of the period transition correction unit 131j will be described.
The period transition correction unit 131j compensates for this error when a zero cross point is specified including an error of one period or more due to a loopback (hereinafter simply referred to as “loopback”) occurring in the change in the elapsed time td. A periodic transition correction amount tc for calculating the value is calculated. The periodic transition correction unit 131j detects that the aliasing has occurred based on the elapsed time td and the prohibition period tg. When this is detected, the periodic transition correction unit 131j calculates the periodic transition correction amount tc corresponding to the direction and propagates it. It outputs to the time calculation part 131h.

Here, the return of the change in the elapsed time td will be described with reference to the time chart shown in FIG. 7 (assuming that ultrasonic waves are emitted in the forward direction).
In the present embodiment, among the received waves Wr, the wave S6 in the sixth cycle is targeted, and the zero-cross point B in the decreasing direction is specified as the reception time point. First, in the first measurement, the reception control signal Sg is switched to the Hi level before the arrival time of the wave S6, and the specification of the zero cross point B is permitted. The rectangular signal Sb transitions to the Hi level with the arrival of the wave S6, and then transitions to the Lo level at the zero cross point B thereafter. For this reason, the correct zero cross point B can be specified by detecting the first falling point of the rectangular signal Sb. In the next measurement, it is assumed that the sound velocity of the test fluid increases or the flow rate Q increases, and the phase of the received wave Wr is earlier than the previous measurement. In this case, the measured elapsed time td is usually shortened according to the amount of change such as the sound speed. However, if a change in sound speed or the like is large and the time point when the reception control signal Sg is switched to the Hi level is later than the original zero cross point B, the specification of the zero cross point is permitted after the original zero cross point B. The zero cross point C is specified by the rectangular signal P7 corresponding to the wave S7 in the seventh cycle, and the measured elapsed time td ′ includes an error (= tc) for one cycle. Such a change in the elapsed time td opposite to the original direction is referred to as folding.

The period transition correction unit 131j calculates a difference tm (= td−tg) between the elapsed time td and the prohibition period tg. This difference tm is the time from when the reception control signal Sg is switched to the Hi level until the zero cross point is specified. The period transition correction unit 131j receives the difference tm and the difference tm _n−1 calculated at the previous measurement, and calculates the difference Dtm (= tm−tm _n−1 ). By dividing the calculated difference Dtm by the ultrasonic cycle tp, the difference Dtm is converted into a change rate (corresponding to “variation rate”) X of the difference tm with the cycle tp as a reference. It is determined whether or not the absolute value of the obtained change rate X is larger than a predetermined value. If it is larger, it is determined that aliasing has occurred. The predetermined value is determined from the rate of change of the flow rate Q and the measurement execution interval. When the change in the flow rate Q that gives a shift of one period to the received waveform Wr is performed over 1 second and the measurement execution interval is 0.1 second, the change in the flow rate Q is linear with respect to time. If it changes, the difference tm (that is, the elapsed time td) will change at a rate of 0.1 (= 1 × 0.1). When the change rate X exceeding 0.1 is calculated, It can be determined that folding has occurred. The period transition correcting unit 131j divides the difference Dtm by the absolute value in parallel with the detection of the aliasing, and determines the direction of change in the elapsed time td. “−” Is set when the elapsed time td is short, and “+” is set when the elapsed time is long. The set code “−” or “+” is added to the quotient Dtm / | Dtm |, and the determination value is set. The sign of this determination value indicates the direction of correction. When turn-back is detected, this determination value (= -1, 1) is subtracted or added to the number of periodic transitions Ncn _-1 calculated at the previous measurement to calculate the current number of periodic transitions. The periodic transition correction unit 131j calculates the periodic transition correction amount tc by the following equation (12) based on the calculated number of periodic transitions and the received wave frequency fr (= fr ′).

tc = Nc × tp ′ = Nc / fr ′ (12)
Here, the reception frequency exists as a variable, but in the present invention, tp ′ or fr ′ can be made constant.
The temperature adjusting unit 131m serves as a temperature adjusting unit that adjusts the diaphragm 121b of the transducers 12a and 12b to a predetermined temperature. The temperature adjusting unit 131m supplies power to a heating element attached to the diaphragm of the transducer 12a (12b). The diaphragm is adjusted to a predetermined temperature by this supply current. The embodiment will be described with reference to FIGS. In FIG. 5, a concentric plate is provided on the surface of the transducer 12a opposite to the surface in contact with the test fluid in the measurement tube 11 so as not to disturb the vibration of the electroacoustic transducer (piezoelectric element) 121d. A heater 121e is adhered.

