JP2511334B2 - Measurement accuracy inspection method for capacitance type liquid level gauge - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for inspecting the measurement accuracy of a capacitance type liquid level gauge, which measures the liquid level in a tank by detecting it as a capacitance.

[0002]

2. Description of the Related Art First, the above-mentioned capacitance type liquid level gauge will be described with reference to FIG. The sensor unit 10 has a level composed of a cylindrical electrode 11 and a cylindrical electrode 12 facing each other.
A required number of sensors, for example, seven sensors S1 to S7 are arranged in the height direction of the tank 1 in which the liquid is stored. Here, the one electrode 12 is commonly connected to which the oscillation voltage of the oscillator 30 is applied. The other electrode 11 is connected to the sensor selection unit 20 independently for each level sensor. The sensor selecting section 20 selects the level sensors S1 to S7 and introduces the capacitances shown therein to the capacitance measuring section 40, where these capacitances are converted into digital or analog capacitance signals, Is output. The capacitance signal output from the capacitance measuring unit 40 is stored in the data storage unit 6
0, transferred to the data calculation unit 70. Data calculation unit 70
In the above, in accordance with the program previously input to the program memory unit 80, the capacitance signal measurement and the liquid level calculation are performed for each level sensor, and the liquid level H output is the output CRT 90, the output. The image is read by the printer 100 or other output display device 110 .

Next, it will be described that the liquid level can be measured by the capacitance type liquid level gauge equipped with the above-mentioned sensor section 10. First, the "liquid level sensor Sc" where the liquid surface exists
The electrostatic capacity of is expressed as the sum of the electrostatic capacity of the part of the liquid level sensor electrode existing in the liquid and the electrostatic capacity of the part existing in the air (the detailed derivation method). Regarding Japanese Patent Application 1-
200984).

Csc = Cec + Cec (ε-1) hc / lc (1) where Csc: capacity of the liquid level sensor Cec: capacity when the entire liquid level sensor is in the air ε: relative permittivity of the liquid hc: liquid Liquid level lc: liquid level sensor length or height The relative dielectric constant ε of the liquid is the ratio of the electrostatic capacitance Cen of the sensor to the electrostatic capacitance Cfn when this sensor is completely present in the liquid. Is expressed as follows.

Ε = Cfn / Cen (2) where n is the sensor number of the level sensor. In this case, the level sensor for measuring ε may be any as long as it exists in the liquid. It can be S1. ε = Cfn / Cen = Cfl / Cel (3) Here, the liquid level hc for the liquid level sensor can be obtained by deleting ε from the equations (1) and (3).

Hc = lc.Cel (Csc-Cec) / Cec (Cfl-Cel) (4) In the formula (4), Cel, Cec, and lc are sensor shapes,
Since it is a constant determined by the dimensions, the liquid level hc of the liquid level sensor can be obtained by measuring Cfl and Csc. The height lx below the liquid level sensor Sc is equal to the sum of the heights of the level sensors below. These heights lx are measured in advance, including the height Ho of the sensor stand, and their fixed values are stored in the data storage unit 60.
By the way, when the liquid level sensor is Sl, there is no level sensor below it for measuring the relative permittivity of the liquid. However, when the sensor S1 is in the air or in the liquid, If the values are stored in the data storage unit 60, it is possible to obtain the relative permittivity ε from the equation (3) by using these, and by applying these Cel and Cfl to the equation (4), The liquid level can be measured and calculated in the same manner as in.

The liquid level H from the tank bottom to the liquid level can be finally obtained as the sum of the liquid level hc measured and calculated by the equation (4) and the height lx to the liquid level sensor Sc. . H = hc + lx (5) Next, as to how to determine which the liquid level sensor Sc is, the following is performed. The sensor S1 sequentially measures and calculates the liquid level hc using the equation (4) for each of these. When the level sensor is completely in the liquid, hc = lc, and for the sensor Sc with the liquid level, 0 <hc <lc, and when the level sensor is completely in the air, hc = lc It goes without saying that it will be 0. From these, it can be determined which is the liquid level sensor Sc. Once it is determined which is the liquid level sensor Sc, the sensor number of this sensor is stored in the data storage unit 60, and this is used as a clue for efficient determination of the liquid level sensor from the next time. It can be implemented well.

