Self-calibration digital measurement system and calibration-and-measurement method thereof

Abstract

The invention provides a self-calibration digital measurement system and a calibration-and-measurement method thereof. The digital measuring system comprises a standard signal source, an ADC conversion module, a high-precision clock reference, a digital engine, a switching circuit and a phase locking unit, and the digital engine is communicated with the standard signal source, the ADC conversion module, the switching circuit, the high-precision clock reference and the phase locking unit. The analog-to-digital conversion module is configured to receive data obtained after different conversion channels of the ADC conversion module perform analog-to-digital conversion on the AC voltage reference signal and perform linear fitting so as to obtain calibration parameters of the corresponding channel ADC, and the analog-to-digital conversion module is further configured to receive data obtained after different conversion channels of the ADC conversion module perform analog-to-digital conversion on the AC voltage signal to be detected; and the calibration parameter of the corresponding conversion channel is called to correct the AC voltage signal to be measured, so that self-calibration and measurement while calibration of the system are realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of metrology, and in particular, to a self-calibrating digital measurement system and a method of self-calibration. BACKGROUND

[0002] In the field of metrological calibration, various electrical measuring devices for measuring voltage, current, electric energy, etc. need to be calibrated or verified periodically to ensure their measurement accuracy meets the requirements. In the industry, the electrical measuring devices are usually calibrated or verified according to the method specified in the relevant calibration / verification regulations using standard devices with higher precision levels. From the aspects of calibration or verification, the method and the standard device used have a decisive influence on the accuracy of the calibration or verification results. The desired method is to avoid the influence of environmental factors on the calibration or verification process as much as possible and avoid the introduction of excessive uncertainty by environmental factors. The level of the standard device used for calibration or verification determines the precision level and error range of the measuring devices that can be calibrated or verified.

[0003] At present, digital measuring devices have gradually replaced traditional analog measuring devices and become the preferred choice in the industry. Digital measuring devices are generally equipped with an analog-to-digital converter (ADC) for converting analog signals into digital signals. The ADC of a digital measuring device usually has a certain conversion error in the process of converting analog signals into digital signals, resulting in a deviation between the measured value and the true value, which is an important source of measurement error of digital measuring devices. In terms of voltage measurement, the quantum voltage reference has been used as the highest level standard device in the value traceability transmission in the industry. The existing technology has attempted to use the quantum voltage step wave synthesized by the programmable Josephson quantum junction array chip as a standard reference signal to realize the accurate measurement of alternating voltage through the differential sampling method. The differential sampling method synchronously samples the difference between the measured alternating voltage signal and the quantum voltage step wave signal, and its measurement accuracy is closely related to the size of the differential signal, and the relative phase difference between the measured alternating signal and the step wave signal needs to be kept stable to ensure the stability of the differential signal.

[0004] The prior art differential sampling method has defects despite using the highest level standard device. On the one hand, the differential sampling system does not consider the conversion error of the ADC itself in the circuit or device for measuring the differential signal, cannot correct the conversion error of the ADC itself at the same time of differential sampling, and must use a gain module for amplification processing due to the small differential signal, which will inevitably introduce certain error. On the other hand, the differential sampling method requires the frequency of the measured AC signal and the step wave signal to be consistent to keep the relative phase difference stable, which causes that the noise in the measured AC signal cannot be attenuated by the conventional frequency multiplication sampling method, which greatly limits the accuracy of the measuring equipment and the frequency range of the signal suitable for calibration by the quantum voltage reference such as the high-level standard device.

[0005] It is well known that the accuracy of voltage, current and energy measurement is ultimately closely related to the accuracy of voltage measurement, because the measurement of current signal or current component in energy pulse can finally be converted into the measurement of voltage signal through a precision current-voltage conversion module. In practice, it is not cost-effective to calibrate the electrical measuring equipment separately in terms of time and cost. Therefore, there is an urgent need for a measuring system with self-calibration function and a new measuring method, which is expected to correct the measurement error introduced by the conversion error of the ADC itself of the measuring system in real time, and effectively attenuate the noise in the measured AC voltage signal in a wide frequency range. SUMMARY

[0006] According to one aspect of the present application, a self-calibration digital measuring system is provided, comprising a standard signal source, an ADC conversion module, a switch circuit, a phase-locked unit, a digital engine and a high-precision clock reference, the standard signal source is connected to the ADC conversion module through the switch circuit, the ADC conversion module is connected to the phase-locked unit and the digital engine respectively, and the digital engine is connected to the phase-locked unit and the high-precision clock reference respectively. The standard signal source is used to generate an AC voltage reference signal, the AC voltage reference signal is a signal with the same amplitude as the measured AC voltage signal and a period N times larger, the high-precision clock reference is used to provide the same time and frequency reference as the generating device of the measured AC voltage signal for the digital measuring system; N is an integer greater than or equal to 2. The switch circuit is used for switching control of the different two conversion channels in the ADC conversion module to alternately input the AC voltage reference signal and the to-be-measured AC voltage signal through the switch position, when the phase-locked unit locks the zero phase point of the AC voltage reference signal, the digital engine performs linear fitting on the data obtained after the whole period sampling and analog-digital conversion of the AC voltage reference signal in the ADC conversion module from the zero phase point of the AC voltage reference signal, to obtain the calibration parameter of the conversion channel where the AC voltage reference signal is currently located; when the phase-locked unit locks the zero phase point of the to-be-measured AC voltage signal, the digital engine calls the calibration parameter of the conversion channel where the to-be-measured AC voltage signal is currently located to correct the data obtained after the N times period sampling and analog-digital conversion of the to-be-measured AC voltage signal in the ADC conversion module from the zero phase point of the to-be-measured AC voltage signal, to obtain the corrected measurement value of the to-be-measured AC voltage signal.

[0007] The self-calibration digital measurement system can accurately measure the conversion error of the ADC itself in the system through the standard signal source, the phase-locked unit and the digital engine, and then can correct the to-be-measured AC voltage signal by calling the calibration parameter of the corresponding conversion channel when the phase-locked unit locks the zero phase point of the to-be-measured AC voltage signal, to realize the instant correction of the measurement error introduced by the conversion error of the ADC itself in the system. The switch circuit is switched without delay to achieve the purpose of calibration and measurement at the same time. The noise in the measured AC signal is effectively attenuated through the frequency multiplication sampling mode, the noise in the measured AC voltage signal is effectively attenuated in a wide frequency range, the AC voltage reference signal and the to-be-measured AC voltage signal can be directly input into the ADC for sampling and analog-digital conversion, without the need to configure an additional gain module, so that the corresponding gain error caused by the additional gain module is also avoided.

