JPH08136320A - Ultrasonic level meter - Google Patents

Abstract

PURPOSE: To easily and stably detect the presence or absence of a liquid by excluding the received waves of ultrasonic waves propagated at the outer periphery of a bath wall from a measurement target according to the quality and shape of the liquid bath. CONSTITUTION: Sensor heads 2a and 2b for transmitting and receiving ultrasonic waves are fitted to the outer surface of the bath wall of a liquid bath 1. The output of the received signal of the sensor heads 2a and 2b is binary-coded in reference to a specific threshold by a comparison circuit 7. A counting circuit 8 measures the signal reception start time and the life time of both binary-coded signals when there is and is not a liquid (a) in advance. An operation processing circuit 6 sets a measurement period so that unneeded reception waves (those received after being propagated at the outer periphery of the bath wall of the liquid bath 1) which appear when there is not liquid (a) in the liquid bath 1 based on both binary-coded signals.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an ultrasonic level meter,
More specifically, the present invention relates to an ultrasonic level meter that detects the presence or absence of a liquid contained in a liquid tank such as a tank or the position of the liquid surface by using ultrasonic waves.

[0002]

2. Description of the Related Art For example, by utilizing ultrasonic waves,
As a means for detecting the presence or absence of a liquid contained in a liquid tank such as a tank (hereinafter, simply referred to as “liquid tank”), a sensor head of an ultrasonic level meter is installed on the side surface of the liquid tank, and The ultrasonic wave is transmitted from the sensor head toward the liquid in the liquid tank, and the reflected wave reflected by the ultrasonic wave hitting the inner wall of the facing liquid tank is received by the sensor head, and the liquid wave is received from the received signal of the reflected wave. There has been proposed a method for determining the presence or absence of liquid in the inside.

[0003]

However, the above-described ultrasonic level meter has the following problems.
The improvement was demanded.

That is, since the ultrasonic waves used in this kind of ultrasonic level meter do not propagate in the air, when there is no liquid in the liquid tank, the reflected waves of the ultrasonic waves transmitted from the sensor head are received. Although it should not occur, the sensor head may receive ultrasonic waves even if there is no liquid, depending on the shape and material of the liquid tank.

For example, taking the case where the liquid tank is a cylindrical tank made of metal, the ultrasonic waves transmitted from the sensor head propagate along the outer circumference of the tank wall of the liquid tank, This is the case when the ultrasonic waves propagated along the outer circumference are received as if there were reflected waves immediately after the ultrasonic waves were transmitted (see the waveform indicated by B ₁ in FIG. 2A). The waveform of the ultrasonic waves propagating around the outer circumference of the liquid tank varies slightly depending on factors such as the material and shape of the liquid tank.However, even if the material is made of resin, the transmitted ultrasonic waves are solid. Since it propagates through the inside, this type of received wave is received at a relatively early point after the ultrasonic wave is transmitted.

Therefore, under such a condition, if an attempt is made to determine the presence or absence of liquid based on the wave received by the sensor head, the undesired reception propagated along the outer circumference of the tank wall of the liquid tank described above. Since the entire period including waves is monitored and the presence or absence of liquid is determined at a constant detection level, the difference between the received waveforms detected by the sensor head when there is no liquid and when there is is small. Even if an attempt is made to detect the presence or absence of liquid by means of such a method, the difference between the two cannot be fully recognized.

Therefore, the ultrasonic level meter as described above has a problem in that the presence or absence of a liquid cannot be stably detected, and the reliability of the measurement result is significantly reduced.

Therefore, the present invention has been proposed in view of the problems associated with the propagation characteristics of such ultrasonic waves, and its object is to set the outer circumference of the tank wall depending on the material and shape of the tank. An object of the present invention is to provide an ultrasonic level meter that can eliminate the propagating ultrasonic wave received from the measurement target and facilitate stable realization of the presence or absence of a liquid.

By applying the present invention, it is also possible to provide an ultrasonic level meter, which has not been provided so far, for detecting the kind of different kinds of liquid mixed in the liquid tank or the position of the interface.

