JPH0552635A - Ultrasonic type liquid level gauge - Google Patents

Abstract

PURPOSE:To provide an ultrasonic type liquid level gauge capable of measuring a distance without being influenced by sound speed change, of reducing an installation area, and also of securing a measurement range sufficiently. CONSTITUTION:An ultrasonic type liquid level gauge is constituted in such a way that a transmitting ultrasonic element 1 and a receiving ultrasonic element 2 are inserted into one edge inside of a pipe 5, and the other edge is dipped into a liquid level 3. Furthermore, a microscopic reflecting plate 7 is arranged in a part of cross section inside of the pipe 5 away by a constant distance from the ultrasonic elements 1 and 2, and ratio of a reflected wave receiving time at the reflecting plate 7 and a reflected wave receiving time at the liquid level 3 is measured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic type liquid level meter for detecting the position of the liquid level of a liquid contained in a container or the like using reflected waves of ultrasonic waves.

[0002]

2. Description of the Related Art As a conventional ultrasonic type liquid level meter,
There is one as shown in FIG. This is because the transmitting ultrasonic element 1 and the receiving ultrasonic element 2 are arranged in a plane, and the ultrasonic waves emitted from the transmitting ultrasonic element 1 are reflected by the liquid surface 3 and returned to the receiving ultrasonic element. The distance X from the ultrasonic element to the liquid surface is obtained by the following equation: X = CT / 2 (C: sound velocity) by measuring the time T received by the acoustic element 2.

[0003]

Since the speed of sound C changes depending on the density of the medium, it is affected by changes in temperature and atmospheric pressure. Especially, for ambient temperature t, C = 331.5 + 0.60.
It changes like 7t (m / s). Therefore, in order to correct this, it is necessary to provide a temperature detecting means separately. As yet another problem, in the conventional configuration, the radiated ultrasonic waves are diffused, so that the reception level sharply decreases when the measurement distance becomes long, and the measurement becomes impossible. In order to avoid this, the ultrasonic element has to be made large in size, which may cause a case where it cannot be accommodated in a limited mounting area.

The present invention has been made in view of the above circumstances, and provides an ultrasonic liquid level meter capable of measuring a distance that is not affected by changes in sound velocity, reducing the mounting area, and ensuring a sufficient measurement range. The purpose is to provide.

[0005]

In order to solve the above problems, the present invention inserts an ultrasonic element into one end inside a tube,
The other end is soaked in the liquid surface, and a minute reflector is provided in a part of the cross section inside the tube that is separated from the ultrasonic element by a certain distance, and the reception time of the reflected wave at the reflector is The ratio of the reflected wave on the liquid surface to the reception time is measured.

[0006]

According to the present invention, the unknown distance is calculated by measuring the ratio of the reception time of the reflected wave to the known distance and the reception time of the reflected wave to the unknown distance. Does not need to be calculated directly and changes in this will not affect the measurement.

Further, since the ultrasonic element is inserted inside the tube and the ultrasonic wave is transmitted while the liquid level is enclosed in the tube, the ultrasonic wave is less diffused and the reflected wave can be received efficiently. .. As a result, a small ultrasonic element can secure a sufficient measurement range.

[0008]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 is a sectional view showing a first embodiment of the present invention. The transmitting ultrasonic element 1 and the receiving ultrasonic element 2 are inserted inside the ultrasonic element holder 4. Further, the ultrasonic element holder 4 is inserted into one end of the tube 5, and the other end of the tube 6 is immersed in the liquid surface 3. Further, a minute reflector 7 is installed on a part of the cross section inside the tube 5 separated from the ultrasonic elements 1 and 2 by a constant distance d. Further, 6 is a ventilation hole for allowing air inside the tube 5 to flow in and out when the level of the liquid surface 3 changes, and is provided in a part of the tube 5 or a part of the ultrasonic element holder 4.

