JPH0148994B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to an ultrasonic pulse signal transmitting/receiving device in an ultrasonic flow meter, a level meter, a thickness meter, etc. [Prior Art] FIG. 5 is a block diagram of a conventional external wall transmission type ultrasonic flow meter. In Fig. 5, 1 is a flow tube through which fluid flows in the direction of arrow V, 2 and 3 are ultrasonic transducers that convert ultrasound signals into electric-acoustic and acoustic-electrical converters, and 4 is an ultrasonic signal that transmits and receives ultrasonic waves. Transducer 2 to 3 or ultrasonic transducer 3 to 2, that is, a transmission/reception switching circuit that switches the ultrasonic signal to propagate in the forward direction along the fluid flow or in the reverse direction against the fluid flow; 5 is a transmission circuit; , 6 is a receiving circuit, 7
is a signal processing method that measures the time of one cycle in which an ultrasonic signal and its corresponding electric signal propagate from the transmitting circuit 5 to the receiving circuit 6 multiple times, and outputs a signal corresponding to the fluid flow velocity based on the measured propagation time. The circuit includes a display device 8 for displaying measurement results, and a timer 9 for outputting timing pulses for controlling the operation of each part of this ultrasonic flowmeter. Note that the output of the transmitting circuit 5 and the input of the receiving circuit 6 are electrical signals, and the signals propagating within the flow tube 1 are ultrasonic signals. To explain the operation of such a conventional external wall transmission type ultrasonic flowmeter, first, a signal output as a transmission wave from the transmission circuit 5 is input to the ultrasonic transducer 3 via the transmission/reception switching circuit 4, and is reversely transmitted through the fluid. The waves propagate in the same direction, reach the ultrasonic wave receiver 2, and are further input to the reception circuit 6 as a reception wave via the transmission/reception switching circuit 4. After this ultrasonic signal propagates in the opposite direction multiple times, when the transmission/reception switching circuit 4 is switched, the signal output from the transmission circuit 5 is input to the ultrasonic transducer 2 via the transmission/reception switching circuit 4. It propagates in the fluid in the forward direction, reaches the ultrasonic transducer 3, and then passes through the transmission/reception switching circuit 4 to the reception circuit 6.
is input. The forward propagation of the ultrasound signal wave is also performed multiple times. The signal processing circuit 7 detects the flow velocity and flow rate of the fluid based on the forward and reverse propagation times of the ultrasonic signal waves using the sing island method, the PLL method, the time difference method, and the like. Next, FIG. 6 is a diagram showing an example of the waveforms of the above-mentioned transmitted waves and received waves. The transmission wave output from the transmission circuit 5 has a waveform as shown in FIG. 6a or FIG. 6b. On the other hand, the received wave input to the receiving circuit 6 has a waveform as shown in FIG. 6c. Because the ultrasonic signal is repeatedly reflected, refracted, and diffused at each boundary between the ultrasonic transducer 2 or 3 and the tube wall, and between the tube wall and the fluid, it reaches the ultrasonic transducer 2 or 3 through a complicated propagation path. , furthermore, the ultrasonic signal passes through a complicated propagation path to the ultrasonic transducer 2.
Or, after reaching 3, the received wave input to the receiving circuit 6 does not disappear immediately and is superimposed on the next transmitted wave, so that the received wave input to the receiving circuit 6 is the signal wave that should originally be received with respect to the transmitted wave. An error occurs in the propagation time of the ultrasonic signal due to the complicated propagation path and being superimposed on the next transmitted wave. The interference wave cannot be removed by the signal processing of the receiving circuit because it is a composite wave that is composed of waves that match and have almost the same frequency band (hereinafter referred to as interference waves). The degree of influence of this interference wave varies depending on the SN ratio between the signal wave and the interference wave, the phase difference between the forward and reverse ultrasonic signals, and the like. For example, the frequency of the ultrasound signal is 1MHz, the phase difference is 0,
When the diameter of the flow tube 1 is 50 mm and the flow velocity of the fluid is 1 m/s, the propagation time difference when an ultrasonic signal is propagated in both forward and reverse directions is about 40 nS. Here, if the SN ratio between the signal wave and the interference wave is 40 dB, an error of 0.8 nS will occur, so 0.8/40 = 0.02, resulting in a measurement error of about 2%. Also, the SN ratio of signal waves and interference waves is 40dB.
In practice, it is quite difficult to achieve this, and the measurement error is 2% or more. Furthermore, when the diameter of the flow tube 1 is small or when the flow rate of the fluid is slow, measurement errors will increase. [Problem to be solved by the invention] In order to avoid the influence of such interference waves, conventionally, the interval at which the transmitted waves are outputted, that is, the period of one cycle, is set sufficiently long, and the interval between the outputs of the transmitted waves, that is, the period of one cycle, is set sufficiently long, and the interval between the outputs of the transmitted waves is made sufficiently long. It was designed to eliminate any interference waves. However, by increasing the period of one cycle, the number of times the propagation time is measured per unit time decreases, resulting in a problem that it takes time to measure the flow velocity of the fluid. The present invention has been made to solve the above-mentioned problems, and provides an ultrasonic pulse transmitting/receiving device that can eliminate interference waves without increasing the period of one cycle. [Means for Solving the Problem] Therefore, in the present invention, either a positive polarity ultrasound signal or a negative polarity ultrasound signal, which have opposite polarity to each other, is transmitted in a preset sequence or a random sequence. an ultrasonic signal output means for selectively outputting the ultrasonic signal and propagating it in the medium to be measured, and a polarity of the ultrasonic reception signal propagated in the medium to be measured corresponding to the polarity of the selectively outputted ultrasonic signal; and an averaging processing means for averaging the propagation times of both polarities detected by the ultrasonic signal detecting means. [Operation] In