JP3197515U - Liquid level sensor - Google Patents

Abstract

A liquid level sensor capable of detecting a liquid level extremely accurately without being affected by changes in liquid properties or temperature. A pair of electrode substrates 10 and 20 are installed in parallel along a displacement direction of a liquid surface. A measurement electrode 11A is printed on one electrode substrate 10 to form a measurement electrode layer 11, and an excitation signal electrode 21A is printed on the other electrode substrate 20 to form an excitation electrode layer 21. The measurement electrode layer and the excitation electrode layer face each other to form the sensing surface F. Each of the electrodes 11A and 21A is divided along the longitudinal direction of the electrode substrate, and the divided electrodes are arranged so as to face each other, and the liquid level is detected by a change in capacitance between the electrode substrates. [Selection] Figure 4

Description

  The present invention relates to a capacitive liquid level sensor that detects a liquid level of engine oil or the like.

  The present applicant has previously proposed a capacitive sensor described in Patent Document 1. This sensor is a liquid level sensor consisting of a coaxial cable. In particular, in order to prevent malfunctions from the outside where the capacitance between the sensors is caused by a phase shift or the like, the conductive layer has a double structure, and an insulating layer is provided between the layers. Intervened.

  That is, a detection signal having the same phase as that of the central conductor is applied to the conductive layer located inside the outer electrode, and a phase shift is detected by a detection circuit provided outside the sensor, thereby preventing a malfunction. It is.

  On the other hand, in the capacitance-type liquid level sensor described in Patent Document 2, a first electrode pair that extends in the displacement direction of the liquid surface and that is opposed to each other at a predetermined interval, A configuration including a second electrode pair extending in the displacement direction and arranged to face the first electrode pair at a predetermined interval is described.

  According to this sensor, the first electrode pair and the second electrode pair have the same structure, and both the capacitance in the air and the rate of change of the capacitance with respect to the displacement of the liquid level are both equal, and The first electrode pair and the second electrode pair can be accurately detected regardless of the dielectric constant of the liquid by arranging the first electrode pair and the second electrode pair in parallel with each other while being displaced in the displacement direction of the liquid surface. Is.

Japanese Patent No. 4116409 Japanese Patent No. 4611143

  According to the sensor described in Patent Document 1, it is possible to prevent a malfunction that occurs due to a phase shift or the like, but there is a disadvantage that a liquid level detection error increases when the dielectric constant of the liquid changes with temperature or the like. there were. In particular, since the temperature differs depending on the properties of the liquid and the air layer, it has been difficult to accurately correct the dielectric constant error due to changes in temperature and properties.

  On the other hand, the sensor described in Patent Document 2 uses a long electrode extending in the direction of displacement of the liquid level, and therefore is affected by an error in the change in the distance between the electrodes and the change in the dielectric constant due to vibration and heat. There is a fear. That is, the difference between expansion and contraction of a long electrode increases with temperature. For this reason, the distance between the electrodes arranged in parallel changes, or the longitudinal end portion bends, so that the change in the distance between the electrodes may hinder accurate measurement. Moreover, in this sensor, it is difficult to accurately correct the dielectric constant due to a change in liquid properties or a change in temperature.

  Therefore, the present invention was created to solve the above-described problems, and an object thereof is to provide a liquid level sensor that can detect the liquid level extremely accurately without being affected by changes in liquid properties or temperature. To do.

In order to achieve the above object, a first means in the present invention is that a pair of electrode substrates 10 and 20 arranged in parallel along the direction of displacement of the liquid surface are installed in parallel, and one electrode substrate 10 has electrodes for measurement. Measurement electrode layer 11 on which 11A is printed and wired;
A pair of sensing surfaces F are formed opposite to the excitation electrode layer 21 in which the excitation signal electrode 21 </ b> A is printed and wired on the other electrode substrate 20, and the liquid is changed by the capacitance change between the electrode substrates 10 and 20. A liquid level sensor for detecting a surface level,
The electrodes 11A and 21A on each sensing surface F are divided along the longitudinal direction of the electrode substrates 10 and 20, respectively, and the liquid level is detected by the electrodes 11A and 21A closest to the liquid surface. .

  In the second means, the electrodes 11A and 21A of the sensing surfaces F are arranged so that the divided measurement electrodes 11A and the excitation signal electrodes 21A face each other on the sensing surface F. The liquid level is detected by the capacitance of the liquid between the sensing surfaces F.

  A third means includes a plurality of guard signal layers 12 and 22 including conductive materials 12A and 22A that transmit guard signals on the opposite sides of the opposing sensing surfaces F on the electrode substrates 10 and 20, respectively. Superposed, a signal in phase with each electrode 11A for measurement is applied to the conductive materials 12A and 22A of the guard signal layers 12 and 22, and a phase shift is detected by a detection circuit provided outside the sensor. It is a thing.

  The fourth means is that a pair of reference electrodes 11B and 21B are installed in the vicinity of both longitudinal end portions of the electrode substrates 10 and 20 on the sensing surface F, respectively, and the reference electrodes 11B and 21B are used in the liquid. And a change in capacitance between the air layer and the air layer are corrected.