  The relationship between the heater current Ih supplied to the plate heater 121e and the heat generation temperature Td will be described with reference to the Ih-Td diagram of FIG. The horizontal axis of the graph shown in FIG. 8 is the temperature Tg of the test fluid, Tl indicates the lowest temperature (0 ° C.) that the test fluid can take, Th is the maximum temperature that the test fluid can take, and the diaphragm 121b The adjustment temperature Ts is shown. As a result, the heater current Ih from the temperature adjusting unit 131m requires the maximum current Is at the minimum temperature Tl. Further, in Th where the temperature of the test fluid and the adjustment temperature Ts of the diaphragm 121b coincide with each other, the heater current Ih becomes 0 because heating is unnecessary. That is, the diaphragm 121b of the transducer 12a (12b) can be maintained at a constant temperature by supplying the heater current Ih corresponding to the difference between the temperature of the test fluid and the adjustment temperature Ts to the plate heater 121e.

  With such a configuration, the natural frequency of the diaphragm 121b can be kept constant, so that the acoustic-electrically converted reception signals Wr1 and Wr2 have a constant frequency. When the reception frequency of the transducer is kept constant (for example, 40 kHz), correction of the frequency change when calculating the propagation time t actually propagated in the test fluid from the detected ultrasonic transmission / reception time Arithmetic and correction coefficients are not required. Therefore, the apparatus can be simplified without degrading accuracy, and low cost and downsizing can be achieved. Also, the measurement error due to the correction calculation error is improved.

Further, the natural frequency of the diaphragm 121b of the transducer is set to have a predetermined received wave frequency at the maximum temperature Th of the test fluid.
With such a configuration, the diaphragm 121b may be heated to a constant temperature regardless of the temperature change of the test fluid, and simplification and measurement accuracy maintenance can be achieved. Further, since the temperature of the diaphragm 121b is always higher than the test fluid temperature, dew condensation on the surface on the side in contact with the test fluid can be prevented, and a secondary effect that a sound wave reception failure can be avoided is also obtained.

  In addition, according to the present embodiment, power for heating can be saved and the heating area of the transducer case 12a (12b (12b) can be saved as compared with the method in which the entire transducer case 112a for storing the transducer 12a (12b) is heated from the outside. Since only the diaphragm 121b of 12b) is small, the measurement error caused by the change of the original fluid temperature due to the test fluid being heated can be ignored in practice.

The temperature adjustment unit 131m is configured to adjust the temperature of the diaphragm 121b so that the reception wave frequency detected by the reception wave frequency detection unit 131g becomes a predetermined frequency.
With such a configuration, the diaphragm 121b can be maintained at a predetermined temperature without providing a means for detecting the temperature of the diaphragm 121b. Therefore, since the natural frequency of the diaphragm 121b does not vary with a simple configuration, the reception frequency of the transducer 12a (12b) can be kept constant.

As a current control method, a method in which a temperature Td of a transducer is detected by a temperature sensor (not shown) and feedback control is generally performed, but here, a difference εt between a reception frequency fr and a frequency fs to be set is zero. Thus, the method of controlling the heater current Ih produces a good result. A control block of the temperature adjustment unit 131m is shown in FIG.
Further, as another example of the temperature adjusting unit 131m, there is a configuration in which a PTC (Positive Temperature Coefficient) heater is used as a heater for heating the diaphragm 121b shown in FIG. The PTC heater is a heater having a self-temperature control characteristic with a positive resistance temperature coefficient, and mainly contains barium titanate or the like. This PTC heater adheres to the diaphragm 121b of the transducer 12a (12b), similarly to the plate heater 121e shown in FIG. This PTC heater has a characteristic that its resistance value Rh increases rapidly when the temperature exceeds a specific temperature. Therefore, as shown in the Td-Rh diagram of FIG. 8, the critical temperature at which the resistance value Rh rapidly increases is self-adjusted by selecting a material that matches the set temperature Ts of the diaphragm 121b as a main component. . Since there are variations in the adjustment temperature for each element, prior calibration is required, but the cost can be reduced as much as it can be compensated.

