JP2002277308A - Liquid surface level detection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid surface level detection device capable of detecting accurately the liquid surface level, which detects the magnetic flux density of a permanent magnet ascending and descending together with a float by magnetic sensors. SOLUTION: In this liquid surface level detection device 1, a first magnetic sensor 21 is arranged on such a position that its output is gradually increased or decreased following ascending or descending of the permanent magnet 5, an a second magnetic sensor 23 is arranged on such a position that its output is gradually decreased or increased, symmetrically with the output of the first magnetic sensor 21. A driving control circuit 31 executes driving control of the first and second magnetic sensors 21, 23, so that the sum of the outputs thereof becomes a prescribed value determined beforehand.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid level detecting device for detecting a liquid level of a stored liquid, and more particularly, to a magnetic sensor which measures a magnetic flux density of a permanent magnet which moves up and down with a float following a liquid level. The present invention relates to a liquid level detection device that detects a liquid level by detecting.

[0002]

2. Description of the Related Art Conventionally, as a liquid level detecting device,
2. Description of the Related Art There has been known an apparatus that detects a liquid level by detecting a magnetic flux density of a permanent magnet that moves up and down together with a float following a liquid level. For example, the actual opening 56-16
No. 9222 discloses a liquid level meter (liquid level detecting device) in which the problem of a liquid level meter having an electrical detection structure based on contact resistance is improved. In this liquid level meter, a permanent magnet is fixed to a float and moved up and down following the liquid level, so that the magnetic flux density that changes accordingly is detected by a magnetically sensitive element (magnetic sensor), and the liquid level is measured. The corresponding electric signal is output from the magnetic sensitive element to detect the liquid level. That is, this is a liquid level meter which has solved the problems of the liquid level meter having the previous contact type detection mechanism by adopting the non-contact type detection mechanism.

For example, Japanese Patent Application Laid-Open No. 2-168123 also discloses a magnetic circuit type liquid level meter (liquid level detector) which has improved the problem of a liquid level sensor having a contact type detection mechanism. I have. This magnetic circuit type liquid level meter is also a non-contact type liquid level meter that detects the magnetic level by detecting the magnetic flux density generated by a permanent magnet attached to a float that moves up and down following the liquid level. It is a surface level meter.

[0004]

However, such a conventional liquid level detecting device has the following problems. That is, since the magnetic sensor that detects the magnetic flux density of the permanent magnet has temperature characteristics, the output changes according to the temperature of the environment in which it is placed. Therefore, its output changes under the influence of the temperature of the liquid to be measured. For example, when a Hall element is used as a magnetic sensor, the output decreases as the liquid temperature increases, and conversely, the output increases as the liquid temperature decreases, even if the elevation position of the permanent magnet does not change. . Further, since the permanent magnet also has temperature characteristics, the magnetic force changes under the influence of the liquid temperature. Specifically, as the liquid temperature increases, the magnetic force decreases, and as the liquid temperature decreases, the magnetic force increases. Therefore, the output of the magnetic sensor also changes due to the temperature change of the permanent magnet. Further, since the magnetic force varies among the individual permanent magnets, the variation causes a difference in the output between the individual liquid level detectors of the same rod. As described above, the output of the magnetic sensor may change irrespective of the position at which the permanent magnet moves up and down, so that the liquid level may not be accurately detected in some cases.

SUMMARY OF THE INVENTION The present invention has been made in view of the above situation, and has a liquid level detecting a liquid level by detecting the magnetic flux density of a permanent magnet that moves up and down with the float following the liquid level. It is an object of the present invention to provide a liquid level detector capable of accurately detecting a liquid level in a detection device.

[0006]

Means for Solving the Problems, Functions and Effects The means for solving the problems includes a float that rises and falls following the liquid surface, a permanent magnet attached to the float, a guide member that guides the float up and down, Attached to the guide member,
A first magnetic sensor that detects a magnetic flux density that changes in accordance with a position at which the permanent magnet moves up and down, and outputs an electric signal corresponding to the magnetic flux density; and a first magnetic sensor attached to the guide member below the first magnetic sensor. A liquid level detection device comprising: a second magnetic sensor having characteristics similar to those of the first magnetic sensor; and a drive control circuit for driving and controlling the first magnetic sensor and the second magnetic sensor. The first magnetic sensor is disposed at a position where the output gradually increases or decreases when the permanent magnet is raised, within a predetermined detection range of the liquid level, and the second magnetic sensor is disposed within the predetermined detection range. The output of the first magnetic sensor is arranged at a position where the output gradually decreases or increases symmetrically with respect to the output of the first magnetic sensor when the permanent magnet rises. Capacitors and such that the sum of the output of the second magnetic sensor becomes a predetermined value, these first magnetic sensor and a second
This is a liquid level detection device that drives and controls a magnetic sensor.

