RU2286551C1 - Method for measuring level of liquid and bar type level meter for realization of method - Google Patents

Abstract

FIELD: measuring equipment engineering, possible use for measuring level of liquid products, in particular, oil and oil products in railroad cisterns.

SUBSTANCE: level meter for measuring level of liquid contains bar with single capacity level indicators, positioned along its length, bar is made in form of hollow elongated construction, inside the construction a pair of electronic boards is positioned in form of rods, mounted in parallel to one another and at fixed distance from each other, forming single capacity level indicators on opposite planes facing each other, by means of electrodes on one electronic board and common electrode on the other board. When measuring level of liquid, serial scanning of indicators is performed in pairs of following indicator with previous one and on basis of received scanning results, level of liquid is calculated.

EFFECT: increased manufacturability, reliability and precision when measuring level of liquid product.

2 cl, 2 dwg

Description

The invention relates to measuring equipment and can be used to measure the level of liquid products, in particular oil and oil products in railway tanks.

Known патент 2042928, publ. 08/27/95, the level gauge contains sections connected in series, each of which consists of discrete and continuous capacitive level sensors, the planes of the input electrodes of the continuous sensor are parallel to each other and overlapped along the length of the section, and discrete level sensors are located in the overlap zones also contains a switch for pulse polling sensors, an analog-to-digital converter, an address generator of sensors and a computing unit.

The electrodes of the level sensors are printed circuit boards made by electroforming on the surface of a flexible dielectric film rolled into a tube, which is a laborious and expensive process, in addition, discrete sensors have a small capacity, which can lead to failures under the influence of destabilizing factors, such as condensate, and loss of accuracy.

Known adopted for the prototype method of measuring the level of dielectric liquid, published application No. 203100414, publication date 2004.07.20, including sequential measurement of the capacitance of individual capacitors, starting from the bottom and find the desired first with an incomplete filling level, and the liquid level is determined after preliminary measurement of the total capacity of the desired the capacitor and connected in parallel with it for the time of measuring the adjacent lower fully filled capacitor and their filling length.

This measurement method does not have sufficient accuracy for use in portable portable level gauges such as rods, where additional errors arise under the action of mechanical loads.

The objective of the proposed technical solution is to eliminate these shortcomings, improving manufacturability, reliability and accuracy of measuring the level of a liquid product.

The problem with the achievement of the technical result is solved due to the fact that in the method of measuring the liquid level immersed in it by a capacitive level gauge containing a rod with single capacitive level sensors located along its length, including a serial survey of the sensors, the determination of the desired number of the sensor immersed in the liquid is not completely, and subsequent measurement of the liquid level from a pair of sensors, sequential interrogation of the sensors is carried out in pairs of the subsequent sensor with the previous one, and the measured level is liquid The values are calculated from the capacitance values of one of the two pairs of sensors with the numbers N (i-1, i) or N (i, i + 1) and according to one of the formulas:

Where

H is the liquid level;

h is the step between the arrangement of the electrodes of single capacitive sensors;

i = 1,2,3,4 ... the number of the required single capacitive sensor, not completely filled with liquid;

dl _{i-1, i} dl _{i, i + 1} - the length of the liquid filling pairs of capacitive unit sensors with numbers N (i-1, i) or N (i, i + 1), respectively;

the choice of a pair of sensors with numbers N (i, i + 1) and formulas (2) for calculating the measured level is carried out provided that the liquid filling length dl _{i, i + 1 of a} pair of unit capacitive sensors N (i, i + 1) is greater than or equal to 1.5D, where D is the interelectrode space of single capacitive sensors.

The problem is also solved due to the fact that in the level gauge for measuring the liquid level, containing a rod with single capacitive level sensors located along its length, the rod is made in the form of a hollow long structure, inside which a pair of printed circuit boards in the form of rails is placed and attached to it mounted parallel to each other and at a fixed distance from each other, forming flat capacitors on the opposite surfaces facing each other or - unit capacitive level sensors, by means of lead electrodes on one printed circuit board and a common output electrode on the opposite printed circuit board, and the printed circuit boards are combined in sections, and the value of the fixed distance D, forming the interelectrode space between the input and output electrodes of the level sensors, is provided by the length of the spacers installed between the parallel printed circuit boards, rigidly attached to the hollow long structure by bushings or brackets, and also due to the fact that the hollow long structure is made in the form of a pipe, fixed the distance D = 6 mm, the input electrodes are spaced from each other with a gap of 0.5 mm between them and with a step of h = 100 mm.

