RU2499232C1 - Device to measure level of dielectric substance - Google Patents

Abstract

FIELD: measurement equipment.

SUBSTANCE: device comprises a standard, which is connected to a switching unit and to the first metering input of the device, at the same time metering inputs of the device from the second to (n+1), where n - quantity of dipoles, are connected to appropriate inputs of the switching unit, the outlet of which via serially connected current-voltage converter, a scale amplifier and an analogue-to-digital converter is connected to the input of the measurement control block, outputs of which are connected to the switching unit, the scale amplifier and the analogue-to-digital converter, and also to the control block by frequency and to a calculator of electric capacitance and a calculator of active resistance. Besides, the measurement control block is connected to a mode control block, outputs of which are connected to inputs of the control block by frequency, the block of substitution circuit setting, a calculator of full increment of electric capacitance, a calculator of current increment of electric capacitance, a level calculator and a block of switching control, the outlet of which is connected to the switching unit. Besides, the electric capacitance calculator is connected to the calculator of current increment of electric capacitance and to the calculator of full increment of electric capacitance, the outlet of which is connected to the level calculator. The substitution circuit setting block is connected to the electric capacitance calculator and to the active resistance calculator, inlets of which are connected to the control block by frequency, at the same time the calculator of full increment of electric capacitance is connected to the level calculator, the outlet of which, as well as outlets of the active resistance calculator and the switching control unit are outlets of the device. At the same time the device comprises a current difference generator, which is connected to the electric capacitance calculator and the active resistance calculator. The outlet of the analogue-to-digital converter is connected to the current difference generator, the inlet of which is connected to the measurement control block, outlets of which are connected to the first and second switches, which are connected in series. The first switch is connected to the first metering inlet of the device, and the second switch is connected to the DC source and the generator of sine voltage, the control inlet of which is connected to the control block by frequency.

EFFECT: higher accuracy of measurement.

3 dwg

Description

The invention relates to electrical engineering, and specifically to measuring the electrical parameters of two-terminal devices used as sensors for physical processes (temperature, pressure, level of liquid and granular media, etc.) at industrial facilities, vehicles, as well as in systems for measuring the level of refueling space technology.

The device “Multipoint level switch (its variants)”, described in RF patent No. 2025666, IPC: G01F 23/26, includes a group of capacitive measuring sensors, an alternating voltage generator, two switches, two current-voltage converters, a subtracting device, was selected as an analogue , synchronous detector, comparator, two triggers, differentiator, clock, coincidence circuit, pulse counter, adder and digital indicator. Moreover, each measuring sensor is made in the form of two plane-parallel capacitors with unequal areas of the electrodes, which are located horizontally and symmetrically with respect to the middle lines of the sensors. In addition, instead of transformer-type current comparators, a subtractor device was used, which can be built on an integrated circuit.

However, the specifics of the operation of rocket and space technology products for measuring the parameters of bipolar sets its own requirements, contributing to the search for new technical solutions in the field of measurements. Denote the most characteristic of them:

- remoteness up to 500 meters of a capacitive level sensor from a measuring instrument. An example of this is the process of determining the parameters of the complex resistance of a capacitive sensor for monitoring the level of a gas station mounted in a rocket tank, which is located in the test building or on the launch complex during its refueling with fuel components;

- high accuracy of measurement of parameters of a remote two-terminal device, which is a capacitive level sensor. Obviously, the accuracy of the measurement is directly related to the volume of guaranteed fuel reserves on board the rocket. The higher the accuracy of the measurement, the lower the required guaranteed fuel reserves, the higher the efficiency of the rocket, allowing to bring a large payload;

- the requirement of high adaptability of rocket preparation, excluding the procedure for pre-setting the measuring instrument by a human operator, as well as allowing the operation of one measuring instrument with several capacitive rocket level sensors in turn;

- high speed measurement of the level of the dielectric substance, which allows to expand the functionality of the device and use it in a similar way in the level gauge of the on-board terminal automatic control system, which is the rocket fuel consumption control system.

The device described in the article by Yu.R. Agamalov, D. A. Bobylev, V. Yu. Kneller “Measuring instrument-analyzer of complex resistance parameters based on a personal computer” in the journal “Measuring Technique”, 1996, No. 2 was chosen as another analogue 6.

The device for determining the parameters of a two-terminal network contains the first and second measuring inputs, a sinusoidal voltage generator, an equivalent circuit setting unit, a standard, the first output of which is connected to the first input of the switching unit, a current-voltage converter, a scale amplifier, and an analog-to-digital converter.

