JPH0355068Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Field of Application of the Invention) The present invention relates to a liquid level detection device that detects the height of a liquid level using induced electromotive force.

(Background of the Idea) As a conventional induction liquid level sensor of this type of electromagnetic liquid level detection device, there is one having a structure shown in FIG. 4, for example. This induced liquid level sensor 12 includes a first coil 122 wound around a synthetic resin core 120;
A second coil 1 is wound around the outer circumference of a plastic case 123 that houses this first coil 122.
24 and a float 125 that moves up and down depending on the liquid level.
and a short ring 126 consisting of a coil provided approximately at the center thereof. Further, the first coil 122 includes an upper coil 1221 wound on the upper part of the core 120 and a lower coil 1222 wound on the lower part, and the upper coil 1221 is composed of the upper multi-turn coil 122 having multiple turns.
21a, and the coil 1 is connected in series adjacent to the coil 1, and the winding density decreases from dense to sparse from above toward the middle point along the direction of change of the liquid level.
221a and an upper unevenly wound coil 1221b that generates magnetic flux in the same direction. The lower coil 1222 has a lower non-uniformly wound coil 1222b whose winding density becomes denser from sparse to denser from the middle point downward along the direction of change in the liquid level, and which generates magnetic flux in the opposite direction to the coil 1221b. , connected in series adjacent to this, and the coil 12
22b, and a lower multiple-turn coil 1222a with multiple turns that generates magnetic flux in the same direction.

The coil 1221 is connected in series to a lower coil 1222, and is also connected to an AC signal power source 1, which will be described later.
1 (see FIG. 5). The second coil 124 is wound around the outer periphery of the plastic case 123 that houses the first coil 122 with substantially uniform density along the direction of change in the liquid level.
It is magnetically coupled to the coil 122 of. Note that the upper and lower unevenly wound coils 1221b, 122
2b and the second coil 124 are wound over the entire liquid level detection range, and the upper and lower unevenly wound coils 1221a and 1222a are wound around the upper and lower unevenly wound coils 1221 outside the liquid level detection range.
a, 1222b.

The shot ring 126 is connected to the float 12.
5 through the first and second coils 122,1
The first and second coils 122, 124 are arranged coaxially with respect to the coil axis of 24.
It is magnetically coupled to the tank, and in that state it moves up and down depending on the liquid level. 11 is an AC signal source that sends an AC signal to the first coil 122 of the inductive liquid level sensor 12, and 13 is a detection control signal generation circuit that outputs a pulsed detection control signal during a half cycle of the AC signal. . 14 is a detection circuit, which includes an amplifier 141 that amplifies the alternating current voltage induced in the second coil 124 of the induction sensor 12, and a switch that is closed during the period when the detection control signal generation circuit 13 outputs the detection control signal. an analog switch 142 that outputs the signal output from the amplifier 141;
It is composed of. 15 is a smoothing circuit that smoothes the signal output from the analog switch 142;
16 is a voltage detection circuit that detects the voltage of the signal smoothed by the smoothing circuit 15; 17 is a detection circuit 16;
This is a display circuit that displays the liquid level according to the detected voltage.

The frequency of the AC signal output from the AC signal power supply 11 is set to a low enough level that circuit elements such as operational amplifiers constituting the amplifier circuit 141 etc. can exhibit the desired characteristics, and that resonance phenomena due to stray capacitance do not occur. Any value can be set; for example, in this conventional example, it is set to 10kHz.

Now, when an AC signal flows to the first coil 122 by the AC signal power source 11, the second coil 12
The AC voltage induced from 4 is output. on the other hand,
A detection control signal is output from the detection control signal generation circuit 13, and this closes the analog switch 142 of the detection circuit 14 for a half cycle of the AC signal, so that the AC voltage output from the second coil 124 is transmitted to the detection circuit. 14, only a half-cycle voltage is output from the detection circuit 14. The detected half-cycle voltage is smoothed into a DC voltage by a smoothing circuit 15, and this DC voltage is detected by a voltage detection circuit 16.

By the way, the induced liquid level sensor 12 having such a configuration
In this case, since the float 125 is externally enclosed in the case 123, when used for detecting the fuel oil level in a vehicle, for example, when the float 125 moves up and down following the fluctuation of the liquid level when the vehicle is running, Since the indicated value of a meter that indicates the liquid level constantly fluctuates and becomes difficult to read, for example, a cylindrical outer cylinder with a small hole at the bottom is prepared separately, and the induction liquid level sensor 12 is installed inside this outer cylinder. It was designed to eliminate the influence of liquid level fluctuations on the float 125 as much as possible.

(Purpose of the invention) The present invention was devised in view of this point of view, and is equipped with an inductive liquid level sensor that is structured to eliminate the effects of liquid level fluctuations without the need for a separate outer cylinder for wave prevention. The object of the present invention is to provide an electromagnetic liquid level detection device.

(Embodiments of the invention) The present invention will be described in detail below based on embodiments shown in the drawings.

FIG. 1 shows a cross-sectional view of an induced liquid level sensor showing an embodiment of the present invention, and the same parts between the structure of this embodiment and the structure shown in the conventional example are designated by the reference numerals cited in the conventional example. A description of the structure of this embodiment will be omitted.

