RU2425334C1 - Capacitance level gage - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: proposed level gage comprises n electrodes (n>1), for example, electrodes 1-7 connected to controller 8. All electrodes are made up of sites arranged on one surface. The latter may represent a plane (preferable version) or any other surface (for example, cylindrical surface). Controller 8 allows sequential measurement of n virtual capacitors so that n_i virtual capacitor is made up in measurement of its capacitance by n_i electrode, on the one side, and by nearest electrode, on the other side. If, for example, electrode 5 makes n_i electrode then relevant n_i virtual capacitor is made up (during measurement of its capacitance) by electrode 5, on the other side, and by nearest electrode, on the other side. Said nearest electrode for electrode 5 is electrode 4 or 6.

EFFECT: higher reliability.

3 cl, 3 dwg

Description

FIELD OF THE INVENTION

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

State of the art

Known capacitive level gauge in the form of series-connected sections, each of which contains alternating discrete and continuous capacitive level sensors, a pulse interrogator of sensor polls, a capacitor into a code and a computing unit, while the input electrodes of continuous capacitive level sensors are parallel and partially overlapped in height and in each zone of their overlap is located the input electrode of one of the discrete capacitive sensors (see ed. St. USSR No. 2005999 of 02/10/92, M.cl. G01F 23/26).

Signs of the known device, matching with the features of the claimed invention, are the presence of capacitive sensors.

The reason that prevents obtaining a technical result in a known technical solution, which is provided by the invention, is that the liquid level is determined by multiplying the step length of the discrete capacitive sensors by the serial number of the upper discrete capacitive sensor immersed in the liquid and adding the calculated length to the above product liquid filling the upper unit continuous level sensor, in the overlapping zone of which is located the last liquid filled Tew discrete sensor. The presence of a known capacitive level gauge of continuous level sensors with a partial overlap of the input electrodes and discrete capacitive sensors located in the overlap zones significantly complicates its design. Since the length of the input electrodes of discrete level sensors is less than 30% of the overlap length of the electrodes of adjacent continuous capacitive sensors, the capacitance of these discrete sensors is excessively small, they are sensitive to scattering fields, stray capacitances, their capacitance significantly depends on changes in temperature and dielectric constant of the measured liquid, which reduces the reliability of determining the number of discrete capacitive sensors immersed in the liquid.

The closest analogue (prototype) is a capacitive level gauge containing a rod with single capacitive level sensors located along its length, while 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 flat capacitors on opposite planes facing each other - unit capacitive level sensors, by means of input electrodes on one printed circuit board and bschego output electrode on the opposite circuit board (Patent RU №2286551 C1 M.kl. G01F 23/26, date of publication 2006.10.27).

Signs of the known device, matching the features of the claimed invention, are the presence of capacitors.

The reason that prevents obtaining the technical result that is provided by the invention is that the capacitors are made in the form of electrodes (pads) facing each other, as a result of which an interelectrode space is formed between the electrodes, which periodically becomes clogged during operation of the level gauge, which leads to distortion of the level measurement results.

Disclosure of invention

The problem to which the invention is directed, is to increase the reliability of the level gauge.

The technical result that mediates the solution of this problem is to exclude the interelectrode space (i.e. the space between the parallel electrodes) due to the absence of a second (parallel) row of electrodes.

The technical result is achieved in that the level gauge comprises a controller and n electrodes for n> 1, each of which is made in the form of a pad of electrically conductive material and connected to the controller, while all the electrodes are located on one surface, and the said controller is capable of measuring capacitances in series n virtual capacitors, so that n _i virtual capacitor is formed at the time of measuring its capacitance electrode n _i, on the one hand, and at least one electrode closest to it, on the other hand s.

The technical result is also achieved by the fact that all the electrodes are located in one plane.

The technical result is also achieved by the fact that the controller is capable of measuring the capacitance n _{i of the} virtual capacitor by measuring the time of its charge when connected to the charge time of the n _i electrode through a constant resistor with a current source, and at least the electrode closest to it with a common controller wire .