When inspecting the measurement accuracy of such a capacitance type liquid level gauge, conventionally, the sensor unit 10 in FIG. 1 is first replaced with a variable variable condenser 10 'for accuracy inspection as shown in FIG. And this variable condenser 10 '
The theoretical liquid level corresponding to the set volume of is calculated in advance. Next, the set volume of the variable condenser 10 'as described above is supplied as an actual input to the control calculation section 5 via the volume measuring section 40 as shown in FIG. 2, and the actual liquid level corresponding to this is supplied. Measure. Here, the above-described theoretical liquid level and the actual measured liquid level are compared to obtain the measurement accuracy of the liquid level gauge.

[0009]

In the measurement accuracy inspection method as described above, the actual measurement sensor unit 10 is separated from the sensor selection unit 20, and a variable variable condenser 10 'for accuracy inspection is connected instead. It includes things. Therefore, the measurement accuracy inspection method has the following drawbacks or problems.

A. It is necessary to separate the sensor unit at each accuracy inspection. b. A variable variable condenser must be prepared in advance as an inspection standard. c. The above variable variable capacitors must be tested in advance. d. In the accuracy inspection method as described above, after all, only the remaining portion of the capacitance type liquid level gauge except the sensor portion is inspected.

The present invention is intended to provide a measuring accuracy inspection method for a capacitance type liquid level gauge which eliminates and eliminates the above-mentioned drawbacks and problems.

[0012]

[Means for Solving the Problems] In the measuring accuracy inspection method for a capacitance type liquid level gauge as described above, each level sensor
Each height is stored as a reference value for each service,
About each level and sensor for which you want to know the inspection accuracy
Is in the liquid and the whole is in the air.
Measure the liquid level and check that the whole is in the liquid.
Difference between the measurement result and the reference value of the level sensor
Therefore, if the whole is in the air, the measurement result
The measurement accuracy of the liquid level gauge was checked from the body .

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention comprises a sensor section in which a plurality of pairs of level sensors composed of pairs of electrodes facing each other are arranged in a tank for storing a liquid in the height direction thereof. A control calculation unit that includes a sensor selection unit that sequentially selects, a capacitance measurement unit, and a program memory that internally performs the capacitance signal measurement and liquid level calculation for each level sensor is provided. In a measurement accuracy inspection method of a capacitance type liquid level gauge, which comprises a level sensor having a liquid level and measuring the liquid level by measuring the liquid level, The measurement of the liquid level is performed for each of the level sensors wholly in the air, and the measurement accuracy is checked by comparing the measurement results with the reference values of the corresponding level sensors. It is.

The actual measurement accuracy inspection can be carried out as follows by an accuracy inspection program preprogrammed and stored in the program memory unit 80. Further, a manual sensor selection unit may be provided to manually perform the accuracy inspection. First: Level sensors Sn are sequentially set from S1 to all levels.
A sensor is selected to obtain these liquid levels hcn (where n is the sensor number).

Second: The liquid level sensor Sc is judged based on the liquid level hcn obtained in the first. Third: The liquid level hcn of all level sensors completely below the liquid level sensor Sc in the liquid is obtained using the equations (3) and (4). It is also possible to adopt the value obtained in the first step as the liquid level hcn.

Fourth: Difference δn between the liquid level hcn obtained in the third and the height lcn (reference value) of the corresponding level sensor previously measured and stored in the data storage unit 60.
Calculate (measurement error). δn = hcn-lcn Fifth: For the level sensor completely above the liquid level sensor Sc, which is completely in the air, the liquid level hcn is obtained in the same manner as in the third case. The same applies to the fact that the value obtained in the first step can be adopted as the liquid level hcn.

At this time, when the relative permittivity of the liquid is measured by the equation (3), the level completely in the liquid as described above
Although a sensor is required, if Cfn of the level sensor cannot be measured due to lack of liquid in the tank, the value when Cfn can be measured due to liquid is stored in the data storage unit 60. You can leave it and use it. Sixth: Find the difference δn (measurement error) between the fifth liquid level hcn and the zero value (reference value) stored in advance.

In this case, since they are hcn when there is no liquid, they should show zero, and therefore, if there are values, they will show the measurement error as they are. δn = hcn-0 = hcn 7th: Regarding the measurement error of the liquid level sensor Sc, when the liquid level in the tank is lowered or raised and the lower or upper level sensor becomes the liquid level sensor, What is necessary is just to measure the measurement error of the liquid level sensor.

