JPS6379016A - Liquid level measuring apparatus - Google Patents

Abstract

PURPOSE:To enable the accurate measurement of correct liquid level free from effect of variations in dielectric constant of a liquid to be measured, by a method wherein a reference electrode and a detection electrode are fastened on a long-sized substrate and the liquid level of the liquid being measured is determined from the ratio of interelectrode capacities of the reference electrode and the detection electrode to prevent the generation of errors due to variations in the opposite interval. CONSTITUTION:A reference electrode 2 consisting of a plurality of linear electrodes 21 formed by printing is formed at the lower end of the surface of a printed circuit board 1, and a detection electrode 3 consisting of a plurality of linear electrodes 31 at the center of the surface thereof 1. Interelectrode capacities of the electrodes 2 and 3 are the sum of capacities between the electrodes 21 and 31. At the measurement, the electrode 2 is always immersed into a liquid and as the electrode 3 crosses the liquid surface, with a rise of the liquid level, the part to be immersed changes. Thus, the use of the ratio of interelectrode capacities of the electrodes 2 and 3 enables the learning of the liquid level of the liquid being measured with a detection circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a liquid level measuring device, and more particularly to a liquid level measuring device having one static N capacity.

[Prior Art] Attempts are being made to use capacitive sensors, which have no mechanically moving parts, are compact, and have high precision, in place of float sensors for measuring the liquid level of gasoline or oil in vehicles. 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 accurate liquid level measurement difficult and rare in practice. Furthermore, there is a problem in that measurement errors occur when the spacing between the rod-shaped electrodes changes.

The present invention solves these problems by providing a capacitive liquid level measuring device that does not produce errors even when the dielectric constant of the liquid to be measured changes, and that maintains a constant facing distance between detection electrodes. The purpose is to provide.

[Means for Solving the Problems] The configuration of the present invention will be explained with reference to FIGS. 1 and 2. The liquid level measuring device includes an elongated base 1 and a predetermined interval at the lower end of the elongated base 1. a pair of reference electrodes 2 which are arranged opposite to each other and are always immersed in the liquid to be measured, and which extend vertically in the longitudinal direction of the elongated substrate 1;
A pair of detection electrodes 3 are arranged oppositely at a predetermined interval and intersect with the surface of the liquid to be measured, and the ratio of the inter-electrode capacitance of the reference electrode 2 to the inter-electrode capacitance of the detection electrode 3 determines the level of the liquid to be measured. It is equipped with a detection circuit 5 that detects the liquid level of the liquid.

[Functions and Effects] In the liquid level measuring device configured as described above, the interelectrode capacitance of the detection electrode 3 depends on the dielectric constant of the liquid to be measured and the length of the electrode portion below the liquid level of the liquid to be measured, that is, the liquid level. Proportional. On the other hand, the reference electrode 2 is always in the liquid to be measured, and its interelectrode capacitance depends only on the dielectric constant of the liquid to be measured.

Here, in the detection circuit 5, the liquid level of the measured liquid is determined from the ratio of the interelectrode capacitance between the reference electrode 2 and the detection electrode 3, so that it is not affected by the dielectric constant fluctuation of the measured liquid. , can measure accurate liquid level.

Furthermore, since the reference electrode 2 and the detection electrode 3 are fixedly attached to the elongated substrate 1, the facing distance between each electrode 2.3 is maintained constant;
The occurrence of errors due to variations in the facing distance is prevented.

[Example] Fig. 1 shows a detection section, in which a rectangular printed circuit board 1 extending vertically has a comb-shaped reference electrode 2 formed at the lower end of the board surface. The reference electrode 2 consists of a plurality of linear electrodes 21 printed at regular intervals vertically, and these are lead electrodes 22 and 23 extending vertically along both side edges of the substrate 1.
are connected alternately. Therefore, the inter-electrode capacitance of the reference electrode 2 is the sum of the capacitances between the respective linear electrodes 21. The reference electrode 2 is constantly immersed in a liquid during measurement.

