JPH10325749A - Capacitive level gauge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a capacitive level gauge which can deal with the increase in the number of sensors without increasing the size, power consumption or the number of components by employing a cross point switch array as means for selecting a measuring sensor. SOLUTION: A plurality of stacked capacitive level sensors S1 -S30 are selected sequentially by a measuring sensor selecting means and the capacitance thereof is measured in order to calculate the level of a tank. A cross point switch array 31, e.g. a 16×16 switch (total 256 cross points), is employed as the measuring sensor selecting means. The column 16 of the cross point switch array 31 is connected with a measuring circuit 21 and the row 16 thereof is used for internal connection. Other 15 columns and 15 rows are used for connecting the sensors. Maximum 30 sensors can be measured selectively using the cross point switch array 31. A correction means 32 corrects a measurement error caused by the difference in the number of connections of the cross point.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacitance type level meter used for measuring the level (liquid level) of a storage tank of, for example, liquefied petroleum gas.

[0002]

2. Description of the Related Art FIG. 3 shows a conventional configuration of this type of capacitance type level meter. The detecting unit 11 includes a plurality of capacitance type level sensors S _{1 to} S _N , and these level sensors S _{1 to} S _N are arranged in multiple stages corresponding to the height of the tank installed as shown in FIG. It has been piled up.
Each of the level sensors S _{1 to SN} includes an outer cylinder electrode 12 and a center electrode 1
The adjacent outer cylinder electrodes 12 are electrically and mechanically connected to each other to integrate the level sensors S _{1 to} S _N. Although not shown in FIG. 4, the connection of the outer cylinder electrodes 12 is performed by screwing flanges provided at both ends of each outer cylinder electrode 12 to each other. Note that the adjacent center electrodes 13 are slightly separated from each other.

[0003] The detecting unit 11 having the above-described configuration is installed on a bottom surface 14 of a tank via a mounting table 15 made of an insulating material, and an upper end thereof is located at an upper portion of the tank. As shown in FIG. 3, a measurement signal generator 17 is connected to the integrated outer cylinder electrode 12 of each of the level sensors S _{1 to} S _N via a safety holder 16, while each center electrode 13 is connected to a safety electrode. Cage 16
And a relay 18 and a measurement circuit 21. The safety retainer 16 is provided so that an overcurrent and an overvoltage are not applied to the detecting unit 11 installed in the tank from the circuit side.

To measure the level in the tank, a measurement signal is supplied from a measurement signal generator 17 to the outer cylinder electrode 12, and detection signals from the level sensors S _{1 to} S _N are selected by a relay 18 and sequentially sent to a measurement circuit 21. This is done by capturing. The measuring circuit 21 measures the detection signal as a voltage, and the capacitance calculating means 22 calculates the capacitance from the detected voltage. The calculated capacitance is input to the control / calculation means 23. The control / calculation means 23 outputs a relay control signal and outputs
8, the capacitance of the level sensors S _{1 to} S _N is obtained from the capacitance calculator 22. Then, the level in the tank is calculated and output from the capacitance.

[0005]

However, with the recent increase in size of the tank, the capacitance type level meter having the above-described structure also requires a larger (higher-rise) detection unit 11. For this reason, the number N of stacking levels of the level sensors is, for example, 25 or more, and it becomes necessary to use twice or more the number of level sensors in the related art.

In this case, in the above-mentioned conventional capacitance type level meter, since the relay 18 is used for selecting the measurement sensor, the relay 18 must be added in accordance with the increase in the number of sensors. However, this leads to an increase in the size of the device and an increase in power consumption, and a decrease in reliability due to an increase in the number of components. SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide a capacitance-type level meter that can cope with an increase in the number of sensors without increasing the size of the device, increasing power consumption, and increasing the number of components. Is to do.

[0007]

According to the first aspect of the present invention, a plurality of stacked capacitance-type level sensors are sequentially selected by a measurement sensor selection means, and the capacitances thereof are measured. In a capacitance type level meter configured to calculate a level of a tank in which a level sensor is installed from a measured capacitance, a cross point switch array is used as a measurement sensor selection unit.

According to a second aspect of the present invention, in the first aspect of the present invention, there is provided means for correcting a measurement error of capacitance caused by a difference in the number of cross points connected in the cross point switch array.

[0009]

Embodiments of the present invention will be described with reference to the accompanying drawings. Parts corresponding to those in FIG. 3 are denoted by the same reference numerals. FIG. 1 shows an embodiment of the present invention. In this example, a cross point switch array 31 is used as a measuring sensor selecting means instead of a conventional relay. In this example, the cross point switch array 31 uses 16 × 16 switches (total of 256 cross points), and as shown in FIG. , And the cross points are represented by rows and columns as (1, 1) to (16, 16).