[0010]

As a technical means for achieving the above object, according to the present invention, a sensor head for transmitting and receiving ultrasonic waves is mounted on the outer surface of a liquid tank wall toward the inside of the liquid tank. An ultrasonic level meter for determining the presence or absence of liquid in a liquid tank by receiving a reflected wave from the tank wall on the opposite side of the ultrasonic wave with the sensor head, and a received wave output of the sensor head is set to a predetermined level. A comparison circuit that binarizes with a threshold value, a counting circuit that measures the reception start time of the binarized signal and its duration in advance with and without liquid in the liquid tank, and the liquid And a calculation processing circuit for setting the measurement period by determining the measurement start time and the measurement end time based on the reception start time and the duration of each of the binary signals when there is no The processing circuit allows the measurement It characterized by determining the presence or absence of the liquid by measuring only during the time and the measurement period comprising a measurement end time.

Then, the arithmetic processing circuit determines the presence or absence of the liquid by the binarized signal output from the counting circuit until the duration time has elapsed from the reception start time of the binarized signal when there is no liquid. The measurement period is set so as not to perform the measurement.

Further, the above-mentioned sensor heads are at least two or more sensor heads which are mounted on the outer surface of the tank wall at predetermined intervals in the vertical direction toward the inside of the liquid tank. It is also possible to determine the liquid surface position from the presence or absence of the liquid detected only during the measurement period consisting of the measurement start time and the measurement end time by the arithmetic processing circuit based on the received wave output.

As an application of the present invention, a sensor head for transmitting and receiving ultrasonic waves is mounted on the outer surface of the tank wall of the liquid tank toward the inside of the liquid tank, and the reflected wave from the tank wall on the opposite side of the ultrasonic waves is applied. An ultrasonic level meter that detects the type of different liquids mixed in a liquid tank or the position of the interface by receiving the sensor head, and binarizes the received wave output of the sensor head with a predetermined threshold value. And a counting circuit for measuring the reception start time of the binarized signal and its duration at the time of the first liquid and the time of the second liquid in the liquid tank, respectively. An arithmetic processing circuit that determines the measurement start time and the measurement end time and sets the measurement period based on the reception start time and the duration of either the first liquid time or the second liquid time. And with this arithmetic processing circuit, It is also possible to determine the position of the type or interface of the liquid by measuring only during the measurement start time and measurement period consisting of the measurement end time.

[0014]

The ultrasonic level meter according to the present invention receives the binarized signal obtained by binarizing the received wave output of the sensor head with a predetermined threshold value when there is no liquid in the liquid tank. The presence / absence of liquid is determined only during the measurement period set based on the start time and its duration and the reception start time and the duration of the reception of the binarized signal obtained in the same way as above when liquid is present. Therefore, it is possible to exclude the undesired received wave without monitoring the whole period of the received wave of the sensor head, the difference in the received waveform between when there is no liquid and when there is a liquid becomes large, and stable detection is possible. realizable.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of an ultrasonic level meter according to the present invention will be described with reference to FIGS.

The ultrasonic level meter of the present invention is a level meter for measuring the presence or absence of the liquid a contained in the liquid tank 1 and the level of the liquid a. As shown in FIG. Sensor heads 2a, 2b fixed to the outer surface of the tank wall
And drive circuits 3a and 3b for driving the sensor heads 2a and 2b, an oscillator circuit 4 for generating ultrasonic waves of a predetermined frequency, and internal processing of reflected waves of ultrasonic waves received by the sensor heads 2a and 2b. The receiving circuit 5 and an arithmetic processing circuit (CP which controls the oscillation circuit 4 and the receiving circuit 5).
U) 6, a comparator circuit 7 that binarizes the ultrasonic wave received wave signal output from the receiver circuit 5 with a predetermined threshold value, and the binarized signal output from the comparator circuit 7 is measured. The counting circuit 8 and the main part are constituted.

Here, the ultrasonic level meter of the present invention is suitably used for measuring the presence or absence of the liquid a in a tank (liquid tank 1) made of metal or resin, and these liquid tanks 1 are also used. As the liquid a contained in the liquid, water, oil or the like is generally considered, but the liquid a is not limited to these and is also used for measuring the presence or absence of liquid in various liquids and the liquid level.

Further, the arithmetic processing circuit 6 includes an input / output circuit 9 and an interface for transmitting / receiving signals to / from various switch groups and indicators provided on the operation panel of the ultrasonic level meter and peripheral devices. A circuit 10 is provided.

