JPH0240501Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a liquid level detection device that detects a liquid level using electromagnetic induction.

[Conventional technology]

As a conventional liquid level detection device, there is one shown in FIG. 7, for example. This is a so-called vertical type, and as shown in the figure, a resistor pattern 2 and a ground pattern 3 printed on the surface of a resistor board 1 are attached to a float 4 that moves up and down depending on the liquid level. A variable resistance type liquid level sensor 6 is provided with a configuration in which a contact piece 5 is in sliding contact, and a change in the liquid level is detected as a change in the resistance value of the liquid level sensor 6 via the float 4. By dividing the output voltage of the power supply 8 between the capacitor and the fixed resistor 7, the resistance value of the liquid level sensor 6 is converted into a voltage value, and this value is detected by the voltage detection circuit 9 and displayed as appropriate by the display circuit 10. It is configured to be displayed in mode.

[Problem that the invention attempts to solve]

However, in such a conventional liquid level detection device, the contact piece 5 slides on the resistance pattern 2 and the ground pattern 3 as the position of the float 4 changes. , there is a problem that the resistance value of the liquid level sensor 6 changes over time due to sliding wear of the printed patterns 2 and 3 or the contact piece 5, and that the printed pattern is broken. Since the output characteristic of the pattern-shaped upper liquid level sensor 6, that is, the change in resistance value with respect to the liquid level is step-like, there is a problem in that the detection accuracy of the liquid level cannot be increased.

This idea was created by focusing on these conventional problems, and it has a structure that can detect the liquid level without contact using electromagnetic induction, and can detect low liquid levels with higher accuracy. The aim is to solve the above problems by doing so.

[Means for solving problems]

Therefore, the liquid level detection device according to this invention has an upper coil formed so that the winding density becomes thinner to sparser from the upper side toward the middle point along the direction of change in the liquid level, and It consists of a series or parallel body with a lower coil whose winding density increases from sparse to dense as the winding density increases, and which is formed to generate magnetic flux in the opposite direction to the upper coil. A main excitation coil for overall detection is provided,
An upper coil is formed so that the winding density becomes denser to sparser from above to an intermediate point along the direction of change in liquid level, and the winding density becomes denser from sparser to lower from the intermediate point. and a sub-column in series or parallel with a lower coil formed to generate magnetic flux in the opposite direction to the upper coil, and provided for the lower range of the liquid level detection range for detecting a small amount. an excitation coil, a detection coil magnetically coupled to the main excitation coil and the sub-excitation coil and formed with substantially uniform winding density, and coil axes of the main excitation coil and sub-excitation coil or a coil axis of the detection coil. An inductive liquid level sensor is provided with an inductive liquid level sensor consisting of a shot ring disposed coaxially with the liquid level and moves up and down according to the liquid level, a first AC signal source is connected to the main excitation coil, and a first alternating current signal source is connected to the main excitation coil. A second AC signal source having a different frequency from the first AC signal source is connected to the excitation coil.

[Effect]

With this configuration, the detection coil generates an induced electromotive force with a waveform that corresponds to the positional relationship of the short ring with respect to the main and sub-excitation coils, and this induced electromotive force is generated every half cycle of the AC signal source. The liquid level is detected by measuring the effective value of the waveform obtained by detection.

[Example] Hereinafter, this invention will be explained in detail based on the drawings.

1 to 4 show a first embodiment of this invention, in which FIG. 1 is its circuit diagram, FIG. 2 is a vertical sectional view showing the schematic structure of the inductive liquid level sensor, and FIG. The figure is a waveform diagram at each point in the circuit of Figure 1, and Figure 4 is an output characteristic diagram of the inductive liquid level sensor.

