CN109581257B - Metering and calibrating device of large-scale grounding device grounding impedance tester - Google Patents
Metering and calibrating device of large-scale grounding device grounding impedance tester Download PDFInfo
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Abstract
The invention discloses a metering verification device of a large grounding device grounding impedance tester, and belongs to the technical field of engineering measurement. The device comprises: the variable current electrode auxiliary grounding resistor, the variable voltage electrode auxiliary grounding resistor, the sampling resistor, the first program-controlled gain amplifier, the second program-controlled gain amplifier, the phase shifter, the adder and the control equipment; the first end of the variable current electrode auxiliary grounding resistor is electrically connected with the current output end of the tested grounding impedance tester, the second end of the variable current electrode auxiliary grounding resistor is electrically connected with the first end of the sampling resistor and the input end of the first program-controlled gain amplifier respectively, the second end of the sampling resistor is electrically connected with the current input end of the tested grounding impedance tester, the output end of the first program-controlled gain amplifier is electrically connected with the voltage input end of the tested grounding impedance tester, the first end of the variable voltage electrode auxiliary grounding resistor is electrically connected with the voltage output end of the grounding impedance tester, and the second end of the variable voltage electrode auxiliary grounding resistor is connected with signal ground.
Description
Technical Field
The invention relates to the technical field of engineering measurement, in particular to a metering and calibrating device of a large grounding device grounding impedance tester.
Background
The grounding device is a generic name of a grounding body formed by a plurality of metal grounding electrodes buried underground at a certain depth and connecting the grounding electrodes by conductors, and has the functions of providing reference potential for the operation of the power system on one hand and playing roles of discharging short-circuit fault current or lightning strike ground current of the power system on the other hand, and is an important device for guaranteeing the safe operation of the power system. Grounding devices can be divided into two categories: a general grounding device and a large-sized grounding device. The large-scale grounding device (grounding grid) refers to a 110kV and above voltage class transformer substation, and a power plant with a installed capacity of more than 200Mw or an equivalent area of 5000m 2 The above grounding device. An important parameter for evaluating the safety performance of a large-scale grounding device is the power frequency grounding impedance of the large-scale grounding device, and a power frequency grounding impedance tester of the large-scale grounding device is generally used for measurement. The grounding impedance of the large grounding device is very small and is usually smaller than 0.5 omega, and the test precision requirement is high. According to the latest DL/T475-2017 (rules for measuring characteristic parameters of grounding devices), a large-scale grounding device The power frequency grounding impedance is a complex number and consists of a resistance component and a reactance component. In order to evaluate the test accuracy of the grounding impedance tester, a metrological verification device is required to perform laboratory verification on the grounding resistance and the grounding impedance indication error of the grounding impedance tester.
The existing DL/T845.2-2004 'general technical condition for resistance measurement device 2 nd part power frequency ground resistance tester' and JJG 366-2004 'national metering verification procedure for ground impedance meter' propose a method for verifying the error of the ground resistance indication value in laboratory. Existing metrological assay devices include: a variable standard resistor RE, a variable electrode auxiliary ground resistor RP1, and a variable current electrode auxiliary ground resistor RC1. The first end of the variable current electrode auxiliary grounding resistor RC1 is electrically connected with the current output end of the grounding impedance tester, the second end of the variable current electrode auxiliary grounding resistor RC1 is electrically connected with the first end of the variable voltage electrode auxiliary grounding resistor RP1, the second end of the variable voltage electrode auxiliary grounding resistor RP1 is electrically connected with the voltage input end of the grounding impedance tester, the first end of the variable standard resistor RE is respectively electrically connected with the current input end and the voltage output end of the grounding impedance tester, and the second end of the variable standard resistor RE is electrically connected with the connecting point of the variable current electrode auxiliary grounding resistor RC1 and the variable voltage electrode auxiliary grounding resistor RP 1.
The ground impedance tester can be used for calibrating indication errors through the existing metering calibrating device. The indication error refers to the indication error of the ground impedance tester. Firstly, respectively setting resistance values of a variable electrode auxiliary grounding resistor RP1 and a variable electrode auxiliary grounding resistor RC1 as set resistance values; secondly, the resistance value of the variable standard resistor RE is regulated to an actual value Rn, wherein Rn is a ground resistance value selected from the range of the ground impedance tester; then, starting a grounding impedance tester, and recording the display reading Rxn on the grounding impedance tester corresponding to each actual value Rn; finally, the indication error E of the grounding impedance tester is obtained through calculation of the following formula (1). In order to obtain more accurate indication errors, a plurality of ground resistance values are generally selected from the range of the ground resistance tester, then the values of the variable standard resistor RE are adjusted according to the selected ground resistance values, the readings are correspondingly recorded on the ground resistance tester, a plurality of indication errors are obtained, and the indication errors of the ground resistance tester are determined according to the plurality of indication errors.
In carrying out the invention, the inventors have found that the prior art has at least the following problems: on the one hand, since the value of RE needs to be set continuously according to the range of the ground impedance tester, it is difficult for standard resistors of one specification to provide all selected resistance values, so that standard resistors of multiple specifications need to be prepared; in the verification process, standard resistors with different specifications need to be replaced, and inconvenience is brought to the verification process. Moreover, the test current input by the tested meter to the metrological verification device may reach 20A or higher, and the variable standard resistor RE heats up and is accompanied by temperature drift; as the resistance increases, the dissipation power of the device must also increase, which results in a larger volume and weight of the variable standard resistor RE, and is inconvenient to use. On the other hand, the grounding impedance comprises a pure resistance part (the real part of the grounding impedance) and a reactance part (the imaginary part of the grounding impedance), and the existing metering and verification device only realizes the measurement of the pure resistance part by a tested grounding impedance tester, cannot meet the verification requirement of the grounding impedance complex parameter and has a certain limitation.
Another proposal adopts the physical resistance and the physical inductance to form a standard impedance device in series. However, the scheme has the problems of multiple physical inductance specifications, poor stability, great influence of environmental factors and working conditions on the standard device and the like besides the inherent problem of physical resistance, so that the detection result is unreliable.
