JP2006145403A - Ultrasonic measurement circuit and liquid-level detection system using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic measurement circuit and a liquid-level detection system using it, allowing reduction of the influence of noise when detecting a reflected wave reflected by an object to be detected, and to accurately measure the position of the object to be detected. <P>SOLUTION: The ultrasonic measurement circuit emits ultrasonic waves toward the object to be detected from an ultrasonic sensor 3 to measure the position of the object to be detected by detecting the reflected wave reflected by the object to be detected. The circuit comprises a transmitting circuit 110 for providing the ultrasonic sensor 3 with a drive signal for emitting ultrasonic waves and a receiving circuit 120 for detecting the reflected wave signal, corresponding to the reflected wave out of reception signals received by the ultrasonic sensor 3. The receiving circuit 120 has an adjustment means 124 for changing the signal level of the reception signal or the decision level of the received signal for a period shorter than the period between the emission of the drive signal and the reception of the reflected wave. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an ultrasonic measurement circuit that measures the position of a detection target using an ultrasonic sensor and a liquid level detection device using the same.

Conventionally, as an application example of an ultrasonic measurement circuit, a liquid level detection device that detects a liquid level of a liquid in a tank is known. In this device, a thin tubular transmission tube is attached in the depth direction of the tank, an ultrasonic sensor (ultrasonic transducer) is attached to the watertight case at the bottom of this transmission tube, and ultrasonic waves are emitted from this ultrasonic sensor. And the liquid level position of a liquid is measured by receiving the reflected wave reflected on the liquid level with an ultrasonic sensor (for example, refer patent document 1).
Japanese Unexamined Patent Publication No. 6-249697

  According to such a configuration, it propagates into the liquid filled in the transmission tube, and is also transmitted from the watertight case to the transmission tube itself to travel through the flesh (ie, body body) of the transmission tube and enter the ultrasonic sensor. To do. That is, the ultrasonic sensor receives two types of reflected waves, that is, a reflected wave from the liquid surface and a reflected wave from the end of the transmission tube. The reflected wave from the liquid surface is a signal necessary for detecting the liquid surface position, but the reflected wave from the end of the transmission tube is so-called noise, and this noise may hinder accurate liquid surface detection.

  This is not limited to the liquid level detection device described above, and is also applied to an ultrasonic measurement circuit that emits an ultrasonic wave to a detection target and detects a reflected wave from the detection target. A reflected wave (that is, noise) from other than the detection target such as a reflected wave from the middle of the path is received, and this noise may hinder accurate position detection of the detection target. It is a problem.

  In view of the above points, the present invention reduces an influence of noise when detecting a reflected wave reflected from a detection target, and uses an ultrasonic measurement circuit capable of more accurately measuring the position of the detection target. An object of the present invention is to provide a liquid level detecting device.

  In order to achieve the above object, the present invention employs technical means described in claims 1 to 9.

According to the ultrasonic measurement circuit of the present invention described in claim 1, the ultrasonic wave is emitted from the ultrasonic sensor to the detection target, the reflected wave reflected from the detection target is detected, and the position of the detection target is measured. An ultrasonic measurement circuit that
A transmission circuit for providing a drive signal for emitting ultrasonic waves to the ultrasonic sensor, and a reception circuit for detecting a reflected wave signal corresponding to the reflected wave from the received signals received by the ultrasonic sensor;
The receiving circuit is characterized by having adjustment means for changing the signal level of the received signal or the determination level of the received signal only for a shorter period than when the reflected wave is received from the time when the drive signal is generated.

  According to the present invention, reflected wave noise from the middle of the propagation path of ultrasonic waves, particularly noise with a relatively high signal level, enters the ultrasonic sensor at a point earlier than the reflected wave of the detection target. The wave is made by paying attention to the fact that the reception time is a little different and that it can be dealt with in time.

  Therefore, in the present invention, reflection from other than the detection target is performed by changing the signal level of the received signal or the determination level of the received signal only for a period shorter than the time when the reflected wave is received from the time when the drive signal is generated using the adjusting unit. It is possible to reduce the influence of wave noise and prevent false detection, and at the time of receiving the reflected wave to be detected, the level change to the received signal is stopped to detect the reflected wave to be detected stably. It becomes possible.

  According to the ultrasonic measurement circuit of the present invention described in claim 2, the reception circuit rectifies the reception signal and converts it into a detection signal, and a comparison for comparing the detection signal of the detection circuit and a threshold value. The adjustment means offsets the signal level of the received signal given to the detection circuit to the low potential side only during the period, so that even if a relatively high level of reflected wave noise is incident on the ultrasonic sensor, It is possible to reliably prevent erroneous detection during the period.