[0008] According to another aspect of the present application, a calibration and measurement method of a digital measurement system is provided, which is based on the above digital measurement system and includes the following steps: In the current measurement, the AC voltage reference signal and the to-be-measured AC voltage signal are respectively input into the different two conversion channels in the ADC conversion module through the switch circuit; the AC voltage reference signal is a signal with the same amplitude as the to-be-measured AC voltage signal and a period N times larger, where N is an integer greater than or equal to 2; judging the locking state of the phase-locked unit to the signals in the different two conversion channels in the ADC conversion module; When the phase-locked unit locks the zero phase point of the AC voltage reference signal, the digital engine performs linear fitting on the data obtained after the whole period sampling and analog-digital conversion of the AC voltage reference signal in the ADC conversion module from the zero phase point of the AC voltage reference signal, to obtain the calibration parameter of the conversion channel where the AC voltage reference signal is currently located; When the phase-locked unit locks the zero phase point of the to-be-measured AC voltage signal, the digital engine calls the calibration parameters of the conversion channel in which the to-be-measured AC voltage signal is currently located to correct the data obtained by sampling and analog-digital conversion of the to-be-measured AC voltage signal from the zero phase point of the to-be-measured AC voltage signal, and obtains a corrected measurement value of the to-be-measured AC voltage signal. By switching the input signals of the different two conversion channels in the ADC conversion module through the switch circuit, the step of judging the locking state of the signals in the different two conversion channels in the ADC conversion module by the phase-locked unit is jumped to, and the next measurement is entered.

[0009] In the preferred embodiments provided according to various aspects of the present application, the ADC conversion module is a dual-channel ADC, the switch circuit is in the first switch state, the AC voltage reference signal is connected to the first conversion channel of the dual-channel ADC, and the to-be-measured AC voltage signal is connected to the second conversion channel of the dual-channel ADC; the switch circuit is in the second switch state, the to-be-measured AC voltage signal is connected to the first conversion channel of the dual-channel ADC, and the AC voltage reference signal is connected to the second conversion channel of the dual-channel ADC.

[0010] In the preferred embodiments provided according to various aspects of the present application, the ADC conversion module includes at least two dual-channel ADCs, the number of switch branches of the switch circuit matches the number of conversion channels of the dual-channel ADC, the two input ends of each switch branch are respectively used to connect the AC voltage reference signal and the to-be-measured AC voltage signal, the output end of each switch branch is connected to a corresponding conversion channel, and each switch branch includes a first switch state and a second switch state.

[0011] In the preferred embodiments provided according to various aspects of the present application, the digital engine includes a data processing unit and a storage unit connected in communication, the data processing unit is connected to the ADC conversion module, the phase-locked unit and the high-precision clock reference respectively; The data processing unit is used for linear fitting and storing the obtained calibration parameters in the storage unit, and is used for calling the calibration parameters of the conversion channel in which the to-be-measured AC voltage signal is currently located to correct the to-be-measured AC voltage signal.

[0012] In the preferred embodiments provided according to various aspects of the present application, the dual-channel ADC in the ADC conversion module is a 24-bit high-speed high-precision ADC, and the high-precision clock reference in the digital measurement system is a rubidium atomic clock with a clock stability reaching 10 -12 orders of magnitude.

[0013] In the preferred embodiments provided according to various aspects of the present application, the period of the AC voltage reference signal generated by the standard signal source is at least 5 times the period of the to-be-measured AC voltage signal.

[0014] In the preferred embodiments provided according to various aspects of the present application, the standard signal source is a programmable Josephson voltage standard, and the generated AC voltage reference signal is a staircase quantum voltage signal.

[0015] In the preferred embodiments provided according to various aspects of the present application, the standard signal source is a pulse-driven AC Josephson voltage standard, and the generated AC voltage reference signal is a sinusoidal quantum voltage signal.

[0016] In the preferred embodiments provided according to various aspects of the present application, the digital measurement system further comprises a display device connected to the data processing unit, and the display device is configured to display the measured value of the AC signal to be measured, the corrected measured value, and the correction amount. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort based on these drawings.

[0018] Figure 1 a schematic block diagram of the self-calibrating digital measurement system provided by the embodiments of the present application is shown; Figure 2 a circuit block diagram of the self-calibrating digital measurement system provided by the embodiments of the present application is shown; Figure 3 a flowchart of the self-calibrating digital measurement system provided by the embodiments of the present application is shown; Figure 4 a flowchart of the self-calibrating digital measurement system provided by the embodiments of the present application is shown; Figure 5 a flowchart of the self-calibrating digital measurement system provided by the embodiments of the present application is shown. DETAILED DESCRIPTION

[0019] In the following description, for the purpose of explanation and not limitation, specific details are set forth, such as particular system configurations, techniques, etc., in order to provide a thorough understanding of the embodiments of the present application. However, it will be apparent to those skilled in the art that the present application can be practiced in other embodiments that depart from these specific details. In other instances, detailed descriptions of well-known systems, devices, circuits, and methods are omitted so as not to obscure the description of the present application with unnecessary detail.

[0020] In addition, the descriptions such as "first", "second" and the like in the present application are only for the purpose of description, and cannot be understood as indicating or implying the relative importance of the technical features indicated, or implying the number of the technical features indicated. Therefore, the features defined as "first", "second" can be explicitly or implicitly included at least one of the features. In the description of the present application, the meaning of "a plurality of" is at least two, for example, two, three, etc., unless otherwise explicitly specified and limited.

[0021] In the present application, unless otherwise explicitly specified and limited, the terms "connection", "communication", "intercommunication" and the like should be understood in a broad sense, for example, "connection" can be physical connection, can also be electrical connection, can also be wireless communication connection; can be direct connection, can also be indirect connection through intermediate medium, can be internal communication of two elements or interaction relationship between two elements, unless otherwise explicitly limited. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0022] In addition, the technical solutions of various embodiments of the present application can be combined with each other, but it must be based on the fact that a person skilled in the art can realize it, when the combination of technical solutions appears contradictory or unachievable, it should be considered that the combination of technical solutions does not exist, and is not within the protection scope required by the present application.