Disclosure of Invention
The embodiment of the invention provides a metering and verification device of a large grounding device grounding impedance tester, which can solve the problems that a plurality of standard variable resistors and standard inductors with different specifications are required to be prepared in the existing metering and verification device, avoids replacement of standard devices with different specifications in the verification process, and brings convenience to the verification process. The technical scheme is as follows:
a metrological verification device for a large ground impedance tester, the device comprising: the variable electrode auxiliary grounding resistor, the sampling resistor, the first program-controlled gain amplifier, the second program-controlled gain amplifier, the phase shifter, the adder and the control device;
the first end of the variable current pole auxiliary grounding resistor is electrically connected with the current output end of the tested grounding impedance tester, the second end of the variable current pole auxiliary grounding resistor is electrically connected with the first end of the sampling resistor, the input end of the phase shifter and the input end of the first programmable gain amplifier respectively, the second end of the sampling resistor is electrically connected with the current input end of the tested grounding impedance tester, the connection point of the sampling resistor and the current input end of the tested grounding impedance tester is connected with signal ground, the output end of the phase shifter is electrically connected with the input end of the second programmable gain amplifier, the output end of the second programmable gain amplifier is electrically connected with the first input end of the adder, the output end of the adder is electrically connected with the voltage input end of the tested grounding impedance tester, the control end of the second programmable gain amplifier and the first end of the phase shifter are electrically connected with the voltage input end of the tested grounding impedance tester respectively, and the output end of the variable current pole auxiliary grounding resistor is electrically connected with the voltage auxiliary grounding resistor;
The control device is further configured to receive a gain adjustment instruction, and adjust gains of the first gain amplifier and the second gain amplifier, respectively, based on the gain adjustment instruction.
Optionally, the first programmable gain amplifier comprises a first resistor, a first operational amplifier and a digital potentiometer,
the first end of the first resistor is grounded, the second end of the first resistor is electrically connected with the inverting input end of the first operational amplifier, the non-inverting input end of the first operational amplifier is electrically connected with the second end of the variable current pole auxiliary grounding resistor, the first end of the sampling resistor and the input end of the phase shifter respectively, the first operational amplifier is electrically connected with the connection point of the first resistor and the input end of the digital potentiometer, the output end of the digital potentiometer is electrically connected with the output end of the first operational amplifier, the connection point of the digital potentiometer and the first operational amplifier is electrically connected with the second input end of the adder, and the control end of the digital potentiometer is electrically connected with the control equipment.
Optionally, the first programmable gain amplifier includes a second resistor, a second operational amplifier, a resistor branch, and an analog cell branch,
The first end of the second resistor is grounded, the second end of the second resistor is electrically connected with the inverting input end of the second operational amplifier, the non-inverting input end of the second operational amplifier is respectively electrically connected with the second end of the variable current pole auxiliary grounding resistor, the first end of the sampling resistor and the input end of the phase shifter, the output end of the second operational amplifier is electrically connected with the second input end of the adder,
the resistor branch is a line formed by connecting m resistors in series,
the analog unit branch is a line formed by serially connecting m analog switch units, each analog switch unit comprises an analog switch and a first inverter for controlling the analog switch to be closed, the analog switch of the ith analog switch unit in the m analog switch units is serially connected with the analog switch of the (i+1) th analog switch unit, each first inverter is electrically connected with the control equipment,
the resistor branch is connected in parallel with the analog unit branch, the connection point of the ith resistor and the (i+1) th resistor, and the connection point of the analog switch of the ith analog switch unit and the analog switch of the (i+1) th analog switch unit are electrically connected, the first connection point of the resistor branch and the analog unit branch, and the connection point of the second resistor and the second operational amplifier are connected,
The resistor branch is connected with a second connection point of the analog unit branch and a connection point of the second operational amplifier and the adder.
Optionally, the phase shifter comprises a capacitor, a third resistor and a third operational amplifier,
the first end of the third resistor is electrically connected with the reverse input end of the third operational amplifier, the second end of the third resistor is electrically connected with the output end of the third operational amplifier, the connection point of the third resistor and the output end of the third operational amplifier is electrically connected with the input end of the second program-controlled gain amplifier, the non-inverting input end of the third operational amplifier is grounded, the first end of the capacitor is electrically connected with the variable current electrode auxiliary grounding third resistor, the sampling third resistor and the first program-controlled gain amplifier respectively, and the second end of the capacitor is electrically connected with the connection point of the third resistor and the reverse input end of the third operational amplifier.
Optionally, the phase shifter includes: an analog-to-digital converter, an integrating unit, a second inverter, an angular frequency calculating unit, a multiplier and a digital-to-analog converter,
the input end of the analog-to-digital converter is electrically connected with the connection point of the sampling resistor and the first program-controlled gain amplifier, the output end of the analog-to-digital converter is electrically connected with the input ends of the integrating unit and the angular frequency calculating unit respectively, the output end of the integrating unit is electrically connected with the input end of the second reverser, the output end of the second reverser is electrically connected with the first input end of the multiplier, the second input end of the multiplier is electrically connected with the output end of the angular frequency calculating unit, the output end of the multiplier is electrically connected with the input end of the digital-to-analog converter, and the output end of the digital-to-analog converter is electrically connected with the input end of the second program-controlled gain amplifier.
Optionally, the resistance value of the sampling resistor is 10-100 milliohms.
Optionally, the resistance adjustable ranges of the variable electrode auxiliary grounding resistor and the variable electrode auxiliary grounding resistor are 0-200 ohms.
Optionally, the control device is further configured to,
after the gains of the first gain amplifier and the second gain amplifier are adjusted, the gains of the first program-controlled gain amplifier and the second program-controlled gain amplifier after adjustment are respectively recorded;
receiving a calculation instruction, wherein the calculation instruction comprises a ground impedance measured value of the measured ground impedance tester;
and under the instruction of the calculation instruction, calculating an indication error of the measured grounding impedance tester based on the recorded gains of the first program-controlled gain amplifier and the second program-controlled gain amplifier after adjustment and the measured grounding impedance value of the measured grounding impedance tester.
