Capacitance-type level measurement device and capacitance-type level measurement method

Abstract

To provide a capacitance level measuring device and a capacitance level measuring method that eliminate the need of complicated adjustment of the zero point and a span at the site, can reduce cost of the apparatus itself and adjustment cost without requiring an electrical component for adjustment of the zero point and the span, and eliminate the need of operations to empty a tank.SOLUTION: A capacitance level measuring device comprises: capacitance detection means that detects the capacitance inside a tank; capacitance digitization means that converts the capacitance detected by the capacitance detection means into a capacitance value that is numerical data; normalization means that normalizes the capacitance value output from the capacitance digitization means; and level value calculation means that converts the capacitance value normalized by the normalization means into a level value.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a capacitance-type level measurement device and a capacitance-type level measurement method for measuring the water level of a tank or the like that stores liquid. [Background technology]

[0002] A variety of level gauges have been proposed and used to measure the water level in tanks that store liquid, etc. Among these, capacitance-type gauges that measure the water level by measuring changes in capacitance related to the liquid being measured have been used.

[0003] With conventional capacitance-type level meters, the floating capacitance inside the tank varies depending on factors such as the installation environment, so the capacitance at zero when the tank is empty (zero point) and the change in capacitance per unit level change (span) must be adjusted on-site each time the capacitance-type level meter is installed.

[0004] In order to solve these problems of conventional capacitance-type level meters, for example, a capacitance-type level meter has been proposed in Patent Document 1. The capacitance-type level meter of Patent Document 1 includes a capacitance measuring means for measuring capacitance, a level signal converting means for converting a signal from the measuring means into a level signal, a zero point and span correction means for supplying a correction value for correcting the zero point and span of the level signal to the level signal converting means, a correction value switching signal sending means for sending a signal to the zero point and span correction means to switch to a correction value according to the change in the dielectric constant of the liquid when the type of liquid in the tank changes, and a zero point adjustment signal sending means for measuring the capacitance of the background level, comparing it with the previous measurement value when the liquid level in the tank reaches zero level, and sending a signal to the zero point and span correction means to adjust the zero point based on the deviation. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2-147918 Summary of the Invention [Problem to be solved by the invention]

[0006] However, conventional capacitance level meters require complicated on-site adjustment of the zero point and span, and also require the installation of electrical components for the adjustment (for example, resistors and capacitors for the adjustment), making it difficult to reduce the cost of the device itself and the adjustment costs.Furthermore, with the capacitance level meter of Patent Document 1, when correcting the zero point and span, the liquid in the tank must be drained to set the liquid level to zero, which is not an easy task to perform in an actual measurement site.

[0007] The present invention has been made in consideration of the above circumstances, and aims to provide a capacitance-type level measurement device and a capacitance-type level measurement method that do not require complicated on-site adjustment of the zero point and span, do not require electrical components for adjusting the zero point and span, can reduce the cost of the device itself and adjustment costs, and do not require work such as emptying the tank. [Means for solving the problem]

[0008] The capacitance type level measurement device according to claim 1 comprises a capacitance detection means for detecting capacitance within a tank, a capacitance data conversion means for converting the capacitance detected by the capacitance detection means into a capacitance value which is numerical data, a normalization means for normalizing the capacitance value output from the capacitance data conversion means, and a level value calculation means for converting the capacitance value normalized by the normalization means into a level value, wherein the normalization means: At two different water levels where there is a predetermined amount and the tank is not considered empty, A feature of this system is that it calculates the zero point, which is the capacitance at zero when the tank is empty, and the span, which is the change in capacitance per unit level change, from the two detected capacitance values.

[0009] The capacitance type level measuring device according to claim 2 is The two capacitance values ​​are the capacitance value at the current water level and the capacitance value at a pseudo-full tank level obtained by raising the water level in the tank from the current water level. It is characterized by:

[0010] The capacitance type level measurement method according to claim 3 converts the capacitance detected by the capacitance detection means for detecting the capacitance in the tank into a capacitance value which is numerical data, normalizes the capacitance value, and At two different water levels where there is a predetermined amount and the tank is not considered empty, From the two detected capacitance values, the zero point, which is the capacitance at zero when the tank is empty, and the span, which is the change in capacitance per unit level change, are calculated and the normalized capacitance value is converted into a level value.