[0023] In order to make the purpose, technical scheme and advantages of the present application more clear, the following will be explained by specific embodiments in combination with the drawings.

[0024] In one embodiment, Figure 1 A schematic block diagram of a self-calibrated digital measurement system 100 according to an embodiment of the present application is shown. As shown in Figure 1 The digital measurement system 100 includes a standard signal source 1, a switch circuit 3, an ADC conversion module 4, a high-precision clock reference 5, a phase-locked unit 6 and a digital engine 7. The standard signal source 1 is connected to the ADC conversion module 4 through the switch circuit 3, the ADC conversion module 4 is connected to the phase-locked unit 6 and the digital engine 7 respectively, and the digital engine 7 is connected to the phase-locked unit 6 and the high-precision clock reference 5 respectively. The standard signal source 1 is used to generate an alternating voltage reference signal, the alternating voltage reference signal is a signal with the same amplitude as the measured alternating voltage signal and the period is N times larger, the high-precision clock 5 is used to provide the same time-frequency reference as the generation device 200 of the measured alternating voltage signal for the digital measurement system 100; N is an integer greater than or equal to 2.

[0025] The switch circuit 3 is used to control different two conversion channels in the ADC conversion module 4 to alternately input the AC voltage reference signal and the to-be-measured AC voltage signal through the switching position switching. When the phase-locked unit 6 locks the zero phase point of the AC voltage reference signal, the digital engine 7 performs linear fitting on the data obtained after the whole period sampling and the analog-digital conversion of the AC voltage reference signal starting from the zero phase point of the AC voltage reference signal in the ADC conversion module 4, to obtain the calibration parameter of the conversion channel where the AC voltage reference signal is currently located. When the phase-locked unit 6 locks the zero phase point of the to-be-measured AC voltage signal, the digital engine 7 calls the calibration parameter of the conversion channel where the to-be-measured AC voltage signal is currently located to correct the data obtained after the N times period sampling and the analog-digital conversion of the to-be-measured AC voltage signal starting from the zero phase point of the to-be-measured AC voltage signal in the ADC conversion module 4, to obtain the corrected measurement value of the to-be-measured AC voltage signal.

[0026] It can be understood that the standard signal source 1 is used to generate the AC voltage reference signal with the equal amplitude and the period N times larger than the to-be-measured AC voltage signal; the signal input module 2 (the connection line in front of the switch circuit 3) includes at least one signal input subunit, each signal input subunit includes two input lines for inputting the AC voltage reference signal and the to-be-measured AC voltage signal respectively; the ADC conversion module 4 has at least two different conversion channels, for example, at least two ADC conversion channels integrated ADC converters can be used for hardware implementation, at least two single-channel ADC converters in parallel can be used for hardware implementation, or at least one double-channel ADC can be used for hardware implementation.

[0027] For the switch circuit 3 used to control different two conversion channels in the ADC conversion module 4 to alternately input the AC voltage reference signal and the to-be-measured AC voltage signal through the switching position switching, for the convenience of description, taking the double-channel ADC as an example, which is configured in pairs with the signal input subunit and includes the first conversion channel and the second conversion channel; the switch circuit 3 connected between the signal input module 2 and the ADC conversion module 4, the switch circuit 3 includes the switch branch corresponding to each signal input subunit and the double-channel ADC, the switch branch can have two switch states (corresponding to the signal access state under two switch positions) such as the first switch state and the second switch state, in the first switch state of the switch branch, the first conversion channel and the second conversion channel of the double-channel ADC receive the AC voltage reference signal and the to-be-measured AC voltage signal respectively, in the second switch state of the switch branch, the first conversion channel and the second conversion channel of the double-channel ADC receive the to-be-measured AC voltage signal and the AC voltage reference signal respectively (that is, the alternately input of different two conversion channels).

[0028] A high-precision clock reference 5, which can be configured to serve as a time-frequency reference common to the digital measurement system 100, the generating device 200 of the to-be-measured AC voltage signal, and the standard signal source 1. A phase-locked unit 6 in communication with the ADC conversion module 4, which is configured to lock the zero-phase points of the AC voltage reference signal and the to-be-measured AC voltage signal. A digital engine 7 in communication with the standard signal source 1, the ADC conversion module 4, the switch circuit 3, the high-precision clock reference 5, and the phase-locked unit 6, which is configured to implement data linear fitting of the corresponding conversion channels to obtain corresponding calibration parameters, and to-be-measured AC voltage signal correction processing of the conversion channels.

[0029] The above-mentioned self-calibrating digital measurement system 100 accurately measures the conversion error of the ADC itself in the system through the standard signal source, the phase-locked unit, and the digital engine, and then can correct the to-be-measured AC voltage signal by calling the calibration parameters of the corresponding conversion channel when the phase-locked unit locks the zero-phase point of the to-be-measured AC voltage signal, thereby realizing the instant correction of the measurement error introduced by the conversion error of the ADC itself in the system. At the same time, the non-delay switching of the switch circuit achieves the purpose of instant calibration and measurement, and the noise in the measured AC signal is effectively attenuated through frequency multiplication sampling, thereby achieving the effect of effectively attenuating the noise in the measured AC voltage signal in a wide frequency range. The AC voltage reference signal and the to-be-measured AC voltage signal can be directly input to the ADC for sampling and analog-digital conversion, without the need to configure an additional gain module, thereby also avoiding the corresponding gain error brought by the additional gain module.

[0030] In one embodiment, as shown in FIG. 1, Figure 2 The ADC conversion module 4 is a dual-channel ADC, and the switch circuit 3 is in a first switching state to connect the AC voltage reference signal to the first conversion channel of the dual-channel ADC and the to-be-measured AC voltage signal to the second conversion channel of the dual-channel ADC. The switch circuit 3 is in a second switching state to connect the to-be-measured AC voltage signal to the first conversion channel of the dual-channel ADC and the AC voltage reference signal to the second conversion channel of the dual-channel ADC.

