JPS6373116A - Measuring device for liquid level - Google Patents

Abstract

PURPOSE:To enable the accurate measurement of a liquid level and to simplify a detection structure, by utilizing the sudden change of the electrostatic capacitance of electrodes whereat the liquid level is present. CONSTITUTION:Opposite electrodes 21 and 22 are formed at certain intervals in the longitudinal direction on long printed circuit boards 1A and 1B respectively, and a liquid level is known by utilizing that an electrostatic capacitance changes suddenly at the electrodes 21 and 22 whereat the surface of the liquid is present. On that occasion, the liquid level can be measured without fail according to that the electrodes 21 and 22 are located in the air or in a liquid to be measured, on a condition that the dielectric constant of the liquid to be measured is different from that of the air. Moreover, with the electrodes 21 and 22 used as capacity elements of a detecting circuit 3, a measuring circuit 4 measures an exact liquid level on the basis of a change in the current or voltage of a signal line 32 connected to the detecting circuit 3.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a liquid level measuring device, and particularly to a capacitive liquid level measuring device.

[Prior Art] For measuring the liquid level of gasoline or oil in a vehicle, attempts are being made to use a compact and highly accurate capacitance sensor that does not have mechanical contacts, instead of a float sensor. This type of capacitive sensor has the feature that it can also be used to measure the level of powder. Conventionally, two rod-shaped electrodes are immersed in the liquid, and the change in capacitance between the electrodes due to fluctuations in the liquid level is used to measure the liquid level. measuring the position.

[Problems to be Solved by the Invention] By the way, in the conventional capacitance type device described above, it is necessary to readjust it each time the dielectric constant changes when new gasoline is refilled, and the oil deteriorates as the oil deteriorates. As a result, the dielectric constant increases, making it difficult to accurately measure the liquid level.

SUMMARY OF THE INVENTION The present invention aims to solve these problems and to provide a capacitive liquid level measuring device that does not cause errors even if the dielectric constant of the liquid to be measured changes.

[Means for Solving the Problems] To explain the configuration of the present invention with reference to FIG. 1, liquid level measuring devices are provided on bases 1A and 1B and at regular intervals in the longitudinal direction of the bases 1A and 1B, at least one pair of counter electrodes 21.22 whose inter-electrode capacitance changes when immersed in the liquid to be measured;
A detection circuit 3 in which 1 is a capacitive element of the circuit;
A signal line 32 (Fig. 3) that connects the above-mentioned signal line 32
The measuring circuit 4 is equipped with a measuring circuit 4 for determining the liquid level of the liquid to be measured from changes in current or voltage.

[Effect] The liquid level measuring device having the above configuration utilizes the fact that the interelectrode capacitance of the counter electrodes 21.22 changes suddenly when the counter electrodes 21.22 are immersed in the liquid to be measured. Alternatively, the liquid level can be determined based on where in the liquid to be measured the liquid is located, so as long as the dielectric constant of the liquid to be measured is different from that of air, the liquid level can be reliably measured.

In particular, if a plurality of the counter electrodes 21.22 are provided, changes in the liquid level can be measured by knowing the position or number of counter electrodes 21.22 where the interelectrode capacitance suddenly changes.

Roughly speaking, by using the counter electrodes 21 and 22 as capacitive elements of the detection circuit 3, it is possible to measure the liquid level more accurately by changing the current or voltage of the signal line 32 connected to the detection circuit 3.

In particular, when a plurality of detection circuits 3 are provided corresponding to a plurality of counter electrodes 21 and 22, by connecting them with the signal line 32, it is possible to accurately measure liquid level changes with a single signal line. can.

[Example 1] Fig. 1 shows a detector of a liquid level measuring device. In the figure,
1A and 1B are long printed circuit boards that extend vertically in parallel and are held at their upper and lower ends by holders 11. Electrodes 21 and 22 are printed on the opposing surfaces of these printed circuit boards 1A and 1B, respectively, and the electrodes 21 are formed at a constant pitch d in the vertical direction, as shown in FIG.
On the other hand, the electrode 22 is formed on the entire surface of the substrate 1B. Thus, the opposing electrodes 21 and 22 each have a capacitance depending on the dielectric constant of the substance present between them.