, где n - целое число. В результате каждого измерительного цикла получается напряжение, которое соответствует проекции вектора измеряемого напряжения на вектор фазосдвигающего опорного напряжения (симметричный прямоугольный меандр). Коды, несущие информацию о проекциях вектора измеряемого напряжения на вектор опорного напряжения, поступают в ПЭВМ для вычисления действительной и мнимой составляющих напряжений на объекте измерения и резистивной мере. Из описания видно, что схема измерения, использованная в аналоге, требует фазовых измерений и четырехпроводной схемы подключения измеряемого объекта. При использовании аналога для измерения параметров удаленного объекта измерения получается результат с большой погрешностью измерения. Это объясняется тем, что синусоидальное воздействие на удаленном объекте измерения получит неоднозначный фазовый сдвиг за счет влияния длинной линии, и поэтому но отношению к циклически фазосдвигающему опорному меандру синусоидальное воздействие будет иметь неопределенный фазовый сдвиг, что приведет к появлению значительной погрешности измерения.The analogue uses a scheme of indirect measurement of parameters when generating a voltage of a sinusoidal effect on the measurement object, which has found application due to the invariance with respect to the nature of the measurement object and its equivalent circuit. In the analogue, two complex currents are measured, which are converted into proportional voltages, the voltage at the measurement object and at the resistive measure standard. In order to obtain the measurement information necessary for calculating the complex resistance or conductivity, the measurement circuit is connected cyclically by signals from a personal electronic computer (PC) first to the measurement object and then to the resistive measure with the corresponding phase switching of the reference voltage with discreteness $$\Delta \psi =\frac{\mathrm{<figure-callout\; id="2"\; label="\pi "\; filenames="00000020.png"\; state="\{\{state\}\}">\pi </figure-callout>}}{2\cdot n}$$

where n is an integer. As a result of each measurement cycle, a voltage is obtained that corresponds to the projection of the measured voltage vector onto the phase-shifting reference voltage vector (symmetrical rectangular meander). Codes that carry information about the projections of the vector of the measured voltage on the vector of the reference voltage are sent to a PC to calculate the real and imaginary components of the voltage at the measurement object and the resistive measure. It can be seen from the description that the measurement circuit used in the analogue requires phase measurements and a four-wire circuit for connecting the measured object. When using an analog to measure the parameters of a remote measurement object, a result is obtained with a large measurement error. This is because the sinusoidal effect on the remote measurement object will receive an ambiguous phase shift due to the influence of a long line, and therefore, but with respect to the cyclically phase-shifting reference meander, the sinusoidal effect will have an indefinite phase shift, which will lead to a significant measurement error.

The disadvantages of analogues include: insufficient accuracy in determining the parameters of a capacitive level sensor remote at a certain distance; low performance in some cases of its use, for example, in signaling devices for the passage of a level of a non-conductive liquid to a given tank height; insufficient technological preparation of the rocket due to the need for preliminary adjustment of the equipment by the operator.

The closest in technical essence and the achieved positive effect to the claimed device is the device described in RF patent 2262668 C2, IPC: G01R 23/26, "Device for measuring the level of dielectric substance", authors Balakina SV, Dolgova B.K. , Khachaturova Ya.V., Odnovola IB, selected as a prototype.

A device for measuring the level of a dielectric substance containing a standard, the first output of which is connected to the first input of the switching unit, and the second output of the standard is connected to the output of the sinusoidal voltage generator and to the first measuring input of the device, while the measuring inputs of the device are from second to (n + 1) -th, where n is the number of two-terminal devices, are connected to the corresponding inputs of the switching unit, the output of which is through a series-connected current-voltage converter, a large-scale amplifier, and analog-to-digital The new converter is connected to the first input of the measurement control unit, the first to fifth outputs of which are connected respectively to the first control inputs of the switching unit, a scale amplifier, and an analog-to-digital converter, as well as to the first input of the frequency control unit and to the first inputs of the electric capacitance calculator and active resistance calculator, and the second input of the measurement control unit is connected to the first output of the mode control unit, the outputs of which are connected from the second to the seventh respectively To the second input of the frequency control unit, to the input of the equivalent circuit assignment unit, to the first input of the calculator of the full increment of the electric capacitance, to the first input of the calculator of the current increment of the electric capacitance, to the first input of the level calculator and to the input of the switching control unit, the output of which is connected to the second control input of the switching unit, and the output of the calculator of the electric capacitance is connected to the second input of the calculator of the current increment of the electric capacitance and to the second input of the calculator a full increment of the electric capacitance, the output of which is connected to the second input of the level calculator, while the output of the equivalent circuit setting unit is connected to the second inputs of the electric capacitance calculator and the active resistance calculator, the third inputs of which are connected to the first output of the control unit in frequency, and the output of the current calculator increments of the electric capacitance are connected to the third input of the level calculator, the output of which, as well as the outputs of the active resistance calculator and the control unit for prison are the outputs of the device.

The experience of the prototype showed that the error in measuring the level of the dielectric substance can be reduced even more if we measure and take into account the bias currents on the long cable line to the measured capacitive level sensor, caused by interference on the long line and the output stages of the amplifiers, and also increase the difference between frequencies at which measurements are made.