[0031] It can be understood that a dual-channel ADC is used in this embodiment to implement the ADC conversion module 4, and the direct application of the dual-channel ADC is used to reduce the circuit complexity of the system with a simple ADC circuit structure.

[0032] In one embodiment, as shown in FIG. 1, Figure 2 The ADC conversion module 4 includes at least two dual-channel ADCs, the switch branches of the switch circuit 3 are matched with the number of conversion channels of the dual-channel ADCs, the two input ends of each switch branch are respectively used to connect the AC voltage reference signal and the to-be-measured AC voltage signal, the output end of each switch branch is connected to a corresponding conversion channel, and each switch branch includes a first switching state and a second switching state.

[0033] It can be understood that in this embodiment, multiple measurement paths that can be calibrated and measured can be expanded according to actual measurement requirements, and each switch branch of the switch circuit 3 can adopt a switch circuit structure with dual-end input and single-end output. For example, but not limited to, a multiplexer or a MOS transistor switch can be used to implement the hardware of each switch branch of the switch circuit 3, thereby realizing efficient signal transmission path control with a simple switch circuit structure.

[0034] In one embodiment, Figure 2 As shown, the digital engine 7 includes a data processing unit and a storage unit in communication with each other. The data processing unit is respectively connected to the ADC conversion module, the phase-locked unit, and the high-precision clock reference. The data processing unit is used to perform linear fitting and store the obtained calibration parameters in the storage unit. It is also used to call the calibration parameters of the current conversion channel of the AC voltage signal to correct the AC voltage signal to be measured.

[0035] Specifically, the digital engine 7 includes a data processing unit and a storage unit that are communicatively connected. The digital engine 7 is configured to, when the switch branch is in the first switching state and it is determined that the phase-locked unit 6 has locked the zero phase point of the AC voltage reference signal, perform linear fitting on the data obtained after sampling the AC voltage reference signal for a full cycle starting from the zero phase point and analog-to-digital conversion for the first conversion channel of the dual-channel ADC, obtain calibration parameters for the first conversion channel of the dual-channel ADC, and store them in the storage unit; when the switch branch is in the second switching state and it is determined that the phase-locked unit 6 has locked the zero phase point of the AC voltage reference signal, perform linear fitting on the data obtained after sampling the AC voltage reference signal for a full cycle starting from the zero phase point and analog-to-digital conversion for the second conversion channel of the dual-channel ADC, obtain calibration parameters for the second conversion channel of the dual-channel ADC, and store them in the storage unit.

[0036] The digital engine 7 is further configured to, when the switch branch is in the first switch state, call the calibration parameters of the second conversion channel of the dual-channel ADC stored in the storage unit to correct the data obtained after sampling the AC voltage signal to be measured N times the period starting from the zero phase point and performing analog-to-digital conversion on the second conversion channel of the dual-channel ADC when it is determined that the phase-locked unit 6 has locked the zero phase point of the AC voltage signal to be measured, and when the switch branch is in the second switch state, when the digital engine 7 determines that the phase-locked unit 6 has locked the zero phase point of the AC voltage signal to be measured, call the calibration parameters of the first conversion channel of the dual-channel ADC stored in the storage unit to correct the data obtained after sampling the AC voltage signal to be measured N times the period starting from the zero phase point and performing analog-to-digital conversion on the first conversion channel of the dual-channel ADC, and obtain the corrected measurement value of the AC voltage signal to be measured.

[0037] In one embodiment, as shown in Figure 2 The digital measurement system 100 described above can further comprise a display device 300 connected to the data processing unit, the display device 300 being configured to display the measured value of the AC signal to be measured, the corrected measured value and the correction amount.

[0038] It can be understood that the digital measurement system 100 in the embodiment can be coupled with the display device 300 to display the measured value of the AC signal to be measured, the corrected measured value and the correction amount. Alternatively, the display device 300 can also be integrated in the digital measurement system 100, and the display device 300 can be a touch or non-touch type display.

[0039] It should be noted that the signal input module 2 can comprise 1, 2, 4 or 6 signal input subunits according to actual measurement needs. Correspondingly, the ADC conversion module 4 comprises 1, 2, 4 or 6 double-channel ADCs configured in pairs with the signal input subunits. As a non-limiting example, Figure 2 The signal input module 2 shown in FIG. 2 comprises two signal input subunits 21, 22, and the ADC conversion module 4 comprises a first double-channel ADC 41 and a second double-channel ADC 42 configured in pairs with the signal input subunits 21, 22. The signal input subunits 21, 22 each comprise two input lines for inputting the AC voltage reference signal generated by the standard signal source 1 and the AC voltage signal to be measured generated by the generating device 200 of the AC voltage signal to be measured. The optional scheme of the switching elements in the switching branch includes but is not limited to low-delay relay switches, optocoupler switches or MOSFET switches. It should be noted that the requirement of the present application for the switching elements to be "low-delay" means that the turn-on time and turn-off time of the switching elements are both less than 0.05 times the period of the AC voltage signal to be measured. Preferably, the turn-on time and turn-off time of the switching elements are both less than 0.01 times the period of the AC voltage signal to be measured.

[0040] The generating device 200 of the AC voltage signal to be measured can be composed of an AC signal source 201 and signal conversion modules 202, 203. The AC signal source 201 can include but is not limited to a voltage source, a current source or a power source, etc. The signal conversion modules 202, 203 can correspondingly include a voltage / voltage conversion module, or a current / voltage conversion module, or both a voltage / voltage conversion module and a current / voltage conversion module. The signal conversion modules 202, 203 are configured to convert the voltage signal and / or the current signal into a nominal voltage signal matching the rated amplitude of the AC voltage reference signal by a certain ratio. The standard signal source 1 is capable of generating an AC voltage reference signal with an equal amplitude and an integer times larger period compared to the nominal voltage signal to be measured. In accordance with the Figure 2In the provided embodiment, the amplitude of the nominal voltage signal and the AC voltage reference signal are in the linear operating range of the dual-channel ADC, so that the two signals can be directly input to the dual-channel ADC for sampling and analog-to-digital conversion without the need to configure an additional gain module, thereby avoiding the gain error caused by the additional gain module.

