JPH038697B2 - - Google Patents

Description

[Detailed Description of the Invention] Purpose of the Invention (Field of Industrial Application) This invention is for storing gasoline, oil, petroleum, water, and other various liquids in tanks and other various containers installed in automobiles, industrial machinery, etc. Pertaining to liquid level meters for detecting and displaying levels,
Specifically, the present invention relates to an LV conversion circuit that converts a change in inductance of a coil in a liquid level detection section into a voltage change.

(Prior Art) Conventionally, there has been an arm float type liquid level meter shown in FIG. To briefly explain this liquid level meter, reference numeral 101 is a set plate attached to a liquid container, and the body 10 has a rotary potentiometer (not shown) built into its lower surface.
2 is installed. A float arm 103 is rotatably attached to the upper part of the body 102, and a float 104 made of foamed rubber is attached to the lower end of the float arm. The upper end of the float arm 103 is connected to the potentiometer so that it can rotate.

105 is a stopper for a float arm provided on the body 102. A shaft 106 extends downward from the lower surface of the body 102, and a cable 108 of a level switch 107 is wound around it. 109 is an output cable.

In this arm float type liquid level meter, accuracy is low due to shape error of the float arm 103, installation accuracy, etc., variation in detection accuracy of the float 104 position due to friction of the bearing part of the float arm, Since it is a rotating type that is susceptible to vibration in the thrust direction,
There were problems such as low linearity between the rotation angle and the liquid level, difficulty in inserting the float arm 103 into the liquid container, and an excessively wide movement range of the float arm 103 within the container.

Furthermore, conventionally, there have been linear potentiometer type liquid level meters shown in FIGS. 15 to 17. To briefly explain this liquid level meter, 1.
10 is a set plate, and 111 is a cylindrical case attached to the lower surface thereof. Reference numeral 112 denotes a bushing rubber attached to the lower end of the case 111, which has a slit-like hole 113 formed in its center and is folded back inward as shown in FIG.

114 is a linear potentiometer provided in the case, and as shown in FIG. 16, it is coated with a common line 115 and a rectangular wave-like resistance pattern 116. The lower end of the linear potentiometer 114 is in close contact with the hole 113. 117 is a float fitted onto the linear potentiometer 114, and is connected to the common line 1.
15 and the resistor pattern 116 are short-circuited. 1
18 is an air vent hole, and 119 and 120 are liquid circulation holes.

In this linear potentiometer type liquid level meter, the friction of the float 117 with respect to the linear potentiometer 114 is
The buoyancy of the float 117 is affected, resulting in lower accuracy.The float 117 becomes larger.A case 111 is required to avoid swinging of the float 117 as much as possible.The linear potentiometer 114 is exposed and has a resistor. Because of the unevenness of the points 115 and 116, there were problems in that dirt in the liquid was likely to adhere to the float, resulting in poor contact and the risk of the float getting caught.

(Problems to be Solved by the Invention) Therefore, the inventor of the present application has recently invented a liquid level meter that solves the above-mentioned problems, but the problems with this liquid level meter are as follows. The question was how to convert changes in coil inductance into changes in voltage accurately and at low cost.

That is, a float with a built-in conductor ring is movably provided around the outer periphery of a coil having a core,
The liquid level meter was configured to drive the indicator by converting the inductance change of the coil due to the movement of the conductor ring into a voltage change by the LV conversion circuit, but it was not possible to use the conventional LV conversion circuit. In this case, there were problems such as low accuracy and reliability, and high cost.

The present invention has been made in order to solve the problems in the above-mentioned LV conversion circuit.

Structure of the Invention (Means for Solving the Problems) In order to solve the above-mentioned problems, the liquid level meter of the present invention has an insulating magnetic core inserted over the entire length of the coil. A float having a conductor ring is movably provided on the outer periphery, and the inductance change of the coil due to the movement of the conductor ring is converted into a voltage change by an LV conversion circuit to drive the indicator. In the liquid level meter, the L-V conversion circuit is connected to the coil by LR.
Connect a resistor that forms a series circuit, connect an oscillation circuit to this LR series circuit, extract the response time until the voltage generated in the LR series circuit reaches the reference voltage, and output a voltage corresponding to the inductance of the coil. It is configured to do so.

