CN110873817A - Method for guaranteeing accuracy and stability of critical current measurement system - Google Patents
Method for guaranteeing accuracy and stability of critical current measurement system Download PDFInfo
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Abstract
The invention relates to the technical field of critical current measurement of low-temperature superconducting wires, in particular to a method for guaranteeing the accuracy and stability of a critical current measurement system, which comprises the following steps: firstly, the measuring instrument is periodically checked, and the use in a checking period is guaranteed. Second, the measurement subsystem is serviced indefinitely, mainly including 1) the sample current source: checking a sample current source to ensure stable and controllable output current; 2) a magnet system: the magnetic field is calibrated and the magnetic coil is checked irregularly, so that an accurate background magnetic field is provided; 3) testing the tool: and checking each current contact point in the sample rod, replacing a signal wire in the sample rod and ensuring the measurement precision of the sample rod. Thirdly, an internal standard sample is formulated, the standard sample is measured before starting up, and the measurement result is guaranteed to be within an error allowable range. Long-time test experiments show that: the method can ensure the accurate operation of the critical current measuring system and provide reliable guarantee for the critical current measurement.
Description
Technical Field
The invention relates to the technical field of critical current measurement of low-temperature superconducting wires, in particular to a method for guaranteeing the accuracy and stability of a critical current measurement system.
Background
Low temperature superconducting wire is currently the most widely used superconductor. The method has extremely wide application in the fields of nuclear Magnetic Resonance Imaging (MRI), nuclear magnetic resonance spectrometer (NMR), large particle accelerator, superconducting energy storage system (SMES), magnetic confinement nuclear fusion device (Tokamak) and the like.
The accuracy and stability of the critical current measurement system are the basis of critical current measurement, however, no clear technical method exists at present for how to guarantee the accuracy and stability of the critical current measurement system, and the invention provides a method for guaranteeing the accuracy and stability of the critical current measurement system. After the measurement system is upgraded and optimized, the accuracy of the measurement system can be verified according to the method; the measurement system can be periodically checked according to the method in long-term measurement, and the stability of the measurement system is guaranteed.
Disclosure of Invention
The invention aims to provide a method for guaranteeing the accuracy and stability of a critical current measuring system, so as to solve the problems in the background technology. The method for guaranteeing the accuracy and stability of the critical current measuring system solves the defect of the conventional method for guaranteeing the accuracy and stability of the critical current measuring system.
In order to achieve the purpose, the invention provides the following technical scheme:
the method for guaranteeing the accuracy and stability of the critical current measuring system divides the critical current measuring system into sub-modules, comprises a measuring instrument, a measuring background magnetic field, a measuring tool, a sample preparation module and a system upgrading module, and respectively checks the accuracy of each module or performs a comparison experiment, and comprises the following steps:
firstly, regularly checking a measuring instrument to ensure that the measuring instrument is used in a checking period;
secondly, performing unscheduled maintenance on the measurement subsystem, which mainly comprises:
1) sample current source: checking a sample current source to ensure stable and controllable output current;
2) a magnet system: the magnetic field is calibrated and the magnetic coil is checked irregularly, so that an accurate background magnetic field is provided;
3) testing the tool: checking each current contact point in the sample rod to be measured, and replacing a signal wire in the sample rod to ensure the measurement precision of the sample rod;
thirdly, an internal standard sample is formulated, the standard sample is measured before starting up, and the measurement result is guaranteed to be within an error allowable range.
Further, instrumental calibration of the system included the collection of sample current and magnetic field using a 2000 multimeter and shunt, and the collection of sample voltage using a 2182 nanovoltmeter.
Further, the background magnetic field accuracy determination guarantee comprises the following steps: firstly, a gauss meter is used for calibrating a magnetic field irregularly; and secondly, regularly checking the resistance of the coil of the magnet to ensure that the coil is not damaged, programming a remote control program of a magnet power supply, and automatically lifting the magnetic field to a set target field.
Further, the consistency of the sample rod tooling measurement comprises a comparison experiment between the sample rods, and the consistency of results between the sample rods is ensured by measuring and comparing samples.
Further, the standard sample preparation process comprises determining a plurality of test processes: 1) preparing a sample, namely selecting a proper balance weight according to different samples, ensuring that the sample is fastened on a sample framework and must not be damaged, and checking whether the sample on the framework is loosened or not and rewinding the loosened sample; 2) installing a sample on a sample rod, wherein a current contact point of the sample and the sample rod is required to be ensured to be in close contact when the sample is assembled so as to prevent test failure, and an operator is required to firstly inspect two end surfaces of a framework before installation so as to ensure brightness, flatness and no impurities; when the voltage signal wire is welded, the welding spot is as small as possible, however, false welding is prevented, the welding spot is clean, contact resistance is reduced as much as possible by cleaning sundries with alcohol after welding, after the sample is installed, contact potentials at two ends of the sample need to be measured, and the contact potential needs to be less than 0.01 mV.