There is a linear dependence of the output codes on the magnitude of the filling length of the sensors dl. With increasing sensor filling length, the absolute measurement error of this one increases due to an increase in the slope error of this linear dependence, therefore, on the one hand, an earlier transition from one pair of electrodes to another leads to an increase in measurement accuracy, however, on the other hand, at the edges of the electrodes there is a curvature of the electric field lines, so an early transition from one pair of electrodes to another leads to a distortion of the linear dependence of the output codes on the amount of filling and an additional error pits. Thus, there is an optimal criterion for choosing a pair of electrodes for measurement, namely: if the liquid filling length dl _{i, i + 1} for the pair of electrodes N (i, i + 1) of the electrodes is greater than or equal to 1.5D, where D is the interelectrode space of the capacitors , then measurements are made from the next pair of electrodes N (i, i + 1), otherwise, from the previous pair with the number N (i-1, i). At distances equal to 1.5 D, a non-linear section arising due to edge effects is guaranteed to be excluded.

The device and method are illustrated by drawings, FIG. 1 is a structural electrical diagram of a level gauge. FIG. 2 is a general view of a section of a level gauge; FIG. 3 is a section along AA.

The level gauge, figure 1, consists of sequentially arranged sections 1, each of which contains single level sensors installed one after another, having input electrodes 2 or a common output electrode 3, a sectional microprocessor device 4, which is connected by an information bus to the central processing unit 5, consisting of an input-output device 6, a memory 7, an arithmetic device 8, a control device 9 and a display device 10. The output electrodes 3 of all sections are connected to an input charge-sensitive amplifier Telem CSA 11, whose output is connected to the input of analog-to-digital converter ADC 12, and the output of the ADC 12 via the input-output unit 6 - the central processing unit 5, and also with the display device 10 display.

The rod type level gauge, FIG. 1 and FIG. 2, is a hollow lengthy structure, in particular a pipe 13, inside which are assemblies of two printed circuit boards in the form of rails 14 and 15, on one of which input electrodes 2 are located with a gap between each other 0.5 mm and in increments of h = 100 mm, and on the other continuous output electrode 3, forming plane-parallel unit capacitors - unit level sensors, the interelectrode distance B = 6 mm is provided by spacer sleeves 16, in the upper part of the level gauge, a plate is fixed on one of the rails microprocess block 5. With the help of semicircular bushings 17 and screw connections, assemblies of rails 14 and 15 are fastened together, increasing the length of the section, and then to the pipe 13. At the ends of the section, a docking unit 18 is installed to combine them into a long-length construction of a rod level gauge with range of level measurement from 1.8 m to 3.5 m.

The level gauge, figure 1, works as follows. Each sectional microprocessor device 4 has its own serial number, which is recorded in its memory. From the Central processing unit 5, a command is sent to the sectional microprocessor device 4 for generating polling voltage pulses for the first pair of sensors. This command contains the number of the sectional microprocessor device and the number of interrogated sensors. Poll sensors produce from the bottom up. The interrogation pulses passing through the input 2 and output electrodes 3 of the 1st and 2nd sensors are fed to the input of the control unit 11, in which the capacitance of the 1st and 2nd sensors is converted to the amplitude of the voltage pulse.

The amplitude of the voltage pulse of the 1st and 2nd sensors in the ADC 12 is converted into binary code, which is transmitted through the input-output device 6 to the central processing unit 5 and stored in memory 7. Then, another pair of sensors of the 2nd and 3rd th and the central processor 5 again receives the binary code, etc. In the non-volatile memory of each sectional microprocessor device 4, "dry" and "wet" codes of pairwise connected sensors are stored. The central microprocessor device 5, comparing the incoming codes from the sensors with the “dry” and “wet” codes recorded in the memory, determines the pairs of sensors located at the air-liquid interface or not completely submerged. For example, at the interface there are two pairs of sensors for i = 2 with numbers N (1,2) and N (2,3). If the filling length of the pair of sensors dl _{2,3 is} less than 1.5D, where D = 6 mm the interelectrode distance between the input and output electrodes of the level sensors, then the calculation is carried out according to the formula (1):

H = dl _1,2

Where

H is the liquid level;

dl _1,2 is the filling length of a pair of sensors with numbers N (1,2), i.e. the measured liquid level N will be equal to the filling length of the pair of sensors with numbers N (1,2). But if the filling length of the pair of sensors dl _{2,3 is} greater than or equal to 1.5D, then the calculation is carried out according to the formula (2), and the measured level H will be equal to

H = h + dl _2,3

Where

H is the liquid level;

h = 100 mm is the spacing of the electrodes of individual sensors;

dl _2,3 - filling length of a pair of sensors with numbers N (2,3).