Now, the ultrasonic wave radiated from the transmitting ultrasonic element 1 is reflected by the reflection plate 7 and reaches the receiving ultrasonic element 2 in time T ₁ , and is radiated from the transmitting ultrasonic element 1. The time required for the reflected ultrasonic waves to be reflected by the liquid surface 3 and reach the receiving ultrasonic element 2 is T ₂ , the distance from the ultrasonic elements 1 and 2 to the liquid surface 3 is X, and the sound velocity is C. Then,
Since there is a relationship of 2d = CT ₁ and 2x = CT ₂ , the distance X to the liquid surface is X = d × (T ₂ / T ₁ ) In the above equation, d is known, so T ₁ and T ₂ X is obtained by measuring the ratio (T ₂ / T ₁ ) with Since the sound velocity C is not included in the equation, even if the sound velocity C changes due to fluctuations in temperature, atmospheric pressure, etc., it does not affect the measurement accuracy.

On the other hand, since the ultrasonic element is inserted inside the tube and the ultrasonic wave is transmitted while the liquid level is confined in the tube, the ultrasonic wave is less diffused and the reflected wave can be received efficiently. .. As a result, a small ultrasonic element can secure a sufficient measurement range.

FIG. 2 is a sectional view showing a second embodiment of the present invention. In this embodiment, directly from the transmitting ultrasonic element 1,
In order to reduce the so-called wraparound wave that enters the receiving ultrasonic element 2, the transmitting ultrasonic element 1 and the receiving ultrasonic element 2 are displaced by a certain distance d ₂ in the ultrasonic wave transmitting direction. It is inserted in the ultrasonic element holder 4.

The distance from the transmitting ultrasonic element 1 to the liquid surface 3 is X, and the distance from the transmitting ultrasonic element 1 to the reflector 7 is d.
_{If it is 1} , 2d ₁ + d ₂ = CT ₁ , 2X + d ₂ = CT
_Since there is a relationship of ₂ , the distance X to the liquid surface is X = (d
In _{1 + d 2/2) (} T 2 / T 1) -d 2 above equation, d _1, from d ₂ are known, the embodiment similarly to T ₁ and the ratio of T ₂ of the (T ₂ / T X can be obtained by measuring ₁ ).

FIG. 3 shows an embodiment of a measuring circuit for measuring (T ₂ / T ₁ ), and FIG. 4 is a diagram for explaining the waveform of each part of the measuring circuit. In FIG. 3, reference numeral 8 denotes a low frequency oscillator, which has a pulse width Δt, as shown in FIG.
It outputs a pulse of period t _c . A high frequency oscillator 9 oscillates at the resonance frequency of the transmitting ultrasonic element 1. 10
Is a NAND gate, which combines the outputs of 8 and 9 and
A modulated signal as shown in (b) is applied to the terminal of the transmitting ultrasonic element 1. Therefore, during Δt, ultrasonic waves are transmitted and this is repeated every t _c seconds. Here, t _c is set to be slightly longer than T ₂ at the time of measuring the longest distance. Reference numeral 11 is an amplifier circuit that amplifies a signal detected by the receiving ultrasonic element 2. Reference numeral 12 is a detection / smoothing circuit, which outputs the positive portion of the envelope of the received waveform. Reference numeral 13 is a differentiating circuit, which differentiates the input waveform and outputs the positive part thereof.
14a is a threshold value setting circuit for obtaining T ₁ .
The rising of the pulse output of the low frequency oscillator 8 is used as a trigger to output a pulse wave having a pulse width t ₁ , a low level of vl, and a high level of vh. 1
4b is a threshold setting circuit for obtaining a T _2, like the threshold setting circuit 14a, the pulse width t _2, low level v1, the high level and outputs a pulse wave of vh.
Reference numerals 15a and 15b are voltage comparators, 16a and 16b are RS flip-flops, 17a and 17b are pulse width / voltage conversion circuits for outputting a voltage proportional to the pulse width, and 18 is a divider.