(Function) When an oscillation voltage is applied from the oscillation circuit to the resistor forming the LR series circuit, a response delay occurs. LR
The response time until the voltage generated in the series circuit reaches the reference voltage varies depending on the inductance of the coil. Since the LV conversion circuit extracts this response time, it accurately outputs a voltage corresponding to the inductance of the coil.

(Embodiment) Hereinafter, an embodiment of the present invention will be described with reference to the drawings in a liquid level meter that is attached to a fuel tank of an automobile and displays the remaining amount of fuel such as gasoline or diesel oil.

First, the overall structure of this embodiment will be briefly explained with reference to FIG. A detection part A consisting of
An L-V conversion circuit B is connected to the same coil and converts the inductance change into a voltage change;
It consists of an output correction circuit C for matching the output voltage of the conversion circuit B to the characteristics of the indicator, and an indicator D for measuring the liquid level. Therefore, these parts A to D
The details will be explained in this order.

Detection part A The detection part A will be explained according to FIGS. 2 to 5. Reference numeral 1 is a fuel tank of an automobile that stores fuel 2 such as gasoline or diesel oil, and only the top plate 3 and bottom plate 4 are shown. . Reference numeral 5 denotes a mounting hole for the detection section A provided in the upper plate 3.

Reference numeral 6 denotes a housing of the detection part A that is attached to the upper plate 3 of the tank 1 with screws 7, and a through hole 8 is provided in the center thereof. Reference numeral 9 denotes a storage recess provided in the upper part of the housing 6, and a cover 10 is attached to the upper surface thereof. 11 is a rubber gasket interposed between the housing 6 and the tank 1.

12 is a rod-shaped coil that is attached to the through hole 8 at the upper end and extends vertically downward to just above the bottom plate 4, and has a core, a winding, and a sleeve as described below. The inductance of the coil 12 is L, and the DC resistance is r. 13 is a rod-shaped core that is attached to the through hole 8 by a core holder 13a made of a non-magnetic material and extends directly above the bottom plate 4, and is made of a magnetic material having high magnetic permeability and insulation properties, such as ferrite, and has a diameter of 10 mm. It is formed with a length of 160mm.

14 is a winding wire of the coil 12 wound around the outer periphery of the core 13, and is wound in the following manner. That is, as particularly shown in FIG.
a is formed, and the distance from the bottom of the core 13 is 10 ~
A flat wound portion 14b is formed in a range of 140 mm and is wound uniformly and in one direction, and the distance from the upper end of the core 13 is
In the range of 10 to 20 mm, there is a densely wound part 14c in which a large number of windings are made.
is formed, and an unwound portion 14d is formed at about 10 mm at the uppermost end of the core 13. 15 is the winding wire 14
A synthetic resin (non-magnetic material) sleeve loosely fitted around the outer periphery of the winding 1 and fitted into the through hole 8.
4, and also guides the vertical movement of the float, which will be described next. 16 is a cap made of synthetic resin (non-magnetic material) fitted to the lower end of the sleeve 15;
Prevents intrusion inside.

17 is a float loosely fitted around the outer circumference of the coil 12 so as to be movable up and down, and is formed into a donut shape from rubber or synthetic resin foam (non-magnetic material), and its specific gravity is smaller than the specific gravity of the fuel 2. . Therefore, the float 17 floats on the fuel 2 and is moved up and down as the liquid level of the fuel 2 changes. Reference numeral 18 denotes a conductor ring attached to the inner circumference of the float 17, which is made of a polymeric material having low specific gravity (close to the specific gravity of fuel 2) and conductivity, such as synthetic resin filled with carbon. . The lower end of the conductor ring 18 is locked to the cap 16 to prevent it from falling.

Reference numeral 19 denotes a board mounted in the storage recess 9 of the housing 6, into which an LV conversion circuit B and an output correction circuit C, which will be described later, are incorporated.

20 is a conductive tube provided between the winding 14 and the sleeve 15, and as shown in FIG. It is made by winding the wire around the outer circumference of the winding wire 14 in a cylindrical shape. Since the winding ends of the conductive sheet 20b are not in contact with each other, no overcurrent loss occurs in the conductive tube 20. The effects of this conductive cylinder 20 will be explained in detail in the section regarding the LV conversion circuit B.