The sensor heads 2a and 2b are both ultrasonic transducers that transmit and receive ultrasonic waves, as described above.
In this embodiment, two ultrasonic transducers of the sensor heads 2a and 2b are used. These two sensor heads 2
The a and 2b are attached to the outer surface of the tank wall of the liquid tank 1 at predetermined intervals in the vertical direction. And this sensor head 2
a and 2b transmit ultrasonic waves in a substantially horizontal direction toward the inside of the liquid tank 1, and the transmitted ultrasonic waves receive a reflected wave reflected by the inner surface of the tank wall facing the liquid tank 1. It is configured.

More specifically, this sensor head 2a,
2b is installed almost vertically on the outer surface of the tank wall of the liquid tank 1, and ultrasonic waves transmitted from the sensor heads 2a and 2b are transferred to the inside of the liquid tank 1 through the tank wall to which the sensor heads 2a and 2b are attached. While propagating to the liquid a, it is reflected by the inner surface of the tank wall of the liquid tank 1 facing the mounting positions of the sensor heads 2a and 2b, and the reflected wave is again reflected by the sensor heads 2a and 2b.
Is configured to be received by.

The oscillation circuit 4 generates a predetermined frequency and is switched by an intermittent pulse to generate a burst signal. In addition, the drive circuits 3a, 3
Reference numeral b is for power-amplifying the burst signal output from the oscillation circuit 4 and supplying it to the sensor heads 2a and 2b. The sensor heads 2a and 2b are driven by the drive circuits 3a and 3b.

The receiving circuit 5 includes the sensor head 2
Predetermined internal processing is performed on the reflected waves of the ultrasonic waves received at a and 2b, and a received wave signal is output. The comparison circuit 7 is
The received wave signal output from the receiving circuit 5 is compared with a preset reference voltage (threshold value) to generate a binarized signal. As a result, the received wave signal such as noise that does not reach the reference voltage is eliminated at the stage of the comparison circuit 7.

Further, the counting circuit 8 determines the reception start time of the binarized signal output from the comparison circuit 7 and its duration as previously described when there is no liquid a in the liquid tank 1 as described later. Measure each time separately. That is, here, the reception start time and the duration of the binary signal, which serves as a reference when the liquid a is not present in the liquid tank 1 and when the liquid a is present, are measured.

The arithmetic processing circuit 6 receives the binarized signal when the liquid a is not present and the reception start time and the duration thereof,
The measurement start time and the measurement end time are determined based on the reception start time and the duration of the binary signal when the liquid a is present, and the measurement period is set, and the measurement start time and the measurement end time are used. The presence or absence of the liquid a is determined by performing the measurement only during the measurement period.

The procedure for determining the presence / absence of the liquid a by the ultrasonic level meter having such a configuration will be described in detail below. When the presence / absence of the liquid a is actually detected, as will be described later, the liquid is previously prepared. The presence or absence of the liquid a is detected after the measurement period is set based on the reception start time and the duration of the reception of the binarized signal with and without a.

2A and 2B show burst signal A, received waves B ₁ and B ₂ , and other signal waveforms based on the two sensor heads 2a and 2b located above and below, respectively. The first burst signal A and the received waves B ₁ and B ₂ are due to one sensor head 2a, and the second one is due to the other sensor head 2b. For example, it is set based on the _first received waves B ₁ and B ₂ .

A: How to Determine Presence / Absence of Liquid a First, based on a command from the arithmetic processing circuit 6, the oscillation circuit 4
By outputting the burst signal A generated in 1. to the drive circuits 3a and 3b and driving the drive circuits 3a and 3b while switching them alternately, the sensor heads 2a and 2b can be prevented from interfering with each other. , 2b
To transmit an ultrasonic wave toward the inner surface of the tank wall facing the liquid tank 1. The sensor heads 2a and 2b receive the reflected waves of the ultrasonic waves reflected on the inner surface of the opposing tank wall, and output the received waves B ₁ and B ₂ from the sensor heads 2a and 2b to the receiving circuit 5.

