JP7813449B2 - Capacitance-type level measurement device and capacitance-type level measurement method - Google Patents

Description

The present invention relates to a capacitance-type level measurement device and a capacitance-type level measurement method for measuring the water level in a tank or the like that stores liquid.

A variety of level gauges have been proposed and used to measure the water level in tanks and other liquid storage areas. Among these, capacitance-type gauges have been used, measuring the water level by measuring changes in capacitance related to the liquid being measured.

With conventional capacitance 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 level meter is installed.

To solve these problems with conventional capacitance level meters, for example, Patent Document 1 proposes a capacitance level meter. The capacitance level meter in Patent Document 1 includes a capacitance measurement means for measuring capacitance, a level signal conversion means for converting the signal from the measurement means into a level signal, a zero and span correction means for supplying the level signal conversion means with correction values for correcting the zero and span of the level signal, a correction value switching signal sending means for sending a signal to the zero and span correction means to switch to a correction value corresponding to the change in the dielectric constant of the liquid when the type of liquid in the tank changes, and a zero adjustment signal sending means for measuring the background level capacitance when the liquid level in the tank reaches zero, comparing it with the previous measurement value, and sending a signal to the zero and span correction means to adjust the zero point based on the deviation.

Japanese Unexamined Patent Publication No. 2-147918

However, conventional capacitance level meters require complicated on-site adjustment of the zero point and span, and require the installation of electrical components for these adjustments (such as resistors and capacitors for adjustment), making it difficult to keep the costs of the device itself and the adjustment costs down. 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.

The present invention was made in light of these circumstances, and aims to provide a capacitance-type level measurement device and a capacitance-type level measurement method that do not require the complicated adjustment of zero and span on-site, do not require electrical components for adjusting zero and span, reduce the cost of the device itself and adjustment costs, and do not require work such as emptying the tank.

The capacitance type level measuring device according to claim 1 comprises a capacitance detection means for detecting the capacitance inside the 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 calculates 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, from two capacitance values detected at two different water levels where there is a predetermined amount and the tank is not considered empty.

The capacitance type level measuring device described in claim 2 is characterized in that 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 .

The capacitance type level measurement method described in claim 3 is characterized in that the capacitance detected by a capacitance detection means that detects the capacitance inside the tank is converted into a capacitance value, which is numerical data, and the capacitance value is normalized. During the normalization, from two capacitance values detected at two different water levels where there is a predetermined amount and the tank is not considered empty, 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, and the normalized capacitance value is converted into a level value.

The capacitance type level measurement method described in claim 4 is characterized in that 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 .

The present invention eliminates the need for complicated on-site adjustments of zero and span, and does not require electrical components for adjusting zero or span, reducing the cost of the device itself and adjustment costs, and eliminating the need to empty the tank.

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 diagram showing an example of the configuration of the capacitance type level measurement device. 3 is an explanatory diagram showing the concept of operation of the capacitance type level measurement device. FIG.

The following describes in detail the embodiments of the present invention with reference to the drawings. Figure 1 is an explanatory diagram showing an example of a capacitance-type level measurement installation according to the present invention. Figure 2 is a configuration diagram showing an example of the configuration of the capacitance-type level measurement device. Figure 3 is an explanatory diagram showing the concept of operation of the capacitance-type level measurement device.

The capacitance-type level measurement device 1 of the present invention is used to measure the water level of a tank T or the like that stores 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.

The capacitance detection means 12 detects the capacitance inside the tank T. The detected capacitance varies depending on the amount of liquid F inside the tank T, and the capacitance is detected 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, with the detection wire 12b hanging down inside the tank T so as to be immersed in the liquid F. Note that the capacitance detection means 12 is not limited in its form as long as it can detect capacitance that varies depending on the amount of liquid F inside the tank T.

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 calculator and its peripheral circuits that converts analog signals into electronic values and performs various calculations, and the calculations are performed by software. However, calculations in the capacitance type level measurement device main body 10 do not necessarily have to be performed solely by software; they can be performed by circuits composed solely of hardware, or they can be performed using both hardware and software.

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

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.

The normalization means 20 normalizes the capacitance value output from the capacitance data conversion means. Details of normalization will be described later.

The output value conversion means 30 and D/A conversion means 32 convert the normalized capacitance value into a level value, which is the water level of liquid F in tank T, according to the desired standard. This depends on the form in which the level value is to be used; in this case, this is output as an analog signal. The scale conversion means 34 converts the normalized capacitance value into a displayable form, which is the water level of liquid F in tank T. In other words, the output value conversion means 30, D/A conversion means 32, and scale conversion means 34 are level value calculation means that convert the capacitance value normalized by normalization means 20 into a level value. In this way, the specifications for converting the capacitance value normalized by 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.

Next, we will explain in detail the operation of the capacitance-type level measurement device 1 of this embodiment. Note that the operation of the capacitance detection means 12 and capacitance data conversion means is as described above, and here we will mainly explain the operation of the normalization means 20.

The normalization means 20 normalizes the capacitance value received from the capacitance data conversion means. The purpose is to determine, from the two detected capacitance values, the zero point Dz, which is the capacitance at zero when the tank T is empty (Lz) as shown in Figure 3, and the maximum point Df, which is the capacitance when the tank T is full (Lmax). Note that determining 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, can be determined through calculation.

Specifically, the normalized capacitance value (Mx: maximum value 1 - minimum value 0) is calculated using two capacitance values (capacitance D1 at level L1 and capacitance value D2 at level L2) that clearly indicate the detected water level (i.e., the normalization described in this embodiment sets the maximum value to 1 and the minimum value to 0).

This normalization is performed by the following equation 1, where Dx (Dz to Df) is the capacitance value output from the A/D conversion means 16.
Mx=(Dx-Dz)/(Df-Dz)...Formula 1

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 L2 (for example, the water level obtained by pouring liquid F into the tank T and raising it above the current water level L1), and the normalization means 20 can then perform the normalization described above.

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 is scaled to the desired level value. The D/A conversion means 32 then produces an analog output (voltage output) that corresponds to the measured level value. Furthermore, 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.

With the capacitance-type level measurement device 1 configured and operated as described above, there is no need for complicated on-site adjustments of the zero point and span, and no electrical components are required for adjusting the zero point or span, which reduces the cost of the device itself and adjustment costs, and there is no need to empty the tank.

This is the effect of eliminating the need for electrical adjustments, whereas in the past, zero and span adjustments had to be made at the C/V conversion means 14, by performing numerical normalization in the present invention. This eliminates the need for passive and moving parts for electrical adjustments, which were previously necessary, and also eliminates the need for measuring instruments for electrical adjustments, significantly reducing adjustment costs.

The present invention allows for 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. In other words, 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 meaning of the equivalent inventions are considered to be within the scope of the present invention.

As described above, the present invention provides a capacitance-type level measurement device and a capacitance-type level measurement method that eliminate the need for complicated on-site adjustment of zero and span, and does not require electrical components for adjusting zero and span, thereby reducing the cost of the device itself and adjustment costs, and does not require work such as emptying the tank.

1. Capacitance type level measuring device 10... Capacitance type level measuring device main body 12... Capacitance detection means 12a... Fixed portion 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 (4)

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. 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. 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. 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.