Next, the measurement operation of (T ₂ / T ₁ ) will be described. The waveform received by the receiving ultrasonic element 2 is amplified by the amplifier circuit 11
When amplified by, a waveform as shown in, for example, FIG. 4C is obtained. Here, the F ₀ part is due to the wraparound wave, the F ₁ part is due to the reflected wave from the reflected wave, and the F ₂ part is due to the reflected wave from the liquid surface, and the time to the F ₁ part is T ₁ , F ₂ is T ₂ . This waveform is as shown in FIG. 4D when passing through the detection / smoothing circuit 12. Further, when passing through the differentiating circuit 13, a differential waveform as shown in FIG. 4E is obtained, and the differential waveforms P ₀ , P ₁ and P ₂ are F ₀ , F ₁ and F ₂ respectively.
Corresponds to the rising part of. Here, when the output of the threshold value setting circuit 14a is set as shown in FIG. 4 (f) and the level of the differential waveform is compared using the voltage comparator 15a, a pulse (reset) as shown in FIG. 4 (g) is obtained. Pulse 1) is obtained. Therefore, when the RS flip-flop 16a is set at the rising edge of the output pulse of the low frequency oscillator 8 and reset by the reset pulse 1, the RS flip-flop 16a
The output of a has a pulse width T _{1 as} shown in FIG.
The pulse has a period of t _c . When this is input to the pulse width / voltage conversion circuit 17a, a voltage proportional to T ₁ is obtained. The pulse width t ₁ of the threshold value setting circuit 14a is
It is set to be longer than the time when P ₀ occurs and shorter than the time when P ₁ occurs. Since the time for which P ₁ occurs varies depending on the temperature, it is only necessary to consider the assumed temperature range and satisfy the above conditions. Further, the low level vl of the threshold setting circuit 14a is set to a value higher than the noise level of the differential waveform and smaller than the peak of the differential waveform, and the high level vh is set to a value sufficiently higher than the peak of the differential waveform. ..

Similarly, a voltage proportional to T ₂ can be obtained as follows. The output of the threshold setting circuit 14b is shown in FIG.
By setting as shown in (i) and comparing this with the level of the differential waveform using the voltage comparator 15b, a pulse (reset pulse 2) as shown in FIG. 4 (j) is obtained. Therefore, when the RS flip-flop 16b is set at the rising edge of the output pulse of the low frequency oscillator 8 and reset by the reset pulse 2, the output of the RS flip-flop 16b is
As shown in (k), the pulse has a pulse width of T ₂ and a period of t _c . When this is input to the pulse width / voltage conversion circuit 17b, a voltage proportional to T ₂ is obtained. The pulse width t ₂ of the threshold value setting circuit 14b is set to be slightly longer than the time when P ₁ is generated. Also low level v
l and the high level vh are the threshold setting circuit 14a.
Set in the same way as.

Here, the measurable range is t ₁ <T ₂
It is a region that satisfies <t _c .

When the voltage proportional to T ₁ and T ₂ obtained as described above is input to the divider 18, (T ₂ / T ₁ )
Is obtained.

FIG. 5A is a sectional view showing a third embodiment of the present invention, and FIG. 5B is a perspective view of a reflector. The ultrasonic element 19 sharing both transmission and reception is inserted inside the ultrasonic element horn 21, and the ultrasonic element horn 21 is inserted at one end of the tube 22, and the other end of the tube 22 is at the liquid level 25. Soaking The ultrasonic element horn 21 enhances the efficiency of transmission and reception, and holds the ultrasonic element 19 at the center of the cross section of the tube 22. In addition, a small reflection plate 2 is formed on a part of the cross section inside the tube 22 separated from the ultrasonic element 19 by a constant distance d.
3 are installed. The shape of the reflection plate 23 is, for example, a ring shape. Further, 24 is the liquid level 2
5 is a ventilation hole for allowing air inside the tube 22 to flow in and out when the level changes, and is provided in a part of the tube 22 or a part of the ultrasonic element horn 21.

Now, the time until the ultrasonic wave radiated from the ultrasonic element 19 is reflected by the reflecting plate 23 and returns is T
₁ , the time until the ultrasonic wave radiated from the ultrasonic element 19 is reflected by the liquid surface 25 and returns, T ₂ , the ultrasonic element 1
If the distance from 9 to the liquid surface 25 is X and the speed of sound is C, then 2
Since there is a relationship of d = CT ₁ and 2x = CT ₂ , the liquid level 25
The distance X to is: X = d × (T ₂ / T ₁ ) In the above equation, d is known, so by measuring the ratio (T ₂ / T ₁ ) of T ₁ and T ₂ , X Is required. Since the sound velocity C is not included in the equation, even if the sound velocity C changes due to fluctuations in temperature, atmospheric pressure, etc., it does not affect the measurement accuracy.

On the other hand, since the ultrasonic element 19 is inserted into the tube 22 and the ultrasonic wave is transmitted while being confined in the tube 22 up to the liquid level 25, the ultrasonic wave is less diffused and the reflected wave is efficiently reflected. Can be received. As a result, a small ultrasonic element can secure a sufficient measurement range. Moreover, since the transmission and reception are shared by one ultrasonic element 19, the mounting area can be reduced.