A detection electrode 3 is formed at the center of the substrate surface of the pudding 1 to the substrate 1, and the detection electrode 3 is composed of a plurality of linear electrodes 31 extending from the upper end to the lower end at regular intervals on the outside. . These linear electrodes 31 have their upper ends alternately connected to lead electrodes 32 and 33, and the interelectrode capacitance of the detection electrode 3 is the sum of the capacitances between the linear electrodes 31.

The detection electrode 3 crosses the liquid level during measurement, and the portion immersed in the liquid changes as the liquid level rises and falls. Note that the lead electrode 33 is formed on the back surface of the printed circuit board 1.

In this embodiment, the intervals and lengths of the linear electrodes 2L 31 are determined so that the interelectrode capacitances of the reference electrode 2 and the detection electrode 3 are approximately equal.

A ground electrode 4 is formed between the reference electrode 2 and lead electrodes 22, 23, and the detection electrode 3 to prevent stray capacitance from occurring between them. Lead electrode 22.2
3, 32, 33 and the ground electrode 4 have their respective upper ends connected to the external terminals 11, respectively.

The reference electrode 2 and the detection electrode 3 are connected to a detection circuit, and the configuration of the detection circuit is shown in FIG. The detection circuit 5 includes an oscillation circuit 51 and a processing circuit 52, and the oscillation circuit 51 has inverters 511, 512, and 513 connected in series. A resistor 514 is connected between the input and output of the inverter 511, and the electrodes 2.3 are connected between the inverters 511 and 512 via analog switches 515 and 516, respectively. Thus, the oscillation frequency of the oscillation circuit 51 is determined by the resistor 514 and the capacitance of the electrode 2.3 selectively connected by the analog switch 515, 516.

The oscillation signal f of the oscillation circuit 51 is input to the processing circuit 52, and the selection signal S for selectively operating the analog switch 515.5-16 is input from the processing circuit 52.
, S are output.

FIG. 3 shows a processing circuit 52, which is composed of a microcomputer 521, a D/F converter 522, and an inverter 523. The oscillation signal f is input to the port P1 of the computer 521, and the selection signal S is output from the port P2 of the computer 521. The selection signal S is obtained by inverting the above signal S with an inverter 523.

The operation of the liquid level measuring device having the above structure will be explained with reference to the program flowchart shown in FIG.

In FIG. 4, in step 101, the memory and the like are initialized, and then a selection signal S of "1" level is generated. As a result, the analog switch 515 (FIG. 2) is activated, and the reference electrode 2 is connected to the oscillation circuit 51.

Then, in this state, the period TSU of the oscillation signal f input from the oscillation circuit 51 is detected (step 103).

By the way, if the period 'sa of the oscillation signal f when the reference electrode 2 is in the air is measured in advance, the dielectric constant ε1 of the liquid to be measured can be determined by the following formula (1).

ε, G = (TSj-T,)A1εa ・------
(1) Here, A is a constant and εa is the dielectric constant of air.

The above calculation is performed in step 104, and then a selection signal of "1" level is output (step 105). As a result, the analog switch 516 is activated instead of the analog switch 515, and the detection electrode 3 is now connected to the oscillation circuit 51.
connected to. In step 106, the period T of the oscillation signal @f of the oscillation circuit 51 with the detection electrode 3 connected is
Calculate X.

Period T of the transmission signal f when the detection electrode 3 is in the air
If a is measured in advance, the difference in period LQ = Tx
-Ta is proportional to the dielectric constant εg and the length of the submerged part of the detection part @3, that is, the liquid level. Therefore, in step 107, the liquid level is calculated using the following equation (2).

h=　　　　　　　　　　　・・・・・・(2)88g Here, B is a constant.

In step 108, the liquid level data h is output from port P3. The liquid level data h is converted and outputted by the D/F converter 522 into a liquid level signal hf having a frequency corresponding to the data.

According to the liquid level measuring device having the above configuration, a reference electrode is provided that is constantly immersed in the liquid, and the dielectric constant of the liquid to be measured is calculated from the oscillation period of the oscillation circuit determined by the interelectrode capacitance of the reference electrode. Since the liquid level is calculated using the dielectric constant, the liquid level can be determined accurately even if the dielectric constant of the liquid to be measured changes.

