Online refractometer calibration method

Abstract

The invention discloses an online refractometer calibration method, which comprises a standard condition calibration mode and a working condition calibration mode, and calibration items comprise temperature indication error, refractive index or concentration indication error, repeatability and stability. The standard condition calibration mode is used for calibration under the conditions of specific refractive index or concentration and specified temperature, and is suitable for a detachable instrument or the condition that the requirement for measurement accuracy is high and the instrument can be used as a reference instrument; the working condition calibration mode is used for calibration under the working medium and working condition, and is suitable for instruments which cannot be detached or the condition that working condition parameters of the instruments need to be calibrated. A standard condition calibration mode can adopt a fixed online refractometer calibration device, and dynamic calibration under a specified temperature condition is realized through a constant-temperature liquid storage tank and a circulating pipeline in the device; the working condition calibration mode can adopt a mobile online refractometer calibration device which is connected with a working condition pipeline provided with a calibrated online refractometer to dynamically calibrate the calibrated online refractometer on a user site under the working condition.

Description

Technical Field

[0001] The invention relates to the field of metrological calibration and instrument process verification, and in particular to an online refractometer calibration method. Background Art

[0002] Refractive index (also known as refractive index or refractive index) is a specific intrinsic property of a substance and changes according to temperature and wavelength. For pure substances, the physical property of refractive index can be used to identify and distinguish samples; for binary mixtures (such as solutes dissolved in solvents), the refractive index can be used to measure concentration (common ones are Brix, which characterizes the concentration of sucrose aqueous solution, and salinity, which characterizes the concentration of sodium chloride aqueous solution); for binary or multicomponent mixtures with known composition ratios, quality control can also be performed by monitoring the refractive index. Online refractive index technology is a type of process analysis technology. Its basic application is to use the data stream provided by the online refractometer to realize process relative trend judgment and real-time monitoring. On this basis, combined with other data streams such as reference data from process variables and analytical laboratories for comprehensive data analysis, it can realize real-time monitoring of key quality attributes of products and associate them with key process parameters, and finally realize real-time release of product indicators. This helps to improve product quality, reduce production costs, improve production efficiency, reduce laboratory testing needs, and determine the timing of process improvement. The ultimate result is to reduce the risk and cost of product production.

[0003] Online refractometers are the core of implementing online refractometer technology. The quality of their performance and the accuracy of their values ​​are related to the effectiveness of subsequent data flows, which ultimately affects product production. Unlike laboratory refractometers, online refractometers are installed in an "in-line", "online" or "near-line" manner. Sample collection and analysis are completed "in situ" or "near in situ". The actual measurement results are often far from the measurement results of laboratory refractometers under reference conditions, resulting in the "reference data" measured by laboratory refractometers not being of reference value for samples under working conditions, thus affecting the actual effect of online refractometer technology. Therefore, the calibration of online refractometers cannot only use the calibration method of laboratory refractometers, but also requires the use of new calibration devices or calibration methods.

[0004] Therefore, an online refractometer calibration method is needed. Summary of the invention

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0006] An online refractometer calibration method is characterized in that: its calibration mode includes a standard condition calibration mode and an operating condition calibration mode.

[0007] For detachable online refractometers that have high requirements for measurement accuracy and can be used as reference instruments, the standard calibration method (S1) is applicable, including the following steps:

[0008] S101: Using water at a specified temperature to continuously flow on the surface of the measuring sensor of the calibrated online refractometer, so that the measuring sensor of the calibrated online refractometer remains stable at the specified temperature;

[0009] S102: Immerse the temperature sensor of the standard thermometer near the measuring sensor of the calibrated online refractometer, record the temperature measurement value of the standard thermometer as the temperature standard value after it stabilizes, and read the temperature measurement value of the calibrated online refractometer for comparison, the difference between the two is the temperature indication error of the calibrated online refractometer at the specified temperature; obtain the indication error data three times in a row, and take the arithmetic mean of the three data as the temperature indication error calibration result of the calibrated online refractometer at the specified temperature;

[0010] S103: changing different designated temperatures, repeating step S102, and obtaining the temperature indication error calibration results of the calibrated online refractometer at different designated temperatures;

[0011] S104: using a uniform liquid with a known specific refractive index or concentration to continuously flow on the surface of the measuring sensor of the calibrated online refractometer, and maintaining it at the same specified temperature as step S101, after the measured refractive index or concentration value of the calibrated online refractometer is stabilized, reading the measured refractive index or concentration value of the calibrated online refractometer and comparing it with the refractive index or concentration standard value of the liquid with the known specific refractive index or concentration, the difference between the two is the refractive index or concentration indication error data of the calibrated online refractometer at the specified temperature; continuously obtaining three indication error data, and taking the arithmetic mean of the three data as the calibration result of the refractive index or concentration indication error of the calibrated online refractometer at the specified temperature;

[0012] S105: replacing a different stable homogeneous liquid with a known specific refractive index or concentration, repeating step S104, and obtaining the indication error calibration results of other different refractive index or concentration measurement points of the calibrated online refractometer at the specified temperature;