Thus, the disadvantage of the prototype is the lack of accuracy in measuring the level of dielectric substance at a remote object from the measuring device.

In connection with the technical result described above, the proposed device for measuring the level of dielectric substance is to increase the accuracy of measuring the level of dielectric substance by a capacitive level sensor, removed using a long cable line from the measuring device.

The technical result is achieved in that in a device for measuring the level of a dielectric substance containing a standard, the first output of which is connected to the first input of the switching unit, and the second output of the standard is connected to the first measuring input of the device, while the measuring inputs of the device are from second to (n + 1 ) -th, where n is the number of two-terminal devices, are connected to the corresponding inputs of the switching unit, the output of which is through a series-connected current-voltage converter, a large-scale amplifier, and analog-digital the converter is connected to the first input of the measurement control unit, the first to fifth outputs of which are connected respectively to the first control inputs of the switching unit, a scale amplifier and an analog-to-digital converter, as well as to the first input of the frequency control unit and to the first inputs of the electric capacitance calculator and calculator active resistance, and the second input of the measurement control unit is connected to the first output of the mode control unit, the outputs of which are connected from the second to the seventh respectively, to the second input of the frequency control unit, to the input of the equivalent circuit assignment unit, to the first input of the calculator of the full increment of the electric capacitance, to the first input of the calculator of the current increment of the electric capacitance, to the first input of the level calculator and to the input of the switching control unit, the output of which is connected to the second input of the switching unit, and the output of the calculator of the electric capacitance is connected to the second inputs of the calculator of the current increment of the electric capacitance and the calculator of the full increment an electric capacitance, the output of which is connected to the second input of the level calculator, the output of the equivalent circuit setting unit being connected to the second inputs of the electric capacitance calculator and the active resistance calculator, the third inputs of which are connected to the first output of the control unit in frequency, while the output of the calculator is the current increment of the electric capacitance connected to the third input of the level calculator, the output of which, as well as the outputs of the active resistance calculator and the switching control unit are outputs devices, unlike the prototype, a current difference shaper is introduced, the output of which is connected to the fourth inputs of the electric capacitance calculator and an active resistance calculator, while the output of the analog-to-digital converter is connected to the first input of the current difference shaper, the second input of which is connected to the sixth output of the control unit measurement, the seventh and eighth outputs of which are connected respectively to the control inputs of the first and second keys, which are connected in series, and the output of the first to The main unit is connected to the first measuring input of the device, and the first and second inputs of the second key are connected respectively to the outputs of the DC source and the sinusoidal voltage generator, the control input of which is connected to the second output of the control unit in frequency.

Signs characterizing the connection of a two-terminal device to the first measuring input through the first and second switches, as well as characterizing the introduction of a current difference shaper and its connection to the output of an analog-to-digital converter and to the inputs of the electric capacitance calculator and active resistance calculator allow, unlike the prototype, to test bipolar from a direct current source or from a sinusoidal voltage generator, providing the greatest difference in measuring frequencies (the second frequency is zero), and also allow to exclude the influence of bias currents arising on a long cable line to the capacitive level sensor due to interference.

The combination of these features allows in the claimed device:

- increase the accuracy of measuring the level of the dielectric substance (since the error in determining the parameters of the capacitive sensor of the filling level decreases from approximately ± 0.2% to ± 0.1%);

- make a measurement of the level of dielectric substance through a long cable communication line with improved accuracy characteristics (in some practical cases, the length of the connecting line can reach from 100 to 500 meters).

Figure 1 presents a functional diagram of a device for measuring the level of dielectric substance.

Figure 2 presents the algorithm of the device for measuring the level of dielectric substance.

Figure 3 presents the algorithm for measuring currents through a capacitive level sensor and a reference.