In the figure, 20 is a hollow resin core, around which a first coil 122 is wound, and a second coil 124 around the first coil 122.
are wound, and these first and second coils 12
2, 124 is covered with a coating layer 21 made of resin material or the like. 22 is a magnetic float having a magnetic substance;
It is placed in the core 20 so as to be vertically movable, and moves up and down in response to changes in the liquid level. The bottom of the core 20 is closed by a bottom cover 24 having a small hole 23 in the center thereof, and liquid flows into and out of the core 20 through this small hole 23. In other words, sudden changes in the liquid level or constant minute fluctuations can cause the core 2
Since the liquid inside the core 20 communicates with the outside liquid through the small hole 23 of the bottom cover 24, the liquid level within the core 20 changes slowly and is maintained at a substantially predetermined level.

In this embodiment, as shown in FIG. 2, the second coil 124 is used as an excitation coil and connected to the AC signal power source 11, and the first coil 122 is used as a detection coil to create a detection circuit. 14
is connected to.

Next, liquid level detection by the liquid level detecting device configured as described above will be explained with reference to a circuit such as that shown in FIG.

The magnetic flux of the first coil 122 at the positions indicated by the symbols ~ is represented by: Position where the float 22 is not present: φ=μ ₁ nAi Position where the float 22 is present: φ′=μ _x nAi.

Here, n: number of turns per unit length of the coil, A:
Coil diameter, i: current, μ ₁ : magnetic permeability in air, μ _x :
The magnetic permeability of the float 22 has the relationship μ _x ≫ μ ₁ .

The induced electromotive force at each position of ~ when the float 22 is at the position is: e ₁ = n ₁ dφ/dt : e ₂ = n ₂ dφ'/dt : e ₃ = n ₃ dφ/dt : e ₄ = 0 : e ₅ = -n ₃ dφ/dt : e ₆ = -n ₂ dφ/dt : e ₇ = -n ₁ dφ/dt And the output E from the first coil 122 at this time is E= e ₁ +e ₂ +e ₃ +e ₄ +e ₅ +e ₆ +e ₇ =n ₁ dφ/dt+n ₂ dφ'/dt+n ₃ dφ/dt+0 -n ₃ dφ/dt−n ₂ dφ/dt−n ₁ dφ/dt =n ₂ (dφ′/dt−dφ/dt) = (μ _x − μ ₁ ) n ₂ nAdi/dt From μ _x ≫ μ ₁ , E=n ₂ μ ₂ nAdi/dt.

Therefore, the float position, that is, the liquid level can be detected by the sensor output E.

That is, the sensor shown in FIG. 4 uses the shot ring 126 to extinguish the magnetic flux at a position of the shot ring 126 and outputs a composite of the induced electromotive force at other positions, but in this embodiment, the magnetic float 22
The magnetic flux at the position of the float 22 is increased by this, and the float position is detected by combining the induced electromotive force.

(Summary of the invention) As explained above, the present invention has an upper coil 1221 formed such that the winding density becomes sparse from the top toward the middle point along the direction of change in the liquid level. A first coil formed in series or in parallel with a lower coil 1222 formed such that the winding density becomes denser from sparse downwards from the intermediate point and generates magnetic flux in the opposite direction to that of the upper coil 1221. a second coil 124 magnetically coupled to the first coil 122 and formed to have a substantially uniform winding density with spacing in the direction of change in the liquid level;
A hollow resin core 20 around which the first coil 122 and the second coil 124 are wound, and a magnetic float 2 housed within the resin core 20.
2, the first
Alternatively, by connecting the AC signal source 11 to either one of the second coils 122, 124, an induced electromotive force is obtained from the other of the first or second coils 122, 124, and the induced electromotive force is This liquid level detection device is characterized in that the detection output is the effective value of a waveform obtained by detecting the AC signal source 11 every half cycle.

(Effect of the invention) Therefore, according to the invention, by inserting the magnetic float 22 into the core 20, the core 20
Since it also acts as a breakwater cylinder, it is possible to eliminate the effects on the magnetic float 22 such as sudden changes in the liquid level and fluctuations in the liquid level, and it is possible to detect a normal liquid level without installing a separate breakwater cylinder in the liquid level sensor. The effect can be obtained by being able to detect the position.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing an embodiment of the sensor of the liquid level detection device according to the present invention, Fig. 2 is its electrical circuit diagram, Fig. 3 is its equivalent circuit diagram, and Fig. 4 is a sectional view of a conventional sensor. , FIG. 5 shows its electrical circuit diagram. 20... Resin core, 21... Covering layer, 22...
...Magnetic float, 23...Small hole, 24...Bottom cover.

Claims (1)

[Scope of utility model registration request] The upper coil 1221 is formed so that the winding density becomes thinner to sparser from above toward the middle point along the direction of change in the liquid level, and the winding density becomes thinner from sparse toward the bottom from the middle point. a first coil 122 formed in series or in parallel with a lower coil 1222 formed to generate magnetic flux in the opposite direction to the upper coil 1221; A second coil 124 is formed to have a substantially uniform winding density in the direction of change in the liquid level, and a hollow resin core 20 around which the first coil 122 and the second coil 124 are wound. and a magnetic float 22 housed in the resin core 20, and an AC signal source 11 is connected to either the first or second coil 122, 124. The induced electromotive force is obtained from the other of the first or second coils 122, 124, and the effective value of the waveform obtained by detecting the induced electromotive force every half cycle of the AC signal source 11 is detected. A liquid level detection device characterized in that it serves as an output.