First, the configuration will be explained based on FIGS. 1 and 2. In the figures, 11 is a first AC signal source;
12 is a second AC signal source, and the first AC signal source 1
1 outputs an alternating current signal a shown in FIG.
32 and the first detection control signal generation circuit 14, respectively. Further, the second AC signal source 12 outputs an AC signal c shown in FIG. supply to each. Note that the first and second AC signal sources 11 and 12
The frequencies of the alternating current signals a and c are such that circuit elements such as operational amplifiers constituting the amplifier circuits 181, 191, etc., which will be described later, can exhibit the desired characteristics, and the frequencies are such that the resonance phenomenon due to stray capacitance does not occur. Any low value can be set, and in this example, the AC signal a is set to 1KHz, and the AC signal c is set to 6KHz.
It is set to Hz. 14 is a first detection control signal generation circuit which inputs the AC signal a and generates a pulsed detection control signal b in synchronization therewith (see Fig. 3b).
Output. Reference numeral 15 denotes a second detection control signal generation circuit which inputs the AC signal c and outputs a pulsed detection control signal d (see FIG. 3d) synchronized therewith. Reference numeral 16 denotes a low-pass filter, which inputs the output signal e (see FIG. 3 e) from the inductive liquid level sensor (this will be explained in detail later) 13, and uses the signal e to filter the second alternating current. Signal source 12
A signal f (see FIG. 3 f) from which high frequency components have been removed is output, which corresponds to the AC signal c. Reference numeral 17 denotes a high-pass filter, which inputs the output signal e from the inductive liquid level sensor 13 and removes a low frequency component corresponding to the AC signal a from the first AC signal source 11 from the signal e. (see Figure 3g).
18 is a first detection circuit, and an amplifier circuit 1 that appropriately amplifies the output signal f from the low-pass filter 16.
81, and an analog switch 182 that detects the signal f based on the detection control signal b from the first detection control signal generation circuit 14. 19 is a second detection circuit, and an amplifier circuit 191 that appropriately amplifies the output signal g from the high-pass filter 17.
and an analog switch 192 that detects the signal g based on the detection control signal d from the second detection control signal generation circuit 15. 20 and 2
1 are first and second smoothing circuits, and the first smoothing circuit 20 receives the output signal h from the first detection circuit 18.
(see FIG. 3h), and the second smoothing circuit 21 outputs the output signal i from the second detection circuit 19 (the third
(see Figure i) respectively. 22 and 23 are the first
and a second voltage detection circuit, the first voltage detection circuit 22 detects the voltage value of the DC voltage signal h' (see h' in Fig. 3 h) output from the first smoothing circuit 20,
Further, the second voltage detection circuit 23 receives the DC voltage signal i' (FIG. 3 i) output from the second smoothing circuit 21.
Detect the voltage values of (see i' in the figure). 24 is a display control circuit in which the voltage value of the voltage signal h' from the first smoothing circuit 20 is at the upper limit of the detection range (fourth
Only when the output data from the second voltage detection circuit 23, that is, the second smoothed voltage detected by the second voltage detection circuit 23 _, is equal to or less than a predetermined value corresponding to Control is performed so that the voltage value of the voltage signal i' from the circuit 21 is output to a child display 252, which will be described later. Reference numeral 25 denotes a parent-child display, which supplies output data from the first voltage detection circuit 22 (voltage value data of voltage signal h') via a parent display 251 that displays a bar graph and the display control circuit 24. and a slave display 252 for digitally displaying output data (voltage value data of voltage signal i') from the second voltage detection circuit 23.