An equivalent circuit of the coil 12 is shown in FIG. Since the core 13 is an insulator and a magnetic material,
The winding component S _c of the core 13 itself is released. Furthermore, since the conductor ring 18 has conductivity, its winding component S _r is short-circuited. S _n is winding 14
winding component, C _n is the stray capacitance of winding 14, C _x
is the capacitance between this conductive tube 20 and the coil 12,
C _y is the capacitance between the conductive cylinder 20 and the conductive ring 18. C _x and C _y remain constant regardless of the movement of the conductor ring 18.

Next, the effects of the detection section A configured as described above will be explained.

When the magnetic circuit of the coil 12 is in an open state, a magnetic flux distribution occurs. Here, if the conductor ring 18 is present, electromagnetic induction will occur in the ring 18, but since it is a conductor, eddy current loss will occur. Therefore, the inductance seen from the winding 14 is reduced. That is, the manner in which the inductance L decreases changes depending on the magnetic flux distribution from the core 13. Incidentally, the conductor ring 18 moves on the outer circumference of the coil 12 as the float 17 moves up and down due to changes in the liquid level, but the magnetic flux density perpendicular to the conductor ring 18 varies depending on the position of the coil 12. , the eddy current losses are also different. Therefore, the inductance L changes as the conductor ring 18 moves.

Note that, as described above, since no eddy current loss occurs in the conductive tube 20, the conductive tube 20 has almost no effect on the magnetic flux distribution.

Here, let the displacement of the float 17 from the lower end of the coil 12 be X, and when the fuel 2 is empty and the float 17 is at the lowest position (hereinafter referred to as Emp level),
X=0, when fuel 2 is filled and float 17 is at the top (hereinafter referred to as Full level), X=F
shall be.

Assuming that all the windings 14 are flat-wound parts, the coil will be vertically symmetrical, and the magnetic flux density perpendicular to the conductor ring 18 will be maximum at the center of the coil 12, so the inductance L will be
becomes minimum when is close to F/2. Therefore, the inductance L cannot maintain linearity over the entire displacement.

However, in this embodiment, the densely wound portion 14c is provided continuously above the flat wound portion 14b to make the magnetic flux distribution asymmetrical, so that the magnetic flux density perpendicular to the conductor ring 18 is reduced near the upper end of the coil 12. become maximum.
Therefore, the position of the conductor ring 18 where the inductance L is minimum rises to near the upper end of the coil 12, and the inductance L constantly decreases as the float 17 moves upward. In addition, the unwound portion 14
a and 14d, the magnetic flux distribution changes and the increase in inductance L near X=F is suppressed.

From the above, the inductance L of the coil 12 is
It changes linearly depending on the displacement X of the float 17. The relationship between the inductance L and the displacement X measured in this example is shown in Figure 3b, and the inductance L changes (decreases) almost linearly from about 450mH to 300mH, indicating that high linearity was obtained. There is.

In addition, the conductor ring 18 has a small specific gravity (fuel 2
Because it is made of a material with a specific gravity close to that of ), it is lightweight and floats with low buoyancy. Therefore, the float 17 can be formed small. Furthermore, the coil 12
It's also thin and doesn't take up much space.

Therefore, the detection part A can be easily attached to the fuel tank 1, and the range of movement within the tank 1 is also small.
Furthermore, since the detection part A is electrically non-contact, the float can move up and down smoothly without being affected by friction. Therefore, there are few malfunctions and decreases in accuracy, and the swinging of the float does not lead to failure.

Furthermore, since the surface of the coil 12 does not have irregularities unlike conventional linear potentiometers, dust in the liquid is less likely to adhere, and malfunctions of the float are significantly reduced. Furthermore, since the float moves linearly around the outer circumference of the coil, there is little loss of accuracy due to horizontal fluctuations in the liquid level. In addition, there is no need for a conventional case to prevent rocking.

In addition, by using a magnetic material with high magnetic permeability and insulation as the material of the core 13, as described above, the core 13
Since the winding component Sc of the conductor ring 3 itself is released and the inductance L changes only by the conductor ring 18, the detection sensitivity increases.

L-V conversion circuit B Next, the L-V conversion circuit B is connected to the detection section A and converts the change in the inductance L of the coil 12 into a voltage change.
Conversion circuit B will be explained with reference to FIGS. 6 to 8.