According to the present invention, the first magnetic sensor is disposed at a position where its output gradually increases or decreases when the permanent magnet rises within a predetermined detection range of the liquid level. The second magnetic sensor is arranged at a position within the predetermined detection range where the output gradually decreases or increases symmetrically with the output of the first magnetic sensor when the permanent magnet rises. For this reason, when the permanent magnet rises within the predetermined detection range of the liquid level, for example, the output of the first magnetic sensor gradually increases accordingly, and in contrast to this, the output of the second magnetic sensor gradually increases. To decrease. On the other hand, when the permanent magnet lowers, for example, the output of the first magnetic sensor gradually decreases, and symmetrically, the output of the second magnetic sensor gradually increases. In such a liquid level detecting device, the sum of the outputs of the first and second magnetic sensors is always substantially constant irrespective of the position at which the permanent magnet moves up and down.

However, simply arranging the first and second magnetic sensors so that the sum of the outputs of the first and second magnetic sensors is always constant irrespective of the position at which the permanent magnet is moved up and down, the first and second magnetic sensors are merely required.
The sum of the outputs of the magnetic sensors cannot always be maintained at a predetermined value. This is because, as described in the prior art, the output of the magnetic sensor due to the change of the liquid temperature, the change of the magnetic force of the permanent magnet due to the change of the liquid temperature, the variation of the magnetic force of the permanent magnet, etc. , The output of the second magnetic sensor changes or fluctuates, so that the sum of the outputs also fluctuates or fluctuates. On the other hand, the present invention further includes a drive control circuit for driving and controlling the first and second magnetic sensors so that the sum of the outputs of the first and second magnetic sensors becomes a predetermined value. For this reason, even if there is a change in the output of the magnetic sensor due to a change in the liquid temperature, a change in the magnetic force of the permanent magnet due to a change in the liquid temperature, or a variation in the magnetic force of the permanent magnet, the sum of the outputs of the first and second magnetic sensors is obtained. Is always controlled to a predetermined value.

Therefore, in this liquid level detection device, the output of the magnetic sensor due to the change in the liquid temperature, the change in the magnetic force of the permanent magnet due to the change in the liquid temperature, and the variation in the magnetic force of the permanent magnet are not affected. The liquid level can be accurately detected. As the magnetic sensor, any sensor can be used as long as it can output an electric signal according to the magnetic flux density generated by the permanent magnet.
For example, a Hall element, a magnetoresistive element, and the like can be given.

Another solution is a float that moves up and down following the liquid surface, a permanent magnet attached to the float, a guide member that guides the float up and down, and a guide member that is attached to the guide member. A first magnetic sensor that detects a magnetic flux density that changes in accordance with a position at which the permanent magnet moves up and down, and outputs an electric signal corresponding to the magnetic flux density; ,
A liquid level detection device comprising: a second magnetic sensor having characteristics similar to those of the first magnetic sensor; and a drive control circuit that drives and controls the first magnetic sensor and the second magnetic sensor. In the magnetic sensor and the second magnetic sensor, their outputs gradually increase or decrease when the permanent magnet rises within a predetermined detection range of the liquid level, and the sum of the outputs increases and decreases the permanent magnet. The drive control circuit is disposed at a position that is constant regardless of the position, and the drive control circuit controls the first magnetic sensor and the second magnetic sensor so that the sum of the outputs of the first magnetic sensor and the second magnetic sensor has a predetermined value. This is a liquid level detection device that drives and controls the sensor.