the ultrasonic pulse transmission/reception method having the above configuration, the ultrasonic signal output means transmits either a positive polarity ultrasonic signal or a negative polarity ultrasonic signal, which have opposite polarities to each other. The ultrasonic signal is selectively output according to a sequence or a random sequence and propagated into the medium to be measured, and the ultrasonic signal detecting means detects the ultrasonic wave propagated into the medium to be measured in accordance with the polarity of the selected and outputted ultrasonic signal. The propagation time is detected by changing the polarity of the sonic reception signal, and the averaging processing means averages the propagation time of both polarities detected by the ultrasonic signal detection means to measure the average time. [Example] Hereinafter, an example of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a block circuit diagram of the main parts of an ultrasonic flowmeter to which the ultrasonic pulse signal transmission/reception method according to the present invention is applied. In FIG. 1, 10 selects either a positive polarity signal or a negative polarity signal, which have opposite polarities to each other, according to a preset sequence or a random sequence, and outputs it as a transmission wave. The transmission signal output means includes a pulse generation circuit 11, a drive circuit 12,
It consists of a transmission amplifier circuit 13 made up of transistors 13A and 13B, and a transmission terminal 14 connected to the ultrasonic transducers 2 and 3 via a transmission/reception switching circuit 4 shown in FIG. Reference numeral 20 denotes a received signal detection means for detecting the arrival time of a signal outputted from the transmitted signal output means 10, propagated in the fluid (measured medium) of the flow tube 1 shown in FIG. 5, and inputted as a received wave. There is a receiving terminal, 21 a receiving amplifier circuit 22 having terminals OUT1 and OUT2 that output signals of the same polarity and opposite polarity (opposite phase) to the input received wave, and analog switches 23A and 23B.
a received wave polarity switching circuit 23 that selects and outputs one of the received waves of opposite polarity output from the amplifier circuit 22, and input terminals IN1 and IN2.
and a comparison reference level.
It is set to OV and consists of a comparison circuit 25 that detects the zero cross point of the received wave. 30 controls the drive circuit 12 and the received wave polarity switching circuit 23 to select transmitted waves of opposite polarity from the ultrasonic signal output means 10 according to a predetermined sequence, and also changes the polarity of the received wave according to the polarity of the transmitted waves. This is a controller that allows you to switch. Reference numeral 40 denotes a signal processing circuit, which uses the rising time of the transmission wave outputted from the transmission signal output means 10 as the transmission time of the transmission signal, and the time when the reception wave inputted to the reception signal detection means 20 passes the zero cross point as the reception signal. The arrival time of , and the difference between the arrival time and the sending time are the propagation time, and the time difference △t between the propagation times tu and td when the ultrasonic signal is propagated multiple times in the backward and forward directions, respectively.
(Δt=tu−td), a signal corresponding to the flow velocity of the fluid is output by the sing-around method, PLL method, or time difference method. 9
is a timer that controls the operation timing of each part. Note that the transmission signal output means 10 is a transistor 1.
3A is turned on and transistor 13B is turned off to output a positive polarity transmission signal, and transistor 13A is turned off and transistor 13B is turned on to output a negative polarity transmission signal. Also, the received signal detection means 20
switches the analog switch 23A to the terminal OUT1 side and the analog switch 23B to the terminal OUT2 side, applies the received ultrasonic signal to the amplifier circuit 24, and switches the analog switch 23A to the terminal OUT2 side,
The analog switch 23B is switched to the terminal OUT1 side, and the received signal is inverted and applied to the amplifier circuit 24. By the way, as mentioned above, the received signal detection means 20
Regardless of whether the transmitted wave is propagated in the forward or reverse direction, the received wave that is input to the transmitter superimposes the signal wave S that should originally be received and the interference wave N on the transmitted wave T, as shown in Figure 2. The result is a composite wave R. The influence of the interference wave N is, for example, when the transmitted wave propagates in the opposite direction, with respect to the propagation time tu when there is no influence of the interference wave N.
The propagation time is delayed by a time α (see Figure 2a).
Furthermore, when the transmitted wave is propagated in the forward direction, the propagation time is increased by α compared to the propagation time td when there is no influence of the interference wave N (see FIG. 2b). Therefore, the propagation time when the ultrasound propagates in the opposite direction
tu and the propagation time when the ultrasound propagates in the forward direction
The propagation time difference △t, which is the difference from td, is (tu−td+2α)
Therefore, an error of only time 2α occurs. Therefore, in the present invention, the transmission signal output means 10 selects either a positive polarity transmission signal or a negative polarity transmission signal, which have opposite polarities to each other, according to a preset sequence or a random sequence. Output as a transmitted wave. The received signal detection means 20 switches the received wave polarity switching circuit 23 according to the polarity of the transmitted wave, and detects a specific point of the received wave, for example, a zero crossing point when the received wave changes from positive to negative. Furthermore, the signal processing circuit 40
The method measures the propagation time difference obtained by propagating the transmitted and received ultrasonic signals in the reverse and forward directions multiple times as described above, and then averages them to determine the influence of interference waves. Obtain the propagation time difference with . The table assumes that the interference waves are the residual effects of the transmitted waves from the previous cycle, and that either a positive polarity ultrasonic signal or a negative polarity ultrasonic signal, which have opposite polarities to each other, is transmitted according to various sequences. It shows the propagation time difference and the average of the propagation time differences in the case of selective output.

