JPS60102525A - Liquid-level detecting method - Google Patents

Abstract

PURPOSE:To detect the liquid level accurately even though a liquid is fluctuated, by arranging ultrasonic-wave transmitting and receiving devices at the upper and lower positions of the level line in the liquid, and detecting the position of the liquid surface based on the change in electric signal generated in the wave receiving device. CONSTITUTION:Piezoelectric elements 2 are stuck to bottom surfaces 1a of metal cases 1 of ultrasonic-wave transmitting and receiving devices T and R. The connecting parts of external extracting cable 6 are contacted by a waterproof paint 7 and a waterproof structure is formed. The wave transmitting device T is arranged under the liquid level line l2 of a liquid l, and the wave receiving device R is arranged over the line l2. The devices are connected to transmitting circuits S1 and S2, respectively. When the liquid surface l1 is lowered below the level line l2, most of the radiated ultrasonic wave pulses from the wave transmitting device T are reflected by the interface between the liquid surface l1 and air, and the output from the wave receiving device R becomes small. Thus whether the liquid surface l1 is located over the specified level or not can be detected by the change in electric signal generated in the wave receiving device R.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of detecting whether the level of a liquid contained in a tank is above a predetermined value using ultrasonic waves.

As schematically shown in FIG. 1, this type of detection method using ultrasonic waves is based on an ultrasonic transmitter T and an ultrasonic wave transmitter T installed externally above the liquid level 11 of the liquid 1 contained in the tank. Receivers R are installed in parallel, and the ultrasonic wave transmitter MT emits an ultrasonic pulse toward the liquid surface 11. The round trip time until this pulse hits the liquid surface 11 and reaches the ultrasonic receiver R as a reflected pulse is as follows. There is a known method of detecting the liquid level by measuring it, but this method is effective when the liquid level is always horizontal and stable, but when the liquid level is undulating, ultrasonic waves are used to detect the liquid level. Pulses are diffusely reflected by the wave front and are not accurately received by the ultrasonic receiver R, and liquids such as oil and gasoline tend to oscillate when driving on slopes and uneven roads, such as in cars and power tillers. It was unsuitable for surface detection.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method that can accurately detect a liquid level even when the liquid surface is undulating due to fluctuation of the liquid.

Embodiments of the present invention will be described below with reference to the drawings.

In FIG. 2, t indicates a tank, ■ indicates a predetermined amount of liquid put into the tank, ■1 indicates the liquid level of the liquid, and 1□ indicates a liquid level line in the liquid to be detected. T is an ultrasonic transmitter that continuously or periodically emits ultrasonic pulses from a transmission surface T1, and R is an ultrasonic wave that generates an electric signal by receiving the ultrasonic radiation pulses from the transmitter T from a delivery surface R. In the receiver, these ultrasonic transmitter T and receiver R are immersed in the liquid l, and the wave transmitting surface T and the wave receiving surface R are separated by a fixed interval above and below the liquid level line 12. and are arranged so as to face each other. In this example, the ultrasonic transmitter T is placed below the liquid level line lz, and the ultrasonic receiver R is placed above it. Further, the wave transmission surface T.

The spacing between the wave receiving surface R7 and the wave receiving surface R7 is set to be equal to a half wavelength integer multiple of the sound velocity of the liquid so as to respond with high sensitivity to the radiation pulse from the wave transmitting surface T. Furthermore, since the ultrasonic transmitter T and the receiver R need to have a waterproof structure to prevent the liquid 1 from entering, in this example, the structure shown in detail in FIG. 3 was used. That is, the piezoelectric element 2 is attached to the inner surface of the bottom surface 1a of a case 1 formed into a cap shape from metal or plastic, and the piezoelectric element 2 is attached to the opening surface of the case 1.
A cover plate 3 is implanted with a pair of terminals 4a, 4b that are electrically connected to the front and back electrodes 2a, 2b via thin metal wires 5a, 5b.
A pair of conducting wires 6a, 6 exposed from one end of the cable 6 for external extraction are connected to the terminals 4a, 4b in a liquid-tight manner.
b is connected and this connected portion is coated with waterproof paint 7.

As can be seen from Figure 3, the ultrasonic transmitter T and receiver R
have the same configuration, but the transmitter T connects the external cable 6 to the transmitting circuit S1, receives an oscillation signal from this, emits an ultrasonic pulse from the case bottom 1a (wave transmitting surface T,), and receives the ultrasonic pulse. The wave device R connects the external lead-out cable 6 to the receiving circuit Sz.
Both are different in that the ultrasonic pulses received from the case bottom 1a (wave receiving surface R,) are connected to the casing bottom surface 1a (wave receiving surface R,) and are converted into electrical signals, which are then fed to the receiving circuit.

