JP2018115881A - Liquid level detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid level detector capable of suppressing electrolytic corrosion in an ultrasonic sensor.SOLUTION: The liquid level detector comprises: an ultrasonic sensor 110 for emitting ultrasonic waves to the surface of the liquid in a tank 10; a driving circuit unit 140 for providing a driving signal (1) to emit ultrasonic waves to the ultrasonic sensor; a receiving circuit unit 150 for detecting a reflected wave signal corresponding to a reflected wave from the liquid surface out of signals received by the ultrasonic sensor; and a control computation unit 160 that controls the emission of a drive signal to the driving circuit unit and calculates the position of the liquid level by using the reflected wave signal from the receiving circuit unit. The control computation unit provides a driving signal (1a) of a positive potential or a negative potential to the ultrasonic sensor as a driving signal, the position of the liquid surface is calculated by use of the reflected wave signal. The control computation unit subsequently provides the other drive signal (1b) of positive potential or negative potential to the ultrasonic sensor but does not execute calculation of the liquid level by the reflected wave signal based on the other drive signal.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a liquid level detection device that detects the position of a liquid level in a tank using an ultrasonic sensor.

  As a conventional liquid level detection device, for example, the one described in Patent Document 1 is known. In the liquid level detection device of Patent Document 1, an ultrasonic wave is emitted from an ultrasonic sensor by a positive drive signal (one pulse) output from a transmission circuit. Then, the reflected wave reflected from the liquid level in the fuel tank is detected by the receiving circuit, and the distance to the liquid level is calculated from the ultrasonic velocity and the time until reception. .

JP 2006-145403 A

  However, in the liquid level detection device of Patent Document 1, a positive drive signal (one pulse) is output to the ultrasonic sensor in order to emit an ultrasonic wave. There has been a problem that electrolytic corrosion occurs in the electrode portion, the terminal portion, and the like on the positive electrode side, leading to poor conduction.

  In view of the above problems, an object of the present invention is to provide a liquid level detection device capable of suppressing the occurrence of electrolytic corrosion in an ultrasonic sensor.

  In order to achieve the above object, the present invention employs the following technical means.

In the present invention, an ultrasonic sensor (110) that emits ultrasonic waves to the liquid level of the liquid in the tank (10);
A drive circuit unit (140) for providing a drive signal (1) for emitting ultrasonic waves to the ultrasonic sensor;
A receiving circuit unit (150) for detecting a reflected wave signal corresponding to a reflected wave reflected from the liquid surface from the received signal received by the ultrasonic sensor;
In a liquid level detection apparatus comprising: a control calculation unit (160) that performs drive signal emission control on the drive circuit unit and calculates a position of the liquid level using a reflected wave signal from the reception circuit unit.
The control calculation unit applies one drive signal (1a) having a positive potential or a negative potential to the ultrasonic sensor as a drive signal, calculates the position of the liquid surface using the reflected wave signal, and then calculates the positive potential or the negative potential. The other drive signal (1b) is given to the ultrasonic sensor, and the liquid surface position calculation by the reflected wave signal based on the other drive signal is not executed.

  According to the present invention, the control calculation unit (160) gives one drive signal (1a) of positive potential or negative potential to the ultrasonic sensor (110), and performs the position calculation of the liquid level (12). The other drive signal (1b) of positive potential or negative potential is applied to the ultrasonic sensor (110). Therefore, the electrolytic corrosion of the positive electrode side portion of the ultrasonic sensor due to the positive potential drive signal is suppressed by the negative potential drive signal, so that the durability can be improved.

  In addition, since the position calculation of the liquid level (12) is executed based on one drive signal (1a), an unnecessary calculation can be performed by not executing the position calculation using the other drive signal (1b). It can be lost.

  In addition, the code | symbol in the bracket | parenthesis of each said means shows a corresponding relationship with the specific means of embodiment description mentioned later.

It is explanatory drawing which shows the whole structure of a liquid level detection apparatus. It is sectional drawing which shows an ultrasonic sensor and its periphery. It is a block diagram which shows the drive circuit part, receiving circuit part, and control calculating part with respect to an ultrasonic sensor. It is explanatory drawing which shows the flow of the liquid level position detection control which a control calculating part performs. It is explanatory drawing which shows each signal waveform in 1st Embodiment. It is explanatory drawing which shows the behavior at the time of the action | operation of an ultrasonic sensor. It is explanatory drawing which shows the detection waveform at the time of a negative voltage application and a positive voltage application. It is explanatory drawing which shows each signal waveform in 2nd Embodiment. It is explanatory drawing which shows each signal waveform in 3rd Embodiment. It is explanatory drawing which shows each signal waveform in 4th Embodiment.