The functional diagram of a device for measuring the level of a dielectric substance shown in FIG. 1 contains n two-terminal devices, in particular, capacitive level sensors 1-1, ..., 1-n, which are connected through a cable line 2 to the measuring input 3 and measuring inputs 4-1, ..., 4-n, standard 5, switching unit 6, current-voltage converter 7, scale amplifier 6, analog-to-digital converter 9, first key 10, second key 11, measurement control unit 12, current difference generator 13, direct current source 14, the generator is sinusoidal about voltage 15, the frequency control unit 16, the mode control unit 17, the equivalent circuit assignment unit 18, the electric capacitance calculator 19, the resistance calculator 20, the full capacitance increment calculator 21, the current capacitance increment calculator 22, the switching control unit 23, level 24 calculator. The measuring inputs 4-1, ..., 4-n are connected to the inputs of the switching unit 6, the output of which is through a current-voltage converter 7, a scale amplifier 8 and an analog-to-digital converter 9, I connect connected to the inputs of the measurement control unit 12 and the current difference shaper 13, the output of which is connected to the inputs of the calculator of the electric capacitance 19 and the active resistance calculator 20, and the measuring input 3 of the level sensors through the first and second switches 10 and 11 connected in series is respectively connected to the outputs of the constant source current 14 and a sinusoidal voltage generator 15. Also, the output of the first switch 10 is connected to a standard 5, the output of which is connected to a switching unit 6, and the outputs of the measurement control unit are are assigned to the control inputs of the first 10 and second 11 keys, a scale amplifier 8, analog-to-digital converter 9, a current difference shaper 13, a switching unit 6, an electric capacitance calculator 19, an active resistance calculator 20, and a frequency control unit 16 whose outputs are connected to the control input of the sinusoidal voltage generator 15 and to the inputs of the calculator of the electric capacitance 19 and the calculator of the active resistance 20, and the unit for setting the equivalent circuit 18 is also connected to the inputs of the calculator electric capacitance 19 and an active resistance calculator 20. The mode control unit 17 is connected to the inputs of the control unit at frequency 16, the equivalent circuit assignment unit 18, the full capacity increment calculator 21, the current capacity increment calculator 22, the level calculator 24, the measurement control unit 12 and a switching control unit 23, the output of which is connected to the input of the switching unit 6, and the calculator of the electric capacitance 19 through the calculator of the current increment of the electric capacitance 22 is connected to the input level calculator 24, the other input of which is connected to the output of the calculator increments full container 21 having an input connected to the output capacitance of the calculator 19. The outputs of the calculator resistance 19, the calculator 24 and the level shift control unit 23 are the outputs of the device. Moreover, n capacitive level sensors are connected to the measuring inputs 4-1, ..., 4-n and measuring input 3 through a shielded cable communication line 2. The screens of the communication line at the measuring inputs are connected and connected to the ground terminal of the device.

We will consider the operation of the device using an example of measuring the level of a dielectric substance, for example, kerosene and oxygen, in tanks of a multi-stage rocket. Capacitive level sensors connected via communication line 2 are 500 meters away from the device. Let the electrical capacitance of the dry level sensor be 500 pF, and the parasitic electric capacitance of the core-screen of the cable communication line, for which, for example, cable PK 75 can be used, can be about 30,000 pF. The equivalent circuit of the capacitive level sensor corresponds to a parallel connected electric capacitance C _P and active resistance R. The active component of the total resistance of the capacitive level sensor is determined by the insulation resistance of the cable communication line, kerosene grade and humidity of the gas tank of the fuel tank. The value of the active component can range from 200 kOhm to 20 mOhm. Therefore, taking this component into account when determining the complex resistance of a capacitive level sensor is of fundamental importance for the accuracy of filling level measurement.

Presented in figure 2, the algorithm of the device for measuring the level of dielectric substance explains the operation of the device shown in figure 1. Blocks marked with a dotted line and including one or another function of the algorithm indicate that this function belongs to the block being covered.

According to the algorithm of figure 2, the operation of the device consists of two modes:

- device configuration mode, which consists in tuning the system to a specific capacitive level sensor. In this case, the currents are measured through each sensor on a long cable line and a standard, followed by calculation of the electric capacitance of each dry (unfilled with a dielectric substance) capacitive level sensor. Then, the total increment of the electric capacitance of each sensor, completely immersed in the dielectric substance, is calculated. When calculating the calculated value of the total increment of the electric capacitance, the calculated value of the electric capacitance of the dry sensor and the specified values of the dielectric constant of the oxidizer, fuel and gas pad are used. Moreover, all measured and calculated values of the values are stored in the memory of the functional blocks of the device;

- level measurement mode, which consists in determining the actual level of fuel filling of each capacitive level sensor during refueling. In this case, currents are measured through each sensor on a long cable line and a standard, followed by calculation of the real, current electric capacitance of each capacitive level sensor filled with dielectric material. Then, the current increment of the electric capacitance of each filled sensor is calculated, after which the relative filling of each capacitive sensor is calculated (the level is calculated).

The mode control unit 17 sets the operation mode of the device. In this case:

- the reference resistance values are output to the calculation units of the electric capacitance 19 and the calculation of the active resistance 20, and the values of the dielectric constants of the oxidizing agent and fuel, as well as the dielectric constants of the gas medium contained in the gas medium, are output to the calculation units of the total increment of the electric capacitance 21 and the current increment of the electric capacitance 22 pillow. These parameters are necessary to obtain the calculated values of the total increment of the electric capacitance of each capacitive sensor, completely immersed in the corresponding dielectric substance,