According to the present invention, the first magnetic sensor and the second magnetic sensor gradually increase or decrease their output when the permanent magnet rises, within a predetermined detection range of the liquid level, and They are arranged at positions where the sum of the outputs is constant irrespective of the position of the permanent magnet. For this reason, when the permanent magnet rises within the predetermined detection range of the liquid level, for example, the output of the first magnetic sensor gradually increases accordingly, and the output of the second magnetic sensor gradually decreases symmetrically. To decrease. On the other hand, when the permanent magnet lowers, for example, the output of the first magnetic sensor gradually decreases, and symmetrically, the output of the second magnetic sensor gradually increases. In addition, the sum of the outputs of the first and second magnetic sensors is almost always constant irrespective of the position of the permanent magnet.

However, simply arranging the first and second magnetic sensors so that the sum of the outputs of the first and second magnetic sensors is always constant irrespective of the position at which the permanent magnet is moved up and down, the first and second magnetic sensors are merely required.
The sum of the outputs of the magnetic sensors cannot be maintained at a predetermined value. On the other hand, the present invention further includes a drive control circuit for controlling the driving of the first and second magnetic sensors so that the sum of the outputs of the first and second magnetic sensors becomes a predetermined value. For this reason, even if there is a change in the output of the magnetic sensor due to a change in the liquid temperature, a change in the magnetic force of the permanent magnet due to a change in the liquid temperature, or a variation in the magnetic force of the permanent magnet, the sum of the outputs of the first and second magnetic sensors is It is always controlled to a predetermined value. Therefore, such a liquid level detection device is also free from the influence of the change in the output of the magnetic sensor due to the change in the liquid temperature, the change in the magnetic force of the permanent magnet due to the change in the liquid temperature, and the variation in the magnetic force of the permanent magnet. The plane level can be accurately detected.

Further, in the liquid level detecting device according to any one of the above, the outputs of the first magnetic sensor and the second magnetic sensor are output within a predetermined detection range of the liquid level by the permanent magnet. It is preferable to use a liquid level detecting device that changes linearly with rising.

According to the present invention, the outputs of the first and second magnetic sensors linearly increase or decrease within a predetermined detection range. That is, the liquid level to be measured linearly corresponds to the output of the first magnetic sensor, and the liquid level and the output of the second magnetic sensor linearly correspond to each other. Therefore, the liquid level can be easily detected based on the output of the magnetic sensor without performing output conversion or the like so that the output of the magnetic sensor becomes linear.

Further, in the liquid level detecting device according to any one of the above, the drive control circuit includes a first amplifier circuit for amplifying an output voltage of the first magnetic sensor, and a drive circuit for the second magnetic sensor. A second amplifying circuit for amplifying the output voltage, and a sum of the output voltages respectively amplified by the first and second amplifying circuits is equal to a predetermined reference voltage.
It is preferable that the liquid level detection device includes an inverting amplifier circuit that performs feedback control of the driving voltages of the first magnetic sensor and the second magnetic sensor.

According to the present invention, the drive control circuit includes a first amplifier circuit, a second amplifier circuit, and an inverting amplifier circuit. For this reason, the output voltage of the first magnetic sensor is amplified by the first amplifier circuit, and the output voltage of the second magnetic sensor is amplified by the second amplifier circuit. Then, the drive voltages of the first magnetic sensor and the second magnetic sensor are feedback-controlled so that the sum of the amplified output voltages and the predetermined reference voltage become equal. Therefore, the drive control circuit of this liquid level detection device is a simple circuit, and controls the first and second magnetic sensors so that the sum of the output voltages of the first and second magnetic sensors always becomes a predetermined value. Drive control is possible.

Further, in the liquid level detecting apparatus according to any one of the above, the liquid level detecting means detects the liquid level based on the output of one of the first magnetic sensor and the second magnetic sensor. It is good to use a detecting device.

The outputs of the first magnetic sensor and the second magnetic sensor change symmetrically within the predetermined detection range of the liquid level according to the elevation position of the permanent magnet. Therefore, the liquid level can be accurately detected only by measuring the output of one of the magnetic sensors. Also, when only the output of either one of the magnetic sensors is measured, the liquid level detecting device can be simpler and less expensive than when measuring the output of both magnetic sensors.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a vertical sectional view of the liquid level detecting device 1 of the present embodiment, and FIG. The liquid level detecting device 1 is installed in an engine oil tank of an automobile and detects a liquid level of engine oil. Liquid level detector 1
Has a float 3 that rises and falls following a liquid level (engine oil level) F. This float 3 is made of foamed NBR, foamed PA66, etc., and has an outer diameter of about 25 mm and an inner diameter of about 12 m.
m, a substantially cylindrical shape having a vertical length (height) of about 15 mm. Above the inner peripheral surface 3n of the float 3, a concave groove 3h is formed, which is depressed over the entire periphery of the inner peripheral surface 3n.