New features of the claimed technical solution lie in the location of all the electrodes on one surface, as well as in the implementation of the controller with the ability to sequentially measure the capacitances of n virtual capacitors, so that n _i virtual capacitor is formed at the time of measuring its capacitance by n _i electrode, on the one hand, and at least one electrode closest to it, on the other hand.

Brief Description of the Drawings

Figure 1 shows the functional diagram of the level gauge, figure 2 and 3 are embodiments of the electrodes.

The implementation of the invention

The level gauge contains n electrodes in the form of n conductive pads (n> 1) and a controller. Figure 1 shows as an example seven electrodes 1-7, which are connected to the controller 8. All electrodes are located on one surface. This can be a plane, as shown in figures 1 and 2 (the preferred embodiment of the level gauge), or another surface, for example a cylindrical (figure 3). In a preferred embodiment of the level gauge in its working position, the electrodes are arranged in the form of one vertically oriented row in which the row electrode 1 (the first electrode) occupies the lowest position, the row electrode 7 occupies the highest position, and any intermediate n _i row electrode, for example, an electrode 5 is located above the previous electrode 4 and below the subsequent electrode 6 of the row. The electrodes can be made in the form of two rows of conductive pads 1 (1) -7 (1) and 1 (2) -7 (2), paired on a rail 9 (printed circuit board) opposite each other and pairwise electrically connected to each other by jumpers 10 to increase the area (figure 2). Thus, two electrodes connected to each other, for example electrodes 1 (1) and 1 (2), due to the connection form one electrode of increased area. In another embodiment, the level gauge electrodes are located on a flexible substrate (tape) of non-conductive material, which is attached to the wall of a cylindrical or spherical container, in which it is necessary to measure the liquid level (figure 3).

The controller 8 is capable of sequentially measuring the capacitances of n virtual capacitors, so that the n _i virtual capacitor is formed at the time of measuring its capacitance n _{i by the} electrode, on the one hand, and at least one electrode closest to it, on the other hand. If, for example, the n _i electrode is electrode 5, then the corresponding n _i virtual capacitor is formed (at the time of measuring its capacitance) by electrode 5, on the one hand, and at least one electrode closest to it, on the other hand. So the electrode 4 or electrode 6 is closest to the electrode 5. The definition of “at least” means that the second electrode of the virtual capacitor under consideration (the first electrode is electrode 5) can be either one of the nearest electrodes 4 or 6, or both electrodes 4 and 6 together, as well as electrodes 3, 4, 6 and 7 together, etc. up to the use of all other electrodes (that is, all but n _i electrodes, in this example, except electrode 5 as the second plate of the virtual capacitor under consideration). In addition, the controller is configured to measure the capacitance n _{i of the} virtual capacitor by measuring the time of its charge when connected to the charge time n _{i of the} electrode through a constant resistor with a current source, and at least the electrode closest to it with a common controller wire. In this example, to measure the capacitance of a virtual capacitor, one electrode of which is electrode 5, this electrode connects the controller to the current source through the resistor for the duration of the capacitance measurement; the other plate of the virtual capacitor under consideration (it forms at least one nearest electrode, for example electrode 4; but two electrodes, for example 4 and 6 can form it; as well as all other electrodes) the controller connects to its common wire.

The operation of the level gauge is as follows.