With such a configuration, the diaphragm 121b can be maintained at a predetermined temperature without providing a temperature detecting means.
FIG. 10 shows still another embodiment of the temperature adjustment unit 131m. The temperature adjustment unit 131m according to this example is provided with a coil 121h in the vicinity of the surface of the transducer 12a '(12b') on the side opposite to the surface in contact with the test fluid in the measurement tube 11. The coil 121h serves as an electromagnetic induction generating means, and generates electromagnetic induction by a supply current from the temperature adjusting unit 131m to heat the diaphragm 121b. The coil 121h is fixed to the transducer body 121a with an appropriate gap from the transducer diaphragm 121b. When an alternating current is passed through the coil 121h, a magnetic flux passes along the path indicated by the arrow H, and an induced current (eddy current) Ie flows in the circumferential direction through the diaphragm 121b. Joule heat is generated by the induced current and the electrical resistance of the diaphragm 121b, and the diaphragm 121b generates heat. As a temperature control method, as shown in the control block of FIG. 9, the coil energization current is adjusted using feedback control so that the difference εt between the reception frequency fr and the frequency fs to be set becomes zero. Can be realized.

With such a configuration, by adjusting the temperature of the diaphragm 121b in a non-contact manner, the amplitude characteristics and transient response characteristics of the diaphragm 121b can be prevented from being affected. Therefore, the degree of freedom in acoustic design of the transducers 12a and 12b can be expanded. In addition, it is not necessary to consider poor adhesion or peeling of the heater.
Next, the activation determination unit 131k illustrated in FIG. 6 will be described. The activation determination unit 131k outputs an activation signal Su that causes the flow rate / concentration calculation unit 132 to start a predetermined calculation when the reception wave frequency fr detected by the reception wave frequency detection unit 131g is within a predetermined frequency range. It becomes an output means. When the surface of the diaphragm 121b of the transducer 12a freezes due to the temperature drop, the spring constant k of the diaphragm 121b increases, so that the received wave frequency fr increases (see the above equation (7)). On the other hand, when a droplet adheres to the surface of the vibration plate 121b, the equivalent mass m of the vibration plate 121b increases, so the received wave frequency fr decreases (see the above formula (7)). Then, when the surface of the diaphragm 121b is in a moderate dry state to a wet state, a normal received wave frequency can be detected. Therefore, by determining in advance the relationship between the surface state of the diaphragm 121b and the reception frequency fr, it is possible to determine the icing of the diaphragm 121b and the droplet adhesion state that cause the measurement error to deteriorate. For example, the reception wave frequency when the surface of the diaphragm 121b is frozen is set as the minimum allowable reception frequency fl, and the reception wave frequency when the droplet is attached to the surface is set as the maximum allowable reception frequency fh. Then, as shown in the table of FIG. 11, when the reception wave frequency fr is equal to or higher than the maximum allowable frequency fh or equal to or lower than the minimum allowable frequency fl, the output of the activation signal Su is turned off. (For example, the output voltage is set to 0V). On the other hand, when the value of the reception wave frequency fr is in a range larger than the minimum allowable frequency fl and smaller than the maximum allowable frequency fh, the output of the activation signal Su is turned on (for example, the output voltage is set to 5V).

The activation signal Su determined in this way is used to prohibit or permit updating of the measurement output of the flow rate / concentration calculation unit 132 shown in FIG.
This is because when the transducers 12a and 12b cannot obtain a normal function due to adhesion of foreign matter to the diaphragm 121b or aging, the water vapor contained in the test fluid is frozen, or the pressure in the measurement tube 11 It is determined that the reliability of the received signal Wr is reduced and normal detection operation cannot be guaranteed because significant condensation or droplets have adhered to the diaphragm 121b due to the rise or the drop in the pipe ambient temperature.

With such a configuration, when splashed water or condensed water adheres to or is detached from the diaphragm 121b of the transducer, a temporary measurement error due to a sudden frequency change is output. Therefore, in the case of flow rate control at the usage destination, it is possible to prevent erroneous control due to measurement error.
When the flow rate / concentration calculation unit 132 receives the activation signal Su, the flow rate Q and density of the hydrogen gas according to the above equations (3) to (6) based on the propagation time t input from the propagation time calculation unit 131h. ρ is calculated. An erroneous output can be prevented by starting measurement of the flow rate Q and the concentration ρ of the test fluid using the activation signal Su thus determined.