Next, the inductive liquid level sensor 13 will be explained. Generally speaking, the inductive liquid level sensor 13 consists of a main excitation coil 13 wound around a core 131.
2, a sub-excitation coil 134 wound around the outer circumference of a plastic inner case 133 that houses the main excitation coil 132, and a detection coil wound around the outer circumference of a plastic outer case 135 that houses this sub-excitation coil 134. It consists of a coil 136 and a short ring 138 which is a coil provided on a float 137 that moves up and down depending on the liquid level.To explain in more detail, the main excitation coil 132
An upper coil 1321 and a lower coil 132 are wound around a core 131 that has a length covering the entire liquid level detection range and is vertically installed in the direction of change in the liquid level.
2, the upper coil 1321
is from the top to the center (the midpoint of 1/2 of the liquid level detection range)
The lower coil 1322 is formed such that the winding density becomes denser from denser toward the center, and the lower coil 1322 is formed so that the winding density becomes denser from sparser toward the center downward. Excitation coil 132
is connected to the first AC signal source 11.
Further, the sub-excitation coil 134 has a small amount detection range (for example,
Here, it consists of a series body of an upper coil 1341 and a lower coil 1342, which are wound over the range from 1/3 to the lower limit of the liquid level detection range. the lower coil 1342
is formed so that the winding density becomes denser from sparse toward the bottom from the center, and furthermore, this sub-excitation coil 134 is connected to the second AC signal source 12 . Further, the detection coil 136 is
The main and sub-excitation coils 132 and 134 are housed in a plastic outer case 135, which is wound with substantially uniform winding density along the direction of change in the liquid level over the entire liquid level detection range on the outer periphery of the plastic outer case 135 that houses the main and sub-excitation coils 132, 134. The main and sub-excitation coils 132 are wound around the outer periphery of the outer case 135.
134. Furthermore, the shot ring 138 is wound around the outer periphery of a float 137 that is loosely fitted around the outer periphery of the outer case 135 around which the detection coil 136 is wound and moves up and down according to the liquid level. It is magnetically coupled to the main and sub excitation coils 132, 134 and the detection coil 136.

The operation of the liquid level detection device configured in this way will be explained.

First, considering the case where the liquid level is at a high level, in this case, the shot ring 138
As shown in FIG. 1 or 2, the coil 132 faces only the upper coil 1321 of the main excitation coil 132, and does not face its lower coil 1322 and the sub-excitation coil 134. Therefore, the upper and lower coils 1341 and 1342 of the sub-excitation coil 134
None of the magnetic flux is shot by the shot ring 138, and the electromotive force induced in the detection coil 136 by the magnetic flux of its upper coil 1341 and the magnetic flux of its lower coil 1342 are induced in the detection coil 136. The induced electromotive force to be outputted from the detection coil 136 by the sub-excitation coil 134 becomes zero because the electromotive force generated by the sub-excitation coil 134 cancels each other out with opposite signs. On the other hand, since the shot ring 138 faces a portion of the upper coil 1321 of the main excitation coil 132, the magnetic energy generated by the portion of the upper coil 1321 facing the shot ring is transferred to the shot ring 138.
As a result, this upper coil 1
Since no magnetic flux is generated by the part of the upper coil 1321 facing the shot ring, only the magnetic flux by the part of the lower coil 1322 that generates the magnetic flux by the part of the upper coil 1321 facing the shot ring acts on the detection coil 136. Only the induced electromotive force due to the magnetic flux generated by a portion of the coil 1322 is not canceled out and the detection coil 13
Output from 6. When the liquid level is at a high level, as shown in the left half of FIG. An induced electromotive force with a peak value corresponding to the liquid level seen from the midpoint of 1/2 is output.

Next, considering the case where the liquid level is at a low level, in this case, the shot ring 138
is the lower coil 1322 of the main excitation coil 132 and the upper or lower coil 134 of the sub-excitation coil 134.
1 and 1342, respectively.
Therefore, the lower coil 132 of the main excitation coil 132
The magnetic energy generated by the shot ring opposing portions of the upper or lower coils 1341 and 1342 of the second and sub-excitation coils 134 is consumed by the shot ring 138, respectively, and as a result,
Since no magnetic flux is generated by the opposing portions of the shot rings, the main excitation coil 132 generates magnetic flux from the upper coil 1321 that cancels the magnetic flux caused by the portions of the lower coil 1322 facing the shot rings.
Only the magnetic flux due to a part of the auxiliary excitation coil 1
34 to its upper or lower coil 1341,1
A lower or upper coil 134 that generates a magnetic flux that cancels the magnetic flux due to the opposing portion of shot ring 342.
Only the magnetic flux generated by a portion of the upper coil 1321 of the main excitation coil 132 and the induced electromotive force due to the magnetic flux generated by a portion of the upper coil 1321 of the main excitation coil 132 act on the detection coil 136, respectively.
Only the induced electromotive force due to the magnetic flux generated by a portion of the lower or upper coils 1342, 1341 of 4 is output from the detection coil 136. When the liquid level is at a low level, as shown in the right half of FIG. The induced electromotive force of the peak value according to the liquid level as seen from the midpoint of 1/2, and the same phase as the AC signal c of the second AC signal source 12, and the midpoint of 1/2 of the detection range at the time of small amount. An induced electromotive force that is superimposed with an induced electromotive force having a wave height corresponding to the liquid level seen from the tank is output.