In the concave groove 3h, a substantially ring-shaped permanent magnet 5 is mounted on the inner peripheral surface 3n of the float 3 and the permanent magnet 5
Are fitted and fixed such that the inner peripheral surface 5n of the second member is substantially flush with the inner peripheral surface 5n. The permanent magnet 5 is made of a rare earth magnet (neodymium magnet), and has an outer diameter of about 18 mm and an inner diameter of about 12 m.
m, the vertical length (height) is about 10 mm. The magnetic force is about 150 mT, the inner peripheral surface 5n side is uniformly magnetized to the N pole, and the outer peripheral surface 5g side to the S pole. Accordingly, magnetic lines of force are generated around the permanent magnet 5 as indicated by broken lines and arrows in FIG.

The liquid level detector 1 has a guide member 11 for guiding the float 3 up and down. The guide member 11 extends in the vertical direction and has a diameter of about 8 mm loosely inserted into the hole of the float 3 and a length (height) in the vertical direction.
It has a substantially cylindrical stem portion 13 of about 30 mm. In addition,
The stem 13 is made of a material such as PA66. The upper and lower ends of the stem 13 are provided with floats 3.
A substantially disk-shaped upper disk portion 15 and a lower disk portion 17 having a diameter of about 20 mm, which is larger than the inner diameter and smaller than the outer diameter, are fixed. Therefore, the float 3 can freely move in the vertical direction along the stem 13 while the upper end disc 1
5 and the lower end disk portion 17, the stem portion 13 (the guide member 1).
1) is prevented.

A substantially rectangular plate-like substrate 19 having a horizontal length of about 7 mm, a vertical length of 28 mm, and a thickness of about 1 mm is inserted and fixed in the stem 13 of the guide member 11. I have. On one surface of the substrate 19, two Hall elements (a first Hall element 21 and a second Hall element 23), which are magnetic sensors, are fixed to be separated from each other in the vertical direction. The first Hall element 21 and the second Hall element 23 are fixed at an interval of about 8 mm, and the first Hall element 21 is fixed above and the second Hall element 23 is fixed below. These first and second Hall elements 21 and 23 have similar characteristics. That is, when a drive voltage is applied to the first and second Hall elements 21 and 23, the magnetic flux density that changes according to the elevation position of the permanent magnet 5 disposed on the float 3 that follows the liquid surface is detected, and the magnetic flux is detected. An electric signal corresponding to the density, more specifically, a voltage substantially linearly corresponding to the magnetic flux density is output. This output voltage is proportional to the drive voltage.

More specifically, the first Hall element 21 raises the liquid level (permanent magnet) within a predetermined detection range (h = 0 to 10 mm) of the liquid level indicated by the up and down arrows in FIG. When the liquid level rises (as shown by the solid line in the graph of FIG. 3), the output gradually increases. Conversely, when the liquid level falls (the permanent magnet 5 falls), the output gradually decreases. Are located in Further, the first Hall element 21 has a predetermined detection range (h = 0 to 0) of the liquid level.
10 mm), the output is increased or decreased almost linearly. Note that FIG.
Indicates the relationship between the liquid level and the outputs of the first and second Hall elements 21 and 23. The liquid level is determined based on the lower limit within a predetermined detection range (h = 0 mm) and the upper limit is set as h = 10 mm. The outputs of the first and second Hall elements 21 and 23 are output from the actual first and second Hall elements 21. , 23 are amplified about 400 times.

On the other hand, when the liquid level rises (the permanent magnet 5 rises) within the above-mentioned predetermined detection range, the second Hall element 23, as shown by a broken line in the graph of FIG.
The output is gradually reduced, and conversely, when the liquid level decreases (the permanent magnet 5 lowers), the output is gradually increased accordingly. Further, the second Hall element 23
Are also arranged at positions where the increase and decrease of the output change almost linearly within a predetermined detection range of the liquid level. Furthermore, the first and second Hall elements 21 and 23
Are arranged such that their output increases or decreases symmetrically.

