JP2000337946A - Liquid level measurement method and device - Google Patents

Abstract

(57) [Problem] To irradiate a beam on an object and receive a reflected beam from the object, and based on a time from a point in time when transmission is performed to a point in time when the reflected beam is received. In the liquid level measuring device for measuring the position of the liquid level of the object, the liquid level is detected with high accuracy. SOLUTION: A determination unit 41 determines whether an ultrasonic wave having a frequency different from the predetermined frequency Fo has been received, and a calculation unit 44 determines the height of the liquid level based on the determination result from the determination unit 41. Is calculated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic transmission for transmitting an ultrasonic wave to an object based on an electric signal of a predetermined frequency, and receiving an ultrasonic wave transmitted from the object to output an electric signal. The present invention relates to a liquid level measuring method and apparatus for measuring the liquid level in a pressure vessel by performing ultrasonic reception.

[0002]

2. Description of the Related Art Conventionally, as the above-mentioned liquid level measuring device, an ultrasonic transmitter for transmitting ultrasonic waves into the atmosphere by vibrating an ultrasonic vibrating body such as a diaphragm exposed to the atmosphere and applying the ultrasonic waves to an object, Liquid level detection of an object in a closed container using an ultrasonic receiver that receives ultrasonic waves sent from the object, and an ultrasonic transceiver that also has the function of the transmitter and the receiver. Is known.

In such a liquid level measuring device, liquid level detection is usually performed as follows. That is, the ultrasonic wave is applied to the object and the reflected wave from the object is received, and the ultrasonic wave transmitted from the transmitter has the same frequency as the ultrasonic wave at a predetermined level or more. As the time of reception, the position of the liquid surface of the object is determined based on the time from when the wave is transmitted from the transmitter to when the reflected wave is received (hereinafter referred to as reflection time). Measure.

[0004]

However, among the ultrasonic waves transmitted from the transmitter, not only those reflected on an object accommodated in a closed container (hereinafter referred to as "reflected waves"). Some reverberation occurs on the inner wall of the closed vessel, or propagates through the walls constituting the closed vessel to produce reverberation (hereinafter referred to as reverberation waves). This reverberation is also received by the receiver. Further, there is also a type that is transmitted from the transmitter and directly received by the receiver (hereinafter, referred to as a direct wave). Among these ultrasonic waves, a direct wave reaches the receiver first, and then a reverberation wave. However, if the reflected wave reaches the receiver before the level of the reverberation wave falls below the predetermined level, the reflected wave is buried in the reverberation wave. Can not. For this reason, it was difficult to accurately determine at which timing the reflected wave was received by the receiver among the ultrasonic waves received by the receiver. As a result, the reflection time is accurately calculated,
There is a problem that it is difficult to accurately detect the liquid level.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a liquid level measuring method and a liquid level measuring apparatus capable of performing liquid level detection with high accuracy.

[0006]

In order to achieve the above object, an object of the present invention is to transmit ultrasonic waves to a liquid surface of a liquid in a pressure vessel and to transmit ultrasonic waves reflected by the liquid surface. By receiving, in the liquid level measuring method for measuring the height of the liquid level, based on the timing at which the ultrasonic wave of a frequency different from the frequency of the transmitted ultrasonic wave is received, the height of the liquid level is It is characterized by measuring.

According to a second aspect of the present invention, the height of the liquid surface is measured by transmitting ultrasonic waves to the liquid surface of the liquid in the pressure vessel and receiving the ultrasonic waves reflected by the liquid surface. In the liquid level measurement device, a determination unit that determines whether an ultrasonic wave having a frequency different from the frequency of the transmitted ultrasonic wave has been received, and the height of the liquid surface based on a determination result from the determination unit. Calculating means for calculating.

According to a third aspect of the present invention, in the liquid level measuring apparatus according to the second aspect, the frequency of the transmitted ultrasonic wave is different from the frequency of the transmitted ultrasonic wave from the timing at which the ultrasonic wave is transmitted from the transmitting section that transmits the ultrasonic wave. The present invention is characterized in that the calculating means is configured to calculate a required time until a timing at which an ultrasonic wave is received, and calculate the height of the liquid level from the required time.