Optionally, the control device calculates the indication error of the measured ground impedance tester according to the following formula:
e is the indication error, Z X Z is the measured value of the measured grounding impedance tester E ＝(G 0 +G 1 *j)*R 0 ，G 0 G is the gain of the first program controlled gain amplifier 1 For the gain of the second programmable gain amplifier, j is the imaginary unit, R 0 And the resistance value of the sampling resistor.
The technical scheme provided by the embodiment of the invention has the beneficial effects that:
the current pole auxiliary grounding resistance of the tested grounding impedance tester is simulated through the variable current pole auxiliary grounding resistance, the voltage pole auxiliary grounding resistance of the tested grounding impedance tester is simulated through the variable current pole auxiliary grounding resistance, the large-scale grounding device is simulated through the sampling resistor, the first program-controlled gain amplifier, the phase shifter and the second program-controlled gain amplifier, the first program-controlled gain amplifier simulates the pure resistance part of grounding impedance, and the phase shifter and the second program-controlled gain amplifier simulate the reactance part of grounding impedance; the user can set the gains of the first program-controlled gain amplifier and the second program-controlled gain amplifier through the control equipment; the ground impedance of the simulated large-scale grounding device is determined by the sampling resistor, the first program-controlled gain amplifier and the second program-controlled gain amplifier, so that after the gains of the first program-controlled gain amplifier and the second program-controlled gain amplifier are changed, the impedance value of the ground impedance of the simulated large-scale grounding device is also changed, and the effects of regulating the resistance value and the reactance value of the ground impedance of the simulated large-scale grounding device are achieved, so that the gains of the first program-controlled gain amplifier and the second program-controlled gain amplifier can be continuously set according to the range of the measured ground impedance tester, and verification of the indication error of the ground impedance is realized; on the one hand, the gain of each program-controlled gain amplifier is controlled by a control signal output by control equipment, and the control signal can be updated in real time, so that when the first program-controlled gain amplifier and the second program-controlled gain amplifier are matched with a sampling resistor, a large number of different resistance values can be provided, standard resistors and standard inductors with a plurality of specifications are not required to be prepared like the existing metering verification device, replacement of the standard resistors and inductors with different specifications in the verification process is avoided, and convenience is brought to the verification process. In addition, the ground impedance of the simulated large-scale grounding device is determined by the sampling resistor, the first program-controlled gain amplifier and the second program-controlled gain amplifier, so that the sampling resistor with a smaller resistance value can be selected, and the temperature drift caused by heating of the sampling resistor is avoided; meanwhile, when the resistance value of the sampling resistor is smaller, the first program-controlled gain amplifier and the second program-controlled gain amplifier are not physical resistors such as standard resistors, so that the situation that the dissipation power of a device is increased along with the increase of the resistance value of the physical resistors and the size and the weight of the variable standard resistor are larger can be avoided, and convenience is brought to the verification process. On the other hand, the metering verification device can realize the simulation of a pure resistance part and a reactance part in the grounding impedance, more truly reflect the grounding impedance of the grounding device, and improve the effectiveness of metering verification evaluation; and when the measured grounding impedance tester can respectively measure the pure resistance part and the reactance part, the measured grounding impedance tester can also be used for detecting the measurement of the pure resistance part and the reactance part, the detection range is wider, and the applicability is stronger.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for the description of the embodiments will be briefly described below, and it is apparent that the drawings in the following description are only some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic diagram of a three-pole method for measuring ground impedance according to an embodiment of the present invention;
fig. 2 is a schematic structural diagram of a metrological verification device of a large-scale grounding device grounding impedance tester according to an embodiment of the present invention;
fig. 3 is a schematic structural diagram of an active two-port network according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of a first programmable gain amplifier according to an embodiment of the present invention;
FIG. 5 is a schematic diagram of a second first programmable gain amplifier according to an embodiment of the present invention;
fig. 6 is a schematic structural diagram of a first phase shifter according to an embodiment of the present invention;
fig. 7 is a schematic structural diagram of a second phase shifter according to an embodiment of the present invention.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the present invention more apparent, the embodiments of the present invention will be described in further detail with reference to the accompanying drawings.
For the convenience of understanding the embodiments of the present invention, a grounding impedance measuring apparatus is first taken as an example, and a grounding impedance measuring process of a large-scale grounding device is described. The power frequency grounding impedance of large grounding devices (also called grounding grids) of substations, power plants and the like is measured by a tripolar method. Drawing of the figure1 is a schematic diagram for measuring the grounding impedance by a tripolar method. Referring to fig. 1, the large-sized ground device ground impedance tester includes a constant current source I, a voltmeter V, a current pole C, and a voltage pole P. Applying a test current I between the current pole C and the ground grid G to be tested by a constant current source I m Test current I m The current flows out from a current output end C1 of the grounding impedance tester, is connected to the ground through a test wire, returns to the ground network through the ground, and is connected to a current input end C2 of the grounding impedance tester from a ground network return point B through the test wire to form a current loop. Voltmeter V measures test current I m A voltage Up generated between the voltage pole P and the ground; one end button of the voltmeter V is a voltage input end P1 of the grounding impedance tester and is connected to the voltage pole P through a test wire; the other end button of the voltmeter V is a voltage output end P2 of the grounding impedance tester and is connected to the ground grid return point B through a test line. According to ohm's law, the power frequency grounding impedance Z of the grounding grid G ＝U P /I m 。
Fig. 2 shows a metrological verification device for a large-scale grounding device grounding impedance tester according to an embodiment of the present invention. Referring to fig. 2, the apparatus includes: the variable-electrode auxiliary grounding resistor RC, the variable-electrode auxiliary grounding resistor RP, the sampling resistor R0, the first programmable gain amplifier PGA0, the second programmable gain amplifier PGA1, the phase shifter 20, the adder 30, and the control device 10. The first end of the variable current pole auxiliary grounding resistor RC is electrically connected with the current output end of the tested grounding impedance tester, the second end of the variable current pole auxiliary grounding resistor RC is electrically connected with the first end of the sampling resistor R0, the input end of the phase shifter 20 and the input end of the first programmable gain amplifier PGA0 respectively, the second end of the sampling resistor R0 is electrically connected with the current input end of the tested grounding impedance tester, the connection point of the sampling resistor R0 and the current input end of the tested grounding impedance tester is connected with signal ground, the output end of the phase shifter 20 is electrically connected with the input end of the second programmable gain amplifier PGA1, the output end of the second programmable gain amplifier PGA1 is electrically connected with the first input end of the adder 30, the second input end of the adder 30 is electrically connected with the voltage input end of the tested grounding impedance tester, the control end of the second programmable gain amplifier PGA1 and the control end of the first programmable gain amplifier PGA0 are respectively connected with the control device 10, and the output end of the variable current pole auxiliary grounding resistor RP is electrically connected with the variable voltage auxiliary grounding impedance tester.
