JPH0240502Y2 - - 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. 6, 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 body with a lower coil formed to generate an induced electromotive force in the opposite direction to the upper coil so that the winding density increases from sparse to dense toward the upper coil, and covers the entire liquid level detection range. a main detection coil for overall detection provided over the entire area, an upper coil formed so that the winding density becomes sparse from the top toward the middle point along the direction of change in the liquid level, and the middle point. It consists of a series body with a lower coil formed to generate an induced electromotive force in the opposite direction to the upper coil so that the winding density becomes denser from sparse toward the bottom, and the liquid level detection range A sub-detection coil for detecting a small amount is provided for the lower range of the sub-detection coil, and is magnetically coupled to the main detection coil and the sub-detection coil, and is formed with a substantially uniform winding density along the direction of change of the liquid level. An induction type consisting of an excitation coil, and a shot ring that is disposed coaxially with the coil axis of the main detection coil and sub-detection coil or the coil axis of the excitation coil, and that moves up and down according to the liquid level. Equipped with a liquid level sensor,
The structure is such that an AC signal source is connected to the excitation coil.

[Effect]

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

〔Example〕

This invention will be explained in detail below based on the drawings.

1 to 4 show a first embodiment of this invention, in which FIG. 1 is a circuit diagram thereof, 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 FIG. 1 and FIG. The AC signal a shown in is output. The frequency of this alternating current signal a is a value that is low enough to allow circuit elements such as an operational amplifier constituting the amplifier circuit 151, etc., which will be described later, to exhibit the desired characteristics, and that does not cause resonance due to stray capacitance. If there is, it can be set arbitrarily, and in this embodiment it is set to 1KHz. Reference numeral 13 denotes a detection control signal generation circuit which inputs the AC signal a and outputs a pulsed detection control signal b (see FIG. 3b) in synchronization with the AC signal a. Reference numeral 14 denotes a selection circuit which outputs an output signal c from the main detection coil 122 (see FIG. 3c) of the inductive liquid level sensor (this will be explained in detail later) 12 and an output from the sub-detection coil 124. A signal d (see FIG. 3 d) is input, and a first control signal g from a level comparison circuit 18, which will be described later, is input.
The former signal c when is not supplied, and
The latter signal d is selectively output when the first control signal g is supplied. 15 is a detection circuit, which includes an amplifier circuit 151 that appropriately amplifies the output signal e (see FIG. 3 e) from the selection circuit 14; and an analog switch 152 for detecting the signal. A smoothing circuit 16 smoothes the output signal f (see f in FIG. 3) from the detection circuit 15. A voltage detection circuit 17 detects the voltage value of the DC voltage signal f' or f'' (see f' or f'' in FIG. 3f) output from the smoothing circuit 16. 18
is a level comparison circuit that detects when the voltage values of the voltage signals f' and f'' from the smoothing circuit 16 have become below a predetermined value corresponding to the upper limit of the small quantity detection range (see L ₀ in Fig. 4). Comparative detection is performed to output first and second control signals g and g', the first control signal g is sent to the selection circuit 14 for sensor output switching control, and the second control signal g' is These are supplied to a bar graph type display 19, which will be described later, for scale display switching control.19 is a bar graph type display, and the output data (voltage signal) from the voltage detection circuit 17 is supplied to
f', f'' voltage value data) by changing the lighting range of bar-shaped segments accordingly, and a bar graph display section 191 that displays the liquid level from the bar display length of the bar graph display section 191. The scale display section 192 includes a main scale display section 1921 for overall detection attached to one side of the bar graph display section 191, and a scale display section 192 for reading the bar graph display section 191.
It consists of a sub-scale display section 1922 for small quantity detection attached to the other side, and the main scale display section 1
921 is selectively displayed when the second control signal g' from the level comparison circuit 18 is not supplied, and the subscale display section 1922 is selectively displayed when the second control signal g' is not supplied from the level comparison circuit 18. selectively displayed when