The substrate 19 in the guide member 11 includes first and second
In addition to having the Hall elements 21 and 23, it has a drive control circuit 31 for controlling the driving of the first and second Hall elements 21 and 23 and guiding the detection output of the liquid level to the outside through the lead wire 25. FIG. 4 is an explanatory diagram schematically showing the drive control circuit 31, and FIG. 5 is a circuit diagram of the drive control circuit 31.

The drive control circuit 31 has a first amplifier circuit 33 for amplifying the output voltage from the first Hall element 21 and a second amplifier circuit 35 for amplifying the output voltage from the second Hall element 23. As shown in FIG. 5, the first amplifying circuit 33 is connected to the Hall voltage output (-) terminal of the first Hall element 21 on the one hand and to the inverting input terminal of the first operational amplifier AM1 on the other hand in addition to the first operational amplifier AM1. First resistor R1 to be connected
On the other hand, the Hall output terminal (+) of the first Hall element 21
It has a second resistor R2 connected to the terminal and the other end connected to the non-inverting input terminal of the first operational amplifier AM1. A fourth resistor R4 and a first capacitor C1 are connected in parallel between the inverting input terminal and the output terminal of the first operational amplifier AM1. Further, a third resistor R3 connected to the other side to the ground is connected to the non-inverting input terminal of the first operational amplifier AM1.

Similarly, the second amplifying circuit 35 is connected to the Hall voltage output (−) terminal of the second Hall element 23 on the one hand and the second operational amplifier A on the other hand in addition to the second operational amplifier AM2.
A fifth resistor R5 connected to the inverting input terminal of M2, and a sixth resistor R6 connected to the Hall voltage output (+) terminal of the second Hall element 23 on the one hand and to the non-inverting input terminal of the second operational amplifier AM2 on the other hand. Having. Further, the second operational amplifier AM
An eighth resistor R8 is connected between the inverting input terminal and the output terminal of
And the second capacitor C2 are connected in parallel. Also,
A non-inverting input terminal of the second operational amplifier AM2 is connected to a seventh resistor R7 which is connected to the other side to the ground. In addition,
The resistance values of the first resistor R1 and the fifth resistor R5, the second resistor R2 and the sixth resistor R6, the third resistor R3 and the seventh resistor R7, the fourth resistor R4 and the eighth resistor R8 are equal, and The capacitances of the first capacitor C1 and the second capacitor C2 are also equal. Therefore, the first amplifier circuit 33 and the second amplifier circuit 3
5 shows a similar amplification factor.

The drive control circuit 31 is an output adjustment circuit for outputting the output voltage of the first Hall element 21 amplified by the first amplifier circuit 33 to an external circuit having a digital meter, an analog meter, and the like. 37. This output adjustment circuit 37 includes a fourteenth resistor R14, a fifteenth resistor R15, a fourth capacitor C4, and a Zener diode ZD, as shown in FIG.

The drive control circuit 31 has an inverting amplifier circuit 41 connected to the output terminal of the first operational amplifier AM1 of the first amplifier circuit 33 and the output terminal of the second operational amplifier AM2 of the second amplifier circuit 35. This inverting amplifier circuit 41 has a third operational amplifier AM3. The inverting input terminal of the third operational amplifier AM3 is connected to the output terminal of the first operational amplifier AM1 via the ninth resistor R9,
The output terminal of the second operational amplifier AM2 is connected via the resistor R10. The thirteenth resistor R13 and the third resistor R13 are connected between the inverting input terminal and the output terminal of the third operational amplifier AM3.
The capacitor C3 is connected in parallel. Further, the inverting amplifier circuit 41 includes an eleventh resistor R11 connected to a power supply.
And a twelfth resistor R12 connected in series with the other and connected to the ground, and a connection point between the eleventh resistor R11 and the twelfth resistor R12 is connected to the non-inverting input terminal of the third operational amplifier AM3. . The output terminal of the third operational amplifier AM3 applies a drive voltage to the first and second Hall elements 21 and 23.
3 is connected to the voltage input (+) terminal. The voltage input (-) terminals of the first and second Hall elements 21 and 23 are connected to the ground. The potential at the connection point between the eleventh resistor R11 and the twelfth resistor R12 is a predetermined reference potential,
In the present embodiment, the eleventh resistor R11 and the twelfth resistor R11 are set so that the reference voltage becomes approximately 3.3 V when a voltage of 5 V is applied.
The resistance value of the resistor R12 is selected.