FIG. 6 is a block diagram showing an embodiment corresponding to FIG. 5 of a measuring circuit for measuring (T ₂ / T ₁ ), and FIG. 7 is a waveform explaining a signal of each part of the measuring circuit of FIG. It is a figure. In FIG. 6, 8 is a low frequency oscillator, and FIG.
As shown in (a), a pulse having a pulse width Δt and a cycle t _c is output. A high frequency oscillator 9 oscillates at the resonance frequency of the ultrasonic element 19. 10 is a NAND gate,
The outputs of 8 and 9 are combined and a modulated signal as shown in FIG. 7B is given to the terminal of the ultrasonic element 19. Therefore, during Δt, ultrasonic waves are transmitted and this is repeated every t _c seconds. Here, t _c is a little more than T ₂ when measuring the longest distance,
Set it to be long. Further, 11 is an ultrasonic element 19
It is an amplifier circuit that amplifies the signal detected by. Reference numeral 12 is a detection / smoothing circuit, which outputs the positive portion of the envelope of the received waveform. Reference numeral 13 is a differentiating circuit, which differentiates the input waveform and outputs the positive part thereof. Reference numeral 14a is a threshold value setting circuit for obtaining T ₁ , which is triggered by the rising edge of the pulse output of the low frequency oscillator 8 and has a pulse width t ₁ and a low (l
It outputs a pulse wave whose ow level is vl and whose high level is vh. 14b is the threshold setting circuit for obtaining a T _2, like the threshold setting circuit 14a, the pulse width t _2, low level v1, the high level is v
The pulse wave of h is output. 15a and 15b are voltage comparators, 16a and 16b are RS flip-flops, 17a,
17b is a pulse width that outputs a voltage proportional to the pulse width /
The voltage conversion circuit, 18 is a divider. Reference numeral 20 denotes an analog switch for switching the ultrasonic element 19 between transmission and reception. When the output of the low-frequency oscillator 8 is at a high level, the terminals 201 and 202 are electrically connected to each other to be in a transmission state and set to a low level. At this time, the terminals 201 and 203 are electrically connected to operate in a receiving state.

Next, the measurement operation of (T ₂ / T ₁ ) will be described. When the waveform received by the ultrasonic element 19 is amplified by the amplifier circuit 11, for example, a waveform as shown in FIG. 7C is obtained.
Where F ₀ is the output due to residual vibration during transmission, and
The part ₁ is the output from the reflected wave from the reflected wave, the part F ₂ is the output from the reflected wave from the liquid surface, and the time to the part F ₁ is T ₁ and the time to the part F ₂ is T ₂ Is. This waveform is as shown in FIG. 7D when passing through the detection / smoothing circuit 12. Further, when passing through the differentiating circuit 13, a differential waveform as shown in FIG. 7E is obtained, and the differential waveforms P ₀ , P ₁ and P ₂ correspond to the rising portions of F ₀ , F ₁ and F ₂ , respectively.
Here, the output of the threshold value setting circuit 14a is set as shown in FIG.
A pulse (reset pulse 1) as shown in FIG. 7 (g) is obtained by comparison using 5a. Therefore, the low frequency oscillator 8
RS flip-flop 16 at the rising edge of the output pulse of
When a is set and reset with reset pulse 1, R
The output of the S flip-flop 16a becomes a pulse having a pulse width T ₁ and a cycle t _c , as shown in FIG. 7 (h). When this is input to the pulse width / voltage conversion circuit 17a, a voltage proportional to T ₁ is obtained. The threshold setting circuit 14
The pulse width t _{1 of a} is longer than the time when P ₀ occurs,
Further, it is set so as to be shorter than the time when P ₁ occurs.
Since the time for which P ₁ occurs varies depending on the temperature, it is only necessary to consider the assumed temperature range and satisfy the above conditions. Further, the low level vl of the threshold value setting circuit 14a is set to a value higher than the noise level of the differential waveform and smaller than the peak of the differential waveform, and the high level vh is set.
Is set to a value sufficiently larger than the peak of the differential waveform.