  As described in claim 1 of the present invention, the electrodes 11A and 21A of each sensing surface F are divided along the longitudinal direction of the electrode substrates 10 and 20, respectively, and the liquid level is detected by the electrode closest to the liquid surface. With such a configuration, unlike the conventional long electrode, there is no error caused by detecting the deep part in the liquid, and the liquid level can be detected very accurately.

  As in claim 2, the electrodes 11 </ b> A and 21 </ b> A on each sensing surface F are arranged so that the divided measurement electrodes 11 </ b> A and the excitation signal electrodes 21 </ b> A are opposed to each other on the sensing surface F. Since the liquid surface level is detected by the capacitance of the liquid between the sensing surfaces F, when the electrode is thermally expanded, the length above and below the electrode changes, and the divided measurement The distance between the sensing surfaces F can be kept constant only by changing the distance between the electrodes 11A and the distance between the electrodes 21A for excitation signals.

  Moreover, even if the length of the electrode changes up and down, since the opposing electrodes are made of the same material, it also changes up and down in the same manner, so that there is less error between the electrodes. Therefore, as in the case of a sensor in which each electrode is constituted by a long electrode, the inconvenience that the entire electrode is thermally expanded and the change in the distance between the electrodes becomes large or the longitudinal end portion is bent is eliminated. Measurements can be made in response to changes in vibration, etc., so stable measurement is always possible. Furthermore, errors due to the surface tension of the liquid adhering to each sensing surface F can be reduced.

  As in claim 3, each electrode substrate 10, 20 is formed by superposing a plurality of guard signal layers 12, 22 having conductive materials 12 A, 22 A for transmitting a guard signal on the opposite side of each opposing sensing surface F. In addition, a signal having the same phase as that of each measurement electrode 11A is applied to the conductive materials 12A and 22A of the guard signal layers 12 and 22, and a phase shift is detected by a detection circuit provided outside the sensor. This reduces the influence of external noise, prevents malfunction between sensors, and enables more accurate measurement. Moreover, it can be set as a compact structure by carrying out printed wiring of each electrode.

  As in claim 4, on the sensing surface F, a pair of reference electrodes 11B and 21B are provided in the vicinity of both longitudinal end portions of the electrode substrates 10 and 20, respectively. By configuring so as to correct the change in capacitance with the layer, it is possible to measure the exact liquid level without being affected by the change in the properties and temperature between the inside and outside of the oil.

  That is, a change in the dielectric constant of oil or the like is detected by differential between the reference electrodes 11B and 21B on the air side and the reference electrodes 11B and 21B inside the oil, and the measurement values obtained from the electrodes 11B and 21B are obtained. By correcting with the change rate of the dielectric constant, it is possible to measure an accurate liquid level corresponding to the change in the properties and temperature between the inside and outside of the oil.

  As described above, according to the present invention, the initial purpose such as being able to detect the liquid level extremely accurately without being affected by the change in the properties of the liquid and the change in temperature has been achieved.

It is a perspective view which shows one Example of this invention. It is a side view which shows one Example of this invention. It is a perspective view which shows one Example of the electrode substrate for a measurement of this invention. It is explanatory drawing which shows the electrode substrate for a measurement of this invention, and the electrode substrate for excitation. It is a top view which shows one Example of the electrode substrate of this invention. It is an end view which shows one Example of the electrode substrate of this invention.

  The present invention is a capacitance level sensor that is installed inside an engine of a transport device, a generator or the like and detects a level of oil or the like.

  The basic configuration of the present invention is that a pair of electrode substrates 10 and 20 arranged in parallel with the liquid surface displacement direction are installed in parallel (see FIGS. 1 and 2). Then, the liquid level is detected by a change in capacitance between the electrode substrates 10 and 20.

  A measurement electrode layer 11 is configured by printing and wiring a measurement electrode 11A on one electrode substrate 10 (see FIG. 3). Further, an excitation electrode layer 21 is configured by printing and wiring an electrode 21A that transmits an excitation signal corresponding to the measurement electrode 11A on the other electrode substrate 20 (see FIG. 4). All of the electrode substrates 10 and 20 have the same shape and size, and are configured so that the size and position of each electrode also coincide.

  Furthermore, the measurement electrode layer 11 and the excitation electrode layer 21 are disposed on the opposing surfaces of the electrode substrates 10 and 20, and constitute opposing sensing surfaces F. Then, the liquid level is detected by the capacitance change between the sensing surfaces F.

  The electrodes 11A and 21A on each sensing surface F are divided along the longitudinal direction of the electrode substrates 10 and 20, respectively. In the illustrated example, three electrodes 11A and 21A are arranged, but the number, size, interval, and the like of the electrodes 11A and 21A can be arbitrarily set. The measurement electrodes 11A and the excitation signal electrodes 21A divided in this manner are arranged so as to face each other on the sensing surface F (see FIG. 4).

  Each electrode 11A for measurement measures the liquid level in the range of each size, and calculates the calculated liquid level by cooperating with the measurement value of the adjacent electrode 11A. That is, the measurement is performed with high accuracy by determining whether the short measurement electrode 11A is full or drought and the adjacent upper and lower electrodes 11A are full or drought, and connecting them. At this time, measurement with higher accuracy is possible by increasing the number of divisions.