The calculation of the liquid level by pairs of electrodes is the next with the previous, with the ideal value of the parameters, i.e. excluding errors from the slope of the linear dependence of the output codes on the size of the filling length of the sensors dl, is equivalent. Almost all values included in formulas (1) and (2) are determined with errors; therefore, formulas (1) and (2) are actually unequal.

The optimal criterion for choosing a pair of electrodes for measurement was experimentally selected, namely: if the filling length of the pair of sensors dl _{i, i + 1 is} greater than or equal to 1.5D, where D is the interelectrode space of the capacitors, then measurements are made from the next pair of electrodes N (i, i +1), i.e. consisting of the i-th and the following (i + 1) -th electrode.

The proposed portable design of the level gauge in the form of a measuring rod with a low weight and the proposed measurement method, providing an error of at least 1 mm, will have advantages over existing direct measurement methods that require financial costs for metrological checks and maintenance.

Claims (10)

1. The method of measuring the liquid level immersed in a capacitive level gauge containing a rod with a single capacitive level sensors located along its length, including sequential interrogation of sensors, determining the desired number of the sensor, not completely immersed in the liquid, and subsequent measurement of the liquid level is carried out by measuring the capacitance of the pair sensors: the desired one and the one adjacent to it, characterized in that the sequential interrogation of the sensors is carried out in pairs of the subsequent sensor with the previous one, and the measured liquid level is islyayut by the capacitance value of one of the two pairs of sensors with the numbers N (i-1, i) or N (i, i + 1) and on one of the formulas:

H is the liquid level; h is the step of the location of the electrodes of single capacitive sensors; i = 1,2,3,4 ... the number of the required single capacitive sensor, not completely filled with liquid; dl _{i-1, i} dl _{i, i + 1} - the length of the liquid filling N (i-1, i) or N (i, i + 1) pairs of capacitive unit sensors, respectively, the selection of a pair of sensors with numbers N (i, i + 1) and formulas (2) for calculating the measured level is carried out under the condition that the liquid filling length dl _{i, i + 1 of the} pair of electrodes of single capacitive sensors N (i, i + 1) respectively, greater than or equal to 1.5D, where D is the interelectrode space of individual capacitive sensors. 2. The level gauge for measuring the liquid level, containing a rod with a single capacitive level sensors located along its length, characterized in that the rod is made in the form of a hollow long structure and a pair of printed circuit boards are fixed inside it in the form of rails mounted parallel to each other and on a fixed distance from each other, forming on the opposite planes facing each other, flat capacitors - unit capacitive level sensors, by means of input electrodes on one printed circuit board and a common output oh electrode on the opposite circuit board. 3. The level gauge according to claim 2, characterized in that the hollow lengthy structure is made in the form of a pipe. 4. The level gauge according to claim 2, characterized in that the fixed distance of the interelectrode space between the input and output electrodes of the level sensors - D is provided by the length of the spacer sleeves connecting the printed circuit boards in parallel. 5. The level gauge according to claim 2, characterized in that the fixed distance of the interelectrode space between the input and output electrodes of the level sensors is D = 6 mm. 6. The level gauge according to claim 2, characterized in that the printed circuit boards are fixed to the hollow lengthy construction by bushings. 7. The level gauge according to claim 2, characterized in that the printed circuit boards are fixed to the hollow lengthy structure with brackets. 8. The level gauge according to claim 2, characterized in that the input electrodes are located from each other with a gap of 0.5 mm 9. The level gauge according to claim 2, characterized in that the input electrodes of the individual sensors are located with a step of h = 100 mm. 10. The level gauge according to claim 2, characterized in that the printed circuit boards are combined in sections.

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