  Next, the decompression detection unit 131o shown in FIG. 6 will be described. The thawing detection unit 131o serves as a thawing detection means for detecting whether or not the ice on the transducers 12a and 12b has been thawed, and outputs a thawing signal St in the thawed state. When the diaphragm 121b freezes, an increase in the spring constant k due to a decrease in temperature becomes dominant, and therefore, as shown in the table of FIG. 11, the icing state can be determined only from the received wave frequency fr. Therefore, for example, by setting the frequency at 0 ° C. to the maximum allowable reception frequency fh and comparing it with the reception frequency fr, it is determined whether or not the diaphragm 121b has been thawed. When the reception wave frequency fr is equal to or higher than the maximum allowable reception frequency fh, the output of the decompression signal St is turned off. On the other hand, when the reception wave frequency fr is smaller than the maximum allowable reception frequency fh, the output of the decompression signal St is turned ON. Then, by using this determination result, starting the measurement of the flow rate Q and the concentration ρ of the test fluid, it is possible to prevent erroneous output.

  Here, as described above, when the diaphragm 121b of the transducer 12a is frozen, the reception frequency fr increases. On the other hand, even when the periphery of the diaphragm 121b is dried, only the equivalent mass m of the diaphragm is obtained, so that the reception frequency fr is also increased. That is, it may be difficult to distinguish between icing and drying only with the reception frequency fr. As described with reference to the graph of FIG. 8, the heater current Ih increases at low temperatures, while the heater current Ih decreases as the temperature rises. Therefore, by determining in advance the relationship between the surface state of the diaphragm 121b and the heater current Ih, it is possible to determine whether or not the diaphragm 121b that causes the measurement error to deteriorate is frozen. For example, the threshold current Ith is the heater current Ih in a state where the surface of the diaphragm 121b is frozen. Then, as shown in the table of FIG. 12, when the received wave frequency fr is larger than the predetermined frequency fth, it is determined that the heater current Ih is larger than the threshold current Ith. Judged to be dry.

  Next, the dryness detection unit 131n shown in FIG. 6 will be described. The dryness detection unit 131n is a dryness detection unit that detects whether or not the transducers 12a and 12b are dry, and outputs a dry signal Sd in a dry state. As shown in FIG. 12, when the diaphragm 121b is dry, the heater current Ih is lower than the threshold current Ith, and the reception wave frequency fr is higher than the predetermined frequency fth. On the other hand, when the diaphragm 121b is wet, the received wave frequency fr is lower than the predetermined frequency fth. Therefore, by determining in advance the relationship between the surface state of the diaphragm 121b and the frequency, the wet state of the test fluid that deteriorates the measurement error can be determined. The dryness detection by the dryness detection unit 131n can be correctly determined by combining the received wave frequency fr and the heater temperature information as shown in the table of FIG. The temperature information is obtained from the heater current Ih output from the temperature adjustment unit 131m.

  Next, an example in which the present invention is applied to a fuel cell will be described with reference to FIG. By mounting the measuring device 1 according to the present invention on the fuel cell system, it can be used for operation control of the fuel cell. The start signal Su and the defrost signal St output from the control unit 13 are input to the low temperature start determination of the power generation control device 7 to determine the defrost state inside the pipe on which the transducer is mounted, and the appropriate start time for starting the fuel cell. Can know. For example, at the time of low temperature start-up, when the thawing of the ice on the diaphragm 121b is detected, it is determined that the liquid in the fuel cell (stack) 6 has also been thawed, and the power generation control device 7 starts power generation. On the contrary, when the droplets are attached to the vibration plate 121b, it can be estimated that the fuel supply is locally blocked in the fuel cell 6 by a large amount of droplets. In this case, operation control such as temporarily closing the water supply control valve 10 to lower the humidification amount and increasing the fuel supply amount to discharge droplets in the fuel cell 6 to eliminate the blocking portion is possible. It is. Further, when the activation signal Su is OFF, an alarm or warning light can be activated to prompt the operator to recognize the abnormality. Further, by feeding back the drying signal Sd output from the control unit 13 to the water supply valve 10 of the humidifier 9, the fuel gas supplied to the fuel cell can be appropriately wetted. As a result, it is possible to efficiently generate power while suppressing deterioration of the performance of the fuel cell.