Furthermore, the system upgrading adopts the integration of an integrated sample power supply and a measurement and acquisition system, and the automation degree of the system is improved.
Further, the system accuracy and stability verification method comprises the following steps: 1) performing a cross validation experiment with other laboratories every year, performing a cross comparison experiment of NbTi and Nb3Sn to verify the system, and passing the comparison result; 2) any accessory in the measuring system is upgraded or updated, and the comparison is measured again by using the comparison sample.
Further, after the system accuracy test is qualified, it is necessary to ensure that each subsequent measurement can maintain good accuracy, which is referred to as system stability verification, and the main method is as follows: 1) firstly measuring a comparison sample at each test starting, analyzing the measurement result of each comparison sample, and carrying out production test only if the measurement result of the comparison sample is within an error allowable range; 2) when the wires of the same type are measured in batch and obvious performance is found to be higher or lower, a group of comparison samples are repeatedly measured.
Compared with the prior art, the invention has the beneficial effects that: the method is suitable for the measurement conditions as follows: a critical current measuring system for low-temperature superconducting wire with magnetic field less than or equal to 12T, temperature of 4.22K and critical current (IC) < 2300A; the method fills the blank that no check guarantee method exists in the critical current measuring system, and low-temperature superconducting wire measuring personnel can guarantee the accuracy and stability of critical current measurement according to the method.
Drawings
FIG. 1 is a schematic diagram of a prior art critical current measurement system.
FIG. 2 is a diagram of a measurement interface of the measurement software developed autonomously in a Labview environment according to the present invention.
Fig. 3 is a front panel of the magnet power supply remote control program of the present invention.
FIG. 4 is a diagram of a power control interface of a sample of the IC (critical current) measurement system of the present invention.
FIG. 5 is a graph showing the measurement of 4 samples of the same international alignment according to the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Referring to fig. 1-5, the present invention provides a technical solution:
a first part: illustrating the principles and overall methodology of the invention
Principle one
The critical current measuring system is divided into submodules, and the submodules comprise a measuring instrument, a measuring background magnetic field, a measuring tool, a sample preparation module and system upgrading, and are used for respectively checking the accuracy of each module or performing a comparison experiment. The instrument and meter can be used in the checking period, and the relative standard uncertainty of the comparison experiment measurement result is ensured to be within 3%.
Second, complete method
1. Instrument and meter calibration
The critical current measuring system (figure 1) of the low-temperature superconducting wire comprises instruments and meters, wherein the instruments and meters comprise 2000 universal meters, shunts (for collecting sample current and magnetic fields), 2182 nanovoltmeters (for collecting sample voltage) and other measuring instruments are periodically checked to ensure the precision of the measuring instruments; and (5) carrying out accuracy guarantee experiment on the system tool upgrading measurement system.
Fig. 2 can reflect the main features of the technical solution of the present invention, such as that Current can determine whether the sample Current is normally loaded; the Field can ensure the accuracy of magnetic Field output, signals in CH2 and CH3 sample rods and the accuracy and stability of critical current (IC) measurement by ensuring the accuracy of each physical quantity, and the diagram is independently developed measurement software in a Labview environment, integrates measurement and control, greatly improves the measurement efficiency, avoids personnel misoperation and ensures the measurement accuracy.
2. Background magnetic field system accuracy determination guarantee
Firstly, a gauss meter is used for calibrating a magnetic field irregularly; and secondly, periodically checking the resistance of the coil of the magnet to ensure that the coil is not damaged, programming a magnet power supply remote control program (figure 3) and automatically lifting the magnetic field to a set target field.
3. Consistency of sample rod tooling measurement
And measuring the comparison experiment among the sample rods, and ensuring the consistency of results among a plurality of sample rods by measuring comparison samples.