The liquid level detecting device 1 operates as follows. That is, when the drive control circuit 31 is operated, a drive voltage is applied to the first and second Hall elements 21 and 23 as shown in FIGS. Then, the first,
The second Hall elements 21 and 23 detect the magnetic flux density of the permanent magnet 5 attached to the float 3 that moves up and down following the liquid level, and detects a voltage proportional to the magnetic flux density (a voltage corresponding to the liquid level). Are output.

Here, as described above, the first Hall element 21 and the second Hall element 23 have the same characteristics, and the first Hall element 21 has a predetermined detection range (h = Within 0 to 10 mm), when the liquid level rises, the output increases linearly as shown by the solid line in the graph of FIG. 3, and conversely, when the liquid level falls, the output linearly increases. Decrease. On the other hand, the second Hall element 23
When the liquid level rises within this predetermined detection range, the output decreases linearly symmetrically with the output of the first Hall element 21, as indicated by the broken line in the graph of FIG.
Conversely, if the liquid level falls, the output will be
The output of the Hall element 21 increases linearly symmetrically.
Therefore, the sum of the outputs of the first and second Hall elements 21 and 23 is always substantially constant irrespective of the liquid level (the position where the permanent magnet 5 is raised and lowered).

The output voltage of the first Hall element 21 is input to the first amplifier circuit 33 and is amplified at a predetermined ratio. The amplified output voltage enters the inverting amplifier circuit 41, and is input to the inverting input terminal of the third operational amplifier AM3 via the ninth resistor R9. The output voltage amplified by the first amplification circuit 33 is also input to the output adjustment circuit 37. Then, a voltage corresponding to the liquid level is output from the output adjustment circuit 37 to the outside, and the liquid level is displayed on, for example, a meter installed in the interior of the automobile. This allows the driver to know the remaining amount of engine oil.

The output voltage of the second Hall element 23 is
The signal is input to the second amplifying circuit 35 and is amplified at a predetermined ratio as in the case of the first amplifying circuit 33. Then, the amplified output voltage enters only the inverting amplifier circuit 41 and is input to the inverting input terminal of the third operational amplifier AM3 via the tenth resistor R10. Therefore, an output voltage obtained by adding the output voltage obtained by amplifying the output of the first Hall element 21 and the output voltage obtained by amplifying the output of the second Hall element 23 is input to the inverting input terminal.

The output voltage input to the inverting input terminal of the third operational amplifier AM3 is compared with a reference voltage (about 3.3 V). At this time, when the input voltage is higher or lower than the reference voltage, a voltage having a magnitude corresponding to the difference is output from the output terminal so that the input voltage becomes equal to the reference voltage. Then, the first and second Hall elements 21 and 23 are driven according to the output voltage. By receiving such feedback control, the first amplifier circuit 3
3 and the output voltage of the second amplifying circuit 35, and therefore the output voltage of the first Hall element 21 and the second Hall element 2
The sum of the three output voltages is always a predetermined value.

More specifically, if the liquid temperature fluctuates, for example, even if the liquid temperature rises so that the outputs of the first and second Hall elements 21 and 23 decrease, the sum of the outputs of the two elements will be calculated. Is controlled to be a predetermined value, so that the drive voltage is controlled to be high.
The outputs of the Hall elements 21 and 23 are both raised, and the sum of the outputs of the two is maintained at a constant predetermined value. Therefore, if the outputs of the first and second Hall elements 21 and 23 are measured, the magnetic flux density, that is, the liquid level can be accurately measured regardless of the fluctuation of the liquid temperature. Further, when there is a variation in the characteristics of the permanent magnets 5 between the individual liquid level detecting devices 1, for example, the permanent magnets 5 having a lower than normal magnetic force are used. Even when the outputs are both low, since the sum of the outputs is controlled to be a predetermined value, the drive voltage is controlled to be high, so that the first and second Hall elements 21 , 23 are raised, and the sum of both outputs is kept at a constant predetermined value. Therefore, if the outputs of the first and second Hall elements 21 and 23 are measured, the liquid level can be accurately measured even if the characteristics of the permanent magnet 5 vary.