Next, the operation of the control unit 13 will be described with reference to the flowchart shown in FIG.
When the power of the measuring device 1 is turned on, this routine is started and initialization is performed. This routine is executed every predetermined time.
In S101, the diaphragm is heated to a predetermined temperature.

In S102, the ultrasonic wave propagation direction is switched.
In S103, an ultrasonic wave is emitted from the transmission transducer, and the elapsed time td is started.
In S104, it is determined whether the prohibition period tg has elapsed and the reception control signal Sg has been switched to the Hi level to allow the specification of the reception time point. This determination is repeated until permission is granted, and if permission is granted, the process proceeds to S105.

In S105, the first falling zero cross point B after the reception time point identification is permitted is specified as the reception time point, and the elapsed time td is measured based on the time of the zero cross point B.
In S106, it is determined whether it is calibration time or measurement time. In this embodiment, switching between calibration and measurement is manually performed by a switch, and this determination is performed by detecting an output signal of the switch. At the time of calibration, the measurement tube 11 is filled with nitrogen gas (the speed of sound is known) from the tank 5, and at the time of measurement, hydrogen gas is circulated through the measurement tube 11.

In S107, based on the rectangular signal Sb (FIG. 7) obtained at the time of calibration, the period tp of the received wave Wr is detected, and the reference received wave frequency fr is detected. This is performed in order to cancel the variation in the natural frequency of the diaphragm and the heating error in S101. (The reception frequency measured here is used for calculating Nr and tc when calculating the propagation time using the transducer.)
In S108, the propagation time for calibration according to the sound speed of nitrogen gas is calculated by the equation (1). The flow rate Vg of the calibration fluid can be detected by installing a simple sensor in the pipe 4. When a single composition gas such as nitrogen gas or hydrogen gas is used as the calibration fluid, the sound velocity Cg is γ as the specific heat ratio, R as the gas constant, T as the temperature, and M as the molar mass. And can be calculated by the following equation (13).

Cg = √ (γ × R × T / M) (13)
In S109, the detection delay time tr is calculated by subtracting the calibration propagation time from the elapsed time td. In the calibration, an ultrasonic wave is emitted a plurality of times, and an elapsed time td is obtained by averaging the elapsed time measured for each emission. The calculated detection delay time tr is stored in the detection delay time setting unit 131i. When the calibration is completed, the switch is switched and hydrogen gas flows through the measurement tube 11.

When the switch is switched to measurement in S106, the process proceeds to S110. In S110, based on the rectangular signal Sb ′ (FIG. 7) obtained at the time of measurement, the period tp ′ of the received wave Wr is detected, and the received wave frequency fr is detected.
In S111, based on the detected received wave frequency fr, it is determined whether or not an abnormality has occurred in the transducers 12a and 12b, such as adhesion of foreign matter to the diaphragm. If an abnormality has occurred, S117 Proceed to This prohibits measurement calculation and output in the event of an abnormality.

In S117, the state of the test fluid is determined based on the reception frequency fr, and a corresponding signal is output.
In S118, the temperature adjusting means or the transmission frequency varying means described later is adjusted in a direction to cancel the difference from the target set frequency.
On the other hand, when it is determined in S111 that no abnormality has occurred, the process proceeds to S112. In S112, it detects that the reception frequency is at a predetermined frequency, and outputs an activation signal indicating the validity of the measurement value.

In S113, it is determined whether or not correction for the aliasing is necessary based on the elapsed time td and the prohibition period tg. If necessary, the periodic transition correction amount tc is calculated by the equation (12) based on the received wave frequency fr. Is calculated.
In S114, the propagation time t is calculated by subtracting the detection delay time tr and the period transition correction amount tc from the elapsed time td.

In S115, based on the calculated propagation time t, the flow rate Q and the density ρ of the hydrogen gas are calculated by the above formulas (3) to (6).
In the present embodiment, in the control unit 13, the reception detection unit 131d is the reception time point specifying unit, the elapsed time measurement unit 131f, the propagation time calculation unit 131h, and the detection delay time setting unit 131i are the propagation time measurement unit, and the flow rate / concentration. The computing unit 132 constitutes computing means, and the prohibition period setting unit 131c constitutes reception time point specifying prohibiting means.