The control device 10 is configured to receive a gain adjustment instruction, and adjust the gains of the first gain amplifier and the second gain amplifier based on the gain adjustment instruction, respectively.
The sampling resistor R0 and the first programmable gain amplifier PGA0 simulate the pure resistive portion of the ground impedance, and the sampling resistor R0, the second programmable gain amplifier PGA1 and the phase shifter 20 simulate the reactive portion of the ground impedance, so that the pure resistive portion and the reactive portion are measured by the ground impedance tester to be tested.
According to the embodiment of the invention, the current pole of the tested grounding impedance tester is simulated through the variable current pole auxiliary grounding resistor RC, the variable voltage pole auxiliary grounding resistor RP simulates the voltage pole of the tested grounding impedance tester, the sampling resistor R0, the first programmable gain amplifier PGA0, the phase shifter 20 and the second programmable gain amplifier PGA1 simulate large-scale grounding devices, the first programmable gain amplifier PGA0 simulates the pure resistance part of grounding impedance, and the phase shifter 20 and the second programmable gain amplifier PGA1 simulate the reactance part of grounding impedance; the user can set the gains of the first programmable gain amplifier PGA0 and the second programmable gain amplifier PGA1 through the control device; because the grounding impedance of the simulated large grounding device is determined by the sampling resistor R0, the first programmable gain amplifier PGA0 and the second programmable gain amplifier PGA1, after the gains of the first programmable gain amplifier PGA0 and the second programmable gain amplifier PGA1 are changed, the impedance value of the grounding impedance of the simulated large grounding device is also changed, so that the effects of adjusting the resistance value and the reactance value of the grounding impedance of the simulated large grounding device are achieved, and the gains of the first programmable gain amplifier PGA0 and the second programmable gain amplifier PGA1 can be continuously set according to the range of the measured grounding impedance tester, thereby realizing verification of the indication error of the grounding impedance; on the one hand, the gains of the program controlled gain amplifiers are controlled by the control signals output by the control equipment, and the control signals can be updated in real time, so that when the first program controlled gain amplifier PGA0 and the second program controlled gain amplifier PGA1 are matched with the sampling resistor R0, a large number of different resistance values can be provided, and the conventional metering verification device does not need to prepare a plurality of standard resistors with variable specifications, so that the replacement of the standard resistors with different specifications in the verification process is avoided, and convenience is brought to the verification process. In addition, as the grounding impedance of the simulated large grounding device is determined by the sampling resistor R0, the first programmable gain amplifier PGA0 and the second programmable gain amplifier PGA1, the sampling resistor R0 with a smaller resistance value can be selected, and the temperature drift caused by heating of the sampling resistor R0 is avoided; meanwhile, when the resistance value of the sampling resistor R0 is smaller, the first program controlled gain amplifier PGA0 and the second program controlled gain amplifier PGA1 are not real object resistances such as standard resistors, so that the situation that the real object resistance is increased along with the increase of the resistance value, the dissipation power of the device is also required to be increased, and the size and the weight of the variable standard resistor RE are larger can be avoided, and convenience is brought to the verification process. On the other hand, the metering verification device can realize the simulation of the pure resistance part and the reactance part in the grounding impedance, more truly reflect the grounding impedance of the grounding device, improve the effectiveness of metering verification results, and can also verify the measurement of the pure resistance part and the reactance part by the grounding impedance tester to be tested when the grounding impedance tester to be tested is used for measuring the pure resistance part and the reactance part respectively, so that the verification range is wider, and further improve the accuracy of the metering verification results; in addition, in the metering verification device, the second program-controlled gain amplifier PGA1 and other analog reactance parts are adopted, so that the reactance value is not the physical inductance, the problems that the physical inductance is large in specification and poor in stability, the standard device is greatly affected by environmental factors and working conditions and the like are avoided, and the reliability of a detection result is improved.
The principle of operation of the metrological verification device shown in figure 2 is briefly described below.
Referring to fig. 3, in the metrological verification device, the sampling resistor R0, the first programmable gain amplifier PGA0, the second programmable gain amplifier PGA1, the phase shifter 20 and the adder 30 form a network W (shown in the line box in fig. 2), and the network W includes two input ports and two output ports, so that the network W can be regarded as an active two-port network. According to the Z parameter equation of the active two-port network, when the output port of the active two-port network is open, the transfer impedance of the output port to the input port is Z21.
In the formula (2), U o To output the voltage of the port, I i Is the current at the input port.
Referring to fig. 1, according to the principle of the source meter of the conventional large-scale ground impedance tester, it can be known that the voltage pole P is actually an input of a voltmeter, and the input impedance is very large. If the voltage pole P is connected to the network W, it can be considered that the output port of the network W has no output current, i.e. the condition of the output port open circuit of the active two-port network is satisfied. During verification, the output port of the network W is connected to the variable voltage pole auxiliary ground resistor RP, which is used for simulating the voltage pole P. Similarly, equation (2) applies to the network W, where the output ports of the network W are considered to meet the condition of an open output port of the active two-port network without output current.
