JP2015068671A - Ultrasonic flowmeter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize an ultrasonic flowmeter which, in a simple configuration, can reduce the effect of an offset caused by non-uniformity, etc., in an electric circuit element and a cable and can perform measurement with high accuracy.SOLUTION: Provided is an ultrasonic flowmeter equipped with an ultrasonic transducer for sending/receiving an ultrasonic signal on the upstream and downstream sides of an outer wall of a measurement tube in which a fluid to be measured flows, wherein the ultrasonic flowmeter is characterized in that the ultrasonic transducers on the upstream and downstream sides are connected via a cable for delivering time information to each other.

Description

  The present invention relates to an ultrasonic flow meter, and more particularly, to reducing the effect of offset due to variations in propagation time of ultrasonic signals.

  FIG. 3 is a configuration explanatory view showing an example of an ultrasonic flowmeter based on a conventionally used transmission method. In FIG. 3, two ultrasonic transducers 2 a and 2 b that transmit and receive ultrasonic signals in response to switching, sandwiching the measurement tube 1, are placed on the outer wall of the measurement tube 1 through which the fluid to be measured flows. The propagation paths A and B of the sound wave signals are disposed opposite to the upstream side and the downstream side in a positional relationship where the propagation paths A and B intersect with each other at a predetermined angle with respect to the tube axis of the measurement tube 1.

  The ultrasonic transducers 2a and 2b are each composed of a piezoelectric element having a piezoelectric effect. The ultrasonic transducer 2a is connected to one fixed contact b of the switching unit SWa via the cable 3, and is connected to one fixed contact b of the switching unit SWb via the cable 4, and the ultrasonic transducer 2b is connected to the cable. 5 is connected to the other fixed contact c of the switching unit SWa through 5, and is connected to the other fixed contact c of the switching unit SWb through the cable 6.

  One transmitter 7 and one receiver 8 are connected to the movable contact a of the switching unit SWa, and the other transmitter 9 and the other receiver 10 are connected to the movable contact a of the switch SWb. . Output signals of the receiving units 8 and 10 are input to the data processing unit 11. The switching units SWa and SWb, the transmission units 7 and 9, the reception units 8 and 10, and the data processing unit 11 are comprehensively controlled by the control unit 12.

  The switching units SWa and SWb are switched and controlled by the control unit 12 so that the ultrasonic transducers 2a and 2b transmit and receive ultrasonic signals in a complementary manner. In a state where the movable contact a of the switching unit SWa is connected to one fixed contact b and the movable contact a of the switching unit SWb is connected to the other fixed contact c as shown by a solid line in FIG. 3, for example, ultrasonic conversion The device 2a generates and outputs an ultrasonic signal inside the measurement tube 1 by the piezoelectric effect based on the ultrasonic drive signal input from the transmission unit 7 via the switching unit SWa, and the other ultrasonic transducer 2b includes the measurement tube. 1 receives an ultrasonic signal propagating through the inside of 1 and outputs an electrical signal converted by the piezoelectric effect to the receiving unit 10 via the switching unit SWb.

  An electrical signal based on the ultrasonic signals received and converted by the ultrasonic transducers 2a and 2b is taken into the receiving unit 8 through the switching unit SWa, amplified, and output to the data processing unit 11, and the switching unit. The signal is taken into the receiving unit 10 via SWb, amplified, and output to the data processing unit 11.

  The data processing unit 11 receives the transmission time signals of the transmission units 7 and 9 input from the control unit 12 and the reception time signals of the ultrasonic signals received by the reception units 8 and 10. The propagation time is calculated, the flow velocity of the fluid to be measured is calculated, and the flow rate of the fluid to be measured is finally calculated.

Specifically, the flow velocity V of the fluid to be measured includes the time difference ΔT (= Tus−Tds) between the propagation time Tus in the propagation path A and the propagation time Tds in the propagation path B, the propagation time Tus or Tds, and the cable assumed in advance. Based on the propagation time T in the measuring tube 1 calculated in consideration of the propagation time due to the length, the delay time of the electric circuit, and the like, the following equation is obtained.
Velocity V∝ △ T / T

  However, the propagation time is greatly affected by delays due to variations in electrical circuit elements and cables, particularly variations in the on-resistances of the switch elements constituting the switching units SWa and SWb. ) Cannot be removed, and these variations are measured as offsets and appear as errors in the flow rate value.