  A plurality of modes for carrying out the present invention will be described below with reference to the drawings. In each embodiment, parts corresponding to the matters described in the preceding embodiment may be denoted by the same reference numerals, and redundant description may be omitted. When only a part of the configuration is described in each mode, the other modes described above can be applied to the other parts of the configuration. Not only combinations of parts that clearly indicate that the combination is possible in each embodiment, but also a combination of the embodiments even if they are not clearly specified unless there is a problem with the combination. It is also possible.

(First embodiment)
The liquid level detection apparatus 100 of 1st Embodiment is demonstrated using FIGS. The liquid level detection device 100 is a device that detects the position of the liquid level 12 of fuel 11 such as gasoline in a fuel tank 10 for a vehicle, for example. The fuel 11 corresponds to the liquid of the present invention. As shown in FIGS. 1 to 3, the liquid level detection device 100 includes an ultrasonic sensor 110, a case 120, a transmission tube 130, a drive circuit unit 140, a reception circuit unit 150, a control calculation unit 160, and the like. An ultrasonic sensor 110, a case 120, a transmission pipe 130, and the like are provided on the bottom surface 13 of the fuel tank 10.

  The ultrasonic sensor 110 is an ultrasonic transducer that emits ultrasonic waves to the liquid surface 12 of the fuel 11 in the fuel tank 10. The ultrasonic sensor 110 is formed into a disk shape by a material having a piezo effect (a characteristic that changes its volume when a voltage is applied, and generates a voltage when it receives an external force), such as PZT (lead zirconate titanate). Is formed. The ultrasonic sensor 110 is accommodated in a space formed by the case 120 and the lid 121.

  The case 120 is a container body made of resin and having a bottomed cylindrical shape, and is arranged so that the cylinder axis faces the horizontal direction. The lid 121 is a resin plate-like member and is provided so as to close the opening side of the case 120. The lid part 121 is provided with two through holes 121a. The ultrasonic sensor 110 is disposed so as to contact the bottom 120 a of the case 120.

  Electrodes 111 that are electrically connected to the outside are respectively formed on the front and back surfaces (left and right end surfaces in FIG. 2) of the ultrasonic sensor 110 by printing. Each electrode 111 is formed over substantially the entire surface of the ultrasonic sensor 110 and substantially the entire back surface.

  One end side of the lead wire 112 is connected to each electrode 111 by soldering or pressure welding. The other end side of each lead wire 112 extends so as to pass through the through hole 121 a of the lid 121, and a terminal 113 is provided on the other end side of each lead wire 112. Further, a lead wire 114 is connected to the terminal 113.

  When a voltage is applied between both electrodes 111, the ultrasonic sensor 110 oscillates in the axial direction (the left-right direction in FIG. 1) which is the thickness direction due to the piezoelectric effect described above and emits ultrasonic waves. ing.

  In the case 120, a vibration isolator 115 is provided between the ultrasonic sensor 110 and the lid 121. The vibration isolator 115 is made of a flexible resin material or rubber material, for example, nitrile rubber. The vibration isolator 115 is compressed and elastically deformed in the case 120 by fixing the lid 121 to the case 120. The ultrasonic sensor 110 is pressed against the bottom 120 a of the case 120 by the elastic force of the vibration isolator 115.

  The vibration isolator 115 suppresses reverberation vibration of the ultrasonic sensor 110 and absorbs ultrasonic pulses leaking from the ultrasonic sensor 110 to the back (the lid 121 side). Therefore, the ultrasonic pulse emitted from the ultrasonic sensor 110 travels toward the fuel 11 in the horizontal path 132 of the transmission tube 130 described later.

  The transmission tube 130 propagates the ultrasonic wave emitted from the ultrasonic sensor 110 toward the liquid level 12 of the fuel 11 and transmits the ultrasonic wave reflected by the liquid level 12 to the ultrasonic sensor 110 again (propagation path). ). The transmission tube 130 includes a housing 131, a horizontal path 132, a vertical path 133, and a reflection plate 134.

