RU2458353C1 - Apparatus for determining parameters of two-terminal device - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: apparatus comprises the measured two-terminal device, a reference, a current-to-voltage converter, a scaling amplifier, an analogue-to-digital converter, a measurement control unit, a mode control unit, a first switch, a frequency control unit, an equivalent circuit setting unit and a sinusoidal voltage generator, and is characterised by that it has a second and a third switch, a direct current source and a current difference former, wherein the first measuring input of the two-terminal device is connected through the second switch to the output of the third switch, the first input of which is connected to the direct current source, and the second input of the third switch is connected to the output of the sinusoidal voltage generator. Control inputs of the second and third switches are respectively connected to the sixth and seventh outputs of the measurement control unit, the eighth output of which is connected to the first input of the current difference former, the second input of which is connected to the output of the analogue-to-digital converter, and the output of the current difference former is connected to the fourth input of a device for determining parameters of the two-terminal device, the output of which is the output of the apparatus.

EFFECT: high accuracy of measuring parameters of a two-terminal device which is separated by a long line from the measuring apparatus.

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Description

The invention relates to electrical engineering, and in particular to the measurement of electrical parameters of two-terminal devices, which is of significant practical interest for monitoring a wide range of manufactured radio products (resistors, capacitors, inductors), as well as two-terminal devices used as sensors of physical processes (temperature, pressure, liquid level and bulk media, etc.) at industrial facilities and vehicles.

The known device, selected as an analog, is a digital AC bridge type CE 5002 TU 25-7516.0033-88, which is an automatic balancing measuring bridge circuit. The measuring circuit balances the reactive and active components of the complex resistance of the measured bipolar.

Another analogue is 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, synchronous detector, comparator and 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.

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 the measuring object from the 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 in measuring the 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 less guaranteed fuel reserves can be selected, the higher the efficiency of the rocket, allowing to bring a large payload;

- the requirement of high technology rocket preparation, excluding the procedure for pre-setting the measurement equipment by a human operator.

The disadvantages of analogues include: low accuracy in determining the parameters of a two-terminal terminal remote for some distance (for example, a capacitive level sensor); 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; insufficiently high adaptability of rocket preparation, due to the need for preliminary adjustment of equipment by the operator.

The closest in technical essence and the achieved positive effect to the claimed device is the device described in the patent of the Russian Federation 2262115 C2, IPC: G01R 27/14, "Device for determining the parameters of a two-terminal device", authors Balakina SV and Dolgova B.K., selected as a prototype.

A device for determining the parameters of a two-terminal device, containing a standard connected to the first measuring input and the first input of the first key, the second measuring input of the device is connected to the second input of the first key, the output of which is connected through a series-connected current-voltage converter, a scale amplifier, and an analog-to-digital converter the first input of the measurement control unit, and the control input of the analog-to-digital converter is connected to the first output of the measurement control unit, the rest the outputs of which are connected respectively to the control inputs of the first key, a large-scale amplifier, to the first input of the two-terminal parameter determinant and to the first input of the frequency control unit, 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 respectively via the equivalent circuit setting unit to the second input of the two-terminal parameter determinant and to the second input of the frequency control unit, the outputs of which are connected respectively to the generator input sinusoidal voltage and to the third input of the determinant of two-terminal parameters.

The prototype experience has shown that the error in determining the parameters of a two-terminal can be further reduced if we measure and take into account the bias currents on the long connecting line to the measured two-terminal, caused by interference on the long line and the output stages of the amplifiers, and also increase the difference between the frequencies at which measurements.

Thus, the disadvantage of the prototype is the lack of accuracy in measuring the parameters of a two-terminal device at a remote measurement object.

In connection with the foregoing, the objective of the proposed device for determining the parameters of a two-terminal device is to increase the accuracy of measuring the parameters of a two-terminal device, removed using a long line from the measuring device. Moreover, the measuring instruments created on its basis while maintaining high metrological qualities should remain fairly simple to implement.