- the unit for specifying the equivalent circuit 18 will issue to the calculator of the electric capacitance 19 and the calculator of the active resistance 20, respectively, the calculated dependencies of the following type, which are fixed in the above blocks:

$$C=\frac{\mathrm{one}}{\omega R_{ET}}\sqrt{{\left(\frac{J_P^{~}}{J_{ET}^{~}}\right)}^2-{\left(\frac{J_P^{=}}{J_{ET}^{=}}\right)}^2};\left(\mathrm{one}\right)$$

$$R=\frac{J_{ET}^{=}}{J_P^{=}}{R}_{ET},\left(2\right)$$

, $$J_P^{=}$$

, $$J_{ЭТ}^{~}$$

, $$J_{ЭТ}^{=}$$

- значения токов через датчик и эталон с учетом токов смещения, которые необходимо вычислять как в процессе настройки, так и в процессе измерения, причем индексы ~ и = указывают, что измерение проводится на переменном или постоянном токе соответственно;where ω is the frequency of the measuring signal, the value is known and is set by the control unit at a frequency of 16; R _ET - the known value and is set by the mode control unit 17; $$J_P^{~}$$

, $$J_P^{=}$$

, $$J_{ET}^{~}$$

, $$J_{ET}^{=}$$

- the values of the currents through the sensor and the reference, taking into account the bias currents, which must be calculated both during the setup process and during the measurement process, and the indices ~ and = indicate that the measurement is carried out on alternating or direct current, respectively;

- the measurement control unit 12 displays the number of necessary measurements, in this case 3 for each sensor, which are AC current measurement through the sensor, DC current measurement through the sensor and bias current measurements. The values of currents obtained through the measurement through each sensor and the reference will be used in the future to calculate the real dry electrical capacitance of each sensor in the setup mode and to calculate the real current electric capacitance of each sensor in the level measurement mode (when each sensor is filled with a dielectric substance), and to calculate the resistance of the sensor and compensation of bias currents;

- in the control unit at a frequency of 16, the value of the frequency ω is set at which the currents will be measured;

- the number of capacitive level sensors connected to the device is set in the switching control unit 23, and a signal is also output through which the block 23, through the switching unit 6, controls the connection of the current-voltage converter 7 of the level sensors 7.

After the mode control unit 17 has brought the device to its initial state, it connects the first level sensor using unit 23 through unit 6. Then the device enters the setup mode.

In this case, according to FIG. 2, the measurement control unit 12 measures and fixes currents through the first capacitive level sensor and a reference in accordance with the algorithm of FIG. 3. According to Fig. 3, the measurement control unit 12, to which the number of measurements is set by the mode control unit 17 (in this case 3), sets the characteristic i of the positions of the first 10 and second 11 keys and sets this characteristic to 1. The keys 10 and 11 implement 3 combinations, according to to which the ac voltage or dc voltage is applied to the inputs of capacitive level and reference sensors, or the inputs of the sensors and reference are disconnected from the supply circuits for measuring bias currents. Then, the measurement control unit 12 sets the signal to the frequency control unit 16, according to which the latter sets the frequency value to the sinusoidal voltage generator 15. Also, the frequency control unit 16 sets and fixes the frequency value ω in the calculator of the electric capacitance 19 and in the calculator of the active resistance 20.

Next, the measurement control unit 12, according to the current measurement index, provides a control signal to the second switch 11, which connects a sinusoidal voltage generator 15 to the sensor supply circuits, which generates a sinusoidal signal with a frequency ω, and the first switch 10 remains in the closed position. Also, the measurement control unit 12 exposes and fixes in the calculator of the electric capacitance 19 and in the calculator of the active resistance 20 the type of the current measurement, which is an alternating current measurement.

The voltage of a given frequency U _{ωi is} supplied to the measuring inputs of the device to power the connected capacitive level sensor and reference. Next, the measurement control unit 12 establishes the position key j of the switching unit 6. The position of the key is 2, and the value j is assigned the value 1. According to this feature, the first or current capacitive level sensor is disconnected from the measuring circuit, and instead of it, the reference 5 is connected to the measuring circuit. As a reference, a resistor of resistance R _ET can be used.

The current value is measured as follows. According to figure 1, the current through the reference from the output of the switching unit 6 is fed through a current-voltage converter 7 to the input of the scale amplifier 8. The scale amplifier provides voltage amplification in accordance with the scale that the measurement control unit 12 sets to it. From the output of the scale amplifier, the voltage is supplied to input analog-to-digital Converter 9 integrating type. The analog-to-digital converter (ADC) is a push-pull integrator. The choice of this type of ADC is primarily due to the high linearity of the characteristics, high resolution and good suppression of high-frequency noise. The ADC operates in two cycles, the first cycle is the charge of the integrator, the second cycle is its discharge. In the first cycle, the input signal is integrated, which is a periodic function, in the second cycle, the signal from the reference voltage source is integrated. The resolution of the ADC, which determines the resolution of the device as a whole, is proportional to the time of the second cycle (discharge of the integrator), as well as the frequency of the filling pulses. The ADC clock switching and the supply of filling pulses are controlled by the measurement control unit 12. The digitized value of the measured current is supplied to the measurement control unit 12 to control the gain scale. The control of the gain scale is aimed at improving the accuracy of the ADC. The scaling is designed in such a way that the digital value of the signal taken from the ASC should not be less than half the capacity of the ADC. The scaling algorithm is presented in figure 2. According to this algorithm, the number α is analyzed, which is equal to the ratio of the total ADC capacitance to the digital value of the measured current. Based on the calculated value of α, one of four scales is selected (16; 8; 4; 2; 1). After the amplification scale of the measured current is determined, it is fixed in the calculator of the electric capacitance 19 and in the calculator of the active resistance 20 for further operations to determine the parameters of the capacitive level sensor. Measured with an appropriate scale, the current value is recorded in the shaper of the difference of currents 13 for further compensation of bias currents. Further, according to Fig. 3, if j is not equal to 2, then its value in the measurement control unit 12 is increased by one and a control signal is generated there to switch the key of the switching unit 6 to the second position. This corresponds to the fact that the standard is switched off and a capacitive level sensor is connected to the measuring circuit.