  The housing 131 is a cylindrical member having an L shape, and is formed of, for example, a resin material having excellent stability with respect to the fuel 11 in the fuel tank 10. The cross-sectional shape of the housing 131 is circular. The housing 131 is provided with an L-shaped horizontal portion 131a on one side and a vertical portion 131b on the other side. The horizontal portion 131a is a fuel tank so that the end of the vertical portion 131b faces upward. 10 is fixed to the bottom surface 13. And the case 120 (ultrasonic sensor 110) is being fixed inside the edge part of the horizontal part 131a. The bottom portion 120a of the case 120 is disposed so as to enter the inner side in the axial direction on the end portion side of the horizontal portion 131a.

  The horizontal portion 131a is formed so that the inner diameter is gradually reduced (reduced) from the case 120 side toward the vertical portion 131b side. Further, the end portion of the vertical portion 131b extends to an intermediate position in the depth direction of the fuel tank 10.

  The horizontal path 132 has a circular cross-sectional shape and is a cylindrical member provided so as to be in contact with the inside of the horizontal portion 131a of the housing 131, and is formed of a metal member, for example, an alloy for aluminum die casting. The horizontal path 132 may be formed of a resin material. Similar to the horizontal portion 131a of the housing 131, the horizontal path 132 is formed such that the inner diameter is gradually reduced (reduced) from the case 120 side toward the vertical portion 131b side.

  A reference surface 132 a is formed on the side of the horizontal path 132 opposite to the case 120. The distance from the ultrasonic sensor 110 to the reference surface 132a is a predetermined reference distance L set in advance. The reference surface 132 a has a step shape in the axial direction of the horizontal path 132, a ring shape in the circumferential direction, and is formed as a surface facing the ultrasonic sensor 110. Accordingly, a part of the ultrasonic wave emitted from the ultrasonic sensor 110 is incident on the reference surface 132a, reflected by the reference surface 132a, travels toward the ultrasonic sensor 110 again, and enters the ultrasonic sensor 110. ing.

  The fuel 11 enters the horizontal path 132 through an opening provided on the lower side (the bottom surface 13 side) of the housing 131.

  The vertical path 133 has a circular cross-sectional shape and is a cylindrical member provided so that one end side thereof is in contact with the inside of the vertical portion 131b of the housing 131. Similarly to the horizontal path 132, the vertical path 133 is a metal member such as an aluminum die cast. It is made of an alloy. The vertical path 133 may be formed of a resin material. The vertical path 133 is substantially orthogonal to the horizontal path 132. The other end side of the vertical path 133 is set to protrude upward by a predetermined length from the liquid level 12 when the fuel 11 is full. The diameter dimension of the vertical path 133 is formed to be equal to the diameter dimension of the horizontal path 132 on the reduced diameter side.

  The fuel 11 enters the vertical path 133 continuously from the horizontal path 132. The upper position of the fuel 11 in the vertical path 133 is the same position as the liquid level 12 in the fuel tank 10.

  The reflection plate 134 is a plate member provided between the horizontal path 132 and the vertical path 133, and is formed of, for example, a metal material such as an iron-based metal, preferably a stainless steel plate. The reflection plate 134 is disposed so as to be inclined by about 45 ° with respect to the bottom surface 13 of the fuel tank 10, and reflects the ultrasonic wave emitted from the ultrasonic sensor 110 toward the liquid level 12 of the fuel 11. The ultrasonic wave reflected by the liquid surface 12 is reflected toward the ultrasonic sensor 110.

  The drive circuit unit 140 forms a transmission circuit, and is a circuit unit that gives the ultrasonic sensor 110 a drive signal (1) for emitting ultrasonic waves. The drive circuit unit 140 includes, for example, a high-frequency oscillator that oscillates at a predetermined frequency and an amplifier circuit that amplifies the oscillation signal. When receiving an instruction from the control calculation unit 160 described later, the drive circuit (1) is converted into an ultrasonic wave. It outputs with respect to the sensor 110, drives the ultrasonic sensor 110, and emits an ultrasonic wave. As the drive circuit unit 140, a high frequency transmitter may be omitted, and a signal on which a high frequency signal is superimposed may be given from the control calculation unit 160.