Similarly, a voltage proportional to T ₂ can be obtained as follows. The output of the threshold value setting circuit 14b is shown in FIG.
When the voltage is set as shown in (i) and the differential waveform level is compared with the voltage comparator 15b, a pulse (reset pulse 2) as shown in FIG. 7 (j) is obtained. Therefore, when the RS flip-flop 16b is set at the rising edge of the output pulse of the low-frequency oscillator 8 and reset by the reset pulse 2, the output of the RS flip-flop 16b is as shown in FIG.
As shown in (k), the pulse has a pulse width of T ₂ and a period of t _c . When this is input to the pulse width / voltage conversion circuit 17b, a voltage proportional to T ₂ is obtained. The pulse width t ₂ of the threshold value setting circuit 14b is set to be slightly longer than the time when P ₁ is generated. Also low level v
l and the high level vh are the threshold setting circuit 14a.
Set in the same way as.

The measurable range is t ₁ <T ₂
It is a region that satisfies <t _c .

When the voltage proportional to T ₁ and T ₂ obtained as described above is input to the divider 18, (T ₂ / T ₁ )
Is obtained.

[0027]

As described above, in the present invention, an ultrasonic element is inserted into one end inside the tube, and a minute reflector is provided on a part of the cross section inside the tube that is separated from the ultrasonic element by a certain distance. Since it is provided and the ratio of the reception time of the reflected wave at the reflecting plate to the reception time of the reflected wave at the liquid surface is measured, accurate measurement can always be performed even if the sound velocity changes. Further, since the ultrasonic element is inserted inside the tube and the ultrasonic wave is transmitted while being confined in the tube up to the liquid surface, the ultrasonic wave is less diffused and the reflected wave can be efficiently received. As a result, a small ultrasonic element can secure a sufficient measurement range.

[Brief description of drawings]

FIG. 1 is a sectional view showing a first embodiment of the present invention.

FIG. 2 is a sectional view showing a second embodiment of the present invention.

FIG. 3 is a block diagram showing an embodiment corresponding to FIGS. 1 and 2 of a measuring circuit according to the present invention.

FIG. 4 is a waveform diagram illustrating signals of various parts of the measurement circuit of FIG.

FIG. 5 is a configuration diagram showing a third embodiment of the present invention.

6 is a block diagram showing an embodiment corresponding to FIG. 5 of the measuring circuit according to the present invention.

FIG. 7 is a waveform diagram illustrating signals of various parts of the measurement circuit of FIG.

FIG. 8 is a diagram illustrating a conventional technique.

[Explanation of symbols]

1 ... Transmission ultrasonic element, 2 ... Reception ultrasonic element, 3, 2
5 ... Liquid level, 4 ... Ultrasonic element holder, 5, 22 ... Tube, 6,
24 ... Vents, 7, 23 ... Reflector, 8 ... Low frequency oscillator,
9 ... High-frequency oscillator, 10 ... NAND gate, 11 ... Amplification circuit, 12 ... Detection / smoothing circuit, 13 ... Differentiation circuit, 14
a, 14b ... Threshold setting circuit, 15a, 15b ... Voltage comparator, 16a, 16b ... RS flip-flop, 17
a, 17b ... Pulse width / voltage conversion circuit, 18 ... Divider, 19 ... Ultrasonic element sharing transmission and reception, 20 ... Analog switch, 21 ... Ultrasonic element horn.

Claims (3)

[Claims] 1. An ultrasonic liquid level meter for detecting a distance to a liquid surface by radiating ultrasonic waves to the liquid surface, receiving a reflected wave of the ultrasonic wave, and measuring a time between the reflected waves. The element is inserted into one end inside the tube, the other end of the tube is immersed in the liquid surface, and a minute reflection plate is provided on a part of the cross section inside the tube at a certain distance from the ultrasonic element. The ratio (T ₂ / T) of the reception time T ₁ of the ultrasonic waves reflected by the reflector and the reception time T _{2 of the} ultrasonic waves reflected by the liquid surface is provided.
_An ultrasonic liquid level meter, which is characterized by detecting the distance to the liquid surface by measuring ₁ ). 2. The ultrasonic liquid level meter according to claim 1, wherein a transmitting ultrasonic element and a receiving ultrasonic element are used as the ultrasonic element. 3. A single ultrasonic element that shares transmission and reception is used as the ultrasonic element.
The ultrasonic type liquid level meter described.