4. Standard sample preparation process
Improper operation can also influence the measurement result, and in order to eliminate the influence brought by personnel operation difference, a plurality of inspection processes are determined while specifying detailed operation processes for some important operation links, such as sample preparation and sample installation processes: 1) and (3) preparing a sample, selecting a proper balance weight according to different samples, and ensuring that the sample is fastened on a sample framework and must not be damaged. The wound sample is required to be tested whether the sample on the framework is loosened or not, and the loosened sample is required to be wound again; 2) when the sample is mounted on the sample rod, the sample must be assembled while ensuring that the sample is in intimate contact with the current contact point of the sample rod to prevent test failure. Before installation, operators must firstly check two end faces of the framework to ensure brightness, flatness and no impurities; when the voltage signal wire is welded, the welding spot is as small as possible, but to prevent false welding, the welding spot is clean, and after welding, impurities are cleaned by alcohol to reduce contact resistance as much as possible. After the sample is mounted, the contact potential at both ends of the sample needs to be measured, and the contact potential must be less than 0.01 mV.
5. System upgrade
In order to avoid the misoperation of personnel, the integrated sample power supply control (figure 4) is integrated with the measurement and collection system, so that the automation degree of the system is improved.
6. System accuracy and stability verification method
On the basis of guaranteeing the accuracy of each link of the system, the accuracy of the whole measuring system is also verified, and the existing method comprises the following steps: 1) performing a cross validation experiment with other laboratories every year, performing a cross comparison experiment of NbTi and Nb3Sn to verify the system, and passing the comparison result; 2) upgrading or updating any accessory in the measurement system, such as a flow diverter, a sample rod, a differently designed sample skeleton, etc., requires re-measuring the alignment with the alignment sample.
After the system accuracy test is qualified, the good accuracy of each subsequent measurement must be ensured, which is called as system stability verification, and the main method is as follows: 1) firstly measuring a comparison sample at each test starting, analyzing the measurement result of each comparison sample, and carrying out production test only if the measurement result of the comparison sample is within an error allowable range; 2) when the wires of the same type are measured in batch and obvious performance is found to be higher or lower, a group of comparison samples are repeatedly measured.
A second part: feasibility of the method in conjunction with specific case demonstration
First, system tool upgrading
When critical current is measured, upgrading the system according to measurement requirements, including upgrading a shunt, and upgrading the shunt of 75mV _1000A and 75mV _1000A into a shunt of 75mV _2500A, so that all samples with critical current less than 2300A can be measured, and the accuracy of the system is verified by comparing the measurement of the samples after upgrading; the single-channel sample rod is upgraded into a double-channel measurement sample rod, and the change of the groove shape of the sample skeleton needs to be compared to measure the sample.
Second, standard sample preparation and measurement
By formulating sample preparation and measurement specification requirements, the sample is ensured to be wound without looseness, whether a welding sample is completely wrapped on a copper ring by a solder is visually observed during sample welding, the copper ring is ensured to be in good contact with a framework copper ring (current is good), whether contact potential is less than 0.01mV is checked after a potential line is welded, and a magnetic field is observed during measurement to ensure that a provided background magnetic field must be accurate. The specification check items are as follows:
and a third part: the system accuracy and stability effectiveness by adopting the method are proved
Firstly, proving the accuracy and effectiveness
Taking 4 international comparison samples to perform a cross comparison experiment, the measurement curve of the experiment is good (fig. 5), and the measurement results are as follows:
the relative standard uncertainty of the measurement result is less than 3%, the requirement is met, and the cross comparison experiment is passed, and the ITER certification is passed.
Secondly, proving the validity of stability
After the system accuracy test is qualified, the good accuracy of each subsequent measurement must be maintained, which is called system stability verification, an internal comparison sample is set, the comparison sample is measured during each measurement, and the measurement result is as follows:
the relative standard uncertainty of the measurement result is 0.09% and less than 3%, the repeatability is good, and the requirement is met.
The fourth part: example demonstration
Example 1: experiment of system accuracy
1. The shunt is replaced: after the system is upgraded according to the requirement, the shunt of 75mV _1000A and 50mV _1000A is upgraded into the shunt of 75mV _2500A, and the measurement results are as follows:
the relative standard uncertainty of the measurement result is less than 3%, and the requirement is met.
2. Sample skeleton variation: according to the change of sample size, need change the sample skeleton, change little skeleton into the diameter skeleton slightly bigger, measure experiment comparison result as follows:
the relative standard uncertainty of the measurement result is less than 3%, and the requirement is met.
3. Upgrading the sample rod tool: in order to improve measurement efficiency, under the condition that the background magnetic field is evenly removed to allow, upgrade single channel measurement sample pole frock and upgrade to the binary channels measurement sample pole, choose for use inside standard sample to compare as the trade sample and measure the experiment, the measuring result is as follows:
the relative standard uncertainty of the measurement result is less than 3%, and the requirement is met.