Further, in this embodiment, as shown in FIG. 3, the outputs of the first and second Hall elements 21 and 23 change almost linearly within a predetermined detection range (h = 0 to 10 mm). Therefore, the output conversion or the like performed when the output of the first and second Hall elements 21 and 23 is a curve or the like is unnecessary, and the liquid level can be easily detected from the output of the first and second Hall elements 21 and 23. can do.

Further, the drive control circuit 31 of the present embodiment
First amplifier circuit 33, second amplifier circuit 35, and inverting amplifier circuit 4
1 is provided. For this reason, the output voltage of the first Hall element 21 is amplified by the first amplification circuit 33 and
Is amplified by the second amplifier circuit 35. Then, the first and second Hall elements 21 and 22 are set such that the sum of the amplified output voltages and the predetermined reference voltage become equal.
3 is feedback-controlled. Therefore, the drive control circuit 31 is a simple circuit, and the first and second Hall elements 21 and 21 are controlled so that the sum of the output voltages of the first and second Hall elements 21 and 23 always becomes a predetermined value.
23 can be drive-controlled.

The output of the first Hall element 21 and the output of the second Hall element 23 correspond to a predetermined detection range of the liquid level (h = 0 to 0).
10 mm), it changes symmetrically according to the position of the permanent magnet 5 ascending and descending. Therefore, the liquid level can be accurately detected only by measuring the output of one Hall element (first Hall element 21). Further, when only the output of one Hall element is measured, the liquid level detecting device 1 can be made simpler and less expensive than when measuring the output of both Hall elements.

Here, the following investigation was conducted to confirm the effects obtained by applying the present invention. That is, the change in the output of the Hall element with respect to the change in the liquid temperature was measured for the liquid level detector 1 of the present embodiment and the liquid level detector of the comparative example (conventional form). The liquid level detection device of the comparative embodiment has only one Hall element as a magnetic sensor, that is, the second Hall element 23, circuits related thereto, etc. are removed from the liquid level device 1 of the present embodiment. Things.

The investigation was specifically performed as follows. In the liquid level detecting device 1 of the present embodiment, the float 3
The lifting position was fixed. And, the liquid temperature is -40C to 12C.
The output voltage of the first Hall element 21 at each liquid temperature was measured while changing the temperature by 0 ° C. in steps of 20 ° C. In addition, a liquid level detection device of a comparative example was also investigated. As a result, the graphs shown in FIG. 6 were obtained. Note that the output (sensor output) of the Hall element shown on the vertical axis in FIG. 6 is a value obtained by amplifying the actual output of the Hall element by 400 times.

As can be seen from the graph, in the liquid level detection device of the comparative embodiment, as the liquid temperature increases, the output of the Hall element decreases substantially linearly and greatly. That is,
This shows that the output of the Hall element greatly changes due to a change in the liquid temperature even when the elevation position of the permanent magnet is the same. Therefore, such a conventional liquid level detecting device cannot accurately detect the liquid level.
On the other hand, in the liquid level detecting device 1 of the present embodiment, the output of the first Hall element 21 hardly changes even if the liquid temperature changes greatly from -40 ° C to 120 ° C. Therefore, the liquid level detecting device 1 of the present embodiment can accurately detect the liquid level without being affected by the liquid temperature. As described above, by applying the present invention to the liquid level detecting device, the liquid level can be accurately detected.

In the above, the present invention has been described with reference to the embodiment. However, the present invention is not limited to the above embodiment, and it is needless to say that the present invention can be appropriately modified and applied without departing from the gist of the present invention. Nor. For example, in the above-described embodiment, the liquid level detecting device 1 in which the substantially ring-shaped permanent magnet 5 is fixed to the concave groove 3h on the inner periphery of the float 3 has been described, but the shape of the permanent magnet 5 and the mounting position on the float 4 are described. Are not limited to these, and can be changed as appropriate. For example, a ring-shaped permanent magnet may be mounted inside the float or on the upper or lower surface of the float. It is also possible to use a substantially plate-shaped permanent magnet and attach it to the float.