[0011] The capacitance type level measurement method according to claim 4 comprises: The two capacitance values ​​are the capacitance value at the current water level and the capacitance value at a pseudo-full tank level obtained by raising the water level in the tank from the current water level. It is characterized by: [Effects of the Invention]

[0014] According to the present invention, there is no need for complicated on-site adjustment of the zero point and span, and no electrical components are required for adjusting the zero point or span, making it possible to reduce the cost of the device itself and the adjustment costs, and there is no need to empty the tank. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is an explanatory diagram showing an example of a capacitance type level measurement installation according to the present invention. [Figure 2] FIG. 2 is a diagram showing an example of the configuration of the capacitance type level measurement device. [Figure 3] 3 is an explanatory diagram showing the concept of operation of the capacitance type level measurement device. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Fig. 1 is an explanatory diagram showing an example of a capacitance-type level measurement installation according to the present invention. Fig. 2 is a configuration diagram showing an example of the configuration of the capacitance-type level measurement device. Fig. 3 is an explanatory diagram showing the concept of operation of the capacitance-type level measurement device.

[0017] The capacitance type level measurement device 1 according to the present invention is a device that measures the water level of a tank T or the like that stores a liquid F using capacitance technology. The capacitance type level measurement device 1 is composed of a capacitance type level measurement device main body 10, capacitance detection means 12, etc.

[0018] The capacitance detection means 12 detects the capacitance inside the tank T, and the detected capacitance varies depending on the amount of liquid F inside the tank T, and detects this capacitance as needed. Specifically, the capacitance detection means 12 is composed of, for example, a fixed part 12a fixed to the top of the tank T and a detection wire 12b, and the detection wire 12b hangs down inside the tank T so as to be immersed in the liquid F. Note that the form of the capacitance detection means 12 is not limited as long as it can detect capacitance that varies depending on the amount of liquid F inside the tank T.

[0019] The capacitance type level measurement device main body 10 processes the capacitance detected by the capacitance detection means 12 to calculate the water level of the tank T. The capacitance type level measurement device main body 10 is composed of an electronic computer and its peripheral circuits that convert analog signals into electronic values ​​and perform various calculations, and the calculations are performed by software. However, the calculations in the capacitance type level measurement device main body 10 do not necessarily have to be performed by software alone; they may be performed by a circuit composed of hardware only, or may be performed using both hardware and software.

[0020] The capacitance type level measuring device main body 10 of this embodiment is composed of the C / V conversion means 14, A / D conversion means 16, normalization means 20, output value conversion means 30, D / A conversion means 32, scale conversion means 34, etc., of the components shown in Figure 2.

[0021] The C / V conversion means 14 converts the analog capacitance signal from the capacitance detection means 12 into an analog voltage level. The A / D conversion means 16 converts the analog capacitance voltage level into digital numerical data. In other words, the C / V conversion means 14 and the A / D conversion means 16 constitute a capacitance data conversion means that converts the capacitance detected by the capacitance detection means 12 into a capacitance value, which is numerical data.

[0022] The normalization means 20 normalizes the capacitance value output from the capacitance data conversion means, and the details of normalization will be described later.

[0023] The output value conversion means 30 and the D / A conversion means 32 convert the normalized capacitance value into a level value, which is the water level of the liquid F in the tank T, according to a desired standard, and in this case, output it as an analog signal, depending on how the level value is used. The scale conversion means 34 converts the normalized capacitance value into a level value, which is the water level of the liquid F in the tank T, in a form that can be displayed. In other words, the output value conversion means 30, the D / A conversion means 32, and the scale conversion means 34 are level value calculation means that convert the capacitance value normalized by the normalization means 20 into a level value. In this way, the specifications for converting the capacitance value normalized by the normalization means 20 into a level value by the level value calculation means depend on how the level value is subsequently used, and are arbitrary, including the signal format.

[0024] Next, we will explain in detail the operation of the capacitance type level measurement device 1 of this embodiment. The operations of the capacitance detection means 12 and the capacitance data conversion means are as described above, and here we will mainly explain the operation of the normalization means 20.

[0025] The normalization means 20 normalizes the capacitance value received from the capacitance data conversion means, and its purpose is to obtain, from the two detected capacitance values, the zero point Dz, which is the capacitance at the zero point when the tank T is empty (Lz), and the maximum point Df, which is the capacitance when the tank T is full (Lmax) as shown in Fig. 3. Note that obtaining the zero point Dz and the maximum point Df means that the zero point Dz and the span, which is the change in capacitance per unit level change, are determined by calculation.

[0026] Specifically, two capacitance values ​​(capacitance D1 at level L1 and capacitance D2 at level L2) that clearly indicate the detected level (water level) are used to calculate a normalized capacitance value (Mx: maximum value 1 to minimum value 0) (i.e., the normalization shown in this embodiment is one in which the maximum value is 1 and the minimum value is 0).