Next, the operation of the present invention will be explained.

Now, as shown in Fig. 2A, when the liquid 1 in the tank is sufficiently drained and the liquid level 11 is above the liquid level line 12 to be detected, the ultrasonic transmitter T and receiver R are connected. When covered with liquid 1, when an alternating voltage with a predetermined resonance frequency is applied to the piezoelectric element 2 through the external extraction cable 6 connected to the transmission circuit S installed outside the tank, the piezoelectric element 2 vibrates together with the case bottom 1a, and an ultrasonic pulse is emitted from the wave transmitting surface TI.The emitted ultrasonic pulse passes through the liquid 1 and reaches the receiving surface R of the ultrasonic receiver R located above. At this time, the wave receiving surface R1 is caused to resonate, and an output with a signal level higher than that of the piezoelectric element 2 is generated. On the other hand, when the liquid level 11 decreases due to the consumption of liquid l and finally becomes below the liquid level line 12 that should not be detected, and the ultrasonic receiver R is released into the air, the ultrasonic wave will be emitted as shown in figure B. The ultrasonic radiation pulse from the transmitter T once passes through the liquid l and reaches the liquid level l.

However, the acoustic impedance of the liquid (ρ/cl−
40μbar/cIII-5ec) compared to the acoustic impedance of air (ρZ C2=1.2X lO#bar
/■・sec) is extremely large, so most of the liquid is at the liquid level l.

The signal is reflected by the interface between the ultrasonic wave receiver R and the air, and the wave receiving surface R1 of the ultrasonic wave receiver R, which is open in the air, does not resonate sufficiently, resulting in a low signal level.

In this way, the electromagnetic switch or alarm included in the receiving circuit S2 is activated depending on the signal level of the ultrasonic receiver R. For example, when the present invention is applied to oil detection in an internal combustion engine, the oil When starting the engine even though the oil level is below the specified level, the engine stops starting, or when the oil level decreases during operation and drops below the specified level, an electromagnetic switch is activated that immediately stops the engine. In this way, accidents such as engine seizure can be prevented.

As described above, according to the method of the present invention, the ultrasonic transmitter and the ultrasonic receiver are respectively made waterproof and placed above and below the level line to be detected in the liquid, and when the liquid level falls below the level line, The ultrasonic transmitter or receiver placed above is released into the air, and a layer of liquid and air with different acoustic impedances is formed between the opposing surfaces of the transmitter and receiver, and this liquid and air The interface with the liquid reflects the ultrasonic radiation pulses that would have previously passed through the liquid and been received by the receiver, preventing them from reaching the receiver. Since it detects whether the liquid level is above a predetermined level by changes in the electrical signal generated in the receiver, it is determined from the arrival time from emitting the ultrasonic pulse to receiving the reflected pulse from the liquid surface. Unlike conventional methods of detecting liquid level, it is completely unaffected by ripples on the liquid level, so it can be used to detect the liquid level of gasoline, oil, etc., which tend to cause fluctuations and ripples in the liquid level, such as those used in automobiles and power tillers. It has the advantage of being applicable to detection.

[Brief explanation of drawings]

Figure 1 is a schematic diagram used to explain the conventional method of detecting liquid level using ultrasonic waves, and Figure 2 is a schematic diagram used to explain the liquid level detection method of the present invention. Here, A indicates a state in which the liquid level is above the predetermined level line, and B indicates a state in which the liquid level is below the predetermined level line. FIG. 3 is a sectional view showing a waterproof ultrasonic transmitter and receiver used in the present invention. T... Ultrasonic wave transmitter, T... Wave transmitting surface, R... Ultrasonic wave receiver, R,... Wave receiving surface, l. ...Liquid, l, ...Liquid level, lz
・・・・・・Level line 1st 1 + 2171 A 2nd □ 尤 Lr ' ・ & Qz ', ``'''''''・ I T l deshi spit e waiting mo; L , T L,, + /

Claims (1)

[Claims] A waterproof ultrasonic transmitter and a waterproof ultrasonic receiver that receives ultrasonic pulses emitted from the transmitter and outputs an electrical signal are connected to the liquid level in the liquid to be detected. When placed above and below the line and the liquid level is above a predetermined level line and both the ultrasonic transmitter and receiver are covered with liquid, the ultrasonic radiation pulse passes through the liquid. On the other hand, when the liquid level falls below a predetermined level line and the ultrasonic transmitter or ultrasonic transducer placed above the level line is exposed to the air, the ultrasonic emission pulse is A liquid level characterized by detecting whether the liquid level is above a predetermined level based on changes in electrical signals that are reflected by the interface between the liquid and air and are not received by the ultrasonic receiver. Level detection method