At this time, if the liquid a does not exist in the liquid tank 1, ideally, the ultrasonic waves transmitted from the sensor heads 2a and 2b cannot propagate in the air in the liquid tank 1 and therefore the received wave. However, depending on the shape and material of the liquid tank 1, ultrasonic waves may propagate along the outer circumference of the tank wall of the liquid tank 1 and a received wave may appear. An example of a received wave that appears when the liquid a is not present is shown in FIG. 2 (a) as a waveform B ₁ .

Then, the received wave B ₁ is subjected to the above-mentioned internal processing (amplification / rectification, etc.) in the receiving circuit 5 to generate a received wave signal C ₁ . The reception wave signal C ₁ output from the reception circuit 5 is input to the comparison circuit 7, where the reception wave signal C ₁ is binarized with a predetermined threshold value D and binarized as an output. The signal E ₁ is generated.

On the other hand, when the liquid a is present in the liquid tank 1, the ultrasonic waves transmitted from the sensor heads 2a and 2b propagate in the liquid a in the liquid tank 1 and are reflected by the inner peripheral surfaces of the opposing tank walls. , Reflected waves are received by the sensor heads 2a and 2b. An example of this reflected wave is shown as waveform B ₂ in FIG. 2 (b).

Such received wave B ₂ is subjected to the same internal processing as that in the above-mentioned case in the receiving circuit 5, and the received wave signal C ₂
Becomes Then, the reception wave signal C ₂ output from the reception circuit 5 is input to the comparison circuit 7 and binarized with a predetermined threshold value D to generate a binarized signal E ₂ .

The two binarized signals E ₁ and E ₂ thus obtained are output from the comparator circuit 7 to the counter circuit 8, and in the counter circuit 8, the two binarized signals E ₁ and E ₂ are output. ₁ , E
₂ reception start times T ₁ and T ₂ and their durations t ₁ and t ₂
Are measured when the liquid a is not present in the liquid tank 1 and when it is present.

Next, in the arithmetic processing circuit 6, the reception start time T ₁ of the binarized signal E ₁ when the liquid a is not present and its duration t ₁ and the binarized signal E when the liquid a is present. _{Based on} the reception start time T _{2 of 2} and its duration t ₂ .
The measurement start time Tm and the measurement end time Tm 'are determined, and the measurement period m is set.

This measurement period m is, as shown in FIG. 2 (a), an unnecessary reception wave (duration of the binarized signal E ₁ shown in FIG. 2 (a), which is seen in the reception wave when there is no liquid a. Since the calculation processing circuit 6 is set in accordance with the reception state of the unnecessary reception wave so as to exclude t ₁ ), the reception waves B ₁ and B ₂ (reception wave) when there is no liquid a The difference between the received waveforms of the signals C ₁ and C ₂ ) becomes large, and the presence or absence of the liquid a is clearly discriminated.

Specifically, the above two binarized signals E ₁ and E
₂ reception start times T ₁ and T ₂ and their durations t ₁ and t ₂
The measurement period m based on is set in the following manner.

A: Procedure for setting measurement period m As a procedure for setting the measurement period m, the method shown in FIG. 3 (a) or (b) is adopted.

Firstly, the method shown in FIG. 3 (a), after measuring the reception start time T ₁ and the duration t ₁ thereof binarized signal E ₁ when there is no liquid a at pre mentioned above procedures, they value stored and held in the counter circuit 8, thereon, when measuring the binary signal reception start time T ₂ and its duration t ₂ of the E ₂ when there is liquid a, stored and held in the above This is a method in which the portion corresponding to the above-mentioned reception start time T ₁ and duration t ₁ is not counted, but counting is started at the time when the duration t ₁ has elapsed from the reception start time T ₁ .

In this method, this counting start point becomes the measurement start time Tm, and the duration t of the binarized signal E ₂ is
_The time when ₂ has elapsed becomes the measurement end time Tm ′, which is set by the arithmetic processing circuit 6 as the measurement period m.

Another method different from the above is shown in FIG.
As shown in, after first measuring the binarized reception start time T ₁ and its duration t ₁ of the signal E ₁ in the absence of liquid a, stores and holds those values, Similarly, liquid a two reception start time value signal E ₂ T ₂ and its duration t when there is
After measuring ₂ , the two values are stored and held in the counting circuit 8.