The controller 8 uses ATtiny13 microcontrollers manufactured by Atmel. Each microcontroller is connected to four electrodes (i.e., the electrodes are grouped in four, so that one microcontroller has four electrodes). Each of the electrodes in the group is connected directly to one of the control outputs of the microcontroller, which are initialized for the output transistor of the microcontroller in the "open collector" mode. Due to this connection method, the function of “pulling” a single electrode to ground is realized with the output transistor open, and when the output transistor is turned off, the charge of a single electrode is carried out through an external charging current supply circuit (through a resistor of 100 kOhm). The measurement of the charge time of the capacitor is made by noting the time from the moment the output transistor is turned off, which controls the charge of the corresponding unit electrode, and the moment the unit electrode is fully charged to the sensor supply voltage. The control over the charge value of a single electrode is carried out by means of a comparator integrated into the microcontroller. The signal is fed to the input of the comparator from a single electrode through a 1 MΩ isolation resistor (not shown), which, together with the other three isolation resistors of the electrode group (through which the charge value is supplied from three other unit electrodes to the comparator input), also acts as a voltage divider. Due to the fact that the comparator response level is determined by the value of the reference voltage source, which can vary from 1 V to 1.2 V, as well as by the fact that the divider is formed by a 100 kΩ charging resistor, a 1 MΩ isolation resistor, and a 300 kΩ composite resistor formed from connected in parallel to the ground by three 1 MΩ resistors (since the three plates are connected by their output control transistors to the ground), divides the total charge of a single electrode, therefore, the sensor supply voltage should not be lower than 4.6 V and ideally should be 5.6 V, which is acceptable for powering the selected microcontroller, operating at voltages up to 6 V. To increase the accuracy of measuring the capacitance of the selected electrode, the microcontroller performs a series of charge-discharges, thus forming a sequence of "saw teeth" and while measuring the total time of the formed series. The number of “teeth” varies depending on the required sensitivity of the group of four electrodes and is given to the microcontroller through a command from the control board located in the “head” of the level sensor. The whole process of measuring the capacitance of four electrodes connected to a microcontroller is reduced to sequentially disconnecting each of the electrodes from the ground and supplying a series of “saw teeth” to it. The start of the measurement process is carried out by a command sent by the control board. The process of transmitting data and commands between the microcontroller and the control board takes place via a single-wire bidirectional channel, to which all microcontrollers of the level gauge are connected in parallel. The choice of the microcontroller to which the command from the control board is addressed is carried out by transmitting in the body of the command frame the address of the microcontroller, which is assigned to the microcontroller in the process of “flashing” it with microprogram during the production of the level gauge based on the position of the microcontroller on the level gauge board. Also, the body of the command frame contains the required number of “saw teeth”, which the microcontroller must supply to the single capacitive sensors connected to it. The integrity of the command frame as well as the response frame of the microcontroller is protected by computing a single-byte CRC key. Data transmission is carried out by means of a self-synchronizing, voltage-modulated square wave method of the supply voltage. The control board is located in the "head" of the level gauge. The powerful 32-bit microcontroller located on it performs the function of interrogating the microcontrollers of the electrode groups, analyzing the obtained data, calculating the values of the liquid layer levels and issuing the resulting data through the current, frequency and digital (I2C) interfaces.

Thus, the proposed level gauge eliminates the need for a common lining of the capacitors and, therefore, eliminates the problem of clogging of the interfacial space characteristic of known capacitive sensors. In this case, data collection from all individual electrodes for subsequent analysis is carried out by the control board located in the head of the level sensor. The calculation of the liquid level is performed through complex mathematical calculations. When using the proposed level gauge, it becomes possible not only to control the upper liquid level, but also to control the levels of the liquid layers in the case of measurements in heterogeneous liquids.

Claims (3)

1. A capacitive level gauge containing a controller and n electrodes for n> 1, each of which is made in the form of a pad of electrically conductive material and connected to the controller, while all the electrodes are located on one surface, and the said controller is capable of sequential measurement of capacitances of n virtual capacitors, so that the n _i virtual capacitor is formed at the time of measuring its capacitance n _{i by the} electrode on the one hand and at least one electrode closest to it, on the other hand. 2. The capacitive level gauge according to claim 1, in which all the electrodes are located in one plane. 3. The capacitive level gauge according to claim 1, in which the controller is configured to measure the capacitance n _{i of the} virtual capacitor by measuring the time of its charge when connected to the charge time n _{i of the} electrode through a constant resistor with a current source, and at least the electrode closest to it - with a common controller wire.

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