JPS5832668B2 - Ultrasonic measuring device - Google Patents

Description

Detailed Description of the Invention The present invention uses ultrasonic waves that last only for a short time in a stationary or flowing medium, such as an ultrasonic distance measuring device (including an ultrasonic water level gauge) or an ultrasonic current measuring device. The ultrasonic wave is emitted from the transmitter as a transmitted wave, and is received by the receiver as a received wave either directly or through a reflective surface. The present invention relates to an ultrasonic measuring device for calculating the minute velocity of a medium in a direction related to the total length of a passage or along the passage.

The ultrasonic distance measuring device calculates the length related to L based on the relationship L=VXT between the sound velocity v1 in the medium, the elapsed time T, and the total length of the ultrasonic path,
The ultrasonic flow velocity measuring device measures L=(■+υ・cosθ)×T
In other words, the flow velocity υ is calculated based on υ·cos θ=(L/T)−V, and the measurement value of the elapsed time T is used as the basis for calculating the collapse.

The transmitter of this type of device is formed into a flat plate whose resonance frequency is the ultrasonic frequency using a dielectric material such as ceramics, and both sides are covered with a conductive coating. By applying an alternating voltage with one resonant frequency, an oscillatory change is caused in the distance between the two surfaces due to electrostrictive phenomena, which forces the adjacent air to vibrate. Even when a voltage is applied, the amplitude only increases gradually due to the inertia of the dielectric itself and the internal friction of the coating.

Therefore, as shown in Figure 1a, when an alternating voltage with a uniform amplitude is applied throughout the period, the transmitted wave that is generated has an extremely small initial amplitude, as shown in Figure 1A, and therefore the received wave is also similar. The initial amplitude is usually very small.

By the way, in conventional ultrasonic measurement devices, the time from the start point of the transmitted wave to the start point of the received wave is used as the elapsed time T, and the start point of the transmitted wave is determined accurately based on the operation of the transmitted wave generating means. However, due to the above-mentioned circumstances, it is extremely difficult to detect the starting point of the received wave, so there is a problem in that a measurement error of one to two cycles cannot be avoided.

This measurement error can be solved by choosing a large frequency f and wavelength λ=
Even if V/f is reduced, the situation will not be improved at all because in this case, the lζ amplitude will become smaller due to attenuation, making it difficult to detect the starting point.

Due to these circumstances, the frequency f has traditionally been set at 10 to 50.
It is normal to set it to around KHz, but in this case the sound speed V=
340m/s, f=50KHz, wavelength λ=V/
f = 6.8mm, so 1 to 2 times this, or 6
．． A distance measurement error of about 8 to 13.6 mm was unavoidable.

To deal with this, we use a transmitted wave whose amplitude gradually increases from almost 0 and then rapidly decreases, create a delayed signal that is half a cycle behind the received signal based on the received wave, and add this to the received signal. It has been proposed to leave the last peak and cancel out most of the others, detect the point at which the last peak occurs, and actually measure the elapsed time from the last peak of the transmitted wave to the last peak of the received wave.

←Unexamined Japanese Patent Publication No. 52-6556) However, the amplitude of the received wave is
In reality, due to the release of energy due to the inertia of the dielectric itself and the reflected waves passing through other paths than the original one, the wave gradually decreases at the trailing edge compared to the transmitted wave shown in Figure 1, and therefore the received signal When added to the delayed signal, many low waves are generated in place of the last peak in response to the gradual decrease in amplitude, and the phase is shifted by half a cycle compared to when the amplitude gradually increases, so even if the height of the peak is somewhat higher, , it is difficult to accurately measure the elapsed time because there is no significant enough difference to clearly detect the point at which the amplitude begins to decrease.

For this reason, for example, in an open channel flow meter, a level meter that measures the distance to the liquid surface by arranging a transmitter and a receiver whose object is the liquid surface above the liquid level is used. Conventional ultrasonic distance measuring devices have too large an error to be practical when used for objects with a small range of 20,071 m or less, and ultrasonic flowmeters with a small total length of ultrasonic path also cannot be used. There was a problem in that it was not practical for the same reason.

This invention uses ultrasonic waves of the same frequency as conventional ones,
Moreover, the present invention aims to realize an ultrasonic measuring device that solves the above-mentioned problems by minimizing measurement errors.