  The reception circuit unit 150 includes a reference wave signal corresponding to a reflected wave reflected from the reference surface 132 a of the horizontal path 132 and a reflected wave reflected from the liquid surface 12 among reception signals received by the ultrasonic sensor 110. It is a circuit unit for detecting a liquid surface wave signal (reflected wave signal) corresponding to the above. The reception circuit unit 150 includes an amplifier circuit 151, a detection circuit unit 152, and a comparison circuit unit 153.

  The amplifier circuit 151 is a circuit unit that amplifies a signal received by the ultrasonic sensor 110 and generates an amplified signal (2). The detection circuit unit 152 is a circuit unit that converts the amplified signal (2) into a detection signal (3) by half-wave rectification. The detection signal (3) is formed as a signal connecting the peaks of the half-wave rectified waveform (FIG. 7). The comparison circuit unit 153 compares the detection signal (3) with the threshold signal (4) output from the control calculation unit 160, and the detection signal (3) is larger than the threshold signal (4). As a comparison signal (5).

  The control calculation unit 160 controls (instructs) the emission of the drive signal (1) from the drive circuit unit 140 to the ultrasonic sensor 110, and compares the signal (5) (reflected wave signal) from the reception circuit unit 150. Is used to calculate the position of the liquid level 12 (details will be described later).

  The liquid level detection device 100 is configured as described above, and the operation and effect thereof will be described below with reference to FIGS.

  4 and 5 show a control flow and signal waveforms in the liquid surface position detection control. The control calculation unit 160 causes the ultrasonic sensor 110 to perform the first ultrasonic emission and the second ultrasonic emission, and controls the first and second times for one cycle (one cycle). Hereafter, this is repeated. The control time in the first ultrasonic emission and the second ultrasonic emission is a time during which reception of a reference wave and a liquid surface wave described later is possible. Here, the control time is about 100 ms (minute time), for example.

  Then, the position of the liquid surface 12 is detected from the reflected ultrasonic wave based on the first ultrasonic emission in one cycle. Further, in the second ultrasonic emission, the second reflected ultrasonic wave is assumed to give the ultrasonic sensor 110 a drive signal (1b) having a reverse potential to the drive signal (1a) for the first ultrasonic emission. Is not used for detecting the liquid surface position. Here, the drive signal (1a) for the first ultrasonic emission is a positive potential drive signal, and the drive signal (1b) for the second ultrasonic emission is a negative potential drive signal.

  This will be specifically described below. S100 to S170 in FIG. 4 show the flow of the liquid level position detection based on the first ultrasonic emission, and S200 to S270 show the flow of performing the second ultrasonic emission but not detecting the liquid level position. ing.

  First, in S100, the control calculation unit 160 causes the drive circuit unit 140 to output a positive potential drive signal (1a) to the ultrasonic sensor 110. The positive potential drive signal (1a) is, for example, a rectangular wave of about + 5V. The potential of the drive signal (1a) is not limited to + 5V, and can be set as appropriate. Further, the drive signal (1a) may be a half wave of a sine wave, a trapezoidal wave, or the like instead of the rectangular wave.

  In response to the positive potential drive signal (1a), the ultrasonic sensor 110 emits ultrasonic waves. The emitted ultrasonic wave propagates in the transmission tube 130 (S110).

  Among the propagated ultrasonic waves, some ultrasonic waves are reflected by the reference surface 132a in the horizontal path 132 (S120), and the ultrasonic sensor 110 receives as a reference wave (S130). Of the ultrasonic waves to be propagated, other ultrasonic waves propagate through the horizontal path 132, the reflector 134, and the vertical path 133, are reflected by the liquid surface 12 (S140), and further propagate in the opposite direction. The ultrasonic sensor 110 receives the liquid surface wave (S150).

  The reception circuit unit 150 generates an amplification signal (2), a detection signal (3), and further a comparison signal (5) from the reference wave and the liquid surface wave from the ultrasonic sensor 110, and generates the comparison signal (5). The result is output to the control calculation unit 160. The control calculation unit 160 calculates the ultrasonic wave based on the temperature at that time from the round-trip distance (2 × reference distance L) between the ultrasonic sensor 110 and the reference surface 132a and the propagation time from emission to reception in the reference wave. Calculate the velocity (= 2L / propagation time). Further, the control calculation unit 160 calculates the distance from the ultrasonic sensor 110 to the liquid surface 12 (= ultrasonic velocity × propagation time / 2) from the calculated ultrasonic velocity and the propagation time from emission to reception in the liquid surface wave. ) And the position of the liquid level 12 is calculated based on this distance (S160).