Further, the binarized signal E when the liquid a is present
_{The difference} between the reception start time T _{2 of 2} and its duration t ₂ and the reception start time T ₁ of the binarized signal E ₁ when there is no liquid a and its duration t ₁ is calculated and measured from this value. Start time Tm
The measurement end time Tm 'is determined, and the arithmetic processing circuit 6 sets the measurement period m.

In this way, a measurement period m shorter than the entire period of the received wave is preset based on the received wave when the liquid a is absent and when the liquid a is present, and then the measurement is performed as shown in FIG. The actual presence / absence determination of the liquid a is executed using only the period m as a window. That is, if there is no count output from the counting circuit 8 within the measurement period m, it is determined that there is no liquid a in the liquid tank 1, and if there is a count output from the counting circuit 8,
It is determined that the liquid a exists.

With this configuration, as described above, the difference between the received waveforms when the liquid a is absent and when the liquid a is present becomes remarkable (the binarized signals are "ON" and "OFF"), and therefore stable. In addition to the determination result obtained, the arithmetic processing circuit 6 can automatically set the measurement period.

Further, in this embodiment, since the two sensor heads 2a and 2b are provided above and below the outer wall surface of the liquid tank 1, the liquid level is at the upper limit position by the sensor head 2a located above. It is possible to determine whether or not the liquid level is at the lower limit position by the sensor head 2b located below, and further it is determined that the liquid a does not exist by the sensor head 2a located above, and When it is determined that the liquid a is present by the sensor head 2b located at, the liquid level is between the upper limit position and the lower limit position,
That is, the level of the liquid surface position can also be detected.

In the above embodiment, the case where the two sensor heads 2a and 2b are provided on the outer surface of the tank wall has been described, but the present invention is not limited to this, and at least one sensor head may be used. Also, three or more sensor heads can be used if the switching timing can be set appropriately.

Further, as an application technique of the present invention, according to the ultrasonic level meter of the present invention, as shown in FIG.
It is also possible to perform liquid discrimination when two or more kinds of different liquids (for example, water a and oil b) that form an interface are contained. Also, with this applied technique, it is possible to detect the interface position between the liquids a and b as in the above-described embodiment.

That is, this application example uses the fact that the propagation speed of ultrasonic waves is different between water a and oil b. If ultrasonic waves are simultaneously transmitted to water a and oil b, the reflected waves will be received. It utilizes the fact that there is a time lag in the time taken (see FIGS. 6 (a) and 6 (b)).

More specifically, also in this application example, a device configuration similar to that of the above-described embodiment is used, and instead of the presence and absence of water in the above-mentioned embodiment, the binarized signal in each of different liquids is used. The reception start time and its duration are measured, and the measurement start time and measurement end time are determined based on the reception start time and its duration of one of them, and the measurement period is set. The type of liquid is determined based on the measurement result during the measurement period.

Therefore, when the measurement period m ₁ of the water a is set as the window (see FIG. 6 (c)), if the count output is present for the entire period or for a certain period or longer, the liquid is water a. It can be determined that there is (Figure 6 (d)
On the contrary, if the count output does not reach the certain period, it can be determined that the oil is b (FIG. 6).
(e).)

That is, in this case, the total period m ₂ in which the ultrasonic wave transmitted to the oil b in the liquid tank 1 is received as a reflected wave is not counted, and in that case, it is the oil b. The judgment is made.

In this example, one sensor head 2 is provided, but if two sensor heads are provided as in the above embodiment (see FIG. 1), the presence or absence of liquid and its type Not only that, but also the interface of different liquids can be identified. In other words, the water a
When it is determined that the oil b exists and the oil b exists by the other sensor head, the interface between the water a and the oil b exists between the mounting positions of the two sensor heads. Can be determined.

[0051]

According to the present invention, when there is no liquid in the liquid tank,
The reception start time of the binarized signal obtained by binarizing the received wave output of the sensor head with a predetermined threshold value and its duration, and the reception start time of the binarized signal when liquid is present and Since the presence / absence of the liquid is determined only during the measurement period set based on the duration, it is possible to exclude the undesired received wave without monitoring the entire period of the received wave of the sensor head. Therefore, during the measurement period, there is a large difference between the received waveforms of the sensor head when there is no liquid and when there is liquid, so stable detection can be realized when binarized, and a highly reliable ultrasonic level meter is provided. It becomes possible to do.