The solution to this problem is achieved by the fact that in the device for determining the parameters of a two-terminal device containing a standard connected to the first measuring input and the first input of the first key, the second measuring input of the device is connected to the second input of the first key, the output of which is scaled through a series-connected current-voltage converter the amplifier and the analog-to-digital converter are connected to the first input of the measurement control unit, and the control input of the analog-to-digital converter is connected to the first the output of the measurement control unit, the other outputs of which are connected respectively to the control inputs of the first key, a scale amplifier, the first input of the two-terminal parameter determiner and the first input of the frequency control unit, the second input of the measurement control unit is connected to the first output of the mode control unit, the outputs of which respectively connected through the unit for setting the equivalent circuit to the second input of the determinant of two-terminal parameters and to the second input of the control unit in frequency, the outputs of the cat They are connected respectively to the input of the sinusoidal voltage generator and to the third input of the two-terminal parameter determiner, in contrast to the prototype, a second and third key, a DC source and a current difference shaper are introduced, the first measuring input of the two-terminal being connected through the second key to the output of the third key, the first the input of which is connected to a direct current source, and the second input of the third key is connected to the output of the sinusoidal voltage generator, and the control inputs of the second and third the keys are connected respectively to the sixth and seventh outputs of the measurement control unit, the eighth output of which is connected to the first input of the current difference shaper, the second input of which is connected to the output of the analog-to-digital converter, and the output of the current difference shaper is connected to the fourth input of the two-terminal parameter determiner, the output of which is the output of the device.

Signs characterizing the connection of a two-terminal to the first measuring input through the second and third keys, which, unlike the prototype, allow testing the tested two-terminal from a direct current source or from a sinusoidal voltage generator, provide the greatest difference in the measuring frequencies (the second frequency is zero), which significantly increases the accuracy determining the parameters of a two-terminal device. Signs characterizing the introduction of a current difference shaper, its connection to an analog-to-digital converter and a two-terminal parameter determinant can also improve the accuracy of determining two-terminal parameters by eliminating the influence of bias currents arising on the long line to the measured two-terminal due to pickups and imperfections in the output stages of amplifiers .

The combination of these features allows in the claimed device:

- increase the accuracy of determining the parameters of the two-terminal network (so the accuracy of determining the capacitance of the refueling level sensor increases from approximately ± 0.2% to ± 0.1%);

- to determine the parameters of a two-terminal network through a long line without reducing the metrological 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 determining the parameters of a two-terminal network.

Figure 2 presents the algorithm of operation of the device for determining the parameters of a two-terminal network.

The functional diagram of the device for determining the parameters of a two-terminal device shown in Fig. 1 contains a definable two-terminal device 1, which is connected via a cable communication line 2 to the measuring inputs 3, 4, which are respectively connected to a standard 5 and the first key 6, the output of which is through a series-connected current converter -voltage 7, a scale amplifier 8 and an analog-to-digital converter 9, is connected to the input of the measurement control unit 12, which is connected to the input through the current difference shaper 13 For the parameters of a two-terminal network 19, the measurement input 3 through series-connected second and third switches 10 and 11 is connected to the inputs of a direct current source 14 and a sinusoidal voltage generator 15, the control input of which is through a frequency control unit 16, a mode control unit 17, and a circuit setting unit substitution 18 is connected to the input of the determinant of the parameters of a two-terminal device, the output of which is the output of the device. The outputs of the measurement control unit are connected to the control inputs of the keys, a large-scale amplifier, an analog-to-digital converter, a two-terminal parameter determinant, and to the frequency control input. The screens of the cable line at the measuring inputs are connected and connected to the earth terminal of the sinusoidal voltage generator.

We will consider the operation of the device by the example of determining the parameters of a two-terminal device, which is used as a capacitive level sensor that is removed by a cable line from the device at a certain distance, for example, 500 meters. Let the electrical capacitance of the dry level sensor be 500 nF, and the parasitic electric capacitance of the cable communication line, which can be used, for example, PK 75 cable, will be about 20,000 nF. The equivalent circuit of a capacitive level sensor corresponds to a parallel connected capacitance C _P and active resistance R. The active component of the total resistance of a capacitive level sensor is determined by the insulation resistance of the cable line, humidity in the tank, and also the grade of kerosene, which is characterized by leakage currents through the dielectric. The value of the active component can range from 200 kOhm to 5 mOhm. Therefore, taking this component into account when determining the resistance of a two-terminal network is of fundamental importance for the accuracy of determining the parameters of a capacitive level sensor and, accordingly, the accuracy of measuring the level of the charge.

Signs characterizing the connection of a two-terminal device, on the one hand, through the second measuring input and key 6 to the input of the current-voltage converter, on the other hand, to the first measuring input through the second 10 and third 11 to the output of the sinusoidal voltage generator 15 or DC source 14, removal supply alternating or direct current to the first measuring input two-terminal network 10 using a key, provide measurement of currents through the two-pole and the standard 5 a frequency ω _1, at constant current, and measuring displacements currents tions with the power switched off completely. And the signs characterizing the introduction of the shaper of the difference of currents 13 provide the subtraction of bias currents, and can significantly increase the accuracy of determining the parameters of the two-terminal network. These distinctive features of the prototype allow you to measure the parameters of the two-terminal, remote from the measuring instruments, with an error of (0.1-0.15)%.