【table】

〔Effect of the invention〕

As explained above, according to the present invention, either one of positive polarity or negative polarity transmission signals having opposite polarity to each other is selectively outputted according to a preset sequence or a random sequence,
Regardless of the polarity of the selectively output transmitted signal, the influence of interference waves is removed by the average effect of the propagation time difference obtained by setting the arrival time of the ultrasonic signal to the time when the received signal reaches a predetermined change point. be able to.

[Brief explanation of drawings]

Fig. 1 is a block circuit diagram of the main parts of an ultrasonic flowmeter to which an ultrasonic pulse signal transmitting/receiving device according to the present invention is applied, Fig. 2 is a waveform diagram showing an example of the waveform of a transmitted wave, Figs. Fig. 4 is a block circuit diagram showing another embodiment of an ultrasonic flowmeter to which the ultrasonic pulse signal transmission/reception method according to the present invention is applied, and Fig. 5 is a block diagram of a conventional external wall transmission type ultrasonic flowmeter. FIG. 6 is a waveform diagram showing an example of the waveforms of the transmitted wave and the received wave. DESCRIPTION OF SYMBOLS 10... Transmission signal output means, 11... Pulse generation circuit, 12... Drive circuit, 13... Transmission amplifier circuit, 14... Transmission terminal, 20... Reception signal detection means, 21... Reception terminal, 22... ...Reception amplifier circuit, 23, 26...Polarity switching circuit, 24...Amplification circuit, 25, 27, 28...Comparison circuit, 29...
OR gate, 30...controller, 40...signal processing circuit.

Claims (1)

[Claims] 1. A positive polarity ultrasonic signal and a negative polarity ultrasonic signal having opposite polarities to each other are selectively outputted according to a preset sequence or a random sequence, and are outputted into a medium to be measured. ultrasonic signal output means for propagating; and ultrasonic detection for detecting propagation time by changing the polarity of the ultrasonic reception signal propagated in the medium to be measured in accordance with the polarity of the selectively outputted ultrasonic signal. What is claimed is: 1. An ultrasonic pulse transmitting/receiving device comprising: means for averaging propagation times of both polarities detected by the ultrasonic signal detecting means.