JPS63173920A - Ultrasonic gas current meter - Google Patents

Abstract

PURPOSE:To perform accurate measurement with good accuracy, by calculating a flow speed on the basis of the difference between the propagation times of an ultrasonic wave in forward and reverse directions. CONSTITUTION:Transmitter-receivers P1, P2 simultaneously emit ultrasonic waves in the gas flowing through a flow pipe 10 and the ultrasonic waves propagated so as to go across the gas are received by the transmitter-receivers P2, P1 opposed to each other Coupling circuits 21, 22 receive the receiving wave signals from the transmitter-receivers P1, P2 to input the same to receiving circuits 41, 42 through a change-over circuit 30. Receiving wave signal detection circuits 43, 44 compare the outputs from the receiving circuits 41, 42 with a reference signal to issue outputs to FF circuits 51, 2. Counters 61, 62 count a clock pulse during a time when the outputs of the FF circuits 51, 52 are at an H-level. An operation circuit 100 multiplies the difference between the count values of the counters 61, 62 by a predetermined constant to calculate the flow speed of the gas.

Description

DETAILED DESCRIPTION OF THE INVENTION a. Field of Industrial Application The present invention relates to an ultrasonic gas flow meter for measuring the flow velocity of gas flowing inside a pipe using ultrasonic waves.

b. Prior Art Devices that propagate ultrasonic waves in gas flowing inside a pipe and measure the flow rate or flow rate of the gas inside the pipe by utilizing changes in the propagation speed are conventionally known. For example, a pair of probes for transmitting and receiving ultrasonic waves are placed diagonally opposite each other on the peripheral wall of a flow tube, and the probes transmit and receive ultrasonic waves alternately in the forward and reverse directions relative to the flow. There is a method that measures the flow velocity of the gas in the tube by determining the difference in the propagation time (or its reciprocal) in both the forward and reverse directions of the ultrasonic wave propagating across the flow tube.

Problems to be solved by the C0 invention However, when ultrasonic waves propagate in gas, the amount of attenuation changes depending on the gas components, temperature, dust, etc. Due to its nature, reflection and refraction occur on the propagation path, and these have a significant effect compared to liquids.

Therefore, if the transmission and reception of ultrasonic waves are alternately switched as in the conventional example, the symmetry of the propagation path of the ultrasonic waves in the forward and reverse directions is lost, that is, the amplitude and phase of the received ultrasonic waves are changed. This poses a problem in that it is difficult to accurately measure the flow velocity.

The present invention has been made in view of the above-mentioned problems, and its purpose is to solve the above-mentioned problems and, when measuring the flow velocity of gas, to
It avoids the asymmetry of the ultrasonic propagation path in the reverse direction over time, eliminates the effects of asymmetry associated with the receiving system, such as fluctuations in gain and offset of the receiving circuit system, and drift, and stabilizes it. Another object of the present invention is to provide an ultrasonic gas flow meter with high measurement accuracy.

Means for Solving the d0 Problem The structure of the present invention for achieving the above-mentioned object is such that the wall surface of the gas flow path is provided with a structure that is diagonal to the longitudinal direction of the flow path.
Alternatively, a pair of ultrasonic transducers that face each other to transmit and receive ultrasonic waves from diagonal directions is installed, and the ultrasonic waves propagate in the forward and reverse directions of the gas flow, thereby reducing the ultrasonic waves propagating in the flow path. In a current meter that measures the gas flow velocity based on the difference between the respective propagation times in both forward and reverse directions or the respective reciprocals, the transmission signal from one transmission circuit is sent only to the ultrasonic transducer side of each of the pair. , and at the same time, two sets of coupling means that connect the two transducers to drive them and conduct the received signals from the respective transducers only to the receiving circuit side; It is characterized by comprising two sets of switching means for alternately switching and inputting signals to the 2u receiving circuits, and means for switching the two sets of switching means at a cycle longer than the repetition cycle of the transmission signal.

e. Operation The pair of ultrasonic transducers are simultaneously driven by a transmission signal from a single transmission circuit to simultaneously emit ultrasonic waves, and the ultrasonic waves are transmitted in the same forward and reverse directions with respect to the gas flow. The paths are propagated so that they are not influenced by gas flow velocity distribution, temperature distribution, or other non-uniformities due to differences in their respective propagation times or their reciprocals. Furthermore, two sets of receiving circuits are provided in the receiving system, and the received signals from the respective transducers are alternately switched and inputted with a cycle longer than the repetition cycle of the transmitted signal, and the gain of the circuit is
Eliminate effects such as offset variations and drift.

f. Examples Hereinafter, preferred embodiments of the present invention will be described in detail by way of example based on the drawings.

FIG. 1 is a block diagram of an ultrasonic gas flow meter showing an embodiment of the present invention. In the figure, a pair of ultrasonic transmitting/receiving waves are mounted on the wall surface of a flow tube 10 through which gas flows in the direction of the arrow, and transmit and receive ultrasonic waves in a diagonal direction with respect to the long axis direction of the flow tube 10 or oppositely from an oblique direction. vessels P+ and Pz are arranged.