[0041] According to the embodiment of the present application, the digital measurement system 100 is a high-precision measurement facility, in which the dual-channel ADC uses a bit high-speed high-precision ADC, and the corresponding high-precision clock reference is a rubidium atomic clock with a clock stability of 10 -12 orders of magnitude.

[0042] As a preferred solution, the standard signal source 1 can be selected as an AC quantum voltage standard, because the quantum voltage is established on the basis of a natural constant, and the reference value remains constant and is not affected by time and external environment, and has the advantages of good stability, high reproduction accuracy and easy replication. Selecting the AC quantum voltage standard as the signal source for calibration can accurately measure the conversion error of the ADC itself in the digital measurement system 100, and then when measuring the to-be-measured signal, the measurement error of each conversion channel of the dual-channel ADC can be corrected, thereby obtaining a more accurate measurement value.

[0043] It is known to those skilled in the art that the AC quantum voltage standard is divided into two schemes: a programmable Josephson AC quantum voltage standard and a pulse-driven AC quantum voltage standard, one of which is a programmable Josephson voltage standard (PJVS), which works by changing the number of Josephson junctions in the working state to synthesize an AC waveform with voltage steps; the other is a pulse-driven AC Josephson voltage standard (JAWS), which synthesizes the required voltage waveform by changing the frequency of the microwave. JAWS uses the principle of magnetic flux quantum and uses a series of high-speed current pulses to drive the Josephson junction array. The uncertainty of the effective value of the synthesized voltage of the above two AC quantum voltage standards is better than 1x10 -6 , and both can be used as AC quantum voltage signals in the present application to measure the conversion error of each conversion channel of the dual-channel ADC of the digital measurement system. The difference is that when PJVS is used as the standard signal source, the generated AC quantum voltage signal is a staircase quantum voltage; when JAWS is used as the standard signal source, the generated AC quantum voltage signal is a sinusoidal quantum voltage.

[0044] According to a preferred embodiment of the present invention, the period of the AC quantum voltage signal generated by standard signal source 1 is at least five times the period of the AC voltage signal to be measured generated by AC voltage signal generator 200. This significantly reduces the impact of environmental noise on measurement results, thereby improving the measurement accuracy of measurement system 100 and expanding the frequency range of signals suitable for calibration of high-level standards such as quantum voltage references.

[0045] Below Figure 2 The AC signal source 201 shown in the figure is a single-phase AC power source, used as a non-limiting example to further illustrate the connection between the switching circuit 3 of the present invention, the device 200 for generating the AC voltage signal to be measured, and the standard signal source 1. The switching circuit 3 includes eight switching elements S1, S2, S3, S4, S5, S6, S7, and S8, connected between the signal input module 2 and the ADC conversion module 4. The switching elements S1, S2, S3, and S4 form the corresponding switching branch between the signal input subunit 21 and the first dual-channel ADC 41, while the switching elements S5, S6, S7, and S8 form the corresponding switching branch between the signal input subunit 22 and the second dual-channel ADC 42. The device 200 for generating the AC voltage signal to be measured includes an AC signal source 201 configured as a single-phase AC power source, a signal conversion module 202 configured as a precision voltage / voltage conversion module, and a signal conversion module 203 configured as a precision current / voltage conversion module. The signal conversion module 202 is used to convert the voltage component in the power signal output by the AC signal source 201 into a nominal voltage signal that matches the rated amplitude (for example, 1V) of the AC voltage reference signal of the standard signal source 1 at a certain ratio, while the signal conversion module 203 is used to convert the current component in the power signal output by the AC signal source 201 into a nominal voltage signal that matches the rated amplitude of the AC voltage reference signal of the standard signal source 1 at a certain ratio.

[0046] The voltage signal output from the signal conversion module 202 is a first voltage signal to be measured, which can be input to one of the two input lines of the signal input subunit 21 and connected to the switching elements S2 and S3 in the switching circuit 3 through a one-to-two line. The AC voltage reference signal generated by the standard signal source 1 is input to the other of the two input lines of the signal input subunit 21 and connected to the switching elements S1 and S4 in the switching circuit 3 through a one-to-two line. In the first switching state of the switching branch composed of the switching elements S1, S2, S3 and S4, the switching elements S1 and S3 are turned on while the switching elements S2 and S4 are turned off, and the first conversion channel CH1 and the second conversion channel CH2 of the first dual-channel ADC 41 receive the AC voltage reference signal and the to-be-measured AC voltage signal respectively. In the second switching state of the switching branch, the switching elements S2 and S4 are turned on while the switching elements S1 and S3 are turned off, and the first conversion channel CH1 and the second conversion channel CH2 of the first dual-channel ADC 41 receive the to-be-measured AC voltage signal and the AC voltage reference signal respectively.

[0047] Similarly, the voltage signal output from the signal conversion module 203 is a second voltage signal to be measured, which can be input to one of the two input lines of the signal input subunit 22 and connected to the switching elements S6 and S7 in the switching circuit 3 through a one-to-two line. The AC voltage reference signal generated by the standard signal source 1 is input to the other of the two input lines of the signal input subunit 22 and connected to the switching elements S5 and S8 in the switching circuit 3 through a one-to-two line. In the first switching state of the switching branch composed of the switching elements S5, S6, S7 and S8, the switching elements S5 and S7 are turned on while the switching elements S6 and S8 are turned off, and the first conversion channel CH1' and the second conversion channel CH2' of the second dual-channel ADC 42 receive the AC voltage reference signal and the to-be-measured AC voltage signal respectively. In the second switching state of the switching branch, the switching elements S6 and S8 are turned on while the switching elements S5 and S7 are turned off, and the first conversion channel CH1' and the second conversion channel CH2' of the second dual-channel ADC 42 receive the to-be-measured AC voltage signal and the AC voltage reference signal respectively.