Further, the setting of the above measurement period is automatically set appropriately by the arithmetic processing circuit according to the situation such as the type (material, shape, etc.) of the liquid tank, so that the liquid level detection according to the measurement situation can be performed. It will be possible.

Furthermore, according to the present invention, in addition to the presence or absence of the above liquid, it is possible to measure the type and interface position of liquid in different liquids stored in the same liquid tank.

[Brief description of drawings]

FIG. 1 is a circuit configuration block diagram showing an embodiment of an ultrasonic level meter according to the present invention.

FIG. 2 (a) is a characteristic diagram showing a received wave of ultrasonic waves and other signal waveforms when there is no liquid, and FIG.
FIG. 6 is a characteristic diagram showing a received wave of ultrasonic waves and other signal waveforms when a liquid is present.

3 (a) and 3 (b) are flowcharts showing two examples of how to set a measurement period in the arithmetic processing circuit of FIG.

FIG. 4 is a flowchart showing a procedure for determining the presence / absence of a liquid based on a measurement period in the arithmetic processing circuit of FIG.

FIG. 5 is a cross-sectional view showing a liquid tank that accommodates water and oil and is equipped with one sensor head.

FIG. 6 is a timing chart for discriminating different kinds of liquids.

[Explanation of symbols]

1 liquid tank 2a, 2b sensor head 6 arithmetic processing circuit 7 comparison circuit 8 counting circuit a, b liquid B ₁ , B ₂ received wave C ₁ , C ₂ received wave signal D threshold E ₁ , E ₂ binarized signal T ₁ , T ₂ reception start time t ₁ , t ₂ duration m measurement period Tm measurement start time Tm 'measurement end time

Claims (4)

[Claims] 1. A sensor head for transmitting and receiving ultrasonic waves is mounted on an outer surface of a tank wall of the liquid tank toward the inside of the tank, and the sensor head receives a reflected wave from the tank wall on the opposite side of the ultrasonic waves. This is an ultrasonic level meter that determines the presence or absence of liquid in the liquid tank, and a comparison circuit that binarizes the received wave output of the sensor head with a predetermined threshold, and the reception start of the binarized signal. Time and its duration,
Based on the counting circuit that measures beforehand when the liquid is in the liquid tank and when it is not, and the reception start time and the duration of each binary signal when there is no liquid and when there is liquid. The presence / absence of a liquid is provided by including a calculation processing circuit that determines a start time and a measurement end time and sets a measurement period, and by the calculation processing circuit measuring only the measurement period consisting of the measurement start time and the measurement end time. An ultrasonic level meter characterized by discriminating between. 2. The arithmetic processing circuit determines the presence / absence of liquid based on a binarized signal output from a counting circuit from the reception start time of the binarized signal when there is no liquid until the duration thereof elapses. The ultrasonic level meter according to claim 1, wherein the measurement period is set so as not to perform. 3. The sensor head comprises at least two or more sensor heads which are mounted on the outer surface of the tank wall toward the inside of the liquid tank at predetermined intervals in the vertical direction. The liquid level position is determined by the arithmetic processing circuit based on the output based on the presence or absence of liquid detected only during a measurement period consisting of the measurement start time and the measurement end time. The described ultrasonic level meter. 4. A sensor head for transmitting and receiving ultrasonic waves is mounted on an outer surface of a tank wall of the liquid tank toward the inside of the liquid tank, and the sensor head receives a reflected wave from the tank wall on the opposite side of the ultrasonic waves. This is an ultrasonic level meter for detecting the type of different liquids mixed in the liquid tank or the position of the interface, and a comparison circuit for binarizing the received wave output of the sensor head with a predetermined threshold value, The reception start time of the binarized signal and its duration are
A counting circuit for measuring each of the time of the first liquid and the time of the second liquid in the liquid tank, and one of the time of the first liquid and the time of the second liquid An arithmetic processing circuit that determines the measurement start time and the measurement end time and sets the measurement period based on the reception start time and its duration, and the arithmetic processing circuit configures the measurement start time and the measurement end time. An ultrasonic level meter characterized by determining the type of liquid or the position of the interface by measuring only during the measurement period.