  A plurality of guard signal layers 12 and 22 are superposed on the back side of the sensing surface F of each electrode substrate 10 and 20 (see FIG. 4). The guard signal layers 12 and 22 are printed wiring of conductive materials 12A and 22A for transmitting a guard signal to the insulating layer 12B. The detection signals in phase with the measurement electrodes 11A are transmitted to the conductive materials 12A and 22A. Application and detection of a phase shift by a detection circuit provided outside the sensor prevents malfunction between the sensors.

  At this time, it is possible to use a part of the guard signal layer 12 of the electrode substrate 10 provided with the measurement electrode layer 11 as an excitation signal. It is also possible to use a part of the guard signal layer 22 of the electrode substrate 20 provided with the excitation electrode layer 21 as an excitation signal or a ground electrode (GND). The conducting wires 13 and 23 transmit and receive signals from the measurement electrode 11A and the excitation signal electrode 21A, and measure the sensing surface F through the excitation electrode layer 21 so as not to contact the conductive materials 12A and 22A. The electrode layer 11 and the excitation electrode layer 21 are energized (see FIG. 6).

  On the other hand, on each sensing surface F, a pair of reference electrodes 11B and 21B are installed in the vicinity of both longitudinal ends of the electrode substrates 10 and 20 (see FIG. 4). These reference electrodes 11B and 21B are disposed so as to face each other on the sensing surface F. Then, the electrode substrates 10 and 20 are installed so that one of the electrodes 11B and 21B is immersed in the oil and the other is positioned outside the oil. Then, changes in the dielectric constant of the oil or the like are measured with the reference electrodes 11B and 21B immersed in the oil, and the dielectric of the air layer above the liquid level is measured with the reference electrodes 11B and 21B arranged outside the oil. Measure the rate change. Then, by correcting these measured values with the change ratio, an accurate liquid level is measured from the dielectric constant corresponding to the property change such as oil and the temperature change.

表１は、従来の単層電極基板のセンサを対面配置して測定したレベル出力結果を示すデータである。このデータによると、実液位Ａに対し、センサで測定した計算液位Ｂに大きな誤差Ｃが生じていることが分かる。 Next, test results when measured with the sensor of the present invention and when measured with a conventional sensor are shown. In this test, the level of engine oil was changed from 0 mm to 70 mm, the actual liquid level and the calculated liquid level measured by each sensor were displayed, and the error was shown.

Table 1 shows data indicating a level output result measured by arranging the sensors of the conventional single-layer electrode substrate facing each other. According to this data, it can be seen that there is a large error C in the calculated liquid level B measured by the sensor with respect to the actual liquid level A.

表２は、本考案のセンサで測定したレベル出力結果を示すデータである。このデータでは、実液位Ａに対し、センサで測定した計算液位Ｂに生じる誤差Ｃが小さく、出力も安定していることが分かる。

Table 2 shows data indicating the level output result measured by the sensor of the present invention. In this data, it can be seen that the error C generated in the calculated liquid level B measured by the sensor is smaller than the actual liquid level A, and the output is stable.

  It should be noted that the present invention is not limited to the illustrated configuration, and the design can be freely changed without changing the gist of the present invention. Moreover, the usage example of this invention is not limited.

DESCRIPTION OF SYMBOLS 10 Electrode board 11 Measurement electrode layer 11A Electrode 11B Electrode 12 Guard signal layer 12A Conductive material 12B Insulating layer 13 Conductor 20 Electrode substrate 21 Excitation electrode layer 21A Electrode 21B Electrode 22 Guard signal layer 22A Conductive material 22B Conductive material 23 Conductor

Claims (4)

  A pair of electrode substrates arranged along the direction of displacement of the liquid surface are installed in parallel, a measurement electrode layer in which measurement electrodes are printed on one electrode substrate, and an excitation signal on the other electrode substrate A liquid level sensor that detects a liquid level by a change in capacitance between each electrode substrate, and that includes a pair of sensing surfaces opposed to an excitation electrode layer on which electrodes are printed and wired. Each of the electrodes is divided along the longitudinal direction of the electrode substrate, and the liquid level is detected by an electrode closest to the liquid level.   Each electrode of each sensing surface is arranged such that each divided measurement electrode and each excitation signal electrode face each other on the sensing surface, and the capacitance of the liquid between the sensing surfaces The liquid level sensor according to claim 1, configured to detect a liquid level.   In each of the electrode substrates, a plurality of guard signal layers including a conductive material that transmits a guard signal are superimposed on the opposite sides of the opposing sensing surfaces, and each electrode for measurement is formed on the conductive material of the guard signal layer. The liquid level sensor according to claim 1, wherein a detection signal having the same phase as that of the sensor is applied and a phase shift is detected by a detection circuit provided outside the sensor.   On the sensing surface, a pair of reference electrodes is installed in the vicinity of both longitudinal ends of the electrode substrate, and the reference electrodes are configured to correct the change in capacitance between the inside and outside of the liquid. The liquid level sensor according to claim 1.

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