Further, the procedure for measuring current through a level sensor is determined by the steps described when measuring current through a standard. After the measured value of the current through the capacitive level sensor is recorded in the imaging device for the current difference 13, the algorithm according to figure 3 will go on to analyze the condition in which j is 2. Since the key of the switching unit 6 is in the second position, the condition will be satisfied and the algorithm proceeds to the analysis of the following condition, in which the analysis of the current measurement will be carried out. Since the measurement was carried out on alternating current (the first measurement), the condition will not be fulfilled, and the algorithm will proceed to the execution of the action but setting the second measurement, which is the direct current measurement.

As a result, the action i: = i + 1 will be performed and the measurement control unit 12 using the second key 11 will connect a DC source to the inputs of the measuring sensors and the reference. After that, the measurement control unit 12 initiates the measurement. The direct current measurement procedure is repeated as described above.

After the currents through the standard and the capacitive level sensor are measured and recorded during direct current measurement, the measurement control unit 12 will assign the current measurement index i to 3, according to which it will open the first switch 10. In this case, the current measurement through the standard and the capacitive sensor level will be carried out when the sensors and the standard of the sinusoidal voltage generator and the DC source are disconnected from the input. This is necessary to further compensate for bias currents caused by pickups on a long communication line in order to improve measurement accuracy. The measured values of the bias currents are also recorded in the shaper of the difference of the currents 13.

After the number of measurements i is equal to 3, then the condition of the last block of the algorithm according to figure 3 will be satisfied and the algorithm will finish its work.

This will correspond to the completion of the current measurement procedure through the first capacitive level sensor. Then, according to the algorithm of FIG. 2, in the current difference shaper 13, the values of each measured current through the sensor and the reference are calculated according to the following relationships:

$$\begin{array}{l}{J}_P^{~}=I_P^{~}-I_P^{\mathrm{from}m};J_{ET}^{~}=I_{ET}^{~}-I_{ET}^{\mathrm{from}m}\\ J_P^{=}=I_P^{=}-I_P^{\mathrm{from}m};J_{ET}^{=}=I_{ET}^{=}-I_{ET}^{\mathrm{from}m}\left(3\right)\end{array}$$

, $$I_P^{=}$$

, $$I_P^{см}$$

, $$I_{ЭТ}^{~}$$

, $$I_{ЭТ}^{=}$$

, $$I_{ЭТ}^{см}$$

- токи через рабочий датчик уровня и эталон, причем индекс "см" указывает на то, что измерение проводилось при отключенных генераторе синусоидального напряжения и источнике постоянного тока.Where $$I_P^{~}$$

, $$I_P^{=}$$

, $$I_P^{\mathrm{from}m}$$

, $$I_{ET}^{~}$$

, $$I_{ET}^{=}$$

, $$I_{ET}^{\mathrm{from}m}$$

- currents through a working level sensor and a standard, and the index "cm" indicates that the measurement was carried out when the sine voltage generator and the direct current source were turned off.

, $$J_P^{=}$$

, $$J_{ЭТ}^{~}$$

, $$J_{ЭТ}^{=}$$

, они фиксируются в вычислитель электрической емкости 19 и вычислитель активного сопротивления 20.After the shaper calculates the difference of the currents 13 values; $$J_P^{~}$$

, $$J_P^{=}$$

, $$J_{ET}^{~}$$

, $$J_{ET}^{=}$$

, they are fixed in the calculator of the electric capacitance 19 and the calculator of the active resistance 20.

Next, the algorithm calculates in blocks 19 and 20 the values of the electric capacitance and active resistance of the first capacitive level sensor according to formulas (1), (2). The results of calculating the value of the electric capacitance from the block 19 are sent to the block for calculating the full increment of the electric capacitance 21 and to the block for calculating the current increment of the electric capacitance 22, in which they are fixed by a command from the control unit of the modes 17 in the memory cells corresponding to the number of the connected measuring input. The calculated value of the active resistance from the output of block 20 enters the output R of the device. The value of active resistance characterizes the state of the land and onboard cable networks and is analyzed by the equipment interfaced with the device for compliance with the required operational characteristics.