R1 is a resistor connected to one end of the coil 12, and its resistance value is R. This resistor R1 constitutes an LR series circuit together with the coil 12,
Its time constant is several tens of microseconds. 22 is the coil 12
An oscillator circuit connected to the other end, 10~15k
It is designed to be able to oscillate Hz square wave pulses. The pulse voltage of this rectangular wave is V _f , the period is T,
Let the frequency be f. FIG. 7a shows a rectangular wave pulse voltage V _f , and FIG. 7 b shows a voltage V _r occurring across the resistor R1 in the LR series circuit. In addition, this L-V
Let the power supply voltage of conversion circuit B be _Vdd .

R2 is a variable resistor that generates the reference voltage _Vs.
23 is a voltage comparator circuit connected to the LR series circuit to compare V _r and V _s , as shown in Figure 7c.
When V _r becomes lower than V _s , the output voltage V _a becomes a constant positive voltage. 24 is an AND logic circuit connected to the voltage comparison circuit 23 and the oscillation circuit 22, and has a buffer 24a, and as shown in FIG. 7d, the rectangular wave pulse voltage V _f and the output voltage V _a are When both are positive, the output voltage V _aod has a value equal to the power supply voltage V _dd . Let this output time be the phase time t _x .

25 is a low pass filter connected to the AND logic circuit 24, which includes a resistor R3 and a capacitor C1.
It consists of a CR circuit. The output voltage V _b is shown in Figure 7e.
Shown below.

Next, the effects of this LV conversion circuit B will be explained. This circuit B utilizes the transient response accompanying the rectangular wave pulse applied to the LR series circuit.

First, when a high level rectangular waveform is applied to the LR series circuit, the LR series circuit enters a charging state.
V _r changes as shown in the formula below.

Furthermore, when the rectangular waveform is at a low level, the LR series circuit is in a discharge state, and V _r changes as shown in the equation below.

Note that in this V _r waveform, waveform distortion is eliminated by the action of the conductive cylinder 20 of the detection section A.

That is, if there were no conductive cylinder 20, a resonance circuit would be formed by the stray capacitance between the coils 12, the capacitance between the coil 12 and the conductive ring 18, and the inductance of the coil 12.
In this case, when the conductor ring 18 is located at a certain point on the coil 12, the voltage of the coil 12 will be divided at that point, and the resonant frequency will change as the conductor ring 18 moves. . Therefore, distortion occurs in the V _r waveform due to the transient phenomenon, as shown by the dotted line in FIG. 7b.

However, in the detection unit A of this embodiment, the conductive tube 20 is provided around the outer periphery of the coil 12 as described above, and the coil 1
2 and the conductor ring 18 are electrostatically isolated. In other words, the capacitance C _x between the conductive tube 20 and the coil 12 and the capacitance C _y between the conductive tube 20 and the conductive ring 18 are kept constant regardless of the movement of the conductive ring 18. , no transient phenomenon occurs and the above distortion does not occur.

Output voltage V _aod of AND logic circuit 24 (Fig. 7d)
gives the delay time of the LR series circuit, that is, the phase time t _x from the rise of the pulse to the reference voltage V _s of the voltage V _r for each cycle.

If t _x is determined from equation (1) by setting V _r =V _s , it is as shown in the following equation.

t _x = -ln (1 - V _s / V _dd ) L/R (3) Since V _s , V _dd and R are constants, the phase time t _x
is directly proportional to the inductance L. The output voltage V _aod of the AND logic circuit 24 is a pulse, and its average voltage V _{aod neao} is expressed by the following formula.

V _{aod neao} =V _dd t _x /T (4) From equations (3 and 4), it can be seen that V _{aod neao} is directly proportional to the inductance L. To average the voltage V _aod , the low-pass filter 25 may be used, and the output voltage V _b =V _{aod neao} .

As a result of the above, the output voltage of this L-V conversion circuit B
V _b is directly proportional to the inductance L as shown in the formula below.

V _b = -ln (1 - V _s / V _dd ) V _dd L / RT (5) As mentioned above, since the inductance L has linearity with respect to the displacement X of the conductor ring 18, the output voltage V _b also has linearity with respect to displacement X. Output voltage measured in this example
The relationship between V _b and displacement X is shown in FIG. this is,
The measured values were under the conditions of f = 15 kHz, V _s = 6 V, and V _dd = 8 V, and high linearity was obtained.

The reason why this L-V conversion circuit B is effective is that the coil 12 is modified in various ways to change its inductance L at a relatively large level of 10 to 1000 mH (in this example, 300 to 450 mH as described above). This is due to the fact that

In other words, in order to increase the output voltage V _b , the shorter the period T and the longer the phase time t _x , the better.
It is necessary to satisfy t _x <T/2. By the way, the period T needs to be long enough to ignore the response delay in a general integrated circuit used for the AND logic circuit 24 and the like. Therefore, in order to lengthen the phase time _tx , it is necessary to increase the inductance L.