[0027] In this normalization, if the capacitance value output from the A / D conversion means 16 is Dx (Dz to Df), normalization conversion is performed according to the following equation 1. Mx = (Dx - Dz) / (Df - Dz) Equation 1

[0028] Furthermore, for the two points L1 and L2, the capacitance value D1 can be set at the current water level L1, and the capacitance value D2 can be set at a pseudo-full water level (for example, the water level obtained by pouring liquid into the F tank T and raising the water level relative to the current water level L1) as L2, and the normalization means 20 can perform the normalization as described above.

[0029] Since the normalized capacitance value is between 0 and 1, the output value conversion means 30 performs a numerical conversion of the output value so that the analog output (voltage output) from the D / A conversion means 32 has a scale of the desired level value. Then, the D / A conversion means 32 performs an analog output (voltage output) that matches the measured level value. Note that the scale conversion means 34 performs a numerical conversion of the normalized capacitance value Mx so that it can be displayed as an actual level value (for example, meters) on the display means.

[0030] According to the capacitance type level measuring device 1 having the above-described configuration and operation, there is no need for complicated adjustment of the zero point and span on-site, and no electrical components are required for adjusting the zero point or span, which makes it possible to reduce the cost of the device itself and the adjustment costs, and there is no need for work such as emptying the tank.

[0031] This is an effect of eliminating the need for electrical adjustment by performing numerical normalization in the present invention, whereas in the past it was necessary to perform zero adjustment and span adjustment as electrical adjustments at the C / V conversion means 14. This eliminates the need for passive components, moving components, etc. for electrical adjustments that were previously necessary, and further eliminates the need for measuring instruments for electrical adjustments, allowing for a significant reduction in adjustment costs.

[0032] The present invention allows various embodiments and modifications without departing from the broad spirit and scope of the present invention. Furthermore, the above-described embodiments are intended to explain the present invention and do not limit the scope of the present invention. That is, the scope of the present invention is defined by the claims, not the embodiments. Various modifications made within the scope of the claims and within the scope of the meaning of the invention equivalent thereto are considered to be within the scope of the present invention. [Industrial Applicability]

[0033] As described above, according to the present invention, it is possible to provide a capacitance-type level measurement device and a capacitance-type level measurement method that do not require complicated adjustment of the zero point and span on site, do not require electrical components for adjusting the zero point and span, make it possible to reduce the cost of the device itself and the adjustment costs, and do not require work such as emptying the tank. [Explanation of symbols]

[0034] 1. Capacitive level measuring device 10. Capacitance type level measuring device main body 12. Capacitive sensing means 12a... Fixed part 12b....Detection wire 14. C / V conversion means 16. A / D conversion means 20...Normalization means 30. Output value conversion means 32 D / A conversion means 34. Scale conversion means

Claims

1. A capacitance type level measuring device for measuring the water level in a tank from changes in capacitance, a capacitance detection means for detecting the capacitance in the tank; a capacitance data conversion means for converting the capacitance detected by the capacitance detection means into a capacitance value that is numerical data; normalization means for normalizing the capacitance value output from the capacitance data conversion means; a level value calculation means for converting the capacitance value normalized by the normalization means into a level value, The normalization means From two capacitance values ​​detected at two different water levels where there is a predetermined amount and the tank is not considered empty, A capacitance type level measuring device characterized by determining, through calculation, the zero point, which is the capacitance at zero when the tank is empty, and the span, which is the change in capacitance per unit level change.

2. The two capacitance values ​​are The capacitance value at the current water level; 2. The capacitance type level measuring device according to claim 1, wherein the capacitance value is a capacitance value at a pseudo-full tank level obtained by raising the water level of the tank from the current water level.

3. In a capacitance type level measurement method for measuring the water level in a tank from changes in capacitance, converting the capacitance detected by a capacitance detection means for detecting the capacitance inside the tank into a capacitance value that is numerical data; normalizing the capacitance value; In the normalization, the zero point, which is the capacitance at the zero point when the tank is empty, and the span, which is the change in capacitance per unit level change, are calculated from two capacitance values ​​detected at two different water levels where there is a predetermined amount and the tank is not considered empty; A capacitance type level measurement method, characterized in that the normalized capacitance value is converted into a level value.

4. The two capacitance values ​​are The capacitance value at the current water level; 4. The capacitance type level measurement method according to claim 3, wherein the capacitance value is a capacitance value at a pseudo-full tank level obtained by raising the water level of the tank from the current water level.

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