Next, another embodiment of the present invention will be described.
FIG. 15 shows another configuration of the control unit 13 of the measuring apparatus 1 according to this embodiment. In the present embodiment, the transmission frequency variable unit 131p that can variably control the transmission frequency of the ultrasonic waves emitted from the transducers 12a and 12b is further provided. The transmission frequency variable unit 131p controls the transmission frequency of the transducers 12a and 12b so that the reception wave frequency fr detected by the reception wave frequency detection unit 131g becomes a predetermined frequency. (Target value) The transmission frequency is adjusted so as to cancel the difference from fs. The transmission frequency variable unit 131p can also be easily realized with the same configuration as the diaphragm temperature adjustment by the feedback control described above.

FIG. 16 is a block diagram of the transmission frequency variable unit 131p. Here, the received wave frequency fr is input, and the output ft is adjusted in a direction in which the difference εf between the received wave frequency fr and the set frequency fs is canceled. Control responsiveness can be adjusted by adding a differential or integral element to the feedback function H.
And the transmission drive part 131b in FIG. 15 is provided with the function to vary a drive frequency by external input (ft). Other configurations and operations are the same as those of the embodiment shown in FIG.

  In the embodiment shown in FIG. 15, a transmission frequency variable unit 131p, a reception frequency detection unit 131g, and a temperature adjustment unit 131m are provided, and the diaphragms of the transducers 12a and 12b are adjusted to a predetermined temperature by the temperature adjustment unit 131m. Then, the frequency of the signal propagated through the test fluid is detected by the reception frequency detector 131g, and the frequency difference εf between the reception frequency fr and the predetermined instruction frequency fs is zero. The transmission frequency is adjusted by the transmission frequency variable unit 131p.

  With such a configuration, it is possible to more accurately remove frequency errors and fluctuations that cannot be removed only by the temperature adjustment unit 131m. In other words, when a sudden change in the temperature or wet state of the test fluid occurs, the response delay is relatively large due to the heat capacity of the member only by the temperature adjustment by the temperature adjustment unit 131m. Even you can respond in a timely manner. Therefore, even when the temperature of the test fluid changes suddenly and the response speed of the temperature adjustment unit 131m of the diaphragm is not in time, the difference εf between the reception frequency fr and the predetermined instruction frequency fs is set to zero. Further, it becomes possible to more accurately remove frequency errors and fluctuations that cannot be removed by the temperature adjusting unit 131m.

Similarly, when there is a wider reception frequency change that exceeds the possible heating range of the diaphragm, the difference εf between the reception frequency fr and the predetermined instruction frequency fs can be made zero. This eliminates the need for frequency change correction calculation and correction coefficient even under test fluid conditions with a large change rate or amount of change, and improves measurement errors due to correction calculation errors.
Furthermore, since the transmission frequency is adjusted continuously by the transmission frequency variable unit 131p (analog), there is an effect that calibration is not necessary even if the natural frequency of the transducer varies.

The block diagram of the measuring device which concerns on one Embodiment of this invention Time chart showing the operating principle of the measuring device Time chart showing the measurement principle of propagation time Graph showing changes in transducer frequency characteristics due to differences in natural frequency Sectional drawing which shows one Embodiment of the temperature control means of this invention The block diagram which shows the structure of the control unit which concerns on one Embodiment of this invention. Time chart showing the operation of the measuring device Graph showing adjustment operation of temperature adjustment means Control block diagram of temperature control means of the present invention Sectional drawing which shows other embodiment of the temperature control means of this invention Table showing test fluid condition judgment conditions Table showing other conditions for determining the test fluid The block diagram which shows the example which applied this invention to the fuel cell Flow chart of measurement routine Configuration of a control unit according to another embodiment of the present invention Control block diagram of transmission frequency variable means of the present invention