In other words, when the detector is immersed in the liquid to be measured from the bottom of the diagram,
The capacitance between the electrodes 21 and 22 in the liquid to be measured shows CX depending on the dielectric constant of the liquid to be measured, and the capacitance between the electrodes 21 and 22 not in the liquid to be measured depends on the dielectric constant of the air. The corresponding Ca is shown.

The same number of detection circuits 3 as the respective electrodes 21 are provided on the outer surface of the printed circuit board 1A.
It is connected to through a through hole. Further, each of the detection circuits 3 is waterproof coated with epoxy resin or the like.

A lead wire 6 electrically connected to the detection circuit 3 is connected to the printed circuit board 1A.

FIG. 3 shows the configuration of the detection circuit. In the figure, each detection circuit 3A, 3B, 3C13D has the same configuration and includes a non-inverting buffer 31, a load resistor RL and a delay resistor Rs connected to its output terminal.

Each load resistor R[ is connected to a common ground line 33, and each delay resistor Rs is connected to an input terminal of a non-inverting buffer 31 at the next stage and to each corresponding electrode 21.

A power supply line 32 which connects these non-inverting buffers 31 and also serves as a signal line is input connected to each of the non-inverting buffers 31, and the input terminal of the first-stage non-inverting buffer 131 is connected to the terminal T2. In the figure, TI and T3 are a power supply terminal and a ground terminal, respectively, and the electrode 22 is connected to the ground terminal T3. The lead wire 6 (Fig. 1) is connected to these terminals T1, T2,
Connected to T3.

The figure shows a state where there is a surface of the liquid to be measured between the electrode 21 and the electrode 22 connected to the detection circuit 3C, and the capacitance between each electrode below this electrode 21 is Cx, and the The capacitance between the electrodes above 21 is Ca. Here, Ca is Cx.

A 50% duty rectangular wave (FIG. 4(1)) is input to the terminal T2 from a measuring circuit to be described later. The output of the non-inverting buffer 31 at the first stage also rises in synchronization with the rise of the rectangular wave, but due to the delay circuit formed by the delay resistor R8 and the capacitor Ca, the output signal to the non-inverting buffer 31 of the Buddhist teaching is R6C.
It rises with a time constant of a (Fig. 4 (6)). Such delays also occur in the detection circuits 3B and 3C (Fig. 4 (7),
(8)) As a result, the rise of the signals output from the non-inverting buffers 31 of the detection circuits 3B, 3C, and 3D are sequentially delayed as shown in FIG. 4 (2), (3), and (4). It will be done. In this case, the delay time 10 of the non-inverting buffer outputs of the detection circuits 3B and 3G is determined by the time constant R3Ca, and the delay time t1 of the non-inverting buffer outputs from the detection circuit 3D onward is determined by the time constant R3CX.

Incidentally, a load resistor RL is connected to the output terminal of each of the non-inverting buffers 31, and as the outputs of the buffers 31 rise sequentially as described above, the current 1 of the power supply line 32
0 increases stepwise for each delay time toSti (FIG. 4 (5)). Thus, knowing the change in the duration of the current 10 allows the liquid level to be detected. In addition,
In FIG. 4, VT old VTH2 VTH3 are the threshold voltages of the non-inverting buffers 31 of the detection circuits 3B, 3C, and 3D, respectively.

FIG. 5 shows the configuration of the measuring circuit 4. In the figure, Tv
is the battery terminal, which is connected to the regulator 401 via the resistor R.
After the voltage is made constant, the voltage is supplied from the terminal T1' to the terminal T1 (FIG. 3) of the detection circuit 3. 40
6 is an RC oscillation circuit, and the output of the oscillation circuit 406 is converted into a rectangular wave with a predetermined period by a frequency divider 407, and is supplied to the terminal T2 from the terminal T2-.

Resistance R due to stepwise change in power supply current io of detection circuit 3
The voltage at one end of is shown in FIG. The voltage signal is converted into a differentiator 40.
2 and processed by the waveform shaping circuit 403 to obtain the pulse 5b (FIG. 6(2)). Pulse 5b is binary counter 40
4 and one shot pulse generation circuit 4
10 to obtain timing pulses 5c, 5d, and 5e.