[0013] S106: Select one of the stable homogeneous liquids with a known specific refractive index or concentration, repeat step S104, continuously obtain a set of no less than 6 refractive index or concentration measurement data of the calibrated online refractometer, and use the Bessel formula to calculate the standard deviation of the set of measurement data as the refractive index or concentration repeatability calibration result of the calibrated online refractometer;

[0014] S107: Select one of the stable homogeneous liquids with a known specific refractive index or concentration, repeat step S104, obtain the refractive index or concentration measurement data of the calibrated online refractometer every 15 minutes, and measure continuously for 1 hour, and take the ratio of the difference between the maximum and minimum values ​​of the obtained refractive index or concentration measurement data and the initial measurement value as the refractive index or concentration stability calibration result of the calibrated online refractometer;

[0015] S108: calibrating the online refractometer to be calibrated or correcting the temperature measurement value using one or more temperature indication error calibration results obtained in step S102 or S103 according to the calibration or data correction method in the manual of the online refractometer to be calibrated;

[0016] S109: calibrating the online refractometer to be calibrated or correcting the refractive index or concentration measurement value using one or more refractive index or concentration indication error calibration results obtained in step S104 or S105 according to the calibration or data correction method in the manual of the online refractometer to be calibrated;

[0017] For detachable online refractometers that do not require high measurement accuracy and are not used as reference instruments, the standard calibration method (S2) is applicable, including the following steps:

[0018] S201: Continuously flowing water at a specified temperature on the surfaces of the measuring sensors of the calibrated online refractometer and the reference online refractometer, so that the measuring sensors of the calibrated online refractometer and the reference online refractometer remain stable at the specified temperature;

[0019] S202: immerse the temperature sensor of the standard thermometer near the measuring sensor of the calibrated online refractometer, record the temperature measurement value of the standard thermometer as the temperature standard value after it stabilizes, and read the temperature measurement value of the calibrated online refractometer for comparison, the difference between the two is the temperature indication error of the calibrated online refractometer at the specified temperature; obtain the indication error data three times in a row, and take the arithmetic mean of the three data as the temperature indication error calibration result of the calibrated online refractometer at the specified temperature;

[0020] S203: changing different designated temperatures, repeating step S202, and obtaining the temperature indication error calibration results of the calibrated online refractometer at different designated temperatures;

[0021] S204: using a liquid with a stable refractive index or uniform concentration to continuously flow on the measuring sensor surfaces of the calibrated online refractometer and the reference online refractometer, and maintaining the liquid at the same designated temperature as step S201, after the refractive index or concentration measurement values ​​of the reference online refractometer and the calibrated online refractometer are stable, reading the refractive index or concentration measurement value of the reference online refractometer as the standard value, and reading the refractive index or concentration measurement value of the calibrated online refractometer for comparison, the difference between the two is the refractive index or concentration indication error data of the calibrated online refractometer at the designated temperature; acquiring the indication error data three times continuously, and taking the arithmetic mean of the three data as the refractive index or concentration indication error calibration result of the calibrated online refractometer at the designated temperature;

[0022] S205: replacing a different stable liquid with a uniform refractive index or concentration, and repeating step S204 to obtain the indication error calibration results of other different refractive index or concentration measurement points of the calibrated online refractometer at the specified temperature;

[0023] S206: Select one of the stable liquids with uniform refractive index or concentration, repeat step S204, continuously obtain a set of no less than 6 refractive index or concentration measurement data of the calibrated online refractometer, and calculate the standard deviation of the set of measurement data using the Bessel formula as the refractive index or concentration repeatability calibration result of the calibrated online refractometer;

[0024] S207: Select one of the stable liquids with uniform refractive index or concentration, repeat step S204, obtain the refractive index or concentration measurement data of the calibrated online refractometer every 15 minutes, and measure continuously for 1 hour, and take the ratio of the difference between the maximum and minimum values ​​of the refractive index or concentration measurement data and the initial measurement value as the calibration result of the refractive index or concentration stability of the calibrated online refractometer;

[0025] S208: Calibrate the online refractometer to be calibrated or correct the temperature measurement value using one or more temperature indication error calibration results obtained in step S202 or S203 according to the calibration or data correction method in the manual of the online refractometer to be calibrated;

[0026] S209: calibrating the online refractometer to be calibrated or correcting the refractive index or concentration measurement value using one or more refractive index or concentration indication error calibration results obtained in step S204 or S205 according to the calibration or data correction method in the manual of the online refractometer to be calibrated;

[0027] For online refractometers that cannot be disassembled or require working condition parameter calibration, the working condition calibration method (S3) is applicable, including the following steps:

[0028] S301: using an online refractometer calibrated by the standard condition calibration method (S1) as a reference online refractometer, and installing it on a working position of a mobile online refractometer calibration device containing a standard thermometer;

[0029] S302: connecting the mobile online refractometer calibration device to a working pipeline installed with the online refractometer to be calibrated through a bypass interface, so that the liquid working medium flows through the reference online refractometer and the online refractometer to be calibrated at the same time;