Further, as described above, the large-scale ground impedance tester is a test voltage U passing through the voltage pole P P Divided by the output current I of the current pole C m To obtain the output current I of the current electrode C with the ground impedance m I.e. the input current I of the input port of the active two-port network i Input voltage U of voltage pole P P I.e. the output voltage U of the active two ports o Therefore, the grounding impedance Z measured by the grounding impedance tester of the large-scale grounding network G ＝Z 21 。
According to the characteristics of the active two-port network, the Z parameter of the active two-port network is only related to the active two-port network, internal resistance, capacitance, structure and the like, so that the internal characteristics of the active two-port network can be changed through the first programmable gain amplifier PGA0, the second programmable gain amplifier PGA1 and the signal operation circuit (adder) in the network W, and the transfer impedance high-precision program control of the active two-port network can be realized.
The network W may be divided into two components, an impedance programming component and a signal combining component. The impedance programming section includes R0, PGA0, phase shifter 20, and PGA1; the signal synthesizing section includes an arithmetic circuit constituted by an adder 30.
In the impedance program control part, the sampling resistor R0 is unchanged, the PGA0 realizes the program control of a pure resistor part (real impedance), and the PGA1 realizes the program control of a reactance part (complex impedance). Inside the network W, a current I is first input i Through sampling resistor R 0 Current I i Converted to a voltage. On the one hand, the voltage is amplified and outputted by the PGA0, and the output voltage of the PGA0 is U G0 。
U G0 ＝I i *R 0 *G 0 ……(3)
Wherein G is 0 For the gain of PGA0, R 0 The resistance of the sampling resistor R0.
On the other hand, the sampling resistor R 0 The converted voltage is phase-shifted by 90 DEG by the phase shifter 20 and then amplified by the PGA1, and the PGA1 outputs the voltage U because the vector on the real axis is turned by 90 DEG and then becomes the vector on the imaginary axis G1 Can be expressed as:
U G1 ＝I i *R 0 *G 1 *j……(4)
wherein U is G1 The gain of PGA1, j is a complex unit.
Combining (3) and (4), the output voltage U of the network W can be calculated o 。
U O ＝U G0 +U G1 ……(5)
Combining (2) - (5) to obtain the transmission impedance Z of the network W E The method comprises the following steps:
in the formula (6), (G) 0 +G 1 *j)*R 0 For the transmission impedance of the network W, change G 0 And G 1 I.e. the transmission impedance of the network W can be changed by controlling the device 10 to program G 0 And G 1 The desired transmission characteristics can be obtained. And the combination result of various complex impedance and real impedance can be obtained, and the application range of the verification metering device is increased.
The transmission impedance of the active two-port network is adopted to replace a physical resistance simulation resistance part, a physical inductance simulation reactance part is replaced, and the transmission characteristics of the active two-port network are programmed through the control equipment 10, so that high-precision programming of the transmission impedance is realized, the physical resistance and the physical inductance of various specifications do not need to be prepared according to the measuring range of the detector, and the situation of complicated operation of changing the physical resistance and the physical inductance during verification is avoided; meanwhile, compared with the preparation cost and the volume weight of the physical resistor and the physical inductor, the active two-port network has the advantages that the preparation cost and the volume weight are reduced, and great convenience is brought to verification. In addition, stable complex impedance characteristics can be simulated, precise physical inductance does not need to be prepared, and the situation that physical inductance is poor in stability and greatly influenced by environmental factors and working conditions is avoided.
Illustratively, embodiments of the present invention provide a first programmable gain amplifier PGA0 of two different configurations. It should be noted that the structures of the first programmable gain amplifier PGA0 and the second programmable gain amplifier PGA1 may be the same, and therefore, the structure of the second programmable gain amplifier PGA1 is not described again.
Fig. 4 shows a first configuration of a first programmable gain amplifier. Referring to fig. 4, the first programmable gain amplifier PGA0 includes a first resistor R1, a first operational amplifier U1, and a digital potentiometer RD. The first end of the first resistor R1 is grounded, the second end of the first resistor R1 is electrically connected with the inverting input end of the first operational amplifier U1, the non-inverting input end of the first operational amplifier U1 is electrically connected with the second end of the variable current electrode auxiliary grounding resistor RC, the first end of the sampling resistor R0 and the input end of the phase shifter 20 respectively, the connection point of the first operational amplifier U1 and the first resistor R1 is electrically connected with the input end of the digital potentiometer RD, the output end of the digital potentiometer RD is electrically connected with the output end of the first operational amplifier U1, the connection point of the digital potentiometer RD and the first operational amplifier U1 is electrically connected with the second input end of the adder 20, and the control end of the digital potentiometer RD is electrically connected with the control equipment 10.
In the first configuration, the digital potentiometer 10 is a resistance device with a programmed electric shock position, which has a certain total resistance Rp, similar to the physical potentiometer, the theoretical contact position of the physical potentiometer can be anywhere from 0 to Rp, the contact position of the digital potentiometer RD is determined, and the contact positions are generally distributed on Rp evenly, so the following relationship can be known: resistance of the digital potentiometer RD: r0=rp/n×d, rp is the total resistance of the digital potentiometer RD, N is the number of contacts of the digital potentiometer RD, and D is the contact position of the digital potentiometer RD. According to the gain relation of the forward proportional amplifier, the gain of the first programmable gain amplifier PGA0 is as follows: g0 Taking r1=rp/N, the gain of the first programmable gain amplifier PGA0 is: g0 =rp×d/(n×r1) +1=d+1. If 1024 contacts are selected, the contact positions can be 0-1023, and the gain of the first programmable gain amplifier PGA0 can be continuously adjustable at integer points of 1-1024.