Next, the inductive liquid level sensor 12 will be explained. Generally speaking, the inductive liquid level sensor 12 consists of a main detection coil 12 wound around a core 121.
2, a sub-detection coil 124 wound around the outer circumference of a plastic inner case 123 that houses this main detection coil 122, and an excitation coil wound around the outer circumference of a plastic outer case 125 that houses this sub-detection coil 124. It consists of a coil 126 and a shot ring 128 which is a coil provided on a float 127 that moves up and down depending on the liquid level.To explain in more detail, the main detection coil 122
An upper coil 1221 and a lower coil 122 are wound around a core 121 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 1221
is from the top to the center (the midpoint of 1/2 of the liquid level detection range)
The lower coil 1222 is formed so that the winding density becomes from dense to sparse as the winding density decreases downward from the center so that the lower coil 1222 generates an induced electromotive force in the opposite direction to that of the upper coil 1221. are formed from sparse to dense. Further, the sub detection coil 124 extends over a small amount detection range (for example, a range from 1/3 of the liquid level detection range to the lower limit here) on the outer periphery of the plastic inner case 123 that houses the main detection coil 122. Upper coil 1241 and lower coil 1242 wound together
The upper coil 1241 is arranged in series with
The winding density decreases downward from the center so that the lower coil 1242 generates an induced electromotive force in the opposite direction to that of the upper coil 1241. are formed from sparse to dense. Further, the excitation coil 126 is connected to the main and sub excitation coils 12.
The outer case 125 made of plastic that houses the plastic outer case 125 is wound with a 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 outer case 125. By being wound around the outer periphery of the coil, it is magnetically coupled to the main and sub-detection coils 122 and 124.
Furthermore, this excitation coil 126 is connected to the AC signal source 11. Furthermore, the shot ring 128 is wound around the outer periphery of a float 127 that is loosely fitted around the outer periphery of the outer case 125 around which the excitation coil 126 is wound and moves up and down according to the liquid level, Thereby, it is magnetically coupled to the main and sub detection coils 122, 124 and the excitation coil 126.

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 128
is the excitation coil 1 as shown in Fig. 1 or Fig. 2.
26 to the upper coil 1 of the main detection coil 122
221 and not its lower coil 1222 and sub-detection coil 124. Therefore, the excitation coil 126 is connected to the upper and lower coils 1241 and 1242 of the sub-detection coil 124.
The magnetic flux from the shot ring 128 acts without being shot in any way.
Since the induced electromotive force generated in the upper coil 1241 and the induced electromotive force generated in the lower coil 1242 have opposite signs and cancel each other out, the induced electromotive force that should be output from this sub-detection coil 124 becomes zero. On the other hand, the magnetic energy generated by the part of the excitation coil 126 that is opposed to the shot ring 128, that is, the part that faces the shot ring, is consumed by the shot ring 128, and as a result, the magnetic flux due to the part that faces the shot ring is transferred to the main detection coil 122. Upper coil 122
1, and the induced electromotive force by the upper coil 1221 is no longer generated, so only the induced electromotive force by the lower coil 1222, which should cancel out the induced electromotive force by the upper coil 1221, remains without being canceled. It is output from the main detection coil 122. When the liquid level is at a high level, the main detection coil 122 outputs the AC signal a from the AC signal source 11, as shown in the left half of FIG. 3c.
(Refer to the waveform shown by the dotted line in Figure 3 c) The induced electromotive force is output in the same phase as the waveform shown by the dotted line in Figure 3c, and with a peak value corresponding to the liquid level as seen from the midpoint of 1/2 of the liquid level detection range. However, as shown in the left half of FIG. 3d, no induced electromotive force is output from the sub-detection coil 124.

Next, considering the case where the liquid level is at a low level, in this case, the shot ring 128
is the left detection coil 12 via the excitation coil 126.
2 and the upper or lower coils 1241 and 1242 of the sub-detection coil 124, respectively. Therefore, excitation coil 1
The magnetic energy generated by the opposing portions of the shot rings 128 of the 26 shot rings 128 is consumed by the shot rings 128, and as a result, the magnetic flux due to the shot ring opposing portions is transferred to the lower coil 1222 of the main detection coil 122 and the magnetic energy generated by the shot ring opposing portions. does not act on the upper or lower coils 1241 and 1242 of the sub-detection coil 124, respectively;
Since the induced electromotive force caused by the lower coil 1222 of the main detection coil 122 and the induced electromotive force caused by the upper or lower coils 1241 and 1242 of the sub-detection coil 124 are no longer generated, the main detection coil 12
2, only the induced electromotive force caused by the upper coil 1221 that should cancel out the induced electromotive force caused by the lower coil 1222 remains and is output from the sub-detection coil 124. Lower or upper coils 1242, 124 to cancel the induced electromotive force
Only the electromotive force induced by 1 remains uncancelled and is output. Therefore, when the liquid level is at a low level, the main detection coil 122 detects the
As shown in the right half of , the signal has the same phase as the AC signal a of the AC signal source 11 (see the waveform shown by the dotted line in Figure 3 c) and is viewed from the midpoint of 1/2 of the liquid level detection range. An induced electromotive force having a peak value corresponding to the liquid level is output, and the sub-detection coil 124 outputs an AC signal a from the AC signal source 11 (in Figure 3 d), as shown in the right half of Figure 3 d. An induced electromotive force is output that has the same phase as the waveform shown by the dotted line (see the waveform shown in the dotted line diagram) and has a peak value that corresponds to the liquid level as seen from the midpoint of 1/2 of the detection range when the amount is small.