As will be described later in connection with the embodiments, the present invention uses a transmitting wave whose amplitude decreases relatively rapidly from its maximum value over the course of its duration in the ultrasonic measuring device described above, and which reduces the amplitude of the received wave. It creates an output that follows this, and an output that follows only when it increases and remains unchanged when it decreases, and when the former becomes smaller than the latter, it detects the fact that the amplitude of the received wave has decreased, and at that moment outputs a timing signal. This ultrasonic measuring device is characterized in that it includes a means for detecting a reduction in the amplitude of the received wave to be emitted, and calculates the elapsed time based on the time from the reduction in the amplitude of the transmitted wave to the time signal.

In this type of device, the amplitude of the received wave is generally smaller than the amplitude of the transmitted wave due to attenuation, but the magnitude relationship between the amplitudes of each wave during the duration is similar.

As described above, the present invention uses a transmitted wave whose amplitude decreases relatively rapidly from the maximum value over the course of its duration, so the amplitude of the received wave also changes in the same process, causing a rapid decrease in amplitude. The resulting waves correspond to each other.

The timing of the amplitude reduction of the transmitted wave can be determined by the timing of the reduction in the amplitude of the driving voltage that drives the transmitter to generate the transmitted wave, and the timing of the reduction of the amplitude of the received wave can be determined by the timing of the reduction of the amplitude of the driving voltage that drives the transmitter to generate the transmitted wave. This can be accurately known by using a received wave amplitude reduction detection means that detects the fact that the voltage amplitude is reduced and issues a timing signal at that moment.

Also, there are phase differences between the driving voltage and the transmitted wave, and between the received wave and the received voltage, but these are constant values, so
By correcting this, it is possible to accurately know the elapsed time T from when the transmitted wave is emitted until receiving the received wave, and by correcting the sound speed V in relation to the temperature of the medium, the entire length of the ultrasonic path can be determined. The relevant lengths and flow velocities υ can be calculated accurately.

In the embodiment shown in the block diagram in Fig. 2, a transmitter/receiver that serves as a transmitter and a receiver is provided downward at a fixed position above the liquid level of the open channel flowmeter, and the distance to the liquid level is 2. This is an ultrasonic level meter that measures the liquid level by taking the total length of the ultrasonic path as the length of the ultrasonic wave path, and generates a transmitted wave as follows.

First, the oscillation circuit 1 creates a square wave of 100 KHz, the frequency divider circuit 2 creates a square wave of 50 KHz and lower frequencies, and the synchronous differentiator circuit 3 creates a square wave of 100 KHz as shown in Figure 2g.
2- ” 2K Hz % Square wave with a period of 40.96 m5 and a period of 40.96 m5 as shown in Fig. 2 ζ 0.3
Produces a negative logic pulse lasting Zms.

During the 0.32 ms period of this pulse, the transmission lamp oscillation circuit 4 generates a sawtooth wave whose amplitude gradually increases and decreases as shown in FIG.
As shown in FIG. 2g, 16 transmission pulses of 50 KHz are generated, and the switching modulation circuit 6 generates 16 modulation pulses whose amplitude gradually increases and rapidly changes as shown in FIG.

In response to this, the driver circuit γ generates an oscillating current as shown in the lower part of Figure 2, which is amplified by the power amplifier circuit 8 to create a drive current as shown in Figure 2g.
The 0 KHz transmitter/receiver 9 is driven to generate a transmission wave as shown in the second diagram.

The transmitted wave travels through the air, which is a medium, is reflected from the liquid surface, travels in the opposite direction through the air, and when it reaches the transmitter/receiver 9 as a received wave, the amplitude changes as shown in the lower part of Figure 2. The change trend is similar to that of the transmitted wave, but due to attenuation, the amplitude generally decreases in inverse proportion to the total length of the ultrasound path.

Transmitter/receiver 9 receives the received wave, generates a corresponding received voltage, and transmits it to preamplifier circuit 10 .

In the front-stage amplifier circuit 10, as shown in FIG. 3, a common-emitter transistor (Tr) is used for first-stage amplification in a region where the collector current gradually increases as the voltage between the base and emitter increases, and a gain adjustment circuit is used at the base. A bias is applied by the circuit 11, and this bias is normally 0.6 V, and due to the fall of the square wave output shown in FIG. The circuit is started and gradually increases over time in a predetermined manner, as shown in diagram j at the bottom of Figure 2, so that the range of change in the total length of the ultrasonic path and therefore the entire measurement distance range is At least near the maximum amplitude of the received wave, the number of transistors is set to one within a certain range of the active region, thereby keeping the level of the output of the front stage amplifier circuit 10 almost constant.

The output of the front stage amplifier circuit 10 is amplified by the rear stage amplifier circuit 12,
Furthermore, it is rectified by a half-wave rectifier circuit 13 to produce a positive logic half-wave with a maximum amplitude of about 10V, as shown in FIG. 2k.