  According to the ultrasonic measurement circuit of the present invention as set forth in claim 3, the reception circuit rectifies the received signal and converts it into a detection signal, and a comparison for comparing the detection signal of the detection circuit and a threshold value. The adjustment means increases the threshold value of the comparison circuit only during the period, so that even if a relatively high level of reflected wave noise is incident on the ultrasonic sensor, erroneous detection is reliably performed during the period. It becomes possible to prevent.

According to the ultrasonic measurement circuit of the present invention described in claim 4, the reception circuit has an amplification circuit that amplifies the reception signal before the detection circuit, and the detection circuit includes a rectification circuit that rectifies the reception signal; And a diode detection circuit for detecting a rectified signal rectified by the rectifier circuit,
The adjusting means includes a coupling capacitor that AC-couples the output side of the amplifier circuit and the input side of the rectifier circuit, and uses a ripple component of the received signal that passes through the coupling capacitor as an offset potential.

  Accordingly, it is possible to apply an offset potential to the reception signal using the coupling capacitor without adding a special offset setting circuit. Further, the potential level of the ripple component, which is the offset potential, can be adjusted relatively easily by changing the capacitance of the coupling capacitor.

According to the ultrasonic measurement circuit of the present invention described in claim 5, ultrasonic waves are emitted from the ultrasonic sensor to the detection target and the reference target at a predetermined position closer to the detection target, and the detection target and the reference target are detected. An ultrasonic measurement circuit that detects a reflected wave and a reference wave that are reflected from each to measure the position of a detection target,
A reflected wave signal corresponding to a reflected wave and a reference wave signal corresponding to a reference wave are detected from a transmission circuit that gives a drive signal for emitting ultrasonic waves to the ultrasonic sensor and a received signal received by the ultrasonic sensor. Receiving circuit,
The receiving circuit is characterized by having adjustment means for changing the signal level of the received signal or the determination level of the received signal only for a shorter period than when the reflected wave is received from the time when the drive signal is generated.

  Therefore, in the present invention, reflection from other than the detection target is performed by changing the signal level of the received signal or the determination level of the received signal only for a period shorter than the time when the reflected wave is received from the time when the drive signal is generated using the adjusting unit. It is possible to reduce the influence of wave noise and prevent false detection, and at the time of receiving the reflected wave to be detected, the level change to the received signal is stopped to detect the reflected wave to be detected stably. It becomes possible.

  In addition, since the receiving circuit detects the reference wave signal from the reference object at a predetermined position, the current ultrasonic wave propagation speed is measured by measuring the ultrasonic wave propagation time between known distances, and the measured detection is performed. Temperature correction can be performed on the target position.

  According to the ultrasonic measurement circuit of the present invention described in claim 6, the period is set to a period substantially equal to a period until a secondary reference wave in which the reference wave is reflected again by the reference object is detected. ing. Accordingly, the novel of reflected wave noise received thereafter is further reduced, and in the present invention, at least this period can be covered, and measurement with substantially no false detection becomes possible.

According to the liquid level detection device of the present invention described in claim 7, a liquid level detection device including the ultrasonic measurement circuit according to claim 5,
An ultrasonic sensor is placed at the bottom of the tank that stores the liquid, emits ultrasonic waves from the ultrasonic sensor to the liquid level of the liquid to be detected, and receives reflected waves reflected from this liquid level. The liquid level position of the liquid is detected by processing in a circuit.

  Accordingly, in order to detect a reference wave signal from a reference object at a predetermined position, the liquid liquid is measured without using a temperature sensor that detects the temperature of the liquid by measuring the propagation time of ultrasonic waves between known distances. It is possible to reliably detect the surface position, that is, the liquid remaining amount.

  According to the liquid level detection device of the present invention described in claim 8, a step portion as a reference object is formed in the transmission tube at a predetermined position, and a part of the ultrasonic wave emitted from the ultrasonic sensor is obtained. The reference wave is configured to be reflected to the ultrasonic sensor side as a reference wave, and the reference wave from the reference object at a predetermined position can be obtained relatively easily.

  According to the liquid level detection device of the present invention described in claim 9, each propagation time of the ultrasonic wave from receiving the reflected wave signal and the reference wave signal from the receiving circuit to detecting each signal from the time when the drive signal is generated And control operation means for detecting the liquid level position of the liquid based on each of these propagation times. Therefore, in the present invention, the current ultrasonic wave propagation speed is obtained based on the ultrasonic wave propagation times, and the liquid surface position of the liquid, that is, the liquid remaining amount can be reliably detected.

  Hereinafter, an embodiment of an ultrasonic measurement circuit and a liquid level detection apparatus using the same according to the present invention will be described.

(Structure of liquid level detector)
First, the structure of the detection main body portion of the liquid level detection device will be described. Here, the case where the present invention is applied to the liquid level detection device 1 for detecting the liquid level position of the fuel in the fuel tank of the automobile will be described as an example. However, the present invention is also applicable to the liquid level detection of liquids other than fuel. Applicable.