Fig. 5 shows a second configuration of the first programmable gain amplifier. Referring to fig. 5, the first programmable gain amplifier PGA0 includes a second resistor R2, a second operational amplifier U2, a resistor branch 80, and an analog cell branch 90. The first end of the second resistor R2 is grounded, the second end of the second resistor R2 is electrically connected to the inverting input end of the second operational amplifier U2, the non-inverting input end of the second operational amplifier U2 is electrically connected to the second end of the variable current electrode auxiliary grounding resistor RC, the first end of the sampling resistor R0, and the input end of the phase shifter 20, respectively, and the output end of the second operational amplifier U2 is electrically connected to the second input end of the adder 20.
The resistor branch 80 is a line formed by connecting m resistors 801 in series.
The analog unit branch 90 is a line formed by connecting m analog switch units 901 in series. The analog switch unit 901 includes an analog switch 902 and a first inverter 903 which controls the analog switch 902 to be closed. The analog switch 902 of the i-th analog switch unit 901 of the m analog switch units 901 is connected in series with the analog switch 902 of the i+1th analog switch unit 901, and each of the first inverters 903 is electrically connected to the control device 10.
The resistor branch 80 is connected in parallel with the analog unit branch 90, the connection point of the i-th resistor 801 and the i+1th resistor 801, and the connection point of the analog switch 902 of the i-th analog switch unit 901 and the analog switch 902 of the i+1th analog switch unit 901 are electrically connected, and the first connection point of the resistor branch 80 and the analog unit branch 90, and the connection point of the second resistor R2 and the second operational amplifier U2 are connected.
The resistor branch 80 is connected to a second connection point of the analog unit branch 90 and to a connection point of the second operational amplifier U2 and the adder 20.
In the second configuration, each first inverter 903 is connected to the control device 10 via a control bus. For example, m=9, 9 first inverters 903 may be connected to the control device 10 through control buses D0 to D8, for example, 1 st first inverter 903 may be connected to the control device 10 through control bus D0, 2 nd first inverter 903 may be connected to the control device 10 through control bus D1, and so on. The on and off of the analog switch 902 is controlled by the corresponding first inverter 903. The resistance values of the m resistors 801 are incremented in the order of distribution by an increment of 2 times the resistance value of the preceding resistor 801. Illustratively, when there are 9 resistors 801, the resistance values of the 9 resistors 801 are R, 2R, 4R, 8R, 16R, 32R, 64R, 128R, 256R in order. When the first inverter 903 outputs the control signal from the control device 10 in the backward direction, the on-off of the analog switch 902 is controlled, at this time, the on of the analog switch 902 shorts the corresponding resistor 801, the off of the analog switch 902 causes the corresponding resistor 801 to play a role of resistance, so that the on-off of the analog switch 902 with different numbers and different positions can control the resistor 801 with different numbers and different positions to provide a resistance network, the resistance network will present different resistance characteristics, and the resistance relationship between the control bus data and the resistance network is: resistor network resistance=r×d (where D is the control value of the data buses D0 to D8), so when resistance r2=r, the gain of PGA1 is: g=r×d/r2+1=d+1. The bit width of the control bus is 9 bits, and the value of D can be 0-511, so that the gain of the PGA0 is continuously adjustable at an integer point within 1-512.
The first structure of the first programmable gain amplifier has the advantages of simple circuit and easy realization compared with the second structure of the first programmable gain amplifier, and the first structure has the disadvantages that the linearity of the digital resistor RD is poor and the gain error is large near the maximum and minimum values of the gain. Rp is typically 10kΩ, 50kΩ, 100kΩ, the number of contacts of the digital potentiometer RD is typically 256, 512, 1024, and r1=rp/N results in an endless fraction of R1, so R1 is not easily selected. The second structure has the advantages that the precision is easy to control, and the resistance value is easy to take value; the disadvantage is that the circuit is relatively complex.
Illustratively, embodiments of the present invention provide two structurally different phase shifters 20.
Fig. 6 shows a first structure of the phase shifter. Referring to fig. 6, the phase shifter 20 includes a capacitor C, a third resistor R3, and a third operational amplifier U3. The first end of the third resistor R3 is electrically connected with the reverse input end of the third operational amplifier U3, the second end of the third resistor R3 is electrically connected with the output end of the third operational amplifier U3, the connection point of the third resistor R3 and the output end of the third operational amplifier U3 is electrically connected with the input end of the second programmable gain amplifier PGA1, the non-inverting input end of the third operational amplifier U3 is grounded, the first end of the capacitor C is electrically connected with the connection point of the sampling resistor R0 and the first programmable gain amplifier PGA0, and the second end of the capacitor C is electrically connected with the connection point of the third resistor R3 and the reverse input end of the third operational amplifier U3.
In the first phase shifter, the output voltage U O And input voltage U i The relationship of (2) is as follows:
wherein ω is the input signal angular frequency, R is the third resistor R3C is the value of the capacitor C, Z C Is the impedance of the capacitor C. The phase frequency response of the first phase shifter is fixed, the signal is phase shifted by-90 degrees, and then the signal passes through a first-stage inverter (a third operational amplifier U) to reach the requirement of 90 degrees phase shift.
The amplitude-frequency characteristic (amplitude-frequency response result) of the first phase shifter can be calculated by the equation (8).
It can be seen that the amplitude-frequency characteristic of the first phase shifter has a linear relationship with the input signal angular frequency ω. For example, when the input signal is 50Hz, the angular frequency is 100pi, and the third resistor R3 and the capacitor C are assumed to have values just that enable the amplitude-frequency characteristic to be 1 when the input signal is 50 Hz. With this condition unchanged, then the amplitude-frequency characteristic response becomes 10 when the input signal becomes 500 Hz. Such a linear amplitude-frequency response can be problematic in practice. Problem one: in the grounding impedance test, an inter-frequency method is mostly used, the frequency is generally 40-60 Hz, an excitation source is a high-power program-controlled inversion current source, a relatively high-frequency signal is inevitably caused in an input signal, and then the high-frequency component is amplified by the phase shift of the phase shifter, so that the signal distortion degree is increased. The grounding impedance tester is a frequency-selecting measuring instrument, which is equivalent to reducing the signal-to-noise ratio and reducing the accuracy of the system. And a second problem: when measuring 40-60 Hz signals, the transmission impedance of the network W is not a set result because the result of the amplitude-frequency response is different, but the transmission impedance needs to be converted according to the relation between the reference frequency and the actual frequency, which increases the difficulty of verification. In addition, the first phase shifter uses a capacitor C, which is relatively poor in stability and varies with the environmental temperature, and thus requires that the environmental conditions of the assay metering apparatus be controllable and stable, which limits the applicable environment of the assay metering apparatus, resulting in poor environmental suitability of the assay metering apparatus.