Next, the timing pulse 5e is input to the preset terminal of the presettable binary counter 411, and at the same time as presetting the data of the digital switch 414 to the counter 411, the binary counter 408 is reset. Timing pulse 5d latches the output data of counter 408 into launch 409. Further, 412 is a digital comparator which triggers the D flip-flop 413 according to the output of the comparator 412 at the timing of the timing pulse 5C. The pulse period of the differential pulse 5b corresponding to the power supply current io is counted by a counter 408, the next period of the pulse period is counted by the counter 411 including offset data, and these count values are compared by a comparator 412. , the flip-flop 413 is triggered only when the period of the differential pulse 5b becomes longer than the previous period. Also, since the number of differential pulses 5b is counted by the counter 404,
If the output data of the counter 404 when the Q output of the flip-flop 413 rises is taken into the latch 405, it is possible to know which position from the top of the electrode 21 in FIG. 1 the liquid level is, and this is output from the terminal TD. be done.

The digital switch 414 is used to apply the offset to the differential pulse 5 by eliminating bit errors.
This is to reliably detect an increase in the period of b.

As described above, the liquid level measuring device of this embodiment has counter electrodes 21.
22, and the liquid level is determined by utilizing the sudden change in capacitance at the electrodes 21 and 22 where the liquid level exists.
Even if the dielectric constant of the liquid to be measured changes, as long as it is different from the dielectric constant of air, the liquid level can be measured accurately.

In addition, since the common power supply line 32 of each detection circuit 3 is used as a signal line, and the change in the capacitance between the electrodes is known from the change in the power supply current, there is no need to install a signal line, and the electrode and A fixed number (3) of lead wires is sufficient regardless of the number of detection circuits installed.

FIG. 7 shows a second embodiment of the invention. In this embodiment, the electrode 22 is not grounded as in the above embodiments, but is connected to the terminal T4 as a signal line. Each electrode 21 is directly connected to the output end of each non-inverting buffer 31. In the figure, Ci is the input capacity of each buffer 31 mentioned above.

When a rectangular wave as in the first embodiment is inputted from the terminal T2, each buffer output of the detection circuits 3B and 3D has a time constant R6.
After a delay time to determined by -Ci, the signals rise sequentially. When viewed from the terminal T4, this means that each electrode 2
1 means that the connection of 1 is sequentially switched from the ground line 33 to the power line 32, and as a result, the voltage at the terminal T4 changes at time t.

The height increases in a stepwise manner (Fig. 8). At this time, when the liquid to be measured is present and the electrode 21 with a large interelectrode capacitance CX is switched to the electrode wire 32, the voltage VO at the terminal T4 becomes Vs in the figure.
As at t2, it increases significantly compared to the previous increase Jivstl. In this way, the liquid level can be measured by knowing the sudden change in the amount of voltage rise.

An example of the measurement circuit in this case is shown in FIG. In the figure, 415 is an impedance converter, and 416 is a differential circuit. When the voltage VO at the terminal T4 is input to the impedance converter 415, the voltage V
A pulse output whose size is proportional to the step increase in O is obtained (FIG. 10). Therefore, the liquid level is known from the pulse number at which the peak value suddenly changes from vpl to Vp2.

FIG. 11 shows a detector structure according to a third embodiment of the present invention. In the figure, counter electrodes 21 and 22 are formed adjacent to each other at a constant pitch d in the vertical direction on a single printed circuit board 1. This creates capacitance between adjacent electrodes 21 and 22. Each pair of electrodes 21 and 22 is surrounded by a ground electrode 23 and separated from each other, thereby suppressing the generation of stray capacitance.

The detection circuit in this case is shown in FIGS. 1 and 2. Detection circuit 3A
, 3B have the same number of layers corresponding to the pair of electrodes 21, 22, and each detection circuit 3A, 3B has an oscillation circuit 34 consisting of inverters 341, 342, 343 connected in series. A fixed resistor R and a fixed capacitor Cs iy' are provided between the input and output of each of the inverters 341 and 342,
The counter electrodes 21.22 are provided between the inverters 341.343.

The oscillation frequency of the oscillation circuit 34 varies greatly according to the difference between the capacitance of the capacitor CS and the interelectrode capacitance. And the interelectrode capacitance Ca, Cx and CS are ca<cs<cx
C5 is determined so that Therefore, when the counter electrodes 21 and 22 are in the air, the oscillation frequency is low, and when the counter electrodes 21 and 22 are in the liquid to be measured, the oscillation frequency is high.

The current consumption of each oscillation circuit 34 increases as its oscillation frequency increases. Therefore, the power supply current io flowing through the power supply line 32 is
Proportional to the number 1.22.

Thus, the liquid level is known from the power supply current io.