  FIG. 1 is a partial cross-sectional view of a fuel tank 2 in the liquid level detection device 1.

  As shown in FIG. 1, the liquid level detection apparatus 1 includes a fuel tank 2 as a tank that stores fuel 14 that is liquid, an ultrasonic sensor 3 that is an ultrasonic transducer (also referred to as an ultrasonic transmission element), and an ultrasonic sensor. It is comprised from the body 12 as a transmission tube which forms the propagation path of the ultrasonic wave emitted from the acoustic wave sensor 3.

  The ultrasonic transducer constituting the ultrasonic sensor 3 is a substance 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 (zirconate titanate). It is formed in a disk shape with lead acid). Electrodes (not shown) that are electrically connected to the outside are formed on the front surface and back surface of the ultrasonic sensor 3 (corresponding to both left and right end surfaces in the figure). Both electrodes are formed over almost the entire surface of the ultrasonic sensor 3 and almost the entire back surface.

    When a voltage is applied between both electrodes, the ultrasonic sensor 3 oscillates in the axial direction (left-right direction in FIG. 1) that is the plate thickness direction and emits ultrasonic waves due to the piezoelectric effect described above. Both electrodes are connected to lead wires 6 for electrically connecting both electrodes to the outside. Each lead wire 6 is soldered to an electrode. The ultrasonic sensor 3 is hermetically housed in a bracket 7 and a cover 8 that are cases.

  The bracket 7 serving as one of the cases is formed, for example, from a resin material into a substantially bottomed cylindrical shape, and the ultrasonic sensor 3 is disposed on the bottom portion 71 thereof. A cover 8 serving as the other side of the case is attached to the opening end 72 on the opposite side of the bottom 71 of the bracket 7. The cover 8 is fixed in close contact with the open end 72 of the bracket 7, thereby sealing the ultrasonic sensor 3 in the bracket 7.

    Further, a projection 74 is integrally formed with the bracket 7 as an anti-vibration means on the outer surface of the bracket 7. A plurality of protrusions 74 are provided, and when the bracket 7 to which the cover 8 is attached is attached to the body 12, the protrusion 74 has an inner surface of the body 12 that is a transmission pipe and the guide pipe 9 at the apex of the cone as the tip. Abuts against the end face. Further, on the surface of the bracket 7, each projection 74 is set so that the posture of the bracket 7 in the body 12 is uniquely determined and the tips of all the projections 74 abut against the guide pipe 9 or 9 body 12 at equal intervals. Has been. Thereby, the bracket 7 can stably maintain a coaxial positional relationship with the hole of the body 12.

  The cover 8 is formed of, for example, a resin material, and the locking claw 82 is locked to the locking hole 73 of the bracket 7 and is fixed to the bracket 7. The cover 8 is provided with a through hole 81 for extending the lead wire 6 connected to the ultrasonic sensor 3 to the outside of the cover 8. A connector portion 83 is formed on the surface of the cover 8 opposite to the bracket 7. The connector portion 83 is provided with a terminal 84 made of a conductive material.

    The other end of the lead wire 6 whose one end is connected to the electrode of the ultrasonic sensor 3 is connected to the terminal 84 by soldering or the like. The ultrasonic sensor 3 is electrically connected to the external transmission / reception circuit 100 and the control arithmetic circuit 200 by engaging the connector (not shown) extending from the external electric circuit with the connector 83. Further, a buffer member 4 is disposed between the cover 8 and the ultrasonic sensor 3 in a form that is fixed to the sleeve 5.

  The buffer member 4 is made of a flexible resin material or rubber material, for example, nitrile rubber. When the cover 8 is fixed to the bracket 7, the buffer member 4 is compressed and elastically deformed in the bracket 7. Since the ultrasonic sensor 3 is pressed against the bracket 7 by the elastic force of the buffer member 4, the ultrasonic sensor 3 is fixed at a predetermined position in the bracket 7. The buffer member 4 also plays a role of absorbing ultrasonic pulses that leak from the ultrasonic sensor 3 to the back. Thereby, the ultrasonic pulse emitted from the ultrasonic sensor 3 advances toward the fuel 14 in the guide pipe 9 which is a transmission pipe.