The control signal of the mode control unit 17 in the calculator of the full increment of the electric capacitance 21 calculates the total increment of the electric capacitance of the capacitive level sensor, completely immersed in the dielectric substance according to the following relationship:

$$C_{PR}=C_{\mathrm{FROM}\mathrm{At}X}\left({\epsilon }_F-{\epsilon }_G\right)\left(\mathrm{four}\right)$$

where C _SUH is the electric capacitance of a dry capacitive level sensor, calculated according to dependence (1);

ε _W - dielectric constant of the dielectric substance;

ε _G is the dielectric constant of the gas cushion located in the tank of the rocket above the dielectric substance.

The results of calculating the total increment of the electric capacitance are recorded in the level calculator 24 in the memory cell corresponding to the number of the measured input (the number of the capacitive level sensor).

Then the algorithm proceeds to the analysis of the condition k = n. The condition will not be fulfilled, since the second measuring input (the first capacitive level sensor) has been connected. Therefore, the algorithm proceeds to the action k = k + 1 in the switching control unit 23, which, through the switching unit 6, disconnects the second measuring input and connects the third measuring input.

Further operation of the device will correspond to the above actions until the condition k = n is satisfied, i.e. until the values of the electric capacitances of the dry level sensors are calculated and the values of the electric capacitances completely immersed in the dielectric material of all n-level sensors, connected in series through the cable network 2 to the measuring inputs, are calculated. When the condition k = n is fulfilled, the device setup mode ends.

After that, at the command of the operator, the device can be switched to level measurement mode. In this mode, the calculator of the full increment of the electric capacitance 21 is turned off, since this function is not used in this mode. The calculated values of the electric capacitance of fully immersed capacitive sensors are recorded in the level calculator 24 and will be used to calculate the level for each capacitive sensor in the level measurement mode.

The mode control unit 17 sets the dielectric substance level measurement mode and assigns k value 1 to the switching control unit 23. The switching control unit 23, through the switching unit 6, connects the first measuring input to the measuring circuit. After that, the mode control unit 17 generates a signal to the measurement control unit 12, according to which the latter starts measuring currents through the first capacitive level sensor and a reference filled with a dielectric substance. The procedure for measuring currents through a capacitive level sensor and a reference is presented by the algorithm according to figure 3 and is similar to the above.

After measuring currents through a capacitive sensor and a reference, the current difference shaper 13 calculates the currents taking into account compensation of pickups on the communication line according to the above and fixes them in the calculator of the electric capacitance 19 and the calculator of the active resistance 20.

Then the algorithm according to figure 2 will proceed to calculate the current value of the electric capacitance of the filled level sensor and its active resistance, using the calculated current values through the capacitive level sensor and the reference. The above procedures are performed by blocks 19 and 20. The calculated value of the electric capacitance of the filled sensor C _TEK from the output of block 19 enters the calculator of the current increment of the electric capacitance 22, in which the increment of the electric capacitance of the sensor in the memory cell corresponding to the number of the measuring input is calculated and recorded. The value of the increment of the electric capacity of the filled sensor is calculated by the following dependence:

$$\Delta C_{TE\mathrm{TO}}=C_{TE\mathrm{TO}}-C_{\mathrm{FROM}\mathrm{At}X}\left(6\right)$$

where C _TEK is the current value of the electric capacitance of the level sensor filled with a dielectric substance calculated on the basis of the measured complex currents.

The calculated value of the active resistance of the capacitive level sensor filled with a dielectric substance from the output of block 20 is sent to the R output of the device and is used to assess the state of the sensor and its cable network.

Then, according to the control action of the mode control unit 17, the level transmitter 24 calculates the relative filling of the capacitive level sensor with the dielectric substance, and the transmitter 22 sets the value of the current increment of the electric capacitance ΔC _TEK of the level sensor to be filled into the computer 24.

The level 24 calculator calculates the relative filling of the sensor according to the following relationship:

$$\frac{h}{H}=\frac{\Delta C_{TE\mathrm{TO}}}{C_{PR}}=\frac{C_{TE\mathrm{TO}}-C_{\mathrm{FROM}\mathrm{At}X}}{C_{\mathrm{FROM}\mathrm{At}X}\left({\epsilon }_F-{\epsilon }_G\right)}\left(7\right)$$

The value of the full increment of the electric capacitance of a completely immersed sensor was stored in the memory of the level 24 computer in the device setup mode.

It should be noted that the calculation of the dry electric capacitance, the total increment of the electric capacitance and the current increment of the electric capacitance is made taking into account the influence of a long communication line with the same measuring means. This circumstance minimizes the influence of the communication line on the level calculation result. From the analytical dependence (7), this follows in an obvious way, C _CX and C _{TEK were} determined taking into account the influence of the communication line, C _{PR was} also determined taking into account the influence of the communication line. Therefore, with respect to according to expression (7), the influence of the communication line is minimized.