  Therefore, in order to remove the influence of such an offset, the following measurement and calculation processes are performed.

<1. Measurement of propagation time Tus>
In measuring the propagation time Tus, the control unit 12 disables the receiving unit 8 to enable the receiving unit 10, and switches the movable contact a of the switching unit SWa to the fixed contact b side to switch the switching unit SWb. The movable contact a is switched to the fixed contact c side, and the transmission unit 7 is controlled to output an ultrasonic drive signal.

  The ultrasonic drive signal output from the transmission unit 7 is input from the fixed contact b of the switching unit SWa to the ultrasonic transducer 2a via the cable 3, and the ultrasonic transducer 2a generates and outputs an ultrasonic signal. The ultrasonic signal generated and output from the ultrasonic transducer 2a propagates through the propagation path A in the measurement tube 1, is received by the ultrasonic transducer 2b, and is converted into an electrical signal.

  The electrical signal converted and output from the ultrasonic transducer 2b is input to the receiving unit 10 via the cable 5 and the fixed contact c of the switching unit SWb, amplified, and then input to the data processing unit 11. The data processing unit 11 measures and holds the propagation time Tus from the transmission unit 7 to the reception unit 10.

<2. Measurement of propagation time Tds>
When measuring the propagation time Tds in the direction opposite to the propagation time Tus, the control unit 12 disables the reception unit 10 and controls the reception unit 8 to be enabled, and the movable contact a of the switching units SWa and SWb propagates. The transmitter 9 is controlled to output an ultrasonic drive signal in the same state as the time Tus measurement.

  The ultrasonic drive signal output from the transmission unit 9 is input to the ultrasonic transducer 2b via the fixed contact c of the switching unit SWb and the cable 5, and the ultrasonic transducer 2b generates and outputs an ultrasonic signal. The ultrasonic signal generated and output from the ultrasonic transducer 2b propagates through the propagation path B in the measurement tube 1, is received by the ultrasonic transducer 2a, and is converted into an electrical signal.

  The electrical signal converted and output from the ultrasonic transducer 2a is input to the receiving unit 8 through the cable 3 and the fixed contact b of the switching unit 6a, is amplified, and is input to the data processing unit 11. The data processing unit 11 measures and holds the propagation time Tds from the transmission unit 9 to the reception unit 8.

<3. Measurement of propagation time Tur>
In measuring the propagation time Tur, the control unit 12 disables the receiving unit 8 to enable the receiving unit 10 and switches the movable contact a of the switching unit SWa to the fixed contact c side to switch the switching unit SWb. The movable contact a is switched to the fixed contact b side, and the transmission unit 7 is controlled to output an ultrasonic drive signal.

  The ultrasonic drive signal output from the transmission unit 7 is input to the ultrasonic transducer 2b via the fixed contact c of the switching unit SWa and the cable 6, and the ultrasonic transducer 2b generates and outputs an ultrasonic signal. The ultrasonic signal generated and output from the ultrasonic transducer 2b propagates through the propagation path B in the measurement tube 1, is received by the ultrasonic transducer 2a, and is converted into an electrical signal.

  The electrical signal converted and output from the ultrasonic transducer 2a is input to the receiving unit 10 through the cables 3 and 4 and the fixed contact b of the switching unit 6b, is amplified, and is input to the data processing unit 11. The data processing unit 11 measures and holds the propagation time Tur from the transmission unit 7 to the reception unit 10.

<4. Measurement of propagation time Tdr>
In measuring the propagation time Tdr in the direction opposite to the propagation time Tur, the control unit 12 disables the receiving unit 10 and controls the receiving unit 8 to be enabled, and the movable contact a of the switching units SWa and SWb propagates. The transmitter 9 is controlled to output the ultrasonic drive signal in the same state as the time Tur measurement.