[0009] The ultrasonic waves transmitted into the pressure vessel can hit the walls constituting the pressure vessel and the liquid in the pressure vessel. The liquid surface of the liquid often moves more than the wall surface. Specifically, in many cases, waves are generated on the liquid surface due to minute vibration from the ground, and bubbles are generated due to vaporization of the liquid. On the other hand, the wall surface is stationary. Therefore, of the transmitted ultrasonic waves, those that have reached the receiver as they are without being reflected by the liquid surface, or that are transmitted through the wall constituting the pressure vessel that is a stationary object or reflected by the inner wall surface Those that have arrived at the receiver remain the same frequency as the transmitted frequency, but those that have reflected from the liquid surface change in frequency due to slight movement of the liquid surface It will be.

Utilizing this, in the liquid level measuring method according to the first aspect, based on the timing at which an ultrasonic wave having a frequency different from the frequency of the transmitted ultrasonic wave is received,
The height of the liquid level is measured. Accordingly, it is possible to accurately determine at which timing the ultrasonic wave reflected from the liquid surface among the ultrasonic waves received by the receiver is received by the receiver.

In the liquid level measuring device according to the second and third aspects, the determining means determines whether or not an ultrasonic wave having a frequency different from the frequency of the transmitted ultrasonic wave is received. Then, the height of the liquid level is calculated by the calculating means based on the determination result from the determining means. Accordingly, it is possible to accurately determine at which timing the ultrasonic wave reflected from the liquid surface among the ultrasonic waves received by the receiver is received by the receiver.

According to a third aspect of the present invention, in the liquid level measuring device according to the first aspect of the present invention, the calculating unit determines a frequency different from a frequency of the transmitted ultrasonic wave from a timing at which the ultrasonic wave is transmitted from the transmitting unit transmitting the ultrasonic wave. The height of the liquid level is measured by calculating the required time until the timing at which the determination unit determines that the ultrasonic wave has been received, and calculating the height of the liquid level from the required time.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to an ultrasonic liquid level measuring device (hereinafter, referred to as a liquid level measuring device) for measuring the liquid level in a high-pressure gas container using ultrasonic waves will be described below. . FIG. 1 is a partial sectional view showing a schematic configuration of a liquid level measuring device according to the present embodiment. The liquid level measuring device includes a transmitter 11 and a receiver 21 as ultrasonic devices (hereinafter, referred to as “sensor units”) installed on the top surface of an outer wall 100 a of the high-pressure gas container 100, and a driving signal transmitted to the transmitter 11. And a drive control device 40 for processing the electric signal from the receiver 21. It is assumed that one sensor unit is also used as a transmitter and a receiver, and that the ultrasonic wave is intermittently transmitted from the sensor unit. You may comprise so that a unit may receive a wave.

FIG. 2 is a block diagram of the present liquid level measuring apparatus. This liquid level measuring device includes an ultrasonic wave transmitting unit 10 as a wave transmitting unit, an ultrasonic wave receiving unit 20 as a wave receiving unit, and a drive control device 40.

The ultrasonic transmitting section 10 has a predetermined frequency Fo.
The ultrasonic wave generated by the transmitter 11 based on the reference signal of
A transmitter 1 for transmitting a wave toward a liquid level L in a container, and including an ultrasonic vibrator for converting an electric signal into an ultrasonic wave.
1. A reference oscillator 12 for generating a reference signal of a predetermined frequency Fo, which is ON / OFF controlled by an intermittent control signal from an intermittent controller 41 to be described later, and transmits a reference signal from the oscillator to the transmitter. And an output amplifier 13 for intermittently outputting a signal amplified to a required level.

The ultrasonic wave receiving section 20 receives the ultrasonic waves reflected from the liquid level L by a receiver 21 to generate a reception signal, and converts the ultrasonic waves into electric signals. A receiver 21 including a vibrator or the like, and a preamplifier 22 for amplifying a weak reception signal output from the receiver 21 are provided.

The drive control device 40 determines whether or not the received signal output from the ultrasonic wave receiving section 20 includes a reflected wave signal corresponding to the reflected wave reflected from the liquid surface L. A determination unit 41 and a signal from the determination unit 41 are
Amplifier 42 amplifies to the level required for speed calculation
An intermittent controller 43 that outputs an intermittent control signal for intermittently controlling the transmitter 11 as described above, and an operation that calculates a speed based on the intermittent control signal and the output signal of the amplifier 42. And a portion 44.