Based on the output of the intermediate amplification stage of the subsequent amplification circuit 12, the peak amplitude of each half-wave output from the half-wave rectification circuit 13 is determined through the tuned amplification circuit 14, the pulse generation circuit 15, and the amplitude sampling pulse formation circuit 16. At each instant of value, as shown in Fig. 2,
Create a sampling pulse with a length of 1 μs.

The amplitude sample value holding circuit 11 simultaneously receives the sampling pulse from the amplitude sampling pulse forming circuit 16 and the half wave from the half wave rectifier circuit 13, and stores one of the sampling pulses and its time as shown in FIG. 2m. The output of the half-wave rectifier circuit 13?・The corresponding output is held until the next sampling pulse.

The peak value holding circuit 18 follows the output of the amplitude sample value holding circuit 1γ only when its output increases while maintaining a small value within a range less than the illustrated value S, which is the reduction amount at the time of the first reduction. When the output increases, the output does not change when the output decreases, and the maximum output is maintained as shown in FIG. 2n.

The comparison circuit 19 compares the output m of the amplitude sample value holding circuit 1γ and the output n of the peak value holding circuit 18, and issues a timing signal at the moment the former becomes smaller than the latter.

The time measurement sampling pulse forming circuit 20 generates a time measurement sampling pulse having a length of 2 to 3 μs along with the time measurement signal of the comparison circuit 1a.

With a delay of 2 ms from the fall of the square wave output of the synchronous differentiator 3 shown in FIG. 2a, the output of the reset signal forming circuit 21 becomes low potential.

As a result, the amplitude sample value holding circuit 11 and the peak value holding circuit 18 become operational.

At this time, the reset input terminal R of the flip-flop 22 becomes a low potential, but the output does not change.
When the threshold value detection circuit 23 outputs an output, the set input terminal S of the flip-flop 22 becomes a high potential, and as a result, one output terminal Q becomes a low voltage, and the amplitude sample value holding circuit 1γ starts operating. Then, the peak value holding circuit 18 also starts producing an output.

(See Figure 2 m, n) At the same time one output terminal Q becomes a low voltage, the other output terminal Q becomes a high potential, and from that,
From the start of the output of the amplitude sample value holding four-way 11 in FIG.
After a delay of 0.4 ms, which is a time that slightly exceeds the time until the time signal from the comparator circuit 19, the bias applied to the base of the transistor of the preamplifier circuit 10 returns to 0.6V by the output of the gain adjustment circuit 11.

When the bias is around 0.6V, the output to the half-wave rectifier circuit 13 is corrected even by noise that is not a normal received wave, but as long as it does not exceed 2V, the output is corrected by the amplitude sample value holding circuit 1γ and the peak value holding circuit 18. Since the output is not corrected, there is no risk of being affected by noise.

In addition, the bias is returned to 0.6 V after a while after the time signal from the comparison circuit 19 is received, and the amplitude sample value holding circuit 11 is inactivated via the threshold detection circuit 23 and the flip-flop 22, so that, for example, short measurements can be performed. In the case of distance, etc., the first received wave is opposed again near the transmitting/receiving element 9 and is directed towards the liquid surface.
Even if the second reflected wave from the liquid surface reaches the transmitting/receiving element 9 again, the preceding stage amplifier circuit 10 and subsequent stages do not operate.

In other words, malfunctions due to second and subsequent reflected waves are prevented.

The reference voltage generated by the reference voltage circuit 24 is input to the timekeeping lamp oscillation circuit 25, and the falling edge of the square wave output of the synchronous differentiator circuit 3 shown in FIG. It produces an output that increases linearly over time from 0.6V.

This output reaches its maximum value before the rise of the square wave output of the synchronous differentiator circuit 3 shown in FIG.
Return to 6V.

The maximum value of the elapsed time T and therefore the maximum value of the measured distance is determined by the time from the fall of this square wave until it reaches the maximum value.

The timekeeping sample value holding circuit 26 repeatedly detects the output of the timekeeping lamp oscillation circuit 25 for each sampling pulse of the timekeeping sampling pulse forming circuit 20, smoothes it, and constantly displays the latest value. Remember.

Based on this stored value, the temperature correction circuit 29 performs temperature correction based on the output of the temperature sensor 28, and the required zero point correction is performed using the zero point correction device 2γ. Based on the measured value of the distance to the liquid level, the subtraction circuit 30 converts it to a water level that is directly related to the flow rate, and the span adjustment circuit 31 adjusts the measurement range according to the purpose of use.
A V-I conversion circuit 32 converts the measured value into a related current value and transmits it to a remote receiving device.