In addition, this device, in contrast to the prototype, becomes completely invariant to the communication line, since its influence is excluded in connection with the compensation of interference caused to it.

The value of the h / H level of the capacitive sensor is fed to the output of the device with which the launch complex equipment is interfaced, which controls the supply of fuel components (dielectric substances) through the ground processing equipment to the rocket tanks.

Then the algorithm proceeds to the analysis of the condition k = n. The condition will not be fulfilled since the first measuring input has been connected. Therefore, the algorithm proceeds to the action k = k + 1 in the switching control unit 23, which, through the switching unit 6, disconnects the first measuring input and connects the second measuring input. Further operation of the device will correspond to the above steps until the condition k = n is satisfied, i.e. until the values of the level of filling of the dielectric substance of each capacitive level sensor are calculated.

If the condition k = n is fulfilled, the algorithm proceeds to analyze the condition for filling all the tanks to the required level according to the flight level. If the level in the tanks has not reached one, the mode control unit 17 will assign the value k to one in the switching control unit 23 of the variable k, as a result of which the last will connect the first measuring input through the switching unit 6, and the process of measuring the fill level of each capacitive level sensor will be repeated again . The procedure for cyclically measuring the filling of each level sensor with a dielectric substance will continue until each tank of the rocket is refilled to the required task according to the flight level.

Presented in figure 2, 3, the operation algorithms of the device contain actions that are aimed at calculating expressions (1) through (7).

In the example of the device in formulas (1), (2) and (3) there is such a function as the extraction of the square root. The square root algorithm is widely known (for example, see RF patent RU 2262668 C2, IPC: G01F 23/26).

The claimed device by the authors tested on a breadboard product. Currently, the authors are creating a system for measuring the level of a rocket block refueling system, which is designed to modernize the ground equipment of one of the launch launchers of the Baikonur training ground and the launch complex of the Kuru cosmodrome of the Guiana Space Center.

Used Books

1. Balakin S.V., Dolgov B.K., Khachaturov Y.V., Odnovol I.E. "Device for measuring the level of dielectric substance", RF patent No. 2262668 C2, IPC: G01F 23/26.

2. Agamalov Yu.R., Bobylev D.L., Kneller V.Yu. Measuring instrument-analyzer of complex resistance parameters based on a personal computer. Measuring technique. 1996, No.6, p. 56-60.

3. RF patent No. 2025666, IPC: G01F 23/26, "Multipoint level switch (its variants)."

Claims (1)

A device for measuring the level of a dielectric substance containing a standard, the first output of which is connected to the first input of the switching unit, and the second output of the standard is connected to the first measuring input of the device, while the measuring inputs of the device are from the second to (n + 1) th, where n is the number of two-terminal devices connected to the corresponding inputs of the switching unit, the output of which is connected through a series-connected current-voltage converter, a scale amplifier and an analog-to-digital converter to the first input measurement control lock, the first to fifth outputs of which are connected respectively to the first control inputs of a switching unit, a scale amplifier and an analog-to-digital converter, as well as to the first input of a frequency control unit and to the first inputs of an electric capacitance calculator and an active resistance calculator, the second the input of the measurement control unit is connected to the first output of the mode control unit, the outputs of which are connected from the second to the seventh respectively to the second input of the control unit in frequency, to the input of the equivalent circuit assignment unit, to the first input of the calculator of the full increment of the electric capacitance, to the first input of the calculator of the current increment of the electric capacitance, to the first input of the level calculator and to the input of the switching control unit, the output of which is connected to the second control input of the switching unit, moreover, the output of the calculator of the electric capacitance is connected to the second inputs of the calculator of the current increment of the electric capacitance and the computer of the full increment of the electric capacitance, the output of the cat it is connected to the second input of the level calculator, the output of the equivalent circuit setting unit being connected to the second inputs of the electric capacitance calculator and the active resistance calculator, the third inputs of which are connected to the first output of the frequency control unit, while the output of the current capacity increment calculator is connected to the third input level calculator, the output of which, as well as the outputs of the resistance calculator and the switching control unit are the outputs of the device, characterized in that a current difference shaper is introduced, the output of which is connected to the fourth inputs of the capacitance calculator and the active resistance calculator, while the output of the analog-to-digital converter is connected to the first input of the current difference shaper, the second input of which is connected to the sixth output of the measurement control unit, the seventh and eighth outputs which are connected respectively to the control inputs of the first and second keys, which are connected in series, and the output of the first key is connected to the first flax entry device, and the first and second inputs of the second switch are respectively connected to the outputs of the DC source and the sinusoidal voltage generator, a control input of which is connected to the second output of the control unit in frequency.

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