Therefore, the induced electromotive force e (see FIG. 3 e) output from the detection coil 136 of the induction type liquid level sensor 13 is input to the low-pass filter 16 and the high-pass filter 17, respectively.
As shown in FIG. 3f, a voltage signal is synchronized with the AC signal a of the first AC signal source 11 and has a phase relationship and a peak value with respect to the AC signal a according to the liquid level at that time. f is constantly outputted, and the high-pass filter 17 synchronizes with the AC signal c from the second AC signal source 12 as shown in FIG. The voltage signal g with the corresponding phase relationship and peak value is output only when the liquid level is within the small amount detection range.

The voltage signal f output from this low-pass filter 16 is processed by the first detection circuit 18 based on the detection control signal b output from the first detection control signal generation circuit 14 at the timing shown in FIG. 3b. The first detection circuit 18 outputs a voltage signal h having a waveform shown in FIG. 3h. This output signal h is supplied to the first smoothing circuit 20 and smoothed (see h' in FIG. 3h). The DC voltage h' obtained by this smoothing is due to the fact that the main excitation coil 132 is wound in the direction of change in the liquid level from dense to sparse and then from sparse to dense. The curve in Figure 4 changes depending on the change in
Although the value of the DC voltage changes as shown in h', the value of the DC voltage at each time is determined by the first voltage detection circuit 2
2, the parent-child display 25
The parent display 251 displays a par graph as the current liquid level.

On the other hand, the voltage signal g outputted from the high-pass filter 17 is transmitted to the second detection circuit 19 based on the detection control signal d outputted from the second detection control signal generation circuit 15 at the timing shown in FIG. This second detection circuit 19
A voltage signal i having a waveform shown in FIG. 3i is output from the circuit. This output signal i is supplied to the second smoothing circuit 21 and smoothed (see i' in FIG. 3).
The DC voltage i' obtained by this smoothing is determined by the fact that the sub-excitation coil 134 is wound in the direction of change in the liquid level from dense to sparse and then from sparse to dense. The DC voltage will change as shown by curve i' in FIG. The child display device 252 of the parent-child type display device 25 via the control circuit 24
This will digitally display the current liquid level.

Next, FIG. 5 shows a second embodiment. In this embodiment, the main excitation coil 132 is composed of an upper coil 1321 and a lower coil 1322 in parallel, and the sub-excitation coil 134 is composed of an upper coil 1341 and a lower coil 1342 in parallel. Components that are the same as those of the first embodiment described above are designated by the same reference numerals, and their explanations will be omitted.

The third embodiment shown in FIG. 6 uses a ring-shaped disc 138' made of metal such as aluminum as the shot ring of this invention. do.

The shot ring may also be formed by mixing magnetic powder into a synthetic resin for forming a float. In addition, as a short ring, a coil alone can work in principle, but by inserting a capacitor in series and setting the input frequency to the resonance frequency = 1/2π√LC, the short ring can be connected in series with a coil and a capacitor. By creating a resonant circuit consisting of a circuit, the current value flowing through the series circuit is maximized, and energy consumption within the shot ring is maximized, resulting in an output voltage that is higher than that without a capacitor.