Incidentally, since the oscillation circuit 22 only needs to oscillate a rectangular wave and does not require an accurate sine wave, the configuration can be simple, inexpensive, and highly reliable.

By the way, in the _Vr waveform shown in FIG. 7b, transient ringing occurs at the rise and fall of the rectangular wave pulse (however, it does not interfere with the above-mentioned effect). This is because when the number of turns of the coil 12 is large, a slight stray capacitance generated between the windings 14 is affected, resulting in an effect equivalent to a CR series circuit. In particular, the method of connecting a diode in parallel to the coil 12 to reduce the time constant during discharge is as follows:
This is undesirable because large ringing occurs due to the large capacitance of the diode. As the number of turns decreases, this transient phenomenon also becomes smaller, but ideally it is better to eliminate it.

As a conversion means other than the above-mentioned LV conversion circuit B, there is a method of incorporating a coil into the oscillation circuit and detecting the change in the oscillation frequency due to this inductance, but this increases the number of parts that make up the oscillation circuit.
Each characteristic must be stable. From the opposite point of view, there is a limit to the stability of the characteristics of individual components due to cost considerations, so circuit characteristics vary widely and accuracy decreases. If this accuracy is to be improved, additional circuits will be required, resulting in increased costs and decreased reliability. Furthermore, the number of components of the fV conversion circuit required to convert the oscillation frequency to voltage increases, which is disadvantageous in terms of cost and reliability.

Furthermore, as another conversion means, there is a method of detecting from the phase difference in the LR series circuit. This is a method in which the oscillation waveform is a sine wave and the phase delay of the current in the LR series circuit is detected. However, good sine wave oscillation is required, accurate phase detection is required, and a circuit that converts the phase difference signal to a voltage proportional to the inductance is required.
Moreover, there is a problem in that the circuit must perform tan calculations.

There is also a conversion means that similarly applies a sine wave but detects a divided voltage based on its impedance. However, this method is also disadvantageous in terms of number of parts, accuracy, cost, etc.

However, if the problems are taken into consideration, it is also possible to employ each of the above-mentioned conversion means to the present liquid level meter.

Output correction circuit C and indicator D Next, the output correction circuit C for adjusting the output voltage V _b of the indicator D and the LV conversion circuit B to the characteristics of the indicator D is shown in Figs. 9 to 13. I will explain accordingly.

First, the indicator D shown in FIG. 9 will be explained. Reference numeral 31 is a driving electromagnetic coil for causing the pointer of the indicator D to swing positively. 32 is a braking electromagnetic coil for braking in the opposite direction while controlling the pointer, and is connected in series to the drive electromagnetic coil 31.

The indicator D employed in this embodiment is called a hold type. This type uses an electromagnetic force generated by a current in the driving electromagnetic coil 31 and a braking electromagnetic coil 32.
The pointer moves to a position where the electromagnetic force generated by the movement is balanced. In addition, since it does not have a spring spring, it can be used to power the car.
Even if it is turned off, the instructions at that time can be retained. In other words, there are more opportunities to know the remaining amount of fuel than in the past, and it is therefore possible to significantly reduce the risk of carelessness such as neglecting to refuel and running out of fuel while driving. Furthermore, the structure is simple and inexpensive.

Conventionally, as a circuit for driving this type of indicator D, there has been a circuit shown in FIG. That is,
Resistors R _a and R _b are connected to the driving electromagnetic coil 31, and the rotary potentiometer or linear potentiometer R _x in the prior art described above is connected to the braking electromagnetic coil 32. However, even if the potentiometer R _x had linearity, the relationship between its resistance value R _x and the indicated value m was non-linear as shown in FIG. What is particularly problematic about this non-linear characteristic is that even though the original role of the indicator is to accurately notify the timing of refueling,
This means that the linearity is poor at the Emp level.

In this embodiment, the linearity of the detection section A is improved as described above, but there is no point in reducing this in the indicator. Therefore,
It is necessary to investigate whether the characteristics shown in FIG. 11 are due to the circuit configuration shown in FIG. 10 or the characteristics of the indicator D itself.