  The body 12 which is a transmission pipe is formed of a resin material, for example, a resin material having excellent stability with respect to the fuel 14 in the fuel tank 2. The body 12 holds and fixes the ultrasonic sensor 3. More specifically, a locking claw 12 a for holding and fixing the bracket 7 housing the ultrasonic sensor 3 is formed integrally with the body 12. A plurality of, for example, four locking claws 12a are provided. The locking claw 12a is elastically deformed when locked to the end of the cover 8 serving as a lid of the bracket 7, and the cover 8 is pressed toward the guide pipe 9 by the elastic force. The body 12 includes a guide pipe 9, a reflecting plate 11, and a guide pipe 10 that are actually ultrasonic wave propagation paths. That is, the internal space of the guide pipe 9 and the guide pipe 10 is an ultrasonic wave propagation path. Further, as shown in FIG. 1, the guide pipe 9 and the guide pipe 10 are arranged with their axes A and B orthogonal to each other. However, the guide pipe 9 and the guide pipe 10 are superposed by a reflecting plate 11 arranged between the guide pipes 9 and 10. Ultrasonic waves are propagated between the guide pipes 9 and 10 by reflecting the sound waves.

  The guide pipe 9 is made of a metal material, and one end side (right side in FIG. 1) of the guide pipe 9 is in contact with the bracket 7 that holds and fixes the ultrasonic sensor 3. In detail, it is in contact with the tip of the projection 74 provided on the bracket 7, that is, the apex of the cone. The guide pipe 9 is made of an aluminum die casting alloy.

    The guide pipe 9 has a circular cross-sectional shape in a direction orthogonal to the axis A, and an inner diameter dimension at the ultrasonic sensor 3 side end (right end in FIG. 1) is d1, a reflector described later. The inner diameter dimension at the 11 side end (left end in FIG. 1) is d2. Further, the guide pipe 9 is formed such that the cross-sectional area in the direction orthogonal to the axis A decreases as it moves away from the ultrasonic sensor 3, that is, as it goes from the right end to the left in FIG. . That is, the relationship d1> d2 is established.

    Further, as shown in FIG. 1, a step 91 is formed in the guide pipe 9. The step 91 is formed in a ring shape and as a surface facing the ultrasonic sensor 3. Therefore, a part of the ultrasonic wave emitted from the ultrasonic sensor 3 enters the stepped portion 91. This ultrasonic wave is reflected by the step portion 91, travels toward the ultrasonic sensor 3, and enters the ultrasonic sensor 3.

  Further, on the side opposite to the ultrasonic sensor 3 of the guide pipe 9 (left side in FIG. 1), a reflecting plate for reflecting the ultrasonic wave emitted from the ultrasonic sensor 3 toward the liquid surface 14a in the fuel tank 2. 11 is arranged. The reflecting plate 11 is made of a metal material, for example, an iron-based metal, preferably a stainless steel plate. As shown in FIG. 1, the reflecting plate 11 is installed so as to reflect the ultrasonic wave emitted from the ultrasonic sensor 3 incident on the reflecting surface 11a toward the liquid surface 14a. ° Inclined.

  The guide pipe 10, which is a transmission pipe that forms an ultrasonic wave propagation path between the reflecting plate 11 and the liquid surface 14 a, is formed of a stainless steel pipe, like the guide pipe 9. Further, the guide pipe 10 has a circular cross-sectional shape in a direction orthogonal to the axis B, and the diameter of the guide pipe 10 is uniformly formed over the entire length to a diameter dimension d3. The diameter d3 of the guide pipe 10 is formed to be equal to the diameter d2 at the end of the guide pipe 9 on the reflecting plate 11 side. Further, the front end position of the guide pipe 10 on the liquid surface 14a side is set so as to protrude upward by a predetermined length from the liquid surface 14b when the amount of fuel 14 stored in the fuel tank 2 is maximum, that is, when the tank is full. Yes.

  The guide pipe 9, the reflecting plate 11, and the guide pipe 10 described above form a positional relationship such that the axis A of the guide pipe 9 and the axis B of the guide pipe 10 intersect on the reflecting surface 11 a of the reflecting plate 11. is doing. The body 12 holds and fixes the positional relationship among the guide pipe 9, the reflecting plate 11, and the guide pipe 10 as an ultrasonic propagation path with high accuracy.

(Ultrasonic measurement circuit)
Next, the ultrasonic measurement circuit of the present invention will be described by taking an application circuit to the liquid level detection device 1 as an example, but the circuit of the present invention can be applied to uses other than liquid level detection.

  FIG. 2 is a block diagram showing the overall configuration of the liquid level detection apparatus 1 including the ultrasonic measurement circuit. In FIG. 1, the transmission / reception circuit 100 and the control arithmetic circuit 200 connected to the ultrasonic sensor 3 correspond to each other.

  In FIG. 2, the transmission / reception circuit 100 includes a transmission circuit 110 and a reception circuit 120, and performs ultrasonic emission and ultrasonic reception processing on the ultrasonic sensor 3 for both transmission and reception. Of course, the ultrasonic sensor 3 may be provided separately for transmission and reception. The control arithmetic circuit 200 is composed of a microcomputer or a control logic circuit. For example, when the operation command of the liquid level detection device 1 is received from the outside, such as turning on an ignition switch of an automobile, the control arithmetic circuit 200 operates and an appropriate timing is obtained. The transmitter / receiver circuit 100 is controlled.