Presented in figure 2, the control algorithm for determining the parameters of the two-terminal network provides an explanation of the operation of the device according to figure 1. Blocks marked with a dotted line and including one or another function of the algorithm indicate that this function belongs to the covered block.

Block 17 control modes sets the modes for determining the parameters of the two-terminal network. In this case:

- in block 18, an equivalent circuit is set, in a particular case, an electric capacitance and a resistor are connected in parallel;

- in the measurement control unit 12, the number of necessary measurements is issued and fixed, in this case 2, since the two-terminal device is two-element. Block 12 contains an algorithm that should control the measurement process, including the scaling procedure, analog-to-digital conversion, and control the generation of voltages to the tested two-terminal network both from a sinusoidal voltage generator and from a direct current source;

- in the frequency control unit 16, the frequency values ω ₁ at which current measurements will be made are set and fixed;

- block 18 of the job equivalent circuit will issue in the determinant 19 of the parameters of the two-terminal design dependencies of the following form:

where ω ₁ , R _ET values are known and set by the mode control unit 17, and ΔI _ω1 , ΔI ^ET _ω1 , ΔI ₀ , ΔI ^ET _{0 are the} values of difference currents, which are determined by block 13 based on the results of determining currents through a two-terminal network at frequency ω ₁ , direct current and in the absence of a supply voltage to the two-terminal network when measuring bias currents. For the practical implementation of the determination of the parameters of the two-terminal network, the algorithms for the numerical solution of the dependences according to expressions (1) and (2) are written into the memory of the determinant 19 parameters of the two-terminal network.

Signs characterizing the connection of the control unit 16 in frequency with the sinusoidal voltage generator 15 and the determinant of two-terminal parameters 19 allow the measurement of currents through a defined two-terminal and a reference at n-1 frequencies, the number of which - n corresponds to the number of elements of the two-terminal. The combination of these features, which allows the claimed device to use amplitude measurements at n-1 frequencies and one measurement at direct current, unlike the prototype, where measurements at n frequencies are used, makes it possible to provide more accurate measurement of the parameters of a two-terminal device remote from the measurement object.

For the practical implementation of the above functional blocks of the device, the authors used the technology of computer-aided design of electronics, based on the use of programmable logic integrated circuits (FPGAs) developed by Xilinx. The main features of FPGAs:

- a significant amount of resources;

- high performance;

- High architecture flexibility with many system features: internal distributed and block RAM, accelerated transfer logic; internal buffers with a third state, etc .;

- the ability to program directly in the system.

It uses Foundation Series software. This design package includes a set of tools that allow the development of Xilinx FPGAs, from describing the internal contents of the device to loading the FPGA configuration and debugging directly on the circuit board.

Blocks 12, 19, 16, 17 and 18 are made by the authors on the Xilinx chip XC25200.

According to FIG. 1, the mode control unit 17 starts measuring currents through a defined two-terminal network and a reference. Block 12, to which the number of measurements is set by the mode control block 17 (in this case 2), sets the first frequency frequency setting signal to the frequency control block 16, at which current measurements should be made through the defined two-terminal network and through standard 5. According to FIG. 2, the block 12 sets the index of the current measurement frequency i to 1 and sets the corresponding signal to the frequency control unit 16. After that, the frequency control unit 16 sets and fixes in the determinant 19 of the two-terminal parameters the value of the first frequency ω _i , and to the control input of the sinusoidal voltage generator 15 a signal according to which the latter generates a voltage of a given first frequency ω _i at the output. The sinusoidal voltage generator can be performed in this case on an operational amplifier, in the feedback of which the Wien bridge is included. Frequency change can be implemented through the control of the parameters of the generator timing circuit. Another example of a generator execution may be its execution on an Xil25x XC25200 chip, which is programmed to generate a multi-stage signal with its subsequent supply to a low-pass filter. The voltage of the given first frequency U _{ωi is} supplied to the measuring inputs of the device for supplying the detected two-terminal device or standard. Next, the measurement control unit 12 sets the sign j of the position of the key 6. The positions of the key are 2, and the sign j is assigned the value 1. According to this sign, the detected two-terminal network is disconnected from the measuring circuit, and instead of it, the standard is connected to the measuring circuit 5. As a reference, it can be used resistor with resistance R _ET . A current flows through the reference, the measured value of which determines the output voltage of the sinusoidal voltage generator 15 according to the expression