  The ultrasonic drive signal output from the transmission unit 9 is input to the ultrasonic transducer 2a via the fixed contact b of the switching unit SWb and the cables 4 and 3, and the ultrasonic transducer 2a generates and outputs an ultrasonic signal. The ultrasonic signal generated and output from the ultrasonic transducer 2a propagates through the propagation path A in the measurement tube 1, is received by the ultrasonic transducer 2b, and is converted into an electrical signal.

  The electrical signal converted and output from the ultrasonic transducer 2b is input to the receiving unit 8 through the cables 5 and 6 and the fixed contact c of the switching unit 6a, amplified, and then input to the data processing unit 11. The data processing unit 11 measures and holds the propagation time Tdr from the transmission unit 9 to the reception unit 8.

<5. Arithmetic processing>
Using the average value Tua of the propagation times Tus and Tur in the propagation path A and the average value Tda of the propagation times Tds and Tdr in the propagation path B, a difference ΔT (= Tua−Tda) between these propagation times is calculated. By doing so, the error relating to the circuit is made smaller, and the influence of the offset due to the variation of the electric circuit element and the cable on the flow rate measurement value is reduced.

  Non-Patent Document 1 describes the measurement principle and configuration of an ultrasonic flowmeter of a propagation time difference method based on the transmission method similar to the present invention.

Satoshi Fukuhara, 3 others, “Ultrasonic Flowmeter US350”, Yokogawa Technical Report, Yokogawa Electric Corporation, January 20, 2004, Vol. 48 No. 1 (2004) p. 29-32

  However, according to such a conventional configuration, although errors due to circuit variations can be eliminated to some extent, the influence of variations in the on-resistances of the switch elements constituting the switching units SWa and SWb tends to be large.

  In selecting the switching elements constituting the switching units SWa and SWb, a semiconductor switch is desirable from the viewpoint of the number of switching times and reliability, but taking into account changes in on-resistance, package size, and on-resistance due to temperature. When judging comprehensively, at present, the use of a mechanical relay having a mechanical contact is advantageous.

  However, when a mechanical relay is used as a switching element, deterioration due to aging of the mechanical contact and limitation of life are inevitable. Switching frequency of the switching units SWa and SWb and an ultrasonic flowmeter as a field device are unavoidable. It is also necessary to pay attention to the usage environment.

  The present invention solves such a problem, and its purpose is to have a simple configuration in which an auxiliary cable is simply added, and to influence the offset due to variations in electric circuit elements and cables. The object is to realize an ultrasonic flowmeter that can be reduced and perform highly accurate measurement.

In order to achieve such a problem, the invention according to claim 1 of the present invention is:
In an ultrasonic flowmeter to which ultrasonic transducers that send and receive ultrasonic signals are attached to the upstream side and the downstream side of the outer wall of the measurement pipe through which the fluid to be measured flows,
The upstream and downstream ultrasonic transducers are connected to each other via a cable in order to exchange time information between them.

  2. The ultrasonic flowmeter according to claim 1, wherein the cable branches and transmits about 1/100 of the level of an ultrasonic drive signal input to one ultrasonic transducer to the other ultrasonic transducer. It is characterized by being connected through a relatively high impedance circuit element.

  Accordingly, it is possible to reduce the influence of offset due to variations in electric circuit elements and cables, and to realize an ultrasonic flowmeter capable of performing highly accurate measurement.

It is a configuration explanatory view showing an embodiment of the present invention. It is composition explanatory drawing which shows the other Example of this invention. It is composition explanatory drawing which shows an example of the conventional ultrasonic flowmeter.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is an explanatory diagram showing a configuration of an embodiment of the present invention, and the same reference numerals are given to portions common to FIG. In FIG. 1, two ultrasonic transducers 2a and 2b are connected to each other via a cable 13 in which circuit elements (not shown) having a relatively high impedance are connected in series.

  Here, the impedance value of the circuit element connected in series with the cable 13 is such that a part of the ultrasonic signal output from one ultrasonic transducer (for example, 2a) (for example, about 1/100 of the output level) is the other. It is assumed that the input is branched to the ultrasonic transducer (for example, 2b).

The operation of FIG. 1 will be described.
<1. Measurement of propagation time Tus>
In measuring the propagation time Tus in the propagation path A, the control unit 12 controls the reception unit 8 to be disabled, enables the reception unit 10 to be enabled, and controls the transmission unit 7 to output an ultrasonic drive signal. To do.