In the liquid level measuring apparatus having the above-described configuration, an ultrasonic wave is transmitted from the transmitter 11 toward the liquid level L in the container 100, and a reflected wave from the liquid level L is received by the receiver 21. Receive the wave. Then, the arithmetic unit 43 is configured to transmit the transmitter 11
The timing at which the receiver 21 receives the reception signal determined by the determination unit 41 to include the reflected wave signal corresponding to the reflected wave reflected from the liquid surface L from the timing at which the transmission of the signal from the transmitter is started. Measure the time until. By processing the data of this measurement value, the transmitter 1
The distance between the wave transmitting surface 1 and the liquid level L of the container, that is, the position of the liquid level is calculated.

By the way, as described above, the ultrasonic waves transmitted into the high-pressure gas container 100 can hit the wall constituting the container 100 and the liquid gas in the container 100. In addition, the liquid surface L of the liquid gas often moves more than the wall surface. Specifically, waves are often generated on the liquid surface L due to minute vibrations from the ground, and bubbles are often generated due to vaporization of the liquid gas. On the other hand, the wall surface is stationary. Therefore, of the transmitted ultrasonic waves, those that have reached the receiver as they are without being reflected by the liquid surface, or that are transmitted through the wall constituting the pressure vessel that is a stationary object or reflected by the inner wall surface Those that have arrived at the receiver remain the same frequency as the transmitted frequency, but those that have reflected from the liquid surface change in frequency due to slight movement of the liquid surface It will be.

Therefore, in the liquid level measuring apparatus according to the present embodiment, the height of the liquid level is determined based on the frequency of the transmitted ultrasonic wave, that is, the timing at which the ultrasonic wave having a frequency different from the predetermined frequency Fo is received. Measure the length. Specifically, determining means for determining whether an ultrasonic wave having a frequency different from the predetermined frequency Fo has been received, and calculating means for calculating the height of the liquid level based on the determination result from the determining means Is adopted. Hereinafter, this configuration and operation will be described.

In this liquid level measuring device, the judging section 41 is constituted as the judging means. That is,
By determining whether the received signal output from the ultrasonic wave receiving unit 20 is a signal corresponding to an ultrasonic wave having a frequency different from the predetermined frequency Fo, the received signal is reflected from the liquid level L. It is determined whether or not a reflected wave signal corresponding to the reflected wave is included. Specifically, when the received signal is a signal corresponding to an ultrasonic wave having a frequency different from the predetermined frequency Fo, the received signal is a reflected wave signal corresponding to a reflected wave reflected from the liquid level L. Is determined to be included.

Here, when the frequency of the signal changes due to the Doppler effect or the like, the waveform of the signal changes due to the change, and the duty changes. For example, FIG.
As shown in FIG. 3B, when the frequency of a rectangular wave signal having a duty of 50% increases, as shown in FIG. 3B, the pulse width of each pulse gradually decreases. And
While the pulse width is gradually reduced, the duty of the signal fluctuates. Therefore, as the determination unit 41, one that performs the determination by determining whether the duty of the input signal has changed can be used.

FIG. 4 shows an example of the configuration of the determination section 41. The determination unit 41 includes an inverter 411, a low-pass filter 422 including a capacitor C1 and a resistor R1, and a comparator 413. The inverter 411 converts a waveform of a received signal received in a sine wave state into a rectangular wave. In the low-pass filter 422, the values of the capacitor C1 and the resistor R1 are set such that the average voltage value of the electric signal input to the input terminal IN is output.
For example, as an electric signal corresponding to an ultrasonic wave transmitted from the transmitter, a pulse top voltage is V1 and a pulse base voltage is V0 at a predetermined frequency Fo, for example, 40 kHz and a duty of 50% as shown in FIG. When the rectangular wave signal is used, while the rectangular wave signal is being applied, the output signal from the output terminal OUT is, as shown in FIG. 5A, the average voltage value (V1- V0) / 2. The comparator 413 determines whether the output signal of the low-pass filter 412 fluctuates and deviates from an average voltage value (hereinafter, referred to as a reference average voltage value) of an electric signal corresponding to an ultrasonic wave transmitted from the transmitter. Depending on what, Hig
It outputs a signal of h or Low. For example, it outputs High when it fluctuates, and outputs Low when it does not fluctuate.