First, the linearity of the indicator D itself was investigated and the results are shown in FIG. This is done by keeping the driving current id flowing through the driving electromagnetic coil 31 constant and braking current ib flowing through the braking electromagnetic coil 32.
The measurements were made by changing only the According to the figure, it was found that if id was kept constant, there was extremely good linearity in the range of 0 to 75% of the indicated value m. 0% means Emp level, so
The indicator D itself is more suitable for displaying the remaining amount of fuel at the Emp level.

From this, it is expected that the characteristics shown in FIG. 11 are caused not by the indicator D itself but by the circuit configuration. That is, since both coils 31 and 32 are connected in series, the potentiometer in the conventional circuit is
This is thought to be because not only the braking current ib but also the driving current id changes due to a change in the resistance value of R _x .

In this embodiment, an output correction circuit C is provided between the LV conversion circuit B and the indicator D in order to utilize the characteristics of the indicator D shown in FIG. 12 as is.

First, the basic principle of this output correction circuit C will be explained. The driving electromagnetic coil 31 is controlled with a constant current to adjust the linearity L-V conversion characteristic and the characteristic of the indicator D shown in FIG. 12. That is, conditions are created such that the indicated value m=100% at the displacement X=F and the indicated value m=0% at the displacement X=0, and adjustment is made to obtain linearity within this range.

That is, in FIG. 9, 33 is the L-V
This is an amplifier that amplifies the output voltage V _b of the conversion circuit B, and input resistors R4 and R5 are provided at its positive input terminal. 34 is a buffer circuit for the amplifier 33, and its output is sent to both electromagnetic coils 31 and 32.
It is connected to the connection terminal of the amplifier 33 and fed back to the negative input terminal of the amplifier 33. Let the output voltage of the buffer circuit 34 be _Vput . R6 and R7 are resistors for generating the offset voltage V _pffset and are connected to the negative input terminal of the amplifier 33. 35 is a constant current control circuit connected to the drive electromagnetic coil 31,
It consists of a resistor R8 and a Zener diode D1. That is, the voltage applied to the drive electromagnetic coil 31 is constant, and the drive electromagnetic coil 31 is always driven with a constant current (id constant).

Note that the internal resistance of the drive electromagnetic coil 31 is r1,
The internal resistance of the braking electromagnetic coil 32 is r2, and the amplifier 3 is
Let K be the amplification factor of 3.

Next, the effects of the output correction circuit C and the indicator D will be explained.

In the output correction circuit C, the following formula holds true.

V _put = K (V _b − V _pffset ) (6) V _put = ibr2 (7) Also, V _b at Full level is V _full ,
Letting V _b at the Emp level be V _enp , V _b can be expressed by the following formula.

V _b = - (V _{enp -} V _full )

ib=K(−(V _enp −V _full )X/F+V _enp −V
_pffset ))/r2(9) Also, from FIG. 12, m can be expressed by the following formula.

m=138.8ib/id+100 (10) From equations (9, 10), the following equation holds true for m.

m=138.8KX(V _enp −V _full )/idr2F+100−138.8K(
V _enp −V _pffset )/idr2(11) Here, it is necessary to adjust so that the following formula holds based on the conditions that m=100% when X=F and m=0% when X=0.

V _full =V _pffset (12) 138.8K (V _enp −V _pffset ) /idr2=100 (13) Here, if id is set to a certain value, the amplification factor K is determined. That is, the following formula holds true, and the instruction value m is directly proportional to the displacement X.

m=100X/F (14) Indication value m and displacement X measured in this example
Figure 13 shows the relationship between This is id=50mA
The measured values show high linearity and high indication accuracy.

Note that the following changes can also be made to the above embodiment.

(1) The material of the core 13 is not limited to the above-mentioned ferrite, but any magnetic material having high magnetic permeability and insulation properties may be used.

(2) The coil 12 may be wound in a manner other than the manner described in the above embodiment, for example, the winding density may be gradually increased from the lower end of the core 13, or the flat winding portion 14 may be wound in such a manner that the winding density gradually increases from the lower end of the core 13.
b and the distribution of the tightly wound portion 14c, etc.
Can be changed arbitrarily.

(3) In addition to the carbon-filled synthetic resin mentioned above, the material of the conductor ring 18 may be carbon fiber reinforced resin (CFRP), conductive polyvinyl chloride (PVC), conductive rubber, conductive foam rubber, etc., which has low specific gravity and is conductive. Any polymeric material can be used as long as it has the following properties. Note that if these materials have low corrosion resistance against liquid, a protective material may be provided on the inner periphery of the conductor ring 18.