Although the embodiment shown in FIG. 2 is related to the liquid level needle, the gain adjustment circuit 11 is omitted and the embodiment can also be used to measure the elapsed time T of an ultrasonic flowmeter.

According to the present invention, in an ultrasonic measuring device, the measurement accuracy of a target physical quantity can be improved through the improvement of the measurement accuracy of elapsed time, and therefore it is extremely useful industrially.

[Brief explanation of drawings]

Figures 1a and 1b are diagrams showing the waveforms of transmitted waves and received waves of a conventional ultrasonic measurement device, Figure 2 is a block diagram of an embodiment of the present invention, and Figures 2a-p are , is a diagram showing the output of the main parts of the embodiment of FIG. 2; FIG. 3 is a circuit diagram of the pre-stage amplifier circuit 10. 9... Transmitter, receiver (received wave amplitude reduction detection means), 10... Pre-stage amplifier circuit (amplifier circuit) (received wave amplitude reduction detection means), 12...・Late stage amplifier circuit (amplifier circuit) (received wave amplitude reduction detection means), 13...
...Half-wave rectifier circuit (received wave amplitude reduction detection means), 1
6... Amplitude sampling pulse forming circuit (received wave amplitude reduction detection means), 11... Amplitude sample value holding circuit (received wave amplitude reduction detection means), 18... Peak value holding circuit (received wave amplitude reduction detection means), 19...
...Comparison circuit (received wave amplitude reduction detection means), 11...
...gain adjustment circuit (received wave amplitude reduction detection means), Tr
...Transistor (received wave amplitude reduction detection means)
.

Claims (1)

[Claims] 1 Ultrasonic waves that last only for a short time are emitted from a transmitter as a transmission wave in a stationary or flowing medium, are received by a receiver as a reception wave either directly or via a reflecting surface, and are transmitted. An ultrasonic diversion measuring device that calculates the length related to the total length of the ultrasonic path or the minute velocity of the medium in the direction along the path based on the elapsed time from the time the wave is emitted to the time the received wave is received. In this method, we use a transmitting wave whose amplitude decreases relatively rapidly from its maximum value over the course of its duration, and we have an output that follows the amplitude of the received wave, and an output that follows only when it increases and remains unchanged when it decreases. When the former becomes smaller than the latter, a received wave amplitude reduction detection means is provided which detects the fact that the amplitude of the received wave is reduced and issues a timing signal at that moment, and measures time from the reduction in the amplitude of the transmitted wave. The elapsed time is calculated based on the time until the signal.
Ultrasonic measurement device. 2. In the ultrasonic measuring device according to claim 1, the received wave amplitude reduction detection means includes a receiver that converts the received wave into an electrical signal, an amplification circuit that amplifies the electrical signal of the receiver, and an amplification device. A half-wave rectifier circuit that produces an output that corresponds only to each half-wave of one polarity of the output of the circuit, and an amplitude sampling circuit that emits an instantaneous pulse in accordance with the maximum amplitude of each half-wave of the output of the half-wave rectifier circuit. Pulse forming circuit, amplitude sampling Amplitude sampling value holding circuit that holds the output corresponding to one pulse of the pulse forming circuit and the output of the half-wave rectifier circuit at that time until the next pulse, only when the output of the amplitude sampling value holding circuit increases A peak value holding circuit that holds the output at a small value within a range less than the amount of reduction at the time of the first reduction, increases by following the output, and holds the output unchanged when decreasing; and: Output of the amplitude sample value holding circuit. 1. An ultrasonic measurement device characterized by comprising a comparison circuit that compares the output of the peak value holding circuit with the output of the peak value holding circuit and emits a timing signal at the moment the former becomes smaller than the latter. 3. The ultrasonic measuring device according to claim 2, in which a transmitter emits a transmission wave toward an object, and a receiver receives the reflected wave from the object as a reception wave. In an ultrasonic distance measuring device that calculates the distance from a transmitter or receiver to an object based on the elapsed time from the time the wave is emitted to the time the received wave is received, an amplification device that amplifies the output of the receiver. For the first stage of amplification in the circuit, a transistor is used with its emitter connected to ground in the region where the collector current gradually increases as the voltage between the base and emitter increases.
A gain adjustment circuit is provided at the base of this transistor to apply a bias that gradually increases as time passes after the transmitted wave. An ultrasonic distance measuring device characterized by being able to measure distances within a range of .