  The control calculation unit 160 transmits the position data of the liquid level 12 calculated in S160 to, for example, a liquid level position display device (for example, a fuel remaining amount display unit of a combination meter) of the vehicle (S170).

  Subsequently, after 100 ms has elapsed since the first ultrasonic emission, in S200, the control calculation unit 160 causes the drive circuit unit 140 to output the negative potential drive signal (1b) to the ultrasonic sensor 110. The negative potential drive signal (1b) is, for example, a rectangular wave of about −5V. The potential of the drive signal (1b) is not limited to −5V, and can be set as appropriate. Further, the drive signal (1b) may be a half wave of a sine wave, a trapezoidal wave, or the like instead of the rectangular wave (similar to the drive signal (1a)).

  The negative potential drive signal (1b) has the same magnitude and waveform as the positive potential drive signal (1a) except that the potential is opposite to the positive potential drive signal (1a). ) And the same conditions.

  In response to the negative potential drive signal (1b), the ultrasonic sensor 110 emits ultrasonic waves. The emitted ultrasonic wave propagates in the transmission tube 130 (S210).

  Hereinafter, the flow (contents) of S220 to S250 is the same as S120 to S150 described above. However, as shown in FIG. 5, the phase of the ultrasonic wave emitted by the negative drive signal (1b) is reversed (inverted waveform) from the ultrasonic wave generated by the positive drive signal (1a).

  The receiving circuit unit 150 and the control calculation unit 160 do not calculate the position of the liquid level 12 based on the reference wave and the liquid level wave based on the negative potential drive signal (1b) (S260), and display of the vehicle Data transmission to the apparatus is not performed (S270).

  When the display device of the vehicle takes in the position data of the liquid level in S170 for a predetermined number of times (for example, 32 times) in the repetitive control, the average value is calculated (S300), and the average value is calculated as the liquid level position. (S310).

  In the present embodiment, the control calculation unit 160 gives a positive potential drive signal (1a) to the ultrasonic sensor 110, calculates the position of the liquid surface 12, and then superimposes the negative potential drive signal (1b). The sound wave sensor 110 is given. Therefore, the electric corrosion of the positive electrode side portion (positive electrode 111, terminal 113, etc.) of the ultrasonic sensor 110 due to the positive potential drive signal (1a) is suppressed by the negative potential drive signal (1b). Can be improved.

  In particular, the fuel tank 10 may contain a high concentration of alcohol in addition to gasoline fuel, or may contain a small amount of water, and an environment in which electric corrosion is likely to occur. , Effective suppression of electrolytic corrosion can be performed.

  In addition, since the position calculation of the liquid surface 12 is executed based on the positive potential drive signal (1a) in the first ultrasonic emission, the negative potential drive signal (1b) in the second ultrasonic emission is used. By not performing the position calculation, unnecessary calculations can be eliminated.

  Here, when a drive signal (1b) having a negative potential is applied to the ultrasonic sensor 110, as shown in FIG. 6A, the ultrasonic sensor 110 vibrates in a contracting direction. On the other hand, when a drive signal (1a) having a positive / negative potential is applied to the ultrasonic sensor 110, as shown in FIG. 6B, the ultrasonic sensor 110 swells and vibrates. Therefore, as shown in FIG. 7, when the drive signal (1b) having a negative potential is applied to the ultrasonic sensor 110, the detection is performed as compared with the case where the drive signal (1a) having a positive potential is applied. On the contrary, when the drive signal (1a) having a positive potential is applied, a large detection waveform can be obtained.

  Therefore, as in the present embodiment, in the first ultrasonic emission for detecting the position of the liquid surface 12, the positive potential drive signal (1a) is used, and in the second ultrasonic emission for electric corrosion suppression. By using a negative-potential drive signal (1b), the position detection accuracy of the liquid surface 12 can be improved.

(Second Embodiment)
A second embodiment is shown in FIG. The second embodiment is different from the first embodiment in that the configuration of the liquid level detection device 100 is the same and the contents of the control are changed.

  In the present embodiment, the drive signal in the first ultrasonic emission is a negative potential drive signal (1b) and the drive signal in the second ultrasonic emission is a positive potential drive signal ( 1a). Compared to FIG. 4 described in the first embodiment, in S100, a negative drive signal (1b) of −5V is applied, and in S200, a positive drive signal (1a) of + 5V is applied.