Fig. 7 shows a second structure of the phase shifter. Referring to fig. 7, the phase shifter 20 includes: an analog-to-digital converter ADC 201, an integrating unit 202, a second inverter 203, an angular frequency calculating unit 204, a multiplier 205, and a digital-to-analog converter DAC 206. The input end of the analog-to-digital converter ADC 201 is electrically connected to the connection point between the sampling resistor R0 and the first programmable gain amplifier PGA0, the output end of the analog-to-digital converter ADC is electrically connected to the input ends of the integrating unit 202 and the angular frequency calculating unit 204, the output end of the integrating unit 202 is electrically connected to the input end of the second inverter 203, the output end of the second inverter 203 is electrically connected to the first input end of the multiplier 205, the second input end of the multiplier 205 is electrically connected to the output end of the angular frequency calculating unit 204, the output end of the multiplier 205 is electrically connected to the input end of the digital-to-analog converter DAC 206, and the output end of the digital-to-analog converter DAC 206 is electrically connected to the input end of the second programmable gain amplifier PGA 1.
In the second configuration, the phase shifter 20 adopts a digital signal processing scheme, and the integrating unit 202, the second inverter 203, the angular frequency calculating unit 204, and the multiplier 205 constitute a digital signal processing unit. The signal is firstly subjected to sampling discretization by the ADC 201, so as to facilitate digital signal processing, then enters the integration unit 202 to calculate and output an integration result, meanwhile, the signal enters the angular frequency calculation unit 204 to calculate the angular frequency of the input signal, the integration result is converted into a complex frequency domain signal by the second inverter 203, finally, the multiplier 205 multiplies the complex frequency domain signal by the angular frequency output by the angular frequency calculation unit 204, and the product result is transmitted to the DAC 206 to be output.
Illustratively, after the input voltage Ui is integrated by the integrating unit 202, the integration result of the output is shown as equation (9).
Where s is the laplace transform operator. The product result output from the multiplier 205 is shown in equation (10).
Where ω is the angular frequency calculated by the angular frequency calculation unit 204. The output result of the DAC 206 is shown in equation (11).
In summary, the output result of the phase shifter with the second structure has an amplitude-frequency response of 1, the phase-frequency response of 90 degrees, and after the digital signal processing, the output signal not only realizes 90-degree phase shift, but also has a fixed amplitude-frequency response, so that the problem that harmonic wave or noise is amplified does not occur, and the transmission impedance of the network W does not need to be converted according to the signal frequency. Meanwhile, the whole processing process is digitalized, so that the problem of poor environmental adaptability of the analog circuit is solved.
The resistance of the sampling resistor R0 is, for example, 10 to 100 milliohms. For example, the resistance of sampling resistor R0 is 10, 20, or 50 milliohms. The resistance value of 10-100 milliohms is particularly small, the heating of the sampling resistor R0 can be greatly reduced, the temperature drift problem is solved, meanwhile, only one high-precision, low-temperature drift and high-reliability precise resistor R0 is needed, and the preparation cost of the verification metering device can be reduced. The sampling resistor can also have other resistance values, and even can be matched with a radiator for use, so that the temperature rise caused by heating of the sampling resistor is in a controllable range.
Illustratively, the variable voltage pole auxiliary ground resistance RP and the variable current pole auxiliary ground resistance RC each have a resistance adjustable range of 0 to 200 ohms. In the existing verification metering device, the variable intervals of the resistance values of the variable electrode auxiliary grounding resistor RP and the variable electrode auxiliary grounding resistor RC1 are [0, 1000 omega, 2000 omega, 5000 omega ], and the auxiliary grounding resistor of the large-scale grounding grid grounding impedance tester generally needs not to exceed 200 omega. Therefore, the resistance values of the variable electrode auxiliary grounding resistor RP and the variable electrode auxiliary grounding resistor RC are adjusted to be suitable for the working requirement of the large-scale grounding network grounding impedance tester, and the verification accuracy of the verification metering device is improved.
Illustratively, the control apparatus 10 is further configured to record the adjusted gains of the first and second programmable gain amplifiers PGA0 and PGA1, respectively, after adjusting the gains of the first and second gain amplifiers; receiving a calculation instruction, wherein the calculation instruction comprises a measured value of the grounding impedance tester to be tested; and calculating an indication error of the measured ground impedance tester based on the recorded gains of the first program controlled gain amplifier PGA0 and the second program controlled gain amplifier PGA1 after adjustment and the measured value of the ground impedance of the measured ground impedance tester.
Illustratively, the control apparatus 10 calculates an indication error of the measured ground impedance tester according to the following equation (12).
In the formula (12), E is an indication error, Z X The measured value of the measured grounding impedance tester can be a module value of the measured grounding impedance; z is Z E ＝(G 0 +G 1 *j)*R 0 ，G 0 Gain of the first programmable gain amplifier PGA0, G 1 Is the gain of the second programmable gain amplifier PGA1, j is the imaginary unit, R 0 The resistance of the sampling resistor R0.
The foregoing description of the preferred embodiments of the invention is not intended to limit the invention to the precise form disclosed, and any such modifications, equivalents, and alternatives falling within the spirit and scope of the invention are intended to be included within the scope of the invention.