  An ultrasonic drive signal is transmitted from the transmitter 7 to the ultrasonic transducer 2a via the cable 3, and the ultrasonic transducer 2a generates and outputs an ultrasonic signal. The ultrasonic signal generated and output from the ultrasonic transducer 2a propagates through the propagation path A in the measurement tube 1, is received by the ultrasonic transducer 2b, and is converted into an electrical signal.

  On the other hand, a part of the ultrasonic drive signal input to the ultrasonic transducer 2a is attenuated by the cable 13 to, for example, about 1/100 of the output level and branched as described above, and input to the ultrasonic transducer 2b. The The branched ultrasonic drive signal is further input to the receiving unit 10 via the cable 5, amplified, and input to the data processing unit 11. The data processing unit 11 measures and holds the propagation time Tusc from the transmission unit 7 through the cables 3 and 13 to the reception unit 10.

  The ultrasonic signal propagated through the propagation path A in the measuring tube 1 is received by the ultrasonic transducer 2b and converted into an electrical signal. The electrical signal converted and output from the ultrasonic transducer 2 b is input to the receiving unit 10 via the cable 5 and amplified, and then input to the data processing unit 11. The data processing unit 11 measures and holds the propagation time Tusm from the transmission unit 7 through the propagation path A in the measuring tube 1 to the reception unit 10.

<2. Measurement of propagation time Tds>
In measuring the propagation time Tds in the propagation path B in the direction opposite to the propagation time Tus, the control unit 12 controls the reception unit 10 to be disabled and enables the reception unit 8 to be enabled, and the transmission unit 9 controls the ultrasonic wave. Control to output a drive signal.

  The ultrasonic drive signal output from the transmitter 9 is input to the ultrasonic transducer 2b via the cable 5, and the ultrasonic transducer 2b generates and outputs an ultrasonic signal. The ultrasonic signal generated and output from the ultrasonic transducer 2b propagates through the propagation path B in the measurement tube 1, is received by the ultrasonic transducer 2a, and is converted into an electrical signal.

  On the other hand, a part of the ultrasonic drive signal input to the ultrasonic transducer 2b is branched to, for example, about 1/100 of the output level by the cable 13, and input to the ultrasonic transducer 2a. The branched ultrasonic drive signal is further input to the receiving unit 8 via the cable 3, amplified, and input to the data processing unit 11. The data processing unit 11 measures and holds the propagation time Tdsc from the transmission unit 9 to the reception unit 8 via the cables 5 and 13.

  The ultrasonic signal propagated through the propagation path B in the measuring tube 1 is received by the ultrasonic transducer 2a and converted into an electric signal. The electrical signal converted and output from the ultrasonic transducer 2 a is input to the receiving unit 8 via the cable 3 and amplified, and then input to the data processing unit 11. The data processing unit 11 measures and holds the propagation time Tdsm from the transmission unit 9 to the reception unit 8 via the propagation path B in the measuring tube 1.

<3. Calculation of time difference ΔT>
The time difference ΔT (= Tus−Tds) between the propagation time Tus in the propagation path A and the propagation time Tds in the propagation path B is calculated as follows.
The propagation time Tusc through the cable 13 on the propagation path A can be expressed by the following equation.
Tusc = Tt1 + Tcable1 + Tcable_c + Tcable2 + Tr2
Tt1: Delay time due to the circuit of the transmitter 1 Tcable1: Propagation time of the cable 1 Tcable_c: Propagation time of the cable c Tcable2: Propagation time of the cable 2 Tr2: Delay time due to the circuit of the reception 2

The propagation time Tusm passing through the measuring tube 1 in the case of the propagation path A can be expressed by the following equation.
Tusm = Tt1 + Tcable1 + Tusm_m + Tcable2 + Tr2
Tusm_m: Propagation time of propagation path A in measurement tube 1 Here, when ΔTusmc = Tusm−Tusc is calculated,
Since ΔTusmc = Tusm_m−Tcable_c, it becomes the sum of the propagation time in the measuring tube 1 and the propagation time of the cable 13, and the delay time of the circuit is removed.