  More specifically, the transmission circuit 110 includes, for example, a high-frequency oscillator 111 that oscillates at 40 kHz and an amplification circuit 112 that amplifies the oscillation signal. When the drive signal S1 is received from the control arithmetic circuit 200, the transmission circuit 110 outputs an oscillation signal. Then, the ultrasonic sensor 3, that is, the ultrasonic transducer is driven to emit ultrasonic waves. Incidentally, the high frequency transmitter 111 may be omitted, and the drive signal S1 on which the high frequency signal is superimposed may be supplied from the control arithmetic circuit 200.

  On the other hand, the reception circuit 120 includes an amplification circuit 121 that amplifies the reception signal received by the ultrasonic sensor 3, a detection circuit 122 that rectifies the reception signal into a detection signal, and converts the detection signal into a detection signal. The comparison circuit 123 for comparing with the threshold value, and the signal level of the reception signal or the reception signal only during a period shorter than the time when the reflected wave (in this case, the liquid surface wave) to be detected is received from the generation time point of the drive signal S1 The adjustment unit 124 changes the determination level, that is, the threshold value of the comparison circuit 123.

  Therefore, in this example, the reflection from the liquid surface 14a (14b) of the liquid 14 to be detected and the step 91 provided in the middle of the ultrasonic wave propagation path and at a position away from the ultrasonic sensor 3 by a predetermined distance. A wave (in this case, the former is called a liquid surface wave and the latter is called a reference wave) is detected and processed. The reason for using this reference wave is to enable temperature correction for the measurement position without using the fuel temperature sensor. Originally, the propagation speed of ultrasonic waves is temperature-dependent, and by measuring the propagation time of ultrasonic waves over a known distance, the influence of temperature or the current propagation speed of ultrasonic waves can be determined, and the measured liquid surface position It is possible to perform temperature correction on the.

  Here, the reason why the adjusting means 124 is provided is that the influence of a reflected wave (that is, noise) from other than the detection target is reduced to prevent erroneous detection, and the reflection surface state of the detection target (here, the road surface state of the automobile). This is for the purpose of making it possible to achieve stable measurement even when the signal level of the received signal changes with respect to changes in the liquid level and the change in the liquid level related to the running state.

  In particular, the reflected wave from the middle of the propagation path of the ultrasonic wave, for example, the traveling direction of the ultrasonic wave is changed by 90 degrees by the reflecting plate 11, so that the influence of irregular reflection or the like from the reflecting plate 11 or the reference wave by the step 91 is regenerated. There is an influence of a secondary reference wave that is a reflected wave, and there is a reflected wave (that is, noise) from other than the detection target such as a reflected wave that propagates through the flesh of guide pipes 9 and 10 that are transmission pipes.

  On the other hand, in the present invention, any noise, particularly noise with a relatively high signal level, enters the ultrasonic sensor 3 at a point earlier than the liquid surface wave to be detected, and these reflected wave noise and liquid surface wave are We paid attention to the fact that the reception time is a little different, and that it can be handled by dividing it in time.

  That is, by the action of the adjusting means 124, the signal level of the received signal is lowered for noise countermeasures for a shorter period than when the liquid surface wave to be detected is received from the time when the drive signal S1 is generated, By increasing the determination level, that is, the threshold value of the comparison circuit 123, erroneous detection due to noise is prevented. On the other hand, after the period, the signal level of the received signal is sent as it is without lowering, and the threshold value is kept at a normal value, so that the liquid level wave can be detected with high sensitivity, and the liquid level fluctuation of the liquid 14 and the liquid level can be detected. Even when the signal level of the liquid surface wave is lowered due to the surface inclination, the measurement can be stably performed.

  Next, FIGS. 3A to 3E are time charts showing signal waveforms of respective parts of the ultrasonic measurement circuit shown in FIG. 2. Hereinafter, processing conditions of reception signals received by the ultrasonic sensor 3 will be described. Complement.

(A) shows the drive signal S1 output from the control arithmetic circuit 200 at a predetermined cycle in consideration of the liquid level displacement (displacement speed) that is the detection target. (B) shows the amplified signal S2 obtained by amplifying the received signal by the amplifier circuit 121. The amplified signal S2 is received and amplified in the order of the emission wave S21, the reference wave S22, and the liquid surface wave S23 in time, from the ultrasonic sensor 3 to the detection target. The signal level becomes lower as the distance becomes longer due to attenuation. (C) shows the detection signal S3 detected after half-wave rectification of the amplified signal S2 by the detection circuit 122. (D) shows the potential relationship between the detection signal S3 input to the comparison circuit 123 and the predetermined threshold value Vs. (E) shows the comparison signal S4 output from the comparison circuit 123, time t1 is the propagation time for reciprocating the step 91 from the ultrasonic sensor 3, and time t2 is propagation for reciprocating the liquid level 14a from the ultrasonic sensor 3. Show time.
Next, the measurement operation in the control arithmetic circuit 200 will be described based on the flowchart shown in FIG.