The timer (TIM) 70 generates a repetitive pulse T having a period sufficiently longer than the propagation time for the ultrasonic wave to propagate through the gas flowing in the flow tube 10, and
S) Supply to 20.

The transmitting circuit (PLS) 20 generates a transmitting pulse (TX) based on the signal of the repetitive pulse T, and connects two sets of coupling circuits (NETI) 21. (Through the NET 22, they are simultaneously transmitted to the respective transducers P+, h. The transducer Pl+h simultaneously emits ultrasonic waves into the gas flowing through the flow tube 10, and the transducers p, , The ultrasonic wave propagated through the gas is received by p.

Coupling circuit (Nil!T,)21. (NIE'h)22
receive the received wave signals from the transducers p, , pt, and output them as received wave signals RX, RX through the switching circuit (SW) 30 to the receiving circuit (RECI) 41 . (RECI) 42. Receiving circuit (RHCυ41. (RECz)42
is the received wave signal RX1. It receives RX2 and amplifies it to a predetermined level.

The coupling circuit (NETI) 21. (NETz) 22 is composed of a limiter and an attenuator, and efficiently conducts the transmission pulse TX to the transducer P, , P,
In addition, the receiving circuit (RE) is connected to the receiving circuit (RE) via the switching circuit (SW) 30.
CI)41. (RECz) 42, and efficiently transfer the received wave signals from the transducers p, p2 to the receiving circuit (RECz) 42 via the switching circuit (SW) 30.
RECI)41. (RECz) 42, and
It is designed to prevent contamination from entering the transmitting circuit (PLS) 20.

The switching circuit (SW) 30 has a 2m changeover switch,
It is driven by the signal T2 output from the timer (TIM) TO and performs a switching operation. The signal T! is a square wave signal having a period longer than the repetition period of the repetition pulse T1.

A switching circuit (SW) 30 is a receiving side transducer pg in response to the signal T2.

Pl and receiving circuit (RECI) 41. (The combination connection with the REC circuit 42 is switched alternately at regular intervals using two sets of a and b contacts. For example, while the signal rz is at H level, the received signal from the transducer P1 is connected to the receiving circuit (RECI).
41, the received signal from one transducer P2 is connected to the receiving circuit (RECt) 42, and while the signal T2 is at L level, the received signal from the transducer P is connected to the receiving circuit (RtECg).
) 42, and the received signal from one transducer Pg is connected to the receiving circuit (RECI) 41.

Next, the received wave signal detection circuit (DETI) 43. (D.E.
Tz) 44 is the receiving circuit (RECυ41. (REC
t) Compare the output from 42 with the built-in reference voltage, and determine the arrival time of the received wave signal when the output exceeds the reference voltage (or the next zero-crossing point of that wave). At this point, output pulses are sent to flip-flop circuits (FFI) 51 and (FF2) 52.

Flip-flop circuit (FFI)51. (FFZ)5
2 is set at the sending time of the repetition pulse T from the timer (TIM) 70, that is, the transmission pulse TX, and is reset by the output pulse of the detection circuit (DETI) 43° (DET2) 44. Therefore, the changeover switch in the changeover circuit (SW) 30 is connected to the a contact, and the flip-flop circuit (FFI) 51 is reset by, for example, a signal obtained by amplifying the received wave signal from the downstream transducer P1. In this case, the flip-flop circuit (FFI) 51 is held at the H level during the propagation time of the ultrasonic wave propagating in the forward direction with respect to the gas flow. Similarly, the flip-flop circuit (FF2) 52 is reset by the received wave signal from the upstream transducer P2 in this case, and the flip-flop circuit (ppz) 52 is reset by the received wave signal from the upstream transducer P2, and the flip-flop circuit (ppz) 52 is reset by the reception wave signal from the upstream transducer P2. It is held at H level for a period of time. Also, when the selector switch is connected to the b contact, the mutual connections are switched as shown in FIG. 1, but each circuit operates in the same way.

Counter (CNTI)61. (CNTZ) 62 is the count value of the flip-flop circuit (FF) 51. (
While the output of pFz) 52 is at H level, 53.54
A clock pulse from a clock pulse generation circuit (CPG) 50 is applied via the clock pulse generating circuit (CPG) for counting. These counters (CNTI)61. The count value of (cN'rz) 62 is input to the arithmetic circuit (CPU) 100 via each interface (IP) 80.

The arithmetic circuit (CPU) 100 is a counter (CNTI)
61. The gas flow velocity is calculated by multiplying the difference between the count values of (cN'rz)62 by a predetermined constant. Furthermore, by multiplying this flow velocity value by the cross-sectional area of the flow tube 10 through which the gas flows, it is possible to calculate the flow rate passing through the flow path IO, thereby satisfying the purpose of the flow meter.

The flow velocity value (or its corresponding value) obtained by the arithmetic circuit (CPU) 100 is output to the output circuit (OIJT) 90 via the interface (IF) 80. This output circuit (OUT) 90 includes a display that displays output data from the arithmetic circuit (CPU) 100, a D/A conversion circuit that converts the output data into analog, and outputs the converted data.