Claims (8)
1. A metrological verification device for a large ground impedance tester, the device comprising: the variable electrode auxiliary grounding resistor, the sampling resistor, the first program-controlled gain amplifier, the second program-controlled gain amplifier, the phase shifter, the adder and the control device;
the first end of the variable current pole auxiliary grounding resistor is electrically connected with the current output end of the tested grounding impedance tester, the second end of the variable current pole auxiliary grounding resistor is electrically connected with the first end of the sampling resistor, the input end of the phase shifter and the input end of the first programmable gain amplifier respectively, the second end of the sampling resistor is electrically connected with the current input end of the tested grounding impedance tester, the connection point of the sampling resistor and the current input end of the tested grounding impedance tester is connected with signal ground, the output end of the phase shifter is electrically connected with the input end of the second programmable gain amplifier, the output end of the second programmable gain amplifier is electrically connected with the first input end of the adder, the output end of the adder is electrically connected with the voltage input end of the tested grounding impedance tester, the control end of the second programmable gain amplifier and the first control end of the phase shifter are electrically connected with the voltage input end of the tested grounding impedance tester respectively, and the output end of the variable current pole auxiliary grounding resistor is electrically connected with the voltage auxiliary grounding resistor;
The control device is further configured to receive a gain adjustment instruction, and based on the gain adjustment instruction, adjust gains of the first program-controlled gain amplifier and the second program-controlled gain amplifier, respectively;
the control device is also adapted to control the control device,
after the gains of the first program-controlled gain amplifier and the second program-controlled gain amplifier are adjusted, the gains of the first program-controlled gain amplifier and the second program-controlled gain amplifier after adjustment are respectively recorded;
receiving a calculation instruction, wherein the calculation instruction comprises a ground impedance measured value of the measured ground impedance tester;
and under the instruction of the calculation instruction, calculating an indication error of the measured grounding impedance tester based on the recorded gains of the first program-controlled gain amplifier and the second program-controlled gain amplifier after adjustment and the measured grounding impedance value of the measured grounding impedance tester.
2. The apparatus of claim 1, wherein the first programmable gain amplifier comprises a first resistor, a first operational amplifier, and a digital potentiometer,
the first end of the first resistor is grounded, the second end of the first resistor is electrically connected with the inverting input end of the first operational amplifier, the non-inverting input end of the first operational amplifier is electrically connected with the second end of the variable current pole auxiliary grounding resistor, the first end of the sampling resistor and the input end of the phase shifter respectively, the first operational amplifier is electrically connected with the connection point of the first resistor and the input end of the digital potentiometer, the output end of the digital potentiometer is electrically connected with the output end of the first operational amplifier, the connection point of the digital potentiometer and the first operational amplifier is electrically connected with the second input end of the adder, and the control end of the digital potentiometer is electrically connected with the control equipment.
3. The apparatus of claim 1, wherein the first programmable gain amplifier comprises a second resistor, a second operational amplifier, a resistor branch, and an analog cell branch,
the first end of the second resistor is grounded, the second end of the second resistor is electrically connected with the inverting input end of the second operational amplifier, the non-inverting input end of the second operational amplifier is respectively electrically connected with the second end of the variable current pole auxiliary grounding resistor, the first end of the sampling resistor and the input end of the phase shifter, the output end of the second operational amplifier is electrically connected with the second input end of the adder,
the resistor branch is a line formed by connecting m resistors in series,
the analog unit branch is a line formed by serially connecting m analog switch units, each analog switch unit comprises an analog switch and a first inverter for controlling the analog switch to be closed, the analog switch of the ith analog switch unit in the m analog switch units is serially connected with the analog switch of the (i+1) th analog switch unit, each first inverter is electrically connected with the control equipment,
the resistor branch is connected in parallel with the analog unit branch, the connection point of the ith resistor and the (i+1) th resistor, and the connection point of the analog switch of the ith analog switch unit and the analog switch of the (i+1) th analog switch unit are electrically connected, the first connection point of the resistor branch and the analog unit branch, and the connection point of the second resistor and the second operational amplifier are connected,
The resistor branch is connected with a second connection point of the analog unit branch and a connection point of the second operational amplifier and the adder.
4. The apparatus of claim 1, wherein the phase shifter comprises a capacitor, a third resistor and a third operational amplifier,
the first end of the third resistor is electrically connected with the reverse input end of the third operational amplifier, the second end of the third resistor is electrically connected with the output end of the third operational amplifier, the connection point of the third resistor and the output end of the third operational amplifier is electrically connected with the input end of the second program-controlled gain amplifier, the non-inverting input end of the third operational amplifier is grounded, the first end of the capacitor is electrically connected with the connection point of the sampling resistor and the first program-controlled gain amplifier, and the second end of the capacitor is electrically connected with the connection point of the third resistor and the reverse input end of the third operational amplifier.
5. The apparatus of claim 1, wherein the phase shifter comprises: an analog-to-digital converter, an integrating unit, a second inverter, an angular frequency calculating unit, a multiplier and a digital-to-analog converter,
The input end of the analog-to-digital converter is electrically connected with the connection point of the sampling resistor and the first program-controlled gain amplifier, the output end of the analog-to-digital converter is electrically connected with the input ends of the integrating unit and the angular frequency calculating unit respectively, the output end of the integrating unit is electrically connected with the input end of the second reverser, the output end of the second reverser is electrically connected with the first input end of the multiplier, the second input end of the multiplier is electrically connected with the output end of the angular frequency calculating unit, the output end of the multiplier is electrically connected with the input end of the digital-to-analog converter, and the output end of the digital-to-analog converter is electrically connected with the input end of the second program-controlled gain amplifier.
6. The device of any one of claims 1-5, wherein the sampling resistor has a resistance of 10 to 100 milliohms.
7. The apparatus of any one of claims 1-5, wherein the variable voltage pole auxiliary ground resistance and the variable current pole auxiliary ground resistance each have a resistance adjustable range of 0-200 ohms.
8. The apparatus of any one of claims 1-5, wherein the control device calculates the indication error of the measured ground impedance tester according to the formula:
E is the indication error, Z X Z is the measured value of the measured grounding impedance tester E ＝(G 0 +G 1 *j)*R 0 ，G 0 G is the gain of the first program controlled gain amplifier 1 For the gain of the second programmable gain amplifier, j is the imaginary unit, R 0 And the resistance value of the sampling resistor.
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