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Ultrasonic fluid measuring device, 2 ... Piping, 3 ... Direction switching valve, 4 ... Piping, 5 ... Tank, 6 ... Fuel cell, 7 ... Power generation control device (power controller), 8 ... Drive load (motor), 9 DESCRIPTION OF SYMBOLS ... Humidifier, 10 ... Control valve, 11 ... Measuring tube, 12a, 12b ... Ultrasonic transducer, 121a ... Ultrasonic transducer body, 121b ... Diaphragm, 121c ... Sealing material, 121f, 121g, 121i ... Electric wire, 121e ... heater, 121h ... coil, 13 ... control unit, 131 ... propagation time measurement unit, 131g ... reception frequency detection unit, 131m ... temperature adjustment unit, 131k ... startup determination unit, 131n ... drying detection unit, 131o ... defrost detection unit 131p: Transmission frequency adjustment unit, 132: Flow rate / concentration calculation unit

Claims (12)

A measuring tube for circulating the test fluid;
A first transducer installed on an ultrasonic propagation line set across the measuring tube and emitting ultrasonic waves in a forward direction with respect to the flow;
A second transducer that is disposed downstream of the first transducer on the ultrasonic propagation line and emits an ultrasonic wave in a direction opposite to the flow;
Temperature adjusting means for adjusting at least one of the first or second transducers to a predetermined temperature;
A reception time point specifying means for receiving the ultrasonic wave emitted from each of the first and second transducers by a receiving side transducer and specifying a time point when a predetermined detection delay time has elapsed as a reception time point;
Propagation time measuring means for measuring a propagation time from when the first and second transducers emit ultrasonic waves to propagation to the receiving-side transducer based on the identified reception time point;
Based on the measured propagation time, calculation means for performing a predetermined calculation related to the test fluid in the measurement tube,
An ultrasonic fluid measuring device comprising: A reception wave frequency detection unit configured to detect the frequency of the output waveform of the transducer on the reception side as a reception wave frequency;
2. The ultrasonic fluid measurement apparatus according to claim 1, wherein the temperature adjustment unit adjusts the temperature of the diaphragm so that the reception wave frequency detected by the reception wave frequency detection unit becomes a predetermined frequency. . Comprising transmission frequency variable means capable of variably controlling the transmission frequency of the ultrasonic waves emitted from the first and second transducers;
The transmission frequency variable means controls the transmission frequency of the first or second transducer so that the reception wave frequency detected by the reception wave frequency detection means becomes a predetermined frequency. The ultrasonic fluid measuring device described. The detection delay time is obtained in advance by circulating a calibration fluid whose sound speed is known in the measurement tube,
The ultrasonic fluid measurement apparatus according to claim 2, wherein the reception wave frequency detection unit detects a frequency received during the detection delay time. A heater is provided on the surface opposite to the surface where the diaphragm of the first or second transducer is in contact with the test fluid,
The ultrasonic fluid measurement apparatus according to claim 1, wherein the temperature adjusting unit controls heat generation of the heater.   The ultrasonic fluid measuring device according to claim 5, wherein the heater is a PTC heater having a self-temperature control characteristic. An electromagnetic induction generating means is provided in the vicinity of the surface opposite to the surface where the diaphragm of the first or second transducer contacts the test fluid,
The ultrasonic fluid measuring apparatus according to claim 1, wherein the temperature adjusting unit controls induction heating by the electromagnetic induction generating unit.   The said calculating means prohibits the predetermined calculation regarding the said test fluid based on the comparison result of the received wave frequency detected by the said received wave frequency detection means, and a predetermined frequency. The ultrasonic fluid measuring device according to any one of the above.   2. An activation signal output means for outputting an activation signal for causing the calculation means to start a predetermined calculation when the reception wave frequency detected by the reception wave frequency detection means is within a predetermined frequency range. Item 9. The ultrasonic fluid measurement device according to any one of Items 1 to 8.   2. A thawing detection means for outputting a thawing signal indicating that icing of the diaphragm of the first or second transducer has been thawed based on an adjustment amount of the temperature adjusting means. The ultrasonic fluid measuring device according to any one of ˜9.   The dryness detection means which outputs the dry signal which shows that the said test fluid is a dry state based on the received wave frequency detected with the said received wave frequency detection means is characterized by the above-mentioned. The ultrasonic fluid measuring device according to any one of the above.   12. The natural frequency of the diaphragm of the first or second transducer is set to have a predetermined received wave frequency at a maximum temperature that can be taken by the fluid under test. The ultrasonic fluid measuring device according to one.

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