In the determination section 41, the ultrasonic wave which has not been reflected by the liquid surface L and thus has not been subjected to the frequency modulation, that is, the ultrasonic wave which has reached the receiver without being reflected by the liquid surface, When a signal corresponding to an ultrasonic wave that has reached the receiver after being transmitted through the wall portion constituting the stationary pressure vessel or reflected on the inner wall surface is input, the output of the low-pass filter 412 is:
As shown in FIG. 5A, the reference average voltage value remains as it is. Then, the output signal from the comparator 413 is a signal indicating that the output signal of the low-pass filter 412 does not fluctuate and has the reference average voltage value, for example, Low. On the other hand, as a result of receiving the frequency modulation,
When an ultrasonic wave whose frequency fluctuates and becomes a frequency different from the predetermined frequency, that is, a signal corresponding to the ultrasonic wave reflected from the liquid surface L is input to the determination unit 41, a signal is generated by a change in the frequency. The waveform changes, and the duty fluctuates. For this reason, the average voltage value of this signal fluctuates near the reference average voltage value. That is, the output signal of the low-pass filter 412 fluctuates near the reference average voltage value as shown in FIG. 5B. Then, the comparator 41
The output signal from the signal 3 becomes a signal indicating that the output signal of the low-pass filter 412 fluctuates, for example, High. In this way, it can be determined whether or not the received signal includes a reflected wave signal corresponding to the reflected wave reflected from the liquid surface L.

The determination unit 41 performs not only the determination by determining whether the duty of the input signal fluctuates as shown in FIG. 4 but also the frequency of the input signal. It is also possible to use a device that makes the above determination by directly determining the fact. For example, a quadrature demodulation circuit, a demodulation circuit using a digital delay circuit, P
An LL demodulation circuit or the like can be used. However, as compared with the case where these circuits are used, a configuration in which the above-described determination is performed by determining whether or not the duty of the input signal has changed as shown in FIG. Is preferred in that it is simple.

In the present liquid level measuring device, the intermittent controller 4 is operated by the calculating section 44 as the calculating means.
3 based on the timing at which the intermittent control signal is output and the timing at which the determination unit determines that the received signal includes a reflected wave signal, that is, the timing at which the determination unit 41 outputs a pulse signal. Then, the time required from the timing when the transmission from the transmitter 11 starts to the timing when the ultrasonic wave having a frequency different from the predetermined frequency Fo is received is calculated, and the height of the liquid level is calculated.

As described above, according to the liquid level measuring apparatus according to the present embodiment, when the ultrasonic wave reflected from the liquid level L is received by the receiver among the ultrasonic waves received by the receiver. Can be accurately determined. Therefore, it is possible to accurately determine the reflection time and accurately measure the liquid level.

[0028]

According to the first to third aspects of the present invention, there is an excellent effect that the liquid level can be accurately detected.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view showing a schematic configuration of a liquid level measuring device according to an embodiment of the present invention.

FIG. 2 is a block diagram of the liquid level measuring device.

FIGS. 3A and 3B are explanatory diagrams illustrating how a frequency of a signal changes. FIG.

FIG. 4 is an explanatory diagram showing one configuration example of a determination unit of the liquid level measurement device.

FIGS. 5A and 5B are explanatory diagrams for explaining the operation of a determination unit in FIG. 4;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Ultrasonic wave transmission part 11 Transmitter 12 Reference oscillator 13 Output amplifier 20 Ultrasonic wave reception part 21 Receiver 22 Preamplifier 40 Drive control device 41 Judgment part 42 Amplifier 43 Intermittent controller 44 Operation part 100 High pressure gas container 100a Outer wall Part L Liquid level

Claims (3)

[Claims] 1. A liquid level measuring method for measuring the height of a liquid surface by transmitting ultrasonic waves to a liquid surface of a liquid in a pressure vessel and receiving ultrasonic waves reflected by the liquid surface. A liquid level measuring method, comprising: measuring a height of the liquid level based on a timing at which an ultrasonic wave having a frequency different from the frequency of the transmitted ultrasonic wave is received. 2. A liquid level measuring apparatus for measuring the height of a liquid surface by transmitting ultrasonic waves to the liquid surface of the liquid in the pressure vessel and receiving ultrasonic waves reflected by the liquid surface. A determining unit that determines whether an ultrasonic wave having a frequency different from the frequency of the transmitted ultrasonic wave has been received, and a calculating unit that calculates the height of the liquid surface based on a determination result from the determining unit. A liquid level measuring device comprising: 3. The liquid level measuring device according to claim 2, wherein an ultrasonic wave having a frequency different from the frequency of the transmitted ultrasonic wave is received from a timing at which the ultrasonic wave is transmitted from the transmitting unit that transmits the ultrasonic wave. A liquid level measuring device, wherein the calculating means is configured to calculate a required time up to a predetermined timing and calculate the liquid level height from the required time.