[0048] In one embodiment, a just-in-time calibration and measurement method of a digital measurement system is also provided. Based on the above-described digital measurement system, it can be understood that the steps, procedures and calibration-measurement timing of the just-in-time calibration and measurement method of the digital measurement system 100 provided by the embodiments of the present application are described below with reference to Figures 1-4 Figure 3 ​As shown, the just-calibration-just-measurement method of the digital measurement system 100 includes the following steps: S11, in the current measurement, the AC voltage reference signal and the to-be-measured AC voltage signal are respectively input into different two conversion channels of the ADC conversion module through the switch circuit; S13, judge the locking state of the phase-locked unit to the signals in the different two conversion channels of the ADC conversion module; S15, when the phase-locked unit locks the zero phase point of the AC voltage reference signal, the digital engine performs linear fitting on the data obtained after the ADC conversion module samples and converts the AC voltage reference signal from its zero phase point for a whole period, to obtain the calibration parameter of the conversion channel where the AC voltage reference signal is currently located; S17, when the phase-locked unit locks the zero phase point of the to-be-measured AC voltage signal, the digital engine calls the calibration parameter of the conversion channel where the to-be-measured AC voltage signal is currently located to correct the data obtained after the ADC conversion module samples and converts the to-be-measured AC voltage signal from its zero phase point for N times of period, to obtain the corrected measurement value of the to-be-measured AC voltage signal; S19, after the input signals of the different two conversion channels of the ADC conversion module are swapped through the switch circuit, jump to step S13 and enter the next measurement.

[0049] It can be understood that, in actual application, for example, Figure 4 As shown (taking a dual-channel ADC as an example, other types of ADCs are similar): S10, connect the digital measurement system 100 with the to-be-measured AC voltage signal generation device 200, and through the control of the digital engine 7 of the digital measurement system 100, configure the high-precision clock reference 5 of the digital measurement system 100 as a common time-frequency reference of the digital measurement system 100, the to-be-measured AC voltage signal generation device 200 and the standard signal source 1.

[0050] S20, make the to-be-measured AC voltage signal generation device 200 generate the to-be-measured AC voltage signal, and make the standard signal source 1 generate an AC voltage reference signal with equal amplitude compared with the to-be-measured AC voltage signal, and the period is enlarged to N times.

[0051] S30, through the control of the digital engine 7 of the digital measurement system 100, switch the switch branch corresponding to the signal input subunit 21 and the first dual-channel ADC 41 in the switch circuit 3 of the digital measurement system 100 to the first switch state, that is, the switch element S1 and the switch element S3 are turned on while the switch element S2 and the switch element S4 are turned off, so that the first conversion channel CH1 of the first dual-channel ADC 41 receives the AC voltage reference signal and the second conversion channel CH2 of the first dual-channel ADC 41 receives the to-be-measured first voltage signal.

[0052] S40, when the digital engine 7 judges that the phase-locked unit 6 of the digital measurement system 100 locks the zero phase point of the AC voltage reference signal, linear fitting is performed on the data obtained after the first conversion channel CH1 of the first dual-channel ADC 41 samples and digitizes the AC voltage reference signal from the zero phase point thereof for an integral period, to obtain the calibration parameter of the first conversion channel CH1 of the first dual-channel ADC 41.

[0053] S50, the calibration parameter of the first conversion channel CH1 of the first dual-channel ADC 41 is stored in the storage unit of the digital engine 7.

[0054] S60, the switch branch is switched to the second switch state by the digital engine 7, i.e., the switch element S2 and the switch element S4 are turned on while the switch element S1 and the switch element S3 are turned off, so that the first conversion channel CH1 of the first dual-channel ADC 41 receives the to-be-measured AC voltage signal and the second conversion channel CH2 of the first dual-channel ADC 41 receives the AC voltage reference signal.

[0055] S70, when the digital engine 7 judges that the phase-locked unit 6 of the digital measurement system 100 locks the zero phase point of the AC voltage reference signal, linear fitting is performed on the data obtained after the second conversion channel CH2 of the first dual-channel ADC 41 samples and digitizes the AC voltage reference signal from the zero phase point thereof for an integral period, to obtain the calibration parameter of the second conversion channel CH2 of the first dual-channel ADC 41.

[0056] S80, the calibration parameter of the second conversion channel CH2 of the first dual-channel ADC 41 is stored in the storage unit of the digital engine 7.

[0057] The method further comprises a step S41 occurring after step S80: when the digital engine 7 judges that the phase-locked unit 6 locks the zero phase point of the to-be-measured first voltage signal in the case where the switch branch is in the first switch state, the calibration parameter of the second conversion channel CH2 of the first dual-channel ADC 41 stored in the storage unit is called to correct the data obtained after the second conversion channel CH2 of the first dual-channel ADC 41 samples and digitizes the first voltage signal from the zero phase point thereof for N integral periods, to obtain a corrected measurement value of the first voltage signal.

[0058] The method can further comprise a step S71 occurring after step S60: when the digital engine 7 judges that the phase-locked unit 6 locks the zero phase point of the first voltage signal to be measured, the calibration parameters of the first conversion channel CH1 of the first dual-channel ADC 41 stored in the storage unit are called to correct the data obtained after sampling and analog-digital conversion of the first voltage signal from its zero phase point for N periods, to obtain the corrected measurement value of the first voltage signal, in the case that the switch branch is in the second switch state.

[0059] In particular, Figure 5 The first timing in the exemplary calibration-measurement timing diagram provided (the horizontal axis of which represents time t, and the timings below are similar) shows that, in the case that the PJVS is used as the standard signal source 1 to generate a staircase quantum voltage as an alternating voltage reference signal, after the phase-locked unit 6 of the digital measurement system 100 locks the zero phase point of the staircase quantum voltage in step S40, the digital engine 7 of the digital measurement system 100 performs linear fitting on the data obtained after sampling and analog-digital conversion of the staircase quantum voltage for an integral period from its zero phase point for the first conversion channel CH1 of the first dual-channel ADC 41, and then, through steps 50, 60, in step S71, the calibration parameters of the first conversion channel CH1 of the first dual-channel ADC 41 stored in the storage unit are called to correct the data obtained after sampling and analog-digital conversion of the first voltage signal to be measured for a multiple period from its zero phase point, to obtain the corrected measurement value of the first voltage signal.

[0060] Correspondingly, Figure 5 The second timing in the exemplary calibration-measurement timing diagram provided shows that, after the phase-locked unit 6 locks the zero phase point of the staircase quantum voltage in step S70, the digital engine 7 performs linear fitting on the data obtained after sampling and analog-digital conversion of the staircase quantum voltage for an integral period from its zero phase point for the second conversion channel CH2 of the first dual-channel ADC 41, and then, through steps 80, 30, in step S41, the calibration parameters of the second conversion channel CH2 of the first dual-channel ADC 41 stored in the storage unit are called to correct the data obtained after sampling and analog-digital conversion of the first voltage signal to be measured for a multiple period from its zero phase point, to obtain the corrected measurement value of the first voltage signal.