In this embodiment, the detector can be configured with one printed circuit board, and only two lead wires are required, so the detector structure is simplified.

[Brief explanation of the drawing]

1 to 6 show a first embodiment of the present invention, in which FIG. 1 is a cross-sectional side view of a detector, FIG. 2 is a front view of a printed circuit board, and FIG. 3 is a circuit diagram of a detection circuit. Figure 4 is the signal time chart of the detection circuit, Figure 5 is the circuit diagram of the measurement circuit, and Figure 6 is the signal time chart of the detection circuit.
The figure shows the signal time chart of the measurement circuit, Figures 7 to 1.
Fig. 0 shows a second embodiment of the present invention, Fig. 7 is a circuit diagram of the detection circuit, Fig. 8 is a signal time chart of the detection circuit, Fig. 9 is a circuit diagram of the measurement circuit, and Fig. 10 is a measurement circuit diagram. The signal time charts of the circuit, FIG. 11 and FIG. 12 show the third embodiment of the present invention, and FIG. 11 is a front view of the printed circuit board, and FIG.
The figure is a circuit diagram of the detection circuit. 1.1A, 1B...Printed circuit board (base) 21
．． 22...Counter electrode 3.3A, 3B, 3C13D...Detection circuit 31
...Non-inverting buffer (non-inverting gate) 32...
...Power line (signal line) 33... Earth wire 34... Oscillation circuit 4... Measurement circuit R [... Load resistance R5... ...Delay resistor No. 40 Fig. 5 Fig. 6 Fig. 7 Fig. 8 Fig. 9 Fig. r-Fig. 10

Claims (8)

[Claims] (1) a base, at least one pair of counter electrodes that are provided at regular intervals on the base and whose interelectrode capacitance changes when immersed in the liquid to be measured; A liquid level measuring device comprising: a detection circuit made of a capacitive element; a signal line connecting the detection circuits in series; and a measurement circuit that determines the liquid level of the liquid to be measured from changes in current or voltage of the signal line. (2) The above-mentioned base body is composed of two printed circuit boards arranged in parallel to each other, and one of the above-mentioned counter electrodes is printed on one of the opposing surfaces of these printed circuit boards at regular intervals, and the other of the above-mentioned opposing surfaces is printed. 2. The liquid level measuring device according to claim 1, wherein the other of the opposing electrodes is printed on the entire surface. (3) Liquid level measurement according to claim 1, wherein the base is formed of a single printed circuit board, and each pair of opposing electrodes are formed adjacent to each other at a constant interval on the surface of the printed circuit board. Device. (4) The above detection circuit is provided with a non-inverting gate, and a load resistor with a constant resistance value is provided between the output terminal of the non-inverting gate and the ground wire, and a load resistor is provided between the output terminal of the non-inverting gate and the non-inverting gate input terminal of the next stage detection circuit. The solution according to claim 1, wherein an RC delay circuit is provided between them, a capacitive element of the RC delay circuit is constituted by the opposing electrode, and a power supply line connecting each non-inverting gate is used as the signal line. Position measuring device. (5) The measurement circuit applies a step signal to the non-inverting gate input terminal of the detection circuit in the first stage, and the liquid level of the liquid to be measured increases due to the fluctuation in the steady state duration of the power line current that changes stepwise. 5. The liquid level measuring device according to claim 4, wherein the liquid level measuring device is configured to know which counter electrode is present. (6) The detection circuit is provided with a non-inverting gate, the one of the counter electrodes is connected to the output terminal of the non-inverting gate, and an RC delay circuit is provided between the non-inverting gate input terminal of the next stage detection circuit. 3. The liquid level measuring device according to claim 2, wherein the other counter electrode is used as the signal line. (7) The measurement circuit applies a step signal to the non-inverting gate input terminal of the detection circuit in the first stage, and detects the presence of the liquid level of the liquid to be measured based on the voltage variation of the signal line voltage that changes in a stepwise manner. 7. The liquid level measuring device according to claim 6, wherein the liquid level measuring device is configured to detect the counter electrode. (8) The detection circuit is composed of an RC oscillation circuit with the counter electrode as a capacitive element, and the measurement circuit uses the power line connecting the RC oscillation circuit as the signal line, and is exposed to the power line current value. The liquid level measuring device according to claim 1, which is configured to know the number of counter electrodes immersed in the measuring liquid.