4. Standard sample preparation process experiment
After the sample preparation process is standardized, 4 samples are selected and used for carrying out sample preparation measurement repeatability experiments by two experimenters, and the results are as follows:
the relative standard uncertainty of the measurement result is less than 3%, and the requirement is met.
Example 2: experiment of System stability
One sample 1012E-12210E-1P measured before is selected as an internal standard sample, and repeated measurement is performed on the standard sample every time the computer is started, wherein the measurement results are as follows:
the experimental mean value is 367.6, the experimental standard deviation is 0.8, the experimental standard uncertainty is 0.25, the relative synthesis standard uncertainty is 0.07%, and the COV is 0.2%, which meet the standard requirements.
Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.
Claims (8)
1. The method for guaranteeing the accuracy and stability of the critical current measurement system is characterized in that the critical current measurement system is divided into submodules, the submodules comprise a measuring instrument, a measuring background magnetic field, a measuring tool, a sample preparation module and system upgrading, the accuracy of each module is checked or a comparison experiment is carried out respectively, and the method comprises the following steps:
firstly, regularly checking a measuring instrument to ensure that the measuring instrument is used in a checking period;
secondly, performing unscheduled maintenance on the measurement subsystem, which mainly comprises:
1) sample current source: checking a sample current source to ensure stable and controllable output current;
2) a magnet system: the magnetic field is calibrated and the magnetic coil is checked irregularly, so that an accurate background magnetic field is provided;
3) testing the tool: checking each current contact point in the sample rod to be measured, and replacing a signal wire in the sample rod to ensure the measurement precision of the sample rod;
thirdly, an internal standard sample is formulated, the standard sample is measured before starting up, and the measurement result is guaranteed to be within an error allowable range.
2. The method of claim 1, wherein the method comprises: the instrument and meter calibration of the system comprises the steps of collecting the current and the magnetic field of a sample by adopting a 2000 multimeter and a shunt, and collecting the voltage of the sample by adopting a 2182 nanovolt meter.
3. The method of claim 1, wherein the method comprises: the background magnetic field accuracy determination guarantee comprises the following steps: firstly, a gauss meter is used for calibrating a magnetic field irregularly; and secondly, regularly checking the resistance of the coil of the magnet to ensure that the coil is not damaged, programming a remote control program of a magnet power supply, and automatically lifting the magnetic field to a set target field.
4. The method of claim 1, wherein the method comprises: the sample rod tool is used for measuring consistency, and comprises a comparison experiment for measuring sample rods, and the consistency of results among a plurality of sample rods is ensured by measuring comparison samples.
5. The method of claim 1, wherein the method comprises: the standard sample preparation process comprises the following steps of determining a plurality of test processes: 1) preparing a sample, namely selecting a proper balance weight according to different samples, ensuring that the sample is fastened on a sample framework and must not be damaged, and checking whether the sample on the framework is loosened or not and rewinding the loosened sample; 2) installing a sample on a sample rod, wherein a current contact point of the sample and the sample rod is required to be ensured to be in close contact when the sample is assembled so as to prevent test failure, and an operator is required to firstly inspect two end surfaces of a framework before installation so as to ensure brightness, flatness and no impurities; when the voltage signal wire is welded, the welding spot is as small as possible, however, false welding is prevented, the welding spot is clean, contact resistance is reduced as much as possible by cleaning sundries with alcohol after welding, after the sample is installed, contact potentials at two ends of the sample need to be measured, and the contact potential needs to be less than 0.01 mV.
6. The method of claim 1, wherein the method comprises: the system upgrading adopts the integration of an integrated sample power supply and a measurement acquisition system, and the automation degree of the system is improved.
7. The method of claim 1, wherein the method comprises: the system accuracy and stability verification method comprises the following steps: 1) performing a cross validation experiment with other laboratories every year, performing a cross comparison experiment of NbTi and Nb3Sn to verify the system, and passing the comparison result; 2) any accessory in the measuring system is upgraded or updated, and the comparison is measured again by using the comparison sample.
8. The method of claim 7, wherein the method further comprises: after the system accuracy test is qualified, it is necessary to ensure that the accuracy of each subsequent measurement can be maintained well, which is referred to as system stability verification, and the main method is as follows: 1) firstly measuring a comparison sample at each test starting, analyzing the measurement result of each comparison sample, and carrying out production test only if the measurement result of the comparison sample is within an error allowable range; 2) when the wires of the same type are measured in batch and obvious performance is found to be higher or lower, a group of comparison samples are repeatedly measured.
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Cited By (2)
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Application publication date: 20200310 |