[0061] Thus, by accurate clock control and almost no delay switching state, the first conversion channel CH1 and the second conversion channel CH2 of the first dual-channel ADC 41 of the digital measurement system 100 can measure and correct the to-be-measured voltage signal immediately after the quantum voltage calibration generated by the standard signal source 1, so as to achieve the purpose of calibration and measurement at the same time (i.e., immediate calibration and immediate measurement).

[0062] Figure 5 The third and fourth time sequences in the provided exemplary calibration-measurement timing diagram further show the sampling time sequence of the first conversion channel CH1' and the second conversion channel CH2' of the second dual-channel ADC 42 on the staircase quantum voltage and the to-be-measured second voltage signal, which has a similar overall step sequence to the sampling of the first conversion channel CH1 and the second conversion channel CH2 of the first dual-channel ADC 41. By accurate clock control and almost no delay switching state, the first conversion channel CH1' and the second conversion channel CH2' of the second dual-channel ADC 42 of the digital measurement system 100 can measure and correct the to-be-measured voltage signal immediately after the quantum voltage calibration generated by the standard signal source 1, so as to achieve the purpose of calibration and measurement at the same time, and the specific process is not described here.

[0063] In Figure 5 In the embodiment shown, the whole period length of the staircase quantum voltage is equal to the time length of three times the period of the to-be-measured voltage signal, and the switching elements S1-S8 are also controlled to switch once according to three times the period of the to-be-measured voltage signal. In practice, the switching period of the switching elements S1-S8 can be adjusted according to the requirements of the calibration period by the data engine according to the preset time parameters.

[0064] It should be noted that in steps S40 and S70 of the calibration and measurement at the same time method of the digital measurement system 100 provided according to the embodiment of the present application, the least square method is used to perform linear regression analysis and linear fitting on the data after the analog-to-digital conversion of the alternating voltage reference signal, so as to obtain the calibration parameters of each conversion channel of the dual-channel ADC. If the equation of the fitted straight line is y = a*x + b, the formula for linear regression derivation is as follows:

[0065] where {y1, y2,..., y n} are the data values of the corresponding sampling points obtained after the first conversion channel of the dual-channel ADC performs whole period sampling on the alternating voltage reference signal and is subjected to analog-to-digital conversion, {x1, x2,..., x n} are the ideal data values corresponding to the sampling points of the alternating voltage reference signal, x avg and y avg are {x1， x2, ..., x n} and {y 1， y2, ..., y n}average value.

[0066] According to the above formulas (1-1) and (1-2), the data points (x1, y1), (x2, y2), ..., (x n ,y n ) can find the slope a and intercept b of the best fitting line by performing a straight line fitting. Specifically, select Figure 1 The first dual-channel ADC 41 shown in FIG is used as an example to illustrate the derivation process of calibration parameters for its first conversion channel CH1 and second conversion channel CH2. Assuming that PJVS is used as the standard signal source 1 to generate a step wave quantum voltage, in the first switching state of the switch branch, when the phase-locked unit 6 of the digital measurement system 100 locks the zero phase point of the AC quantum voltage signal, the digital engine 7 of the digital measurement system 100 performs a linear fit on the discrete data values ​​obtained by sampling the quantum voltage signal for a full period starting from the zero phase point (the sampling points are all controlled at the middle of each quantum voltage step) for the first conversion channel CH1 of the first dual-channel ADC 41. The fitting line expression is set to y=k*x+c. According to the above formulas (1-1) and (1-2), the calibration parameters k and c of the first conversion channel CH1 of the first dual-channel ADC 41 can be obtained.

[0067] Similarly, in the second switching state of the switch branch, when the phase-locked unit 6 of the digital measurement system 100 locks the zero-phase point of the AC quantum voltage signal, the digital engine 7 performs linear fitting on the discrete data values ​​obtained by sampling the quantum voltage signal for a full cycle starting from the zero-phase point (the sampling points are all controlled at the middle of each quantum voltage step) and converting it into the second conversion channel CH2 of the first dual-channel ADC 41. The fitting straight line expression is set to y=m*x+d. According to the above formulas (1-1) and (1-2), the calibration parameters m and d of the second conversion channel CH2 of the first dual-channel ADC 41 can be obtained.

[0068] As described above, the calibration parameters k and c of the first conversion channel CH1 and the calibration parameters m and d of the second conversion channel CH2 of the first dual-channel ADC 41 can be stored in the storage unit of the digital engine 7 and used to correct the measured values ​​of the voltages to be measured input to the first conversion channel CH1 and the second conversion channel CH2. Through the high-precision clock reference 5 and the delay-free switching of the switching elements, the purpose of immediate calibration and measurement is achieved.

[0069] The self-calibration digital measurement system 100 and the method of self-calibration and measurement provided by the application can produce the following beneficial effects: (1) the application can use a high-precision clock reference as the time-frequency reference of the digital measurement system, the generating device of the measured AC voltage signal and the standard signal source, and through the digital engine control of the measurement system, the self-calibration and self-measurement of the digital measurement system can be realized, which is more efficient in time and cost compared with separate calibration; (2) the application can use the mainstream AC current voltage reference on the market as the highest level standard device, which greatly improves the accuracy of calibration and measurement; (3) the self-calibration and measurement method adopted by the application can attenuate the noise in the measured AC signal through frequency multiplication sampling, reduce the influence of environmental factors on the calibration and measurement process, further improve the accuracy of calibration and measurement, and at the same time, expand the frequency range of the signal suitable for calibration and measurement by the high-level standard device such as quantum voltage reference.

[0070] Those skilled in the art can understand that the modules, units and algorithm steps of each example described in combination with the embodiments disclosed herein can be realized by electronic hardware or a combination of computer software and electronic hardware. Whether the functions are executed in hardware or software depends on the specific application and design constraints of the technical solution. Professionals can adopt different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of the application.