The current value is measured as follows. According to figure 1, the current through the reference from the output of the switch 6 is supplied through the 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. The scaling process of amplifier 8 is shown in FIG. From the output of a large-scale amplifier, the voltage is supplied to the input of an 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 enters the determinant of two-terminal parameters - 19 for its further use in the calculations according to expressions (1) and (2) and to the measurement control unit 12 for controlling the gain scale. Controlling the gain scale improves 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 exceed half the capacity of the ADC. Based on this, for an example implementation of the invention, the algorithm presented in figure 2 is proposed. 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 (8; 4; 2; 1). After the amplification scale of the measured current is determined, in the determinant 19 of the parameters of the two-terminal device, its value is fixed with the measurement scale, intended for further operations to determine the parameters of the two-terminal device. Further, according to FIG. 2, if j is not equal to 2, then its value in the measurement control unit 12 increases by one and a control signal is generated there to switch the key 6 to the second position. This corresponds to the fact that the standard is switched off and a defined two-terminal device is connected to the measuring circuit. A current flows through a two-terminal network, the value of which is determined by the expression

Further, the procedure for measuring current through a two-terminal network is determined by the steps described when measuring current through a standard. After the value of the current through the two-terminal network is measured and recorded in the determinant 19 of the parameters of the two-terminal device, the algorithm according to Fig. 2 will go on to analyze the condition in which j is 2. Since the key 6 is in the second position, the condition will be satisfied and the algorithm will go over to the analysis of the following condition, in which the analysis of the current measurement frequency will be carried out. Since the measurement was carried out at the first frequency, the condition will not be fulfilled, and the algorithm will proceed to the steps to set the second frequency ω ₀ = 0 Hz, that is, direct current. As a result, the action j: = j + 1 will be performed and the measurement control unit 12 will set a signal to set the second frequency, i.e., direct current. According to this signal, the frequency control unit 16 generates a signal to the sinusoidal voltage generator 2, for setting a second frequency equal to zero Hertz. At the same time, the frequency control unit 16 sets and fixes in the determinant 19 of the two-terminal parameters the value of the second frequency (in our case, Hertz zero), which is used to calculate the two-terminal parameters. At the same time, the control unit 12 turns off with a key 11 a sinusoidal voltage generator 15 and connects a direct current source 14 to supply a two-terminal device and a reference. Then, the measurement control unit 12 initiates a measurement. The procedure for measuring DC currents is repeated as described above. After measuring the constant currents through the two-terminal network and the standard and fixing them in the determinant of parameters 19, the measurement control unit 12 with the key 10 removes power from the two-terminal network and the standard and measures the bias currents according to the above procedure.

After the number of measurements i is equal to n, the condition of the last block of the algorithm according to FIG. 2 will not be satisfied, and the algorithm will proceed to the calculation of the difference currents and parameters of the two-terminal device.

Presented in figure 2, the algorithm of the device contains the action of determining the parameters of the two-terminal network, which is aimed at calculating expressions according to (1) and (2).

In an example of a specific embodiment of the device, an algorithm for computing the parameters of the two-terminal devices C and R, as well as examples of a specific embodiment of the numerical solution of the square root extraction function from a number, are shown in FIGS. 3, 4, 5 of the prototype.

The claimed device by the authors tested on a breadboard product. At present, the authors are creating a system for measuring the level of a missile unit’s refueling, which is designed to modernize the ground equipment of one of the launch launchers of the Baikonur training ground.

Literature

1. Digital AC bridge type CE 5002 TU 25-7516.0033-88.

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

3. RF patent 2262115 C2, IPC: G01R 27/14, “Device for determining the parameters of a two-terminal network” - prototype.

Claims (1)

A device for determining the parameters of a two-terminal device, containing a standard connected to the first measuring input and the first input of the first key, the second measuring input of the device is connected to the second input of the first key, the output of which is connected through a series-connected current-voltage converter, a scale amplifier, and an analog-to-digital converter the first input of the measurement control unit, and the control input of the analog-to-digital converter is connected to the first output of the measurement control unit, the rest the outputs of which are connected respectively to the control inputs of the first key, a large-scale amplifier, to the first input of the two-terminal parameter determinant and to the first input of the frequency control unit, 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 respectively via the equivalent circuit setting unit to the second input of the two-terminal parameter determinant and to the second input of the frequency control unit, the outputs of which are connected respectively to the generator input and a sinusoidal voltage to the third input of the determinant of two-terminal parameters, characterized in that the second and third switches, a direct current source and a current difference shaper are introduced, the first measuring input of the two-terminal being connected through the second switch to the output of the third switch, the first input of which is connected to a constant source current, and the second input of the third key is connected to the output of the sinusoidal voltage generator, and the control inputs of the second and third keys are connected respectively to the sixth and gray the seventh outputs of the measurement control unit, the eighth output of which is connected to the first input of the current difference shaper, the second input of which is connected to the output of the analog-to-digital converter, and the output of the current difference shaper is connected to the fourth input of the bipolar parameter determinant, the output of which is the output of the device.

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