The above explanation shows an example of calculating the flow velocity based on the difference in the propagation time in the forward and reverse directions of the ultrasonic wave. It is also possible to convert and calculate the flow velocity from the difference between them. Further, the arithmetic circuit (CPU) 100
can also be executed on a microcomputer.

As described above, the transducers P+ and h are driven by the same transmission pulse at the same time, and the transducers PI+P! The ultrasonic waves simultaneously emitted from P! propagate in opposite directions on the same propagation path, and the transducers P! and P! , P, is received. Therefore, attenuation 1 reflection and refraction on the propagation path are similarly affected. However, if the amount of attenuation of the ultrasonic wave increases depending on the state of the flowing gas, the received wave signal RX,
RX2 is similarly attenuated and the detection circuit (DET l >43
, (DETz) 44 is delayed, and the propagation time of the ultrasonic wave appears to increase, but the difference in ultrasonic propagation time is canceled out and is not affected.

Furthermore, a receiving circuit (R[IC+, RECt) and a detection circuit (DETI, DETz).

The counters (CNT1.CNTZ) use separate hardware for the forward and reverse directions of the ultrasound, so even if the propagation time is the same for the forward and reverse directions, the counters (CNT+, CN'h) The counted values do not exactly match. Although there are means to perform correction in advance to prevent this, the influence of the hardware drift cannot be removed. In this embodiment, two sets of the hardware are provided, and the signal T2 from the timer (TIM) 70 and the switching circuit (SW) 30 are switched at regular intervals to eliminate errors caused by the hardware such as offset drift. Can be removed. That is, the transducer P,
~(RECI)41. If the calculation result is V + ΔV (Δ■ is the error based on the hardware) for the combination of pg ~ (REC 42), then P, ~ (RECg)
42. In the combination of Pg~(REC1)41, ■−Δ■
Therefore, by taking the average of the above two calculation results, the correct flow velocity value (■) can be obtained. In addition, the arithmetic circuit (CPU
) 100 so as to output the average of the outputs, it is possible to accurately measure the flow velocity without being affected by variations in the hardware.

Note that the technology of the present invention is not limited to the technology in the above-mentioned embodiments, but may also be implemented by means of other modes that achieve the same function (also, the technology of the present invention may be modified in various ways within the scope of the above-mentioned configuration). , can be added.

g0 Effect of the Invention As is clear from the above explanation, according to the present invention, when measuring the gas flow velocity, the ultrasonic waves emitted simultaneously from a certain ultrasonic transducer are directed in the forward and reverse directions relative to the gas flow, respectively. The ultrasonic waves propagate along the same path, and the attenuation, reflection, and refraction of the ultrasonic waves on the propagation path are affected by the same effects, but the difference in the respective ultrasonic propagation times or their reciprocals is not affected by these.

Furthermore, by providing two sets of receiving circuits within the current meter and alternately switching and inputting the received signals from the respective transducers at intervals longer than the repetition period of the transmitted signal,
Changes in gain and offset of the same circuit.

Since the effects of drift and the like are removed and the average of these outputs is output, fluctuations due to the receiving circuit system,
It will not be affected.

As a result, the ultrasonic gas flow meter according to the present invention can measure gas flow velocity stably and accurately.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an ultrasonic gas flow meter showing an embodiment of the present invention. p, pg...Transducer/receiver, 10...Flow tube, 20...Transmit/receive circuit (PLS), 21.22...Coupling circuit (NET,, NET,), 3
0...Switching circuit (SW), 41.42...Receiving circuit (RECI, RECt),
43.44...Detection circuit (DIET,, DETt),
50... Clock pulse generation circuit (CPG), 51.
52...Flip-flop circuit (pp, FFz),
53.54...Gate, 61.62...Counter (CNT+, CNh), 7
0...Timer (TIM), 80...Interface (IF), 90...Output circuit (OUT), 100...Arithmetic circuit (CPU).

Claims (1)

[Scope of Claims] A pair of ultrasonic transducers are disposed on the wall surface of the gas flow path for transmitting and receiving ultrasonic waves in a diagonal direction with respect to the long axis of the gas flow path or facing each other from an oblique direction. Then, the ultrasonic waves are propagated in the forward and reverse directions of the gas flow, and the gas flow velocity is determined based on the difference in the propagation time or the reciprocal of the ultrasonic waves propagating in the flow path in both the forward and reverse directions. In the current meter to be measured, the transmitting signal from the transmitting circuit is conducted only to the ultrasonic transducer side of each of the pair and at the same time to drive both transducers, and from the respective transducer. two sets of coupling means for conducting the received signals from the respective transducers only to the receiving circuit side; two sets of switching means for alternately switching and inputting the received signals from the respective transducers to the two sets of receiving circuits; An ultrasonic gas flow meter comprising: means for switching the two sets of switching means at a cycle longer than the repetition cycle of the transmission signal.