  The control arithmetic circuit 200 gives the drive signal S1 to the transmission circuit 110 at a predetermined cycle (step 201) and starts a timer process to measure the elapsed time t (step 202). Subsequently, when the comparison signal S4 is input from the comparison circuit 123 of the reception circuit 120 and the reference wave signal S22 is received, the elapsed time t1 (that is, the ultrasonic wave) from when the drive signal S1 is generated until the reference wave signal S22 is received. (Propagation time) is calculated by the timer means and temporarily stored in the memory (steps 203 and 204).

  Subsequently, when the liquid surface wave signal S23 is received, an elapsed time t2 (ultrasonic propagation time) from when the drive signal S1 is generated until the reference wave signal S23 is received is calculated by the timer means and temporarily stored in the memory. (Steps 205 and 206) and the timer process is stopped (step 207). Subsequently, based on the obtained elapsed time (propagation time) t1 and the known distance data to the step 91, the current ultrasonic wave propagation velocity is calculated and stored. Based on this propagation speed and the obtained elapsed time (propagation time) t2, the distance to the liquid level 14a, ie, the liquid level height H, is calculated, and the remaining fuel level in the tank 2 is detected. . This remaining amount information can be output to the outside and displayed on a display device (not shown) or the like (step 208).

  The above is the basic configuration of the ultrasonic measurement circuit.

(Adjustment means 124)
Next, the function of the adjusting means 124 which is a main part of the present invention will be described in detail.

  If there is no function to be described later, as shown in the time charts of FIGS. 5A and 5B, the reflected wave noise SN due to irregular reflection from the reflecting plate 11, the secondary reference wave, etc. is received by the reference wave S22. When the signal level of the reflected wave noise SN is higher than the threshold value Vs of the comparison circuit 123, the comparison circuit 123 receives the reflected wave noise signal SN. It is detected and output to the control arithmetic circuit 200. The control arithmetic circuit 200 erroneously determines the signal SN as the liquid surface wave signal S23 and performs measurement processing. Further, it is received earlier than the reference wave S22, such as the reflected wave noise SN from the flesh of the guide pipes 9 and 10, which are transmission pipes, and the signal level of the reflected wave noise SN is higher than the threshold value Vs of the comparison circuit 123. If it is higher, the comparison circuit 123 detects the reflected wave noise signal SN and outputs it to the control arithmetic circuit 200. In this case, the control arithmetic circuit 200 erroneously determines the signal SN as the reference wave signal S22 and performs measurement processing.

  Therefore, as shown in FIG. 5 (c) or (d), the adjustment means 124 of the present invention receives only the adjustment period T1 shorter than the reception of the liquid surface wave S23 to be detected from the time of generation of the drive signal S1. A voltage offset is applied to the lower side to the extent that the signal level of the signal is not erroneously detected. The offset may be a constant level during the adjustment period T1 as shown in FIG. 5C, or the level gradually changes from the lower side to the reference potential Vr during the adjustment period T1 as shown in FIG. 5D. You may let them.

  During this adjustment period T1, a secondary reference wave having a relatively high reception signal level among the reflected wave noise SN, that is, a secondary reference wave formed by reflecting the reference wave S22 again by the step 91 is received. It is desirable to cover the period until. The level of the reflected wave noise SN received after the reception of the secondary reference wave is further reduced. In the present invention, at least this period is covered, so that measurement with substantially no false detection is possible.

  Next, an example of a detailed circuit of the receiving circuit 120 including the adjusting unit 124 is shown in FIG. This example is a circuit for realizing FIG.

  In FIG. 6, a transmission circuit 110, an ultrasonic sensor (that is, an ultrasonic transducer) 3, an amplification circuit 121 that amplifies a reception signal received by the ultrasonic sensor 3 in two stages by amplifiers 121A and 121B, and a main part of an adjustment unit 124. Are connected to the non-inverting input terminal (+) and the other end of the capacitor C1 is connected to the inverting terminal (−) via the resistor 1222; By holding the peak value of the half-wave rectified signal input through the rectifier circuit 122A and the diode 1226 including the half-wave rectifier diodes 1223 and 1224 and performing half-wave rectification of the amplified signal of the amplifier circuit 121, the capacitor C3 Diode detection circuit 122B that forms an envelope waveform output (voltage) of the wave rectified signal, and the envelope waveform output and threshold value Vs Consisting comparator circuit 123 for detecting the reference wave S22 and liquid surface wave S23 received comparison is made in comparator 1231. Note that the rectifier circuit 122A may be a full-wave rectifier circuit.