Furthermore, since both the reference electrode and the detection electrode are printed and formed on the printed circuit board, the spacing between the opposing electrodes does not change, and no errors occur due to this.

Furthermore, since the oscillation circuit is shared between the reference electrode and the detection electrode, and the oscillation frequency is set to be in almost the same region when each electrode is connected, it is possible to avoid errors caused by temperature drift of the oscillation circuit. .

5 and 6 show a side view and a front view, respectively, of a detection section in another embodiment of the present invention. In the figure, a printed circuit board 1 on which reference electrodes and detection electrodes are formed as in the above embodiment is three-dimensionally curved and fixedly supported by a support member 6.

The upper end of the support member 6 is a mounting flange 61.

When the liquid to be measured is gasoline in a vehicle fuel tank, the liquid level varies depending on the inclination angle of the tank.

Figure 7 shows the inclination of the tank 7 in the left-right ((a) to (d>) and front-to-back ((e) to h) directions when the amount of gasoline in the tank 7 increases and decreases in four stages. Shows changes in liquid level.

When observing such liquid level changes, it is known that for each amount of gasoline, there is a point (hereinafter referred to as a constant point) where the liquid level hardly changes when the tank 7 is tilted within a certain angle (30 degrees in this example). The line connecting these constant points becomes a curved line that curves left and right and front and back depending on the tank shape, as shown by broken lines X and y in the figure.

Therefore, if the curvature of the printed circuit board 1 is made to match the curve connecting the constant points, it is possible to always accurately measure the liquid level without being affected by liquid level fluctuations caused by the tilt of the tank. can.

[Brief explanation of the drawing]

1 to 4 show an embodiment of the present invention, in which FIG. 1 is a front view of a printed circuit board constituting a detection section, FIG. 2 is a circuit diagram of a detection circuit, and FIG. 3 is a circuit diagram of a processing circuit. 4 is a flowchart of the processing program, FIGS. 5 to 7 show other embodiments of the present invention, FIG. 5 is a side view of the detection section, FIG. 6 is a front view thereof, and FIG. is a perspective view showing changes in the liquid level in the tank. 1... Printed circuit board (long base) 2...
・Reference voltage yoke 21... Linear electrode 22.23... Lead electrode 3... Detection electrode 31; Linear electrode 32.33... ... Lead electrode 5 ... Detection circuit 51 ... RC oscillation circuit 515,516 ... Analog switch 52 ...
...Processing circuit diagram 3

Claims (5)

[Claims] (1) a long base; a pair of reference electrodes that are disposed opposite to each other at a predetermined interval on the lower end of the long base and are constantly immersed in the liquid to be measured; and a pair of reference electrodes extending vertically in the longitudinal direction of the long base; A pair of detection electrodes are arranged opposite each other at a predetermined interval and cross the liquid level of the liquid to be measured, and the liquid level of the liquid to be measured is determined from the ratio of the inter-electrode capacitance of the reference electrode and the inter-electrode capacitance of the detection electrode. A liquid level measuring device equipped with a detection circuit that detects the (2) The liquid level measuring device according to claim 1, wherein the elongated base body is constituted by a printed circuit board, and the reference electrode and the detection electrode are formed on the printed circuit board. (3) The reference electrode and the detection electrode are each composed of a plurality of linear electrodes formed in parallel at regular intervals, and these linear electrodes are alternately connected to a pair of lead electrodes. Liquid level measuring device as described in section. (4) The detection circuit has an RC oscillation circuit and an analog switch that selectively connects the reference electrode or detection electrode to the capacitive element constituting the RC oscillation circuit, and when the reference electrode is connected, 2. The liquid level detection device according to claim 1, wherein the liquid level of the liquid to be measured is determined from the ratio of the oscillation period of the RC oscillation circuit to the oscillation period when the detection electrode is connected. (5) The liquid level detection device according to claim 1, wherein the elongated base body is formed into a curved surface having a series of constant points where the liquid level does not change depending on the inclination of the container containing the liquid to be measured. .