[0071] If the modules / units are realized in the form of software function units and sold or used as independent products, they can be stored in a computer readable storage medium. Based on this understanding, all or part of the processes in the above-mentioned embodiment methods can also be completed by a computer program instructing related hardware, and the computer program can be stored in a computer readable storage medium. When the processor executes the computer program, the steps of each distributed photovoltaic grid-connected device power quality detection method embodiment described above can be implemented. The computer program includes computer program code, which can be in the form of source code, object code, executable file or some intermediate form, etc. The computer readable medium can include any entity or device that can carry the computer program code, recording medium, U disk, mobile hard disk, magnetic disk, optical disk, computer memory, read-only memory, random access memory, electric carrier signal, telecommunication signal and software distribution medium, etc.

[0072] The above-described embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit the present application; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should be included in the protection scope of the present application.

Claims

1. A self-calibrating digital measurement system, comprising a standard signal source, an ADC conversion module, a switching circuit, a phase-locked unit (PLL), a digital engine, and a high-precision clock reference, wherein the standard signal source is connected to the ADC conversion module via the switching circuit, the ADC conversion module is connected to the PLL and the digital engine, and the digital engine is connected to the PLL and the high-precision clock reference; The standard signal source is used to generate an AC voltage reference signal, wherein the AC voltage reference signal is a signal having the same amplitude as the AC voltage signal to be measured and a period N times larger; the high-precision clock reference is used to provide the digital measurement system with the same time-frequency reference as the device generating the AC voltage signal to be measured, where N is an integer greater than or equal to 2; The switching circuit is used to control two different conversion channels in the ADC conversion module to alternately input the AC voltage reference signal and the AC voltage signal to be measured by switching the switch position. When the phase-locked unit locks the zero-phase point of the AC voltage reference signal, the digital engine performs linear fitting on the data obtained after sampling and analog-to-digital conversion of the AC voltage reference signal in the ADC conversion module for a full cycle starting from its zero-phase point, to obtain calibration parameters of the conversion channel where the AC voltage reference signal is currently located. When the phase-locked unit locks the zero-phase point of the AC voltage signal to be measured, the digital engine uses the calibration parameters of the conversion channel where the AC voltage signal to be measured is currently located to perform correction on the data obtained after sampling and analog-to-digital conversion of the AC voltage reference signal to be measured in the ADC conversion module for N times the cycle starting from its zero-phase point, to obtain a corrected measurement value of the AC voltage signal to be measured.

2. The digital measuring system according to claim 1, characterized in that The ADC conversion module is a dual-channel ADC, and the switch circuit is in a first switch state to connect the AC voltage reference signal to the first conversion channel of the dual-channel ADC, and to connect the AC voltage signal to be measured to the second conversion channel of the dual-channel ADC; When the switch circuit is in the second switch state, the AC voltage signal to be measured is connected to the first conversion channel of the dual-channel ADC, and the AC voltage reference signal is connected to the second conversion channel of the dual-channel ADC.

3. The digital measuring system according to claim 2, characterized in that: The ADC conversion module includes at least two dual-channel ADCs. The switch branches of the switch circuit match the number of conversion channels of the dual-channel ADCs. The two input ends of each switch branch are respectively used to receive the AC voltage reference signal and the AC voltage signal to be measured. The output end of each switch branch is connected to a corresponding conversion channel. Each switch branch includes a first switching state and a second switching state.

4. The digital measuring system according to any one of claims 1 to 3, characterized in that: The digital engine includes a data processing unit and a storage unit that are communicatively connected, and the data processing unit is respectively connected to the ADC conversion module, the phase-locked unit and the high-precision clock reference; The data processing unit is used for performing linear fitting and storing the obtained calibration parameters in the storage unit, and for calling the calibration parameters of the conversion channel where the AC voltage signal to be measured currently resides to correct the AC voltage signal to be measured.

5. The digital measuring system according to claim 2, characterized in that: The dual-channel ADC in the ADC conversion module is a 24-bit high-speed and high-precision ADC, and the high-precision clock reference is a clock with a stability of 10 -12 Rubidium atomic clock of the order of magnitude.

6. The digital measuring system according to claim 1, characterized in that The period of the AC voltage reference signal generated by the standard signal source is at least 5 times the period of the AC voltage signal to be measured.

7. The digital measuring system according to claim 1 or 6, characterized in that: The standard signal source is a programmable Josephson voltage standard, and the generated AC voltage reference signal is a step wave quantum voltage signal.

8. The digital measuring system according to claim 1 or 6, characterized in that: The standard signal source is a pulse-driven AC Josephson voltage standard, and the generated AC voltage reference signal is a sinusoidal quantum voltage signal.

9. The digital measuring system according to claim 4, characterized in that: It also includes a display device, which is connected to the data processing unit and is used to display the measured value, corrected measured value and correction amount of the AC signal to be measured.

10. A method for calibrating and measuring a digital measurement system, characterized in that: Based on the digital measurement system according to any one of claims 1 to 9, the calibration and measurement method comprises the following steps: During the current measurement, an AC voltage reference signal and an AC voltage signal to be measured are input into two different conversion channels of the ADC conversion module through a switching circuit; the AC voltage reference signal has the same amplitude as the AC voltage signal to be measured and has a period N times larger than that of the AC voltage signal to be measured, where N is an integer greater than or equal to 2; Determining the locking status of the phase-locked unit on the signals in two different conversion channels of the ADC conversion module; When the phase-locked unit locks the zero-phase point of the AC voltage reference signal, the digital engine performs linear fitting on data obtained after sampling and analog-to-digital conversion of the AC voltage reference signal in the ADC conversion module for a full cycle starting from the zero-phase point, to obtain calibration parameters of the conversion channel where the AC voltage reference signal is currently located; When the phase-locked unit locks the zero-phase point of the AC voltage signal to be measured, the digital engine uses the calibration parameters of the conversion channel where the AC voltage signal to be measured is currently located to perform correction on the data obtained after sampling and analog-to-digital conversion of the AC voltage signal to be measured in the ADC conversion module at N times the period starting from the zero-phase point, thereby obtaining a corrected measurement value of the AC voltage signal to be measured; After swapping the input signals of the two different conversion channels in the ADC conversion module through the switch circuit, the process jumps to the step of determining the locking status of the signals in the two different conversion channels in the ADC conversion module by the phase-locked unit, and enters the next measurement.

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