  Therefore, a description will be given of giving a voltage offset to the signal level of the received signal using the capacitors C1 and C2 of the adjusting unit 124 with reference to an explanatory diagram shown in FIG.

  First, FIG. 7A shows an amplified received signal waveform before passing through the capacitor C1. It is assumed that the noise SN is received between the emission wave S21 by the drive signal S1 and the reflected wave to be detected. Although the amplified reception signal preferably has an output waveform that fluctuates around the reference potential Vr, it usually indicates that the offset potential Voff is slightly added to the reference potential Vr.

  FIG. 7B shows a received signal waveform after passing through the capacitor C1. Although the DC component of the received signal can be cut by the capacitor C1, since the offset received signal is applied to one end of the capacitor C1, it corresponds to an offset potential that changes from the reference potential Vr to the negative side in relation to the operation of the operational amplifier 1221. A ripple potential Vrip is generated. The magnitude and generation period of the ripple potential Vrip are determined according to the signal level of the received signal itself applied to one end of the capacitor C1, the offset potential Voff included therein, the capacitor capacity, and the like. In this case, since there is another capacitor C2 in the charge / discharge path of the capacitor C1, the capacitance of the capacitor C2 and the resistors 1222 and 1225 are also related.

  Therefore, by adjusting the capacitance, resistance value, etc. of each element C1, C2, 1222, 1225 and changing the ripple waveform (delayed output) corresponding to the offset potential, the generation period (corresponding to the adjustment period T1) is substantially equal. Therefore, it is possible to adjust the offset level so that the level of the noise SN is suppressed and the signal level of the reflected wave to be detected exceeds the threshold value Vs.

  The capacitor C1 generates a ripple potential Vrip every time it receives a reception signal. However, the signal level of the reception signal itself is considerably lower in the reflected wave received after that than the emission wave S21 by the drive signal. Therefore, it has almost no effect and is ignored for convenience.

  Next, another example of the adjusting means 124 is shown in FIG. In this example, without adjusting the signal level of the received signal, the determination level of the received signal is changed only for a period shorter than the time when the reflected wave (liquid surface wave) to be detected is received from the time when the drive signal S1 is generated. Therefore, it corresponds to the noise SN. That is, the threshold is changed to a level that is higher than the noise SN level and lower than the reference wave S22.

  Specifically, as shown in FIG. 8, in order to make the threshold value Vs of the comparison circuit 123 higher than the normal value so that the reference wave S22 can be detected only during the period, a resistor 1242 and an electron in parallel with the threshold value forming resistor 1243 are used. A series circuit of the switches 1241 is connected, and the ON timing of the electronic switch 1241 is controlled by the control arithmetic circuit 200. The electronic switch 1241 needs to be turned on and off in a relatively short time, and it is desirable to use a high-speed switching element for the electronic switch 1241 and the control arithmetic circuit 200 having a high arithmetic speed.

(Other embodiments)
In the above embodiment, the step 91 is formed as the main body structure of the liquid level detection device 1 to generate the reference wave S22. However, the step 91 is omitted as shown in FIG. The ultrasonic wave propagation path may be constituted by a guide pipe 9 having an internal space extending straight in a conical shape. When this structure is used, since the reference wave S22 cannot be received, temperature correction of the ultrasonic wave propagation speed is separately required by a temperature sensor or the like.

  FIG. 10 is an example of an ultrasonic measurement circuit when an embodiment in which the step 91 is omitted is employed. 2 differs from the measurement circuit of FIG. 2 in that a fuel temperature sensor 300 is added, and an addition circuit 122C is added as a detection circuit 122 to perform full-wave rectification to form an envelope waveform output (voltage) of the rectified signal. It is.

  Thus, the control arithmetic circuit 200 can perform temperature correction on the result detected by the receiving circuit 120 using the temperature information of the fuel temperature sensor 300, and can measure an accurate position.

  Note that, by eliminating the step 91 that generates the reference wave in the middle of the ultrasonic wave propagation path from the ultrasonic sensor 3, the degree of freedom in setting the ultrasonic wave propagation path from the ultrasonic sensor 3 to the detection target is increased. As a detection application, it can be easily applied to a device that measures the position of a detection target other than the liquid surface.