Further, in the above embodiment, the liquid level detecting device 1 having the substantially cylindrical float 3 and the guide member 11 in which the stem 13 is loosely inserted into the hole of the float 3 is shown. The shape of the inner circumference and the outer circumference of the guide member 11 is
The float 3 may have any shape as long as it can move up and down along the guide member 11 following the liquid surface.
For example, the cross-sectional shape in the horizontal direction may be elliptical, and the float may not be rotatable with respect to the guide member. Further, a disk-shaped float may be loosely inserted inside the cylindrical guide member, and the float may be moved up and down inside the guide member. In this case, the Hall element may be attached to the cylindrical wall surface of the guide member, or may be attached to the upper and lower ends of the guide member.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a liquid level detecting device according to an embodiment.

FIG. 2 is a cross-sectional view of the liquid level detecting device according to the embodiment.

FIG. 3 illustrates a liquid level detection device according to an embodiment.
5 is a graph showing a relationship between a liquid level and output voltages of first and second Hall elements.

FIG. 4 is an explanatory diagram illustrating a drive control circuit of the liquid level detection device according to the embodiment.

FIG. 5 is a circuit diagram of a drive control circuit of the liquid level detecting device according to the embodiment.

FIG. 6 is a graph showing the relationship between the liquid temperature and the output of the Hall element in the embodiment and the comparative embodiment.

[Description of Signs] 1 Liquid level detection device 3 Float 5 Permanent magnet 11 Guide member 21 First Hall element (first magnetic sensor) 23 Second Hall element (second magnetic sensor) 31 Drive control circuit 33 First amplifier circuit 35 Second amplifier circuit 41 Inverting amplifier circuit

Claims (5)

[Claims] 1. A float that rises and falls following a liquid surface, a permanent magnet attached to the float, a guide member that guides the float up and down, and an ascending and descending position of the permanent magnet that is attached to the guide member. A first magnetic sensor that detects a magnetic flux density that changes according to the first magnetic sensor and outputs an electric signal corresponding to the magnetic flux density; and a first magnetic sensor that is attached to the guide member below the first magnetic sensor. A liquid level detection device comprising: a second magnetic sensor having the same characteristics as described above; and a drive control circuit that drives and controls the first magnetic sensor and the second magnetic sensor. Within a predetermined detection range of the surface level, the output is arranged at a position where the output gradually increases or decreases when the permanent magnet is raised, and the second magnetic sensor is located within the predetermined detection range. At
The output is arranged at a position where the output of the first magnetic sensor gradually decreases or increases symmetrically with the output of the first magnetic sensor when the permanent magnet rises. The drive control circuit includes the first magnetic sensor and the second magnetic sensor. A liquid level detecting device for controlling the driving of the first magnetic sensor and the second magnetic sensor so that the sum of the outputs of the first and second magnetic sensors becomes a predetermined value. 2. A float that rises and falls following a liquid level, a permanent magnet attached to the float, a guide member that guides the float up and down, and an ascending and descending position of the permanent magnet attached to the guide member. A first magnetic sensor that detects a magnetic flux density that changes according to the first magnetic sensor and outputs an electric signal corresponding to the magnetic flux density; and a first magnetic sensor that is attached to the guide member below the first magnetic sensor. A liquid level detection device comprising: a second magnetic sensor having the same characteristics as described above; and a drive control circuit that drives and controls the first magnetic sensor and the second magnetic sensor. In the magnetic sensor, within the predetermined detection range of the liquid level, all of the outputs gradually increase or decrease when the permanent magnet rises, and the sum of the outputs increases when the permanent magnet rises. Each of the first and second magnetic sensors is arranged such that the sum of the outputs of the first and second magnetic sensors becomes a predetermined value. A liquid level detection device that drives and controls the sensor. 3. The liquid level detecting device according to claim 1, wherein outputs of the first magnetic sensor and the second magnetic sensor are within a predetermined detection range of the liquid level. Liquid level detector that changes linearly with the rise of the permanent magnet. 4. The liquid level detecting device according to claim 1, wherein the drive control circuit includes: a first amplifier circuit that amplifies an output voltage of the first magnetic sensor; A second amplifier circuit for amplifying the output voltage of the second magnetic sensor; and the second amplifier circuit, wherein the sum of the output voltages amplified by the first amplifier circuit and the second amplifier circuit is equal to a predetermined reference voltage. A liquid level detection device comprising: an inverting amplifier circuit that feedback-controls a drive voltage of the first magnetic sensor and the second magnetic sensor. 5. The liquid level detecting device according to claim 1, wherein the liquid level is detected based on an output of one of the first magnetic sensor and the second magnetic sensor. A liquid level detector that detects