Therefore, the induced electromotive force c (FIG. 3c) output from the main detection coil 122 of the inductive liquid level sensor 12
) and the induced electromotive force d (see FIG. 3 d) output from the sub-detection coil 124.
The selection circuit 14 is controlled by the first control signal g from the level comparison circuit 18, and when the liquid level is at a high level, the induced electromotive force c from the main detection coil 122 is controlled by the first control signal g from the level comparison circuit 18. is selectively output, and when the liquid level is at a low level, the induced electromotive force d from the sub-detection coil 124 is selectively output. The voltage signal e (see FIG. 3e) output from the selection circuit 14 is sent to the detection circuit 15 based on the detection control signal b output from the detection control signal generation circuit 13 at the timing shown in FIG. 3b. The voltage signal f having the waveform shown in FIG. 3f is output from the detection circuit 15. This output signal f is supplied to the smoothing circuit 16 and smoothed (f' in Fig. 3 f,
f′).The DC voltage obtained by this smoothing is f′,
f″ is determined according to the change in the liquid level because the main and sub-detection coils 122 and 124 are wound from dense to sparse and then from sparse to dense along the direction of change in the liquid level. The DC voltage changes as shown by curves f' and f'' in FIG. The current liquid level will be displayed as a bar graph.

Next, FIG. 5 shows a second embodiment. In this embodiment, a ring-shaped disk 128' made of metal such as aluminum is used as the shot ring of this invention, and this shot ring 128' functions to consume magnetic energy by eddy loss.

The shot ring may also be formed by mixing magnetic powder into a synthetic resin for forming a float. In principle, a coil alone can act as a short ring, but by inserting a capacitor in series and setting the input frequency to the resonant frequency f = 1/2π√LC, the short ring can be used as a combination of a coil and a capacitor. By creating a resonant circuit consisting of a series circuit, the current value flowing through the series circuit is maximized, and energy consumption within the short 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 detection coils 122, 124 and the excitation coil 126 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 each of the above embodiments, the upper coils 1221, 1241 and the lower coils 1222, 1242 are wound so that the main and sub detection coils 122, 124 are centrally symmetrical, respectively.
The center may be asymmetrical so as to obtain an arbitrary output characteristic. Furthermore, in each of the above embodiments, the winding density of the upper and lower two coils 1221, 1241, 1222, 1242 constituting the main and sub detection coils 122, 124 is Although the rate of change is made uniform along the direction of liquid level change, it may be made non-uniform to match the shape of the liquid storage tank or to obtain straight or arbitrary curved output characteristics. good. Furthermore, in each of the above embodiments, the liquid level information is displayed on the bar graph display 19, 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 the drawing]

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 longitudinal sectional view showing an inductive liquid level sensor in the second embodiment, and FIG. 6 is a schematic configuration diagram showing a conventional liquid level detecting device. 11... AC signal source, 12... Inductive liquid level sensor, 122... Main detection coil, 124... Sub detection coil, 126... Excitation coil, 128, 12
8'...Shot ring, 1221, 1241...
...Upper coil, 1222, 1242...Lower coil.

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. The main detection coil 122 consists of a series body with a lower coil 1222 formed to generate an induced electromotive force in the opposite direction to the upper coil 1221, and is provided over the entire liquid level detection range. The upper coil 1241 is formed so that the winding density becomes sparse from above toward the middle point along the direction of change in the liquid level, and the winding density becomes sparse from the middle point downward. The lower coil 1242 is formed in series with a lower coil 1242 formed to be densely arranged so as to generate an induced electromotive force in the opposite direction to the upper coil 1241, and is provided for the lower range of the liquid level detection range. A sub-detection coil 124, an excitation coil 126 magnetically coupled to the main detection coil 122 and the sub-detection coil 124 and formed with substantially uniform winding density along the direction of change in liquid level, and the main detection coil 126. 122 and a shot ring 12 that is disposed coaxially with the coil axis of the sub-detection coil 124 or the coil axis of the excitation coil 126, and that moves up and down according to the liquid level.
8 and 128', and by connecting the AC signal source 11 to the excitation coil 126, the induced voltage is selectively generated from either the main detection coil 122 or the sub-detection coil 124. A liquid level detection device characterized in that the effective value of a waveform obtained by obtaining electric power and detecting the induced electromotive force every half cycle of the AC signal source 11 is used as a detection output.