It is a fragmentary sectional view of tank 2 equipped with a liquid level detection device to which the present invention is applied. It is a block diagram which shows the ultrasonic measurement circuit which becomes one Embodiment of this invention. It is a time chart which shows the signal waveform of each site | part shown in FIG. 3 is a flowchart showing a measurement process in a control arithmetic circuit 200. 3 is a time chart for explaining the function of the adjusting means 124. 3 is a circuit diagram illustrating a detailed circuit example of a reception circuit 120. FIG. It is explanatory drawing for demonstrating the action | operation of the adjustment means 124 shown in FIG. 6 is a circuit diagram showing another example of the adjusting means 124. FIG. It is a fragmentary sectional view of the tank 2 which mounted | wore with the liquid level detection apparatus which the step part 91 to which this invention is applied was omitted. It is a block diagram which shows the ultrasonic measurement circuit used as other embodiment.

Explanation of symbols

1 Liquid level detector 2 Fuel tank (tank)
3 Ultrasonic sensor 4 Buffer member 7 Bracket 8 Cover 9 Guide pipe 91 Step portion 10 Guide pipe 11 Reflector 11a Reflective surface 12 Body 14 Fuel (liquid)
14a, 14b Liquid level 110 Transmission circuit 120 Reception circuit 121 Amplification circuit 122 Detection circuit 122A Rectification circuit 122B Diode detection circuit 123 Comparison circuit 124 Adjustment means 200 Control calculation circuit (control calculation means)

Claims (9)

An ultrasonic measurement circuit that emits ultrasonic waves from an ultrasonic sensor to a detection target, detects a reflected wave reflected from the detection target, and measures the position of the detection target;
A transmission circuit for providing a driving signal for emitting ultrasonic waves to the ultrasonic sensor;
A receiving circuit for detecting a reflected wave signal corresponding to the reflected wave from the received signals received by the ultrasonic sensor;
The reception circuit includes an adjustment unit that changes a signal level of the reception signal or a determination level of the reception signal for a period shorter than the time when the reflected wave is received from the time when the drive signal is generated. Sound wave measurement circuit. The reception circuit includes a detection circuit that rectifies the reception signal and converts it into a detection signal, and a comparison circuit that compares the detection signal of the detection circuit with a threshold value.
2. The ultrasonic measurement circuit according to claim 1, wherein the adjustment unit offsets a signal level of the reception signal applied to the detection circuit to a low potential side for the period. The reception circuit includes a detection circuit that rectifies the reception signal and converts it into a detection signal, and a comparison circuit that compares the detection signal of the detection circuit with a threshold value.
The ultrasonic measurement circuit according to claim 1, wherein the adjustment unit increases the threshold value of the comparison circuit for the period. The reception circuit has an amplification circuit that amplifies the reception signal before the detection circuit;
The detector circuit includes a rectifier circuit that rectifies the received signal, and a diode detector circuit that detects a rectified signal rectified by the rectifier circuit,
The adjusting means includes a coupling capacitor that AC-couples the output side of the amplifier circuit and the input side of the rectifier circuit, and uses a ripple component of the received signal that passes through the coupling capacitor as an offset potential. The ultrasonic measurement circuit according to claim 2. An ultrasonic wave is emitted from an ultrasonic sensor to the detection target and a reference target at a predetermined position closer to the detection target, and a reflected wave and a reference wave reflected from the detection target and the reference target are detected, respectively. An ultrasonic measurement circuit for measuring the position of a detection target,
A transmission circuit for providing a driving signal for emitting ultrasonic waves to the ultrasonic sensor;
A reception circuit for detecting a reflected wave signal corresponding to the reflected wave and a reference wave signal corresponding to the reference wave from the received signals received by the ultrasonic sensor;
The reception circuit includes an adjustment unit that changes a signal level of the reception signal or a determination level of the reception signal for a period shorter than the time when the reflected wave is received from the time when the drive signal is generated. Sound wave measurement circuit.   The ultrasonic measurement according to claim 5, wherein the period is set to a period substantially equal to a period until a secondary reference wave in which the reference wave is reflected again by the reference object is detected. circuit. A liquid level detection apparatus comprising the ultrasonic measurement circuit according to claim 5,
The ultrasonic sensor is disposed at the bottom of a tank that stores liquid, emits ultrasonic waves from the ultrasonic sensor to the liquid level of the liquid to be detected, and is reflected from the liquid level. A liquid level detection apparatus, wherein the reflected wave is processed by the receiving circuit to detect a liquid level position of the liquid. A step portion to be the reference object is formed inside the transmission tube at the predetermined position so that a part of the ultrasonic wave emitted from the ultrasonic sensor is reflected to the ultrasonic sensor side as the reference wave. The liquid level detection device according to claim 7, wherein the liquid level detection device is configured as follows.
  Receiving the reflected wave signal and the reference wave signal from the receiving circuit, each propagation time of the ultrasonic wave from when the driving signal is generated until each signal is detected is obtained, and the liquid is based on these propagation times. The liquid level detection device according to claim 8, further comprising a control calculation unit that detects a liquid level position of the liquid level.

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