JPH0447771B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ultrasonic flow rate measuring device, and more particularly to an ultrasonic flow rate measuring device using a sing-around method.

FIG. 1 is a block diagram of a conventional single-around type ultrasonic flow measuring device, in which mounting elements 4, 7 are mounted on the wall of a pipe 5 through which fluid 6 flows.
The transducers 3 and 8 are mounted diagonally opposite each other via the . The transducers 3 and 8 are connected to a transmitting circuit 2 and a receiving circuit 9 via a switching circuit 1, respectively.
By switching this switching circuit 1, the receiving mode and the transmitting mode can be freely selected. In the case of FIG. 1, the transducer 3 is in the transmitting mode and the transducer 8 is in the receiving mode. In this explanation, this case will be referred to as a forward system, and the opposite case will be referred to as a reverse system. to be called.
Furthermore, a multiplier circuit 11 is connected to the receiving circuit 9, and the output of the multiplier circuit 11 is sent to a difference frequency counting circuit 10.

In FIG. 1, the switching circuit 1 is a forward system, and at this time, a trigger signal immediately after switching causes the transmitting circuit 2 to generate a transmitting signal, and the transmitting signal causes the transmitter to enter the transmitting mode. An ultrasonic pulse is emitted from the transducer 3 in the receiving mode, which is transmitted through the mounting element 4 into the pipe 5 and propagates through the fluid 6 via the mounting element 7 to the transducer 8 in the receiving mode. The signal reaches the receiving circuit 9 and is introduced into the receiving circuit 9. In the receiving circuit 9, an output pulse is emitted at the time when the ultrasonic pulse propagated into the fluid 6 and the signal determined in terms of time and level are received. The output pulse of this receiving circuit 9 is connected so as to be used as a trigger pulse for transmission, and is configured to perform repeated oscillation of transmission and reception. In this case, the period from one reception to the next reception mix is called a sing-around period, and its reciprocal is called a sing-around frequency. If the delay time of the electric circuit system and the propagation time within the pipe 5 and the attachment elements 4 and 7 are negligibly small compared to the propagation time of the ultrasonic wave within the fluid 6, then the sing-around period of the forward system is t ₁ is t ₁ = D / cos θ / C + Vsin θ ... (1) Similarly, the sing-around period t ₂ of the reverse direction system is t ₂ = D / cos θ / C - Vsin θ ... (2) where D: inner diameter of the pipe θ : Launch angle of ultrasonic pulse to fluid C: Speed of sound, and if the difference in sing-around frequency is △f, then △f=1/t ₁ -1/t ₂ ...(3) =C+Vsinθ/D/cosθ-C −Vsinθ／D／cosθ...
...(4) =2Vsinθ/D/cosθ ...(5) =V(2Vsinθ/D/cosθ) ...(6) Since θ and D are known, by detecting △f, the fluid 6 can be determined. Find the flow velocity.

Therefore, the output of the difference frequency counting circuit 10 is the flow velocity,
and is proportional to the flow rate.

Note that the multiplier circuit 11 is inserted to improve the detection accuracy of the difference frequency, and if the multiplier is m, the above formula (3) is △f=m/t ₁ −m/t ₂ ...(7) =V(2msinθ/D/cosθ)...(8).

However, in this conventional single-around type ultrasonic flow rate detection device, the propagation time τ ₂ within the mounting element and the propagation time τ ₃ within the pipe wall thickness cannot be ignored compared to the propagation time in the fluid. There was a serious defect in which the total value τ ₀ was included in the measured value as a direct error.

That is, if τ ₀ = τ ₁ + τ ₂ + τ ₃ ...(9), and _{the forward direction of the sing-around period is T and the reverse direction is T 2 ,} then T ₁ = t ₁ + τ ₀ ... (10) T ₂ = t ₂ + τ ₀ ...(11), and by substituting this into the above equation (3), △f=1/T ₁ -1/T ₂ ...(12) = 1/D/cosθ/C+Vsinθ+τ ₀ -1 /D/cosθ/C−Vsinθ+τ ₀ …(13) =2Vsinθ・cosθ/D+(c+V)τ ₀ cosθ……(13
′), and as is clear from the above equation, the term for the speed of sound in the fluid remains, which has the disadvantage that errors in the speed of sound due to temperature changes are mixed in.

Although the ultrasonic flow measuring device using the single-around method has the drawbacks mentioned above, it has the irreplaceable advantage of being rich in information, and the present invention eliminates the drawbacks of the conventional device. The purpose of this study is to propose a device that takes advantage of the advantages of ultrasonic flow measurement devices using the single-around method, such as the abundance of information. Hereinafter, the configuration will be explained based on an embodiment of the invention shown in FIG. 2 and subsequent figures.

FIG. 2 is a block diagram of an embodiment of the present invention, in which a pair of transducers 3 and 7 are mounted diagonally opposite each other on the wall of a pipe 5 through which a fluid 6 flows, via mounting elements 4 and 4. The transducers 3 and 7 are connected to a transmitting circuit 2 and a receiving circuit 9 via a switching circuit 1, so that transmission and reception can be selectively performed by switching the switching circuit 1. Note that these components are the same as those of the conventional ultrasonic flow rate measuring device shown in FIG.

A delay circuit 12 is provided on the output side of the receiving circuit 9.
is connected, and the received signal is delayed by a control signal from the delay amount control circuit 13. Furthermore, the output of this delay circuit 12 is sent to a difference frequency counting circuit 10 via a multiplier circuit 11.

It should be noted that the delay amount control circuit 13 is configured to be synchronized with the switching of the switching circuit 1, and decrease the delay amount in proportion to the number of transmissions of the transmitting circuit 2 each time the switching circuit 1 switches.