Since the electrodes of the level sensor are generally constructed in the form of a coaxial cylinder or a parallel plate, the capacitance signal has a characteristic of increasing linearly from zero liquid level to full liquid level as shown in FIG. Have In FIG. 3, the chain line indicates the ideal level-capacity signal ideal straight line indicated by the ideal level sensor electrode with zero error. Solid lines a and b indicate liquid level-capacitance signal straight lines respectively shown by the actual level sensor electrodes. When manufacturing an electrode, it is unavoidable that an electrode having slightly different characteristics will be produced even if efforts are made to make the shape, structure, material used, manufacturing process, etc. of the electrode the same. Here, looking at the chain line and the solid line a, the difference in the ordinate direction between them shows a measurement error, which decreases monotonically from the position where the liquid level is zero to the intersection of both straight lines. , Then, it increases monotonically from there to the full liquid level. In this case, the magnitude of the measurement error is maximum at the liquid level zero. Now, looking at the chain line and the solid line b, in this case, the measurement error monotonically increases and reaches the maximum at the full liquid level. Therefore, in any case, it can be read from FIG. 3 that the measurement error becomes maximum at the zero liquid level or the full liquid level. In the present invention, the data storage unit 60 is provided for each level sensor electrode using the capacitance signals at the zero liquid level and the full liquid level corresponding to the ideal capacitance signal as known reference values.
If the reference values of these known capacitance signal memories are compared with the actual measured values showing the maximum measurement error, these are regarded as measurement errors of the liquid level sensor for each level sensor or It can be used to inspect the measurement accuracy of the entire capacitance type liquid level gauge. The error characteristic of the capacity measuring unit is generally linear, and since the accuracy test is performed at the zero liquid level and the full liquid level, it is considered that the accuracy of the entire device was finally tested in the present invention. It will be good.

[0020]

As described above, according to the present invention, the liquid level hcn is measured for each of the level sensor entirely in the liquid and the level sensor entirely in the air, and these measurement results are stored in the data storage unit. Since the measurement accuracy of the above-mentioned level gauge is inspected by comparing with the reference value of the corresponding level sensor stored in, the variable variable condenser is prepared in advance as an inspection standard, and its It goes without saying that no certification is required. In addition, although the present invention performs the actual measurement itself without disconnecting the sensor unit, although it is an accuracy test, it is possible to inspect the accuracy of the entire capacitance type liquid level gauge including the sensor unit. It is a thing.

[Brief description of drawings]

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

FIG. 2 is a diagram for explaining a conventional example of the present invention.

FIG. 3 is a diagram showing characteristics of a level sensor.

[Explanation of symbols]

 1 Tank 2 Liquid 2a Liquid level H Liquid level 10 Sensor part 10 'Variable variable condenser S1-7 Level sensor 11 Level sensor electrode 12 Level sensor electrode Sc Liquid level sensor lc Liquid level sensor height lx Up to liquid level sensor Height hc Liquid level Ho Height of sensor holder 20 Sensor selection unit 5 Control calculation unit 40 Capacity measurement unit 50 Control unit 60 Data storage unit 70 Data calculation unit 80 Program memory unit a Solid line b Solid line

Claims (1)

(57) [Claims] 1. A sensor unit comprising a plurality of pairs of level sensors each comprising a pair of opposing electrodes arranged in a height direction in a tank for storing a liquid, wherein the level sensors are sequentially selected. A sensor calculation unit, a capacitance measurement unit, and a control calculation unit having a program memory for executing the capacitance signal measurement and liquid level calculation for each level sensor, In the measurement accuracy inspection method of a capacitance type liquid level gauge that measures the liquid level by measuring the liquid level of a level sensor with a liquid level, the height of each level sensor is used as a reference. Value and
To is stored in its entirety for each level sensor you want to know the inspection accuracy
Is in the liquid and the whole is in the air.
Then, the above liquid level measurement is performed, and if the whole is in the liquid, the measurement result and its
Due to the difference between the bell sensor and the above reference value,
The measurement accuracy inspection method of the capacitance type liquid level gauge that inspects the measurement accuracy based on the measurement result itself .