Incidentally, in each of the above embodiments, the magnetic coupling between the main and sub-excitation coils 132, 134 and the detection coil 136 is of the core (iron core) type, but this invention is not limited to this only; ) type magnetic coupling may also be used. Further, in the above embodiment, the upper coils 1321, 1341 and the lower coils 1322, 1342 are wound so that the main and sub excitation coils 132, 134 are respectively centrally symmetrical, but arbitrary output characteristics can be obtained. Furthermore, in each of the above embodiments, the rate of change in the winding density of the two upper and lower coils 1321, 1341, 1322, 1342 constituting the main and sub excitation coils 132, 134 is determined by the change in the liquid level. Although it is made to be uniform along the direction, it may be made non-uniform in order to match the shape of the liquid storage tank or to obtain straight or arbitrary curved output characteristics. Furthermore, in each of the above embodiments, the liquid level information is displayed on the parent-child display 25, but it goes without saying that it may be used along with other information as basic data for calculating a certain physical quantity.

[Effect of idea]

As explained above, according to this idea,
Since the liquid level can be detected without contact, a highly durable liquid level detection device can be provided. Further, according to this invention, since the sensor output changes continuously with respect to the liquid level, the resolution when the liquid is full or small is increased, and the accuracy of detecting the liquid level can be increased. Moreover, according to this invention, in addition to the main detection part for detecting the entire liquid level change range, there is also a sub-detection part exclusively for small quantity, so low liquid level can be detected with even higher accuracy. It is possible to obtain effects such as being able to provide a liquid level detection device suitable for vehicle fuel gauges and the like.

[Brief explanation of drawings]

Figure 1 shows the first part of the liquid level detection device according to this invention.
A circuit diagram showing an embodiment, FIG. 2 is a vertical cross-sectional view of the same inductive type liquid level sensor, FIG. 3 is a waveform diagram at each point in the circuit of FIG. 1, and FIG. 4 is also the same inductive type liquid level sensor. Fig. 5 is a main circuit diagram showing the second embodiment, Fig. 6 is a vertical cross-sectional view showing the inductive liquid level sensor in the third embodiment, and Fig. 7 is a conventional liquid level detection device. FIG. DESCRIPTION OF SYMBOLS 11...First AC signal source, 12...Second AC signal source, 13...Inductive liquid level sensor, 132...
...Main excitation coil, 134...Subexcitation coil, 13
6...Detection coil, 138, 138'...Shot ring, 1321, 1341...Upper coil,
1322, 1342...lower coil.

Claims (1)

[Scope of utility model registration request] The upper coil 1321 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. The main excitation coil 132 is formed in series or in parallel with a lower coil 1322 formed to generate magnetic flux in the opposite direction to the upper coil 1321, and is provided over the entire liquid level detection range. , an upper coil 1341 formed such that the winding density becomes sparse from above toward the middle point along the direction of change in the liquid level, and a winding density from sparse to dense from the middle point downward. and a lower coil 134 formed to generate magnetic flux in a direction opposite to that of the upper coil 1341.
A sub-excitation coil 1 is formed in series or in parallel with 2 and is provided for the lower range of the liquid level detection range.
34, a detection coil 136 magnetically coupled to the main excitation coil 132 and the sub-excitation coil 134 and formed with substantially uniform winding density, and a coil axis of the main excitation coil 132 and the sub-excitation coil 134 or the detection coil 136. The main excitation coil 132 includes an inductive liquid level sensor 13 consisting of shot rings 138 and 138' that are disposed coaxially with the coil axis of the coil 136 and move up and down according to the liquid level.
The first AC signal source 11 is connected to the auxiliary excitation coil 134, and the first AC signal source 11 is connected to the
A liquid level detection device characterized in that the liquid level is detected based on the induced electromotive force obtained from the detection coil 136 by connecting a second alternating current signal source 12 having a different frequency.