Column 1 of cross point switch array 31
6 is connected to the measurement circuit 21 and row 16 is used for internal connection. 15 other than these connection columns and connection rows
Columns and 15 rows are used for sensor connection, that is, according to the cross point switch array 31, up to 30 sensors can be selectively measured. On the other hand, in this example, the detection unit 11 is configured by stacking ₃₀ capacitance type level sensors S _{1 to} S ₃₀ so as to make maximum use of the cross point switch array 31. Level sensors S _{1 to} S
₁₅ has its center electrode 13 connected to the rows 1 to 15 of the crosspoint switch array 31 via the safety retainer 16 respectively, and the remaining level sensors S _{16 to} S ₃₀ are similarly arranged in columns 1 to 15 It is connected. In addition, each outer cylinder electrode 1
2 is connected and integrated and connected to a measurement signal generator 17 via a safety retainer 16.

The selection of measurement sensors by the cross point switch array 31 is such that, for example, when the level sensor S ₁ is selected and measured, only the cross point switches (1, 16) are turned on. Also, when selecting measuring the level sensor S ₃₀ turns on the two cross-point switch (16, 15) and (16, 16). Thus, row 1
When selecting the level sensors S _{1 to} S ₁₅ connected to the rows ₁₅ to ₁₅ , the number of cross point connections is 1, and
When selecting a level sensor S ₁₆ to S _30, which is connected to the 15 connections of the cross point is 2.

The correction means 32 is provided for correcting a measurement error caused by the difference in the number of connections at the cross point when the measurement sensor is selected. That is, when the number of cross point connections is one and two, a difference occurs in the total conduction resistance value of the cross points, and this difference causes an error in the measured capacitance. Since this measurement error can be known in advance using the reference capacitance, the value is input to the correction means 32 in advance as a correction value. FIG. 2 exemplifies a measurement error that occurs when the number of connections at the cross point is 2 (in the case of double connection) and when the number of connections is 1 corresponding to the measured capacitance (reference capacitance). It was done.

The control / calculation means 23 is provided with each level sensor S ₁
It calculates the level in the tank from the capacitance of to S _30, in this example outputs the crosspoint switch control signal. The drive of the cross point switch array 31 is controlled by the cross point switch control signal, whereby the detection signals of the level sensors S _{1 to} S ₃₀ are sequentially selected and taken into the measuring circuit 21.

The capacitance calculating means 22 calculates the capacitance from the detected voltage measured by the measuring circuit 21. On the other hand, the correction means 3
2, the cross point switch control signal is also input, and the correcting means 32 determines whether the number of cross point connections is one or two based on the cross point switch control signal.
In this case, the correction value is output to the capacity calculating means 22. When the correction value is input, the capacitance calculation means 22 adds the correction value to the calculated capacitance and outputs the result to the control / calculation means 23. Therefore, the control / calculation means 23 can obtain the exact capacitance of each of the level sensors S _{1 to} S ₃₀ in which the measurement error caused by the difference in the number of cross point connections is corrected, and accurately calculate the level. be able to.

The above-described capacity calculation means 22, control / calculation means 23 and correction means 32 are constituted by, for example, a microcomputer. In the above example, the number of the level sensors is 30. However, the number is appropriately set according to the size of the tank to be used. Also, a cross point switch array 3 of 16 × 16 switches (16 rows, 16 columns)
Although 1 is used, another configuration may be used according to the number of measurement sensors. Note that, for example, a cross point switch array having a larger number of rows may be used, and all of the measurement sensors may be connected to that row.
Since all of them are 1, the above-described correction means 32 is not required.

[0016]

As described above, since the present invention uses a cross point switch array as a means for selecting a measurement sensor, as the conventional relay uses, the number of sensors increases. The problems such as the increase in the size of the device, the increase in power consumption, and the increase in the number of parts have been solved. Obtainable.

Further, according to the second aspect of the present invention, since a measurement error caused by a difference in the number of cross point connections is corrected,
Highly accurate level measurement becomes possible.

[Brief description of the drawings]

FIG. 1 is a block diagram for explaining an embodiment of the present invention.

FIG. 2 is a graph showing an example of a measurement error due to a difference in the number of cross point connections of a cross point switch array.

FIG. 3 is a block diagram for explaining a conventional capacitance level meter.

FIG. 4 is a perspective view showing a schematic configuration of a detection unit in FIG. 3;

Claims (2)

[Claims] 1. A plurality of stacked capacitance-type level sensors are sequentially selected by a measurement sensor selection means, and the capacitance is measured. The level sensor is installed based on the measured capacitance. An electrostatic capacitance level meter having a structure for calculating the level of a tank in which a cross point switch array is used for the measurement sensor selecting means. 2. The capacitance level meter according to claim 1, further comprising: means for correcting a measurement error of the capacitance caused by a difference in the number of connected cross points in the cross point switch array. Characteristic capacitance level meter.