Alternatively, the conductor ring 18 may be made of aluminum, copper or other metal and may be integrally formed on the inner periphery of the float 17, although this will result in a slight increase in weight.

(4) The output correction circuit C drives the drive electromagnetic coil 31 with a constant current, and may be any other circuit as long as it adjusts the characteristics of the indicator D and the characteristics of the LV conversion circuit B. . Furthermore, if very high accuracy is not required, the output correction circuit C may be omitted, or the output correction circuit C may be simplified as long as the drive electromagnetic coil 31 is driven with a constant current.

(5) Another type of indicator D may be used. In particular, if the driving electromagnetic coil 31 and the braking electromagnetic coil 32 are disconnected and made independent, the output correction circuit C can be omitted.

(6) In addition to the liquid level meter in an automobile fuel tank, it can also be embodied as a liquid level meter in various containers such as an oil tank, a water storage tank, a petroleum tank, and an electrolyte tank.

Note that the present invention is not limited to the configuration of the embodiment described above; for example, in the LV conversion circuit B, the frequency f of the oscillation circuit 22, the time constant of the LR series circuit, and the reference voltage V _s of the voltage comparison circuit 23 etc. may be changed and set as desired.

Effects of the Invention As detailed above, in this invention, by making the core material a magnetic material with insulating properties, the winding component of the core itself is released, and the inductance changes only by the conductive ring. This has the excellent effect of increasing detection sensitivity with a simple circuit and being able to obtain voltage corresponding to changes in coil inductance with high linearity.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing the entire embodiment of the present invention as a liquid level meter in a fuel tank of an automobile, Figs. 2 to 5 show the detection section of this embodiment, and Fig. 2 shows the detection section Overall sectional view, Figure 3a
is a front view showing the coil, Fig. 3b is a characteristic example showing the change in inductance of the same coil with respect to float displacement, Fig. 4 is a circuit diagram showing the magnetic equivalent circuit of the same coil, and Fig. 5 is a diagram showing the conduction around the outer periphery of the coil. A perspective view showing the cylinder, and Figs. 6 to 8 show the L-V conversion circuit.
Figure 7 is the circuit diagram, Figure 7 is an explanatory diagram of the operation of the circuit, Figure 7a is the voltage V _f , Figure b is the voltage Vr, Figure c is the voltage V _a , Figure 7 d is the voltage V _aod , Figure 7 e is an operation explanatory diagram showing changes in voltage V _b , Fig. 8 is a characteristic example diagram showing the relationship between the output voltage of the LV conversion circuit and the displacement of the float, and Fig. 9 is an output correction circuit and indicator circuit. Figure 10 is a circuit diagram showing the conventional indicator driving method, Figure 11 is a characteristic example diagram showing the relationship between the conventional indication value and potentiometer, and Figure 12 is the indication value and braking electromagnetic force of this embodiment. An example characteristic diagram showing the relationship with the current flowing through the coil, FIG. 13 is an example characteristic diagram showing the relationship between the indicated value and the displacement of the float, and FIG. 14 is a perspective view showing a conventional arm float type liquid level meter. , 15th
The figure is a perspective view showing a conventional linear potentiometer type liquid level meter, Fig. 16 is a partially enlarged view showing the linear potentiometer, and Fig. 17 is a sectional view showing the linear potentiometer in its installed state. be. Detection unit...A, L-V conversion circuit...B, Output correction circuit...C, Indicator...D, Coil...12,
Core...13, Winding...14, Float...1
7. Conductor ring...18, Oscillation circuit...22.

Claims (1)

[Claims] 1. An insulating magnetic core is inserted over the entire length of the coil, and a float with a conductive ring is movably provided around the outer circumference of the coil, so that the change in inductance of the coil due to the movement of the conductive ring is reduced to In a liquid level meter configured to convert voltage changes by a V conversion circuit to drive an indicator, the L-V conversion circuit connects a resistor forming an LR series circuit to a coil, and connects a resistor forming an LR series circuit to the coil. A liquid level meter characterized in that an oscillator circuit is connected to the circuit, and the response time until the voltage generated in the LR series circuit reaches a reference voltage is extracted to output a voltage corresponding to the inductance of the coil. .