  In the present embodiment, the drive signal in the first ultrasonic emission for detecting the position of the liquid level 12 is a negative potential drive signal (1b), so that the liquid level 12 Although the detection accuracy seems to be somewhat lowered, the effect of suppressing electrolytic corrosion by the negative potential drive signal (1b) and the positive potential drive signal (1a) can be obtained similarly.

(Third embodiment)
A third embodiment is shown in FIG. The third embodiment is different from the first and second embodiments in that the configuration of the liquid level detection device 100 is the same and the contents of the control are changed.

  In the present embodiment, a plurality of drive signals (1a) in the first ultrasonic emission and drive signals (1b) in the second ultrasonic emission are respectively the same number of times in the first embodiment. This is a drive signal. For example, each of the drive signals (1a) and (1b) is a rectangular wave that continues three times. Compared to FIG. 4 described in the first embodiment, in S100, the drive signal (1a) having a positive potential of + 5V is continuously applied (three times), and in S200, the drive signal having a negative potential of −5V (1b) is applied. ) Multiple (three times) continuous application.

  Thereby, although the reverberation time of the ultrasonic wave emitted from the ultrasonic sensor 110 is extended as compared with the first embodiment, the intensity is increased, and the intensity of the reference wave and the liquid surface wave at the time of reception after reflection is increased. Since it can be enlarged, the accuracy of position detection of the liquid surface 12 can be improved.

(Fourth embodiment)
A fourth embodiment is shown in FIG. The fourth embodiment is different from the first to third embodiments in that the configuration of the liquid level detection device 100 is the same and the content of the control is changed.

  In the present embodiment, a plurality of drive signals (1b) in the first ultrasonic emission and a drive signal (1a) in the second ultrasonic emission are respectively repeated the same number of times with respect to the second embodiment. This is a drive signal. For example, each of the drive signals (1b) and (1a) is configured to be three rectangular waves. Compared to FIG. 4 described in the first embodiment, in S100, the drive signal (1b) having a negative potential of −5V is applied multiple times (three times), and in S200, the drive signal having a positive potential of + 5V (1a). A plurality of (three times) continuous application.

  Thereby, compared to the second embodiment, the intensity of the ultrasonic wave emitted from the ultrasonic sensor 110 can be increased, and the intensity of the reference wave and the liquid surface wave at the time of reception can be increased. The accuracy of the position detection of 12 can be improved.

(Other embodiments)
In each of the above embodiments, the liquid level detection device 100 has been described as detecting the position of the liquid level 12 of the fuel 11 in the fuel tank 10, but is not limited to the fuel 11. It can also be widely used for detecting the liquid level of oil, AT fluid and the like.

(1) Drive signal (1a) Positive potential drive signal (positive or negative potential drive signal)
(1b) Negative potential drive signal (positive potential or the other drive signal of negative potential)
10 Fuel tank (tank)
11 Fuel (liquid)
DESCRIPTION OF SYMBOLS 12 Liquid level 100 Liquid level detection apparatus 110 Ultrasonic sensor 140 Drive circuit part 150 Reception circuit part 160 Control calculating part

Claims (3)

An ultrasonic sensor (110) for emitting ultrasonic waves to the liquid level of the liquid in the tank (10);
A drive circuit unit (140) for providing a drive signal (1) for emitting the ultrasonic wave to the ultrasonic sensor;
A receiving circuit unit (150) for detecting a reflected wave signal corresponding to a reflected wave reflected from the liquid surface from the received signals received by the ultrasonic sensor;
A liquid level detection apparatus comprising: a control calculation unit (160) that controls driving signal emission to the driving circuit unit and calculates the position of the liquid level using the reflected wave signal from the receiving circuit unit In
The control calculation unit applies one drive signal (1a) of positive potential or negative potential to the ultrasonic sensor as the drive signal, and calculates the position of the liquid surface using the reflected wave signal. A liquid level detection device that applies the other drive signal (1b) of a positive potential or the negative potential to the ultrasonic sensor, and does not execute the position calculation of the liquid level by the reflected wave signal based on the other drive signal.   The liquid level detection device according to claim 1, wherein the one drive signal is a drive signal having the positive potential.   3. The liquid level detection device according to claim 1, wherein each of the one drive signal and the other drive signal is a plurality of drive signals that are continued at the same number of times. 4.

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