Note that FIG. 4 shows an example of the delay circuit 12 and the delay amount control circuit used in this embodiment.
Although FIG. 5 is a time chart of signal outputs generated in each part, it goes without saying that the delay circuit and delay amount control circuit are not limited to those shown in FIG.

This embodiment has the configuration as described above, and the switching circuit 1 switches the transducers 3 and 8 alternately at regular intervals so that when one of the transducers 3 and 8 is in the transmission mode, the other is in the reception mode. While performing transmission/reception switching control, an ultrasonic pulse is emitted into the pipe 5 through which the fluid 6 flows, and the weak signal from the transducer in reception mode is amplified and discriminated by the reception circuit 9, and then the output pulse is is operated as a trigger for the transmitting circuit 2, and the output pulse of the receiving circuit 9 is sent to the delay circuit 1.
2, where it is synchronized with the switching timing of the switching circuit 1 by a control signal from the delay amount control circuit 13, and the delay amount is decreased in proportion to the number of transmissions by the transmitting circuit 2 for each switching, The output pulse of the delay circuit is multiplied by the multiplier circuit 11, the time difference is detected from the output of the multiplier circuit for switching between transmission and reception by the difference frequency counting circuit 10, and the flow velocity and flow rate of the fluid are determined based on this time difference. This is due to the propagation time τ ₂ within the mounting element, the propagation time τ ₁ within the pulse thickness, the delay time τ ₃ in the electric circuit, etc., which are unavoidable in conventional single-around flow rate measuring devices. It is possible to remove errors and obtain accurate measurement results. The operation will be further explained below based on the time chart shown in FIG. Immediately after switching to the forward system, a set trigger signal is applied to the transmitting circuit 2,
A sing-around is developed, and as shown in waveform B, a receiving circuit output pulse train n ₁ , n ₂ , . . . is generated. Then, the output pulse of this receiving circuit 8 is transmitted to the delay circuit 1.
2, the signal is sequentially delayed by a delay time as shown in waveform C and is then input to the multiplier circuit 11.

That is, the output pulse n ₁ is delayed by i × τ ₀ to N ₁ The output pulse n ₂ is delayed by (i-1) × τ ₀ to N ₂ 〓 The output pulse nj is delayed by (i-j) × τ to N j The delay amount of the output pulse is proportional to the number of pulses and decreases by τ ₀ . Similarly, when switching to the reverse direction system, _p1 lags _P1 by i×τ ₀ , and pj lags Pj by (i−j)×τ.

The singaround period in the forward direction is t ₁ + τ ₀ , as shown in equation 10, and the period T ₁ ′ of the pulse applied to the multiplier circuit via the delay circuit 12 is T ₁ ′=T ₁ − τ _0. Substituting this into equation (10), we get T ₁ ′=t ₁ . Similarly, in the opposite direction, it is t ₂ + τ ₀ , and the period T ₂ ′ of the pulse applied to the multiplier circuit via the delay circuit 12 is T ₂ ′ = T ₂ − τ _0. This can be expressed as equation (11). Assign T ₂ ′=t ₂ . and,
The output of the difference frequency counting circuit via the multiplier circuit 11 is △f'=m/ _T1' -m/ _T2 '=V(2msinθ/D/cosθ), which is the same as equation (8) above. It is clear that the delay amount shown in equation (9) has been eliminated.

That is, in the apparatus of the present invention, the output of the difference frequency counting circuit does not include any amount of delay that causes measurement errors.

Incidentally, it is obvious that the present device is operated in the range of (i-j) τ ₀ +α≧0 (i-j) τ ₀ +β≧0.

This invention operates as described above, and uses a simple configuration to calculate the propagation time within the mounting element, the propagation time within the pipe wall thickness,
It eliminates delays such as electrical circuit delays and errors due to the temperature dependence of sound speed, and accurately determines the fluid flow velocity.
It has an excellent effect of being able to measure the flow rate.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an ultrasonic flow rate measuring device using the conventional sing-around method, Fig. 2 is a block diagram of an embodiment of the present invention, Fig. 3 is a time chart thereof, and Fig. 4 is a block diagram of an ultrasonic flow rate measuring device using the conventional sing-around method. A block diagram of the main parts and a time chart are shown in Figure 5. In the figure, 1 is a switching circuit, 2 is a transmitting circuit, 3 is a receiver, 4 is a mounting element, 5 is a pipe, 6 is a fluid, and 7
1 is a mounting element, 8 is a receiver, 9 is a receiving circuit, 10 is a difference frequency counting circuit, 11 is a multiplier circuit, 12 is a delay circuit, and 13 is a delay amount control circuit.

Claims (1)

[Claims] 1 A pair of ultrasonic transducers are installed diagonally opposite each other at a predetermined angle on the outer wall of a pipe through which the fluid to be measured flows, and when one transducer is in transmitting mode, the other is in receiving mode. There is a switching circuit that alternately controls the switching of transmitting and receiving waves at regular intervals so that the transmitter and receiver are in the transmitting mode, a transmitting circuit that excites the transducer in the transmitting mode, and amplifying the weak signal from the transducer in the receiving mode. , a receiving circuit that performs reception discrimination and operates the output pulse as a trigger for a transmitting circuit;
a delay circuit having a variable element capable of time-delaying the output pulse of the receiving circuit; a delay amount control circuit that is synchronized with transmission/reception switching and decreases the amount of delay in proportion to the number of transmissions of the transmitting circuit for each switching; It consists of a multiplier circuit that multiplies the output pulse from the delay circuit, and a difference frequency counting circuit that calculates the time difference from the output of the multiplier circuit that alternates transmission and reception.・An ultrasonic flow rate measurement device that measures flow rate.