Similarly, the propagation time Tdsc via the cable 13 in the case of the propagation path B can be expressed by the following equation.
Tdsc = Tt2 + Tcable2 + Tcable_c + Tcable1 + Tr1

And the propagation time Tdsm which passed through the inside of the measuring tube 1 at the time of the propagation path B can be expressed by the following equation.
Tdsm = Tt2 + Tcable1 + Tdsm_m + Tcable1 + Tr1
Tdsm_m: Propagation time of the propagation path B in the measuring tube 1 Here, when ΔTdsmc = Tdsm−Tdsc is calculated,
Since ΔTdsmc = Tdsm_m−Tcable_c, the sum of the propagation time in the measuring tube 1 and the propagation time of the cable 13 is obtained, and the delay time of the circuit is eliminated.

The time difference Δt between the propagation path A and the propagation path B for obtaining the flow rate is
Δt = ΔTusmc−ΔTdsmc = Tusm_m−Tdsm_m
Thus, the propagation time of the cable 13 is also removed.

  Conventionally, since this time difference Δt is several tens of nsec, if there is a variation in delay of a circuit or the like, a flow rate error is affected. The propagation time T in the measuring tube 1 is that the propagation times Tusm_m and Tdsm_m of the paths A and B in the measuring tube 1 are Tusm_m = T + ΔT and Tdsm_m = T−ΔT. If this average is taken, the propagation time T can be calculated.

Here, calculating the average of ΔTusmc and ΔTdsmc,
(ΔTusmc + ΔTdsmc) ÷ 2
= (Tusm_m−Tcable_c + Tdsm_m−Tcable_c) ÷ 2
= (T + ΔT + T−ΔT−2 × Tcable_c) ÷ 2
= T-Tcable_c
Thus, if Tcable_c is known, the propagation time T can be calculated.

  Although the value of Tcable_c is determined by the length of the cable 13, the length of the cable 13 is very short compared to the cables 3 and 5, and is several nsec compared to the propagation time of several tens to several hundred μsec in the measuring tube 1. Even if it is not corrected as it is, there is almost no effect. Even if correction is required for accuracy, the length of the cable 13 is determined by the diameter of the measuring tube 1 and the tube diameter itself is a standard value and the size is limited. Does not change drastically. Therefore, there is no problem if one or two fixed values are prepared in advance and set and corrected in advance.

  As described above, the propagation time Tus and the propagation path in the propagation path A in which the circuit delay portion is removed without providing the conventional switching units SWa and SWb and without performing special measurement for correction. The time difference ΔT with respect to the propagation time Tds in B can be accurately measured.

  In the above embodiment, the example in which the ultrasonic transducers 2a and 2b are directly connected via the cable 13 has been described. However, the transmitters 7 and 9 and the receivers 8 and 10 are directly branched and connected. May be.

  Further, in the case of a terminal block shape as shown in FIG. However, in this case, since the term of delay due to the cable from the terminal block 14 to the transmission unit and the reception unit falls into Tdsm + Tusm, it is necessary to consider the influence of the length of the cable and the necessary accuracy.

  As described above, according to the present invention, it is possible to realize an ultrasonic flowmeter capable of reducing the influence of offset due to variations in electric circuit elements and cables and performing highly accurate measurement.

DESCRIPTION OF SYMBOLS 1 Measurement tube 2a, 2b Ultrasonic transducer 3, 5, 13 Cable 7, 9 Transmission part 8, 10 Reception part 11 Data processing part 12 Control part

Claims (2)

In an ultrasonic flowmeter to which ultrasonic transducers that send and receive ultrasonic signals are attached to the upstream side and the downstream side of the outer wall of the measurement pipe through which the fluid to be measured flows,
The ultrasonic flowmeter, wherein the upstream and downstream ultrasonic transducers are connected via a cable in order to exchange time information between them.   The cable passes through a circuit element having a relatively high impedance for branching and transmitting about 1/100 of the level of an ultrasonic drive signal input to one ultrasonic transducer to the other ultrasonic transducer. The ultrasonic flowmeter according to claim 1, wherein the ultrasonic flowmeter is connected.

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