[0030] S303: After the temperature measurement value of the standard thermometer is stable, it is recorded as the temperature standard value, and the temperature measurement value of the calibrated online refractometer is read and compared with it. The difference between the two is the temperature indication error data of the calibrated online refractometer under the working condition; the temperature indication error data are obtained three times in succession, and the arithmetic mean of the three data is taken as the temperature indication error calibration result of the calibrated online refractometer under the working condition;

[0031] S304: after the refractive index or concentration measurement values ​​of the reference online refractometer and the calibrated online refractometer are stable, the refractive index or concentration measurement value of the reference online refractometer is read as the standard value, and the refractive index or concentration measurement value of the calibrated online refractometer is read for comparison, and the difference between the two is the refractive index or concentration indication error data of the calibrated online refractometer under the working medium and working conditions; three indication error data are obtained continuously, and the arithmetic mean of the three data is taken as the refractive index or concentration indication error calibration result of the calibrated online refractometer under the working medium and working conditions;

[0032] S305: Keeping the liquid working medium stable, continuously acquiring a set of no less than 6 refractive index or concentration measurement data of the calibrated online refractometer, and using the Bessel formula to calculate the standard deviation of the set of measurement data as the refractive index or concentration repeatability calibration result of the calibrated online refractometer;

[0033] S306: Keep the liquid working medium stable, obtain the refractive index or concentration measurement data of the calibrated online refractometer every 15 minutes, and measure continuously for 1 hour, and use the ratio of the difference between the maximum and minimum values ​​of the obtained refractive index or concentration measurement data and the initial measurement value as the refractive index or concentration stability calibration result of the calibrated online refractometer;

[0034] S307: Correcting the temperature measurement value of the calibrated online refractometer according to the correction method in the manual of the calibrated online refractometer using the temperature indication error calibration result obtained in step S303;

[0035] S308: According to the correction method in the manual of the calibrated online refractometer, the refractive index or concentration measurement value of the calibrated online refractometer is corrected using the refractive index or concentration indication error calibration result obtained in step S304.

[0036] Furthermore, the concentration refers to a concentration scale converted by refractive index, including sucrose concentration (Brix), fructose concentration, glucose concentration, sodium chloride concentration, calcium chloride concentration, ethanol concentration, urea concentration, ethylene glycol concentration, propylene glycol concentration, isopropanol concentration, polyvinyl alcohol concentration, hydrogen peroxide concentration, ammonia concentration, sodium hydroxide concentration, N-methylpyrrolidone concentration, and dimethylformamide concentration.

[0037] Preferably, in order to ensure metrological traceability, the homogeneous liquid with stable properties and known specific refractive index or concentration in the standard condition calibration method (S1) adopts a certified standard material with a corresponding refractive index or concentration scale, and the expanded uncertainty of the certified standard material should not be greater than 1 / 2 of the expected indication error of the refractive index or concentration of the calibrated online refractometer; if a certified standard material with a corresponding refractive index or concentration scale is not available, a homogeneous liquid with stable properties, whose refractive index or concentration value is determined by a desktop refractometer with a higher traceability level or is obtained by precise preparation of pure substances, can also be used, and the expanded uncertainty of the refractive index or concentration value should not be greater than 1 / 2 of the expected indication error of the refractive index or concentration of the calibrated online refractometer.

[0038] Preferably, in order to ensure metrological traceability, the reference online refractometer of the standard condition calibration method (S2) and the operating condition calibration method (S3) should be calibrated by the standard condition calibration method (S1), and its refractive index or concentration value should be traced back using a certified standard material of the corresponding refractive index or concentration scale, and the refractive index or concentration indication error should be corrected using the traceability result, and the expanded uncertainty of the correction value or correction factor should not be greater than 1 / 2 of the expected indication error of the refractive index or concentration of the calibrated online refractometer; if a certified standard material of the corresponding refractive index or concentration scale cannot be obtained, it can also be traced back to the refractive index or concentration value of a reliably quantified homogeneous liquid with stable properties, and the refractive index or concentration indication error should be corrected using the traceability result, and the expanded uncertainty of the correction value or correction factor should not be greater than 1 / 2 of the expected indication error of the refractive index or concentration of the calibrated online refractometer.

[0039] Preferably, to ensure metrological traceability, the temperature expansion uncertainty of the standard thermometer should be no greater than 1 / 3 of the expected indication error of the temperature of the calibrated online refractometer.

[0040] Preferably, during calibration using the standard condition calibration method, in order to achieve continuous flow of water at a specified temperature on the surface of the measuring sensor of the calibrated online refractometer or the reference online refractometer, a fixed online refractometer calibration device can be used. The calibration device is provided with working positions for the calibrated online refractometer and the reference online refractometer, a constant temperature liquid storage tank and a circulation pipeline, and the liquid medium can be dynamically circulated at a specified temperature. During calibration using the standard condition calibration method (S1), the calibration device is not provided with a reference online refractometer, and during calibration using the standard condition calibration method (S2), the calibration device is provided with a reference online refractometer.

[0041] Preferably, when a fixed online refractometer calibration device is used for standard condition calibration, since the refractive index is a parameter closely related to temperature, in order to ensure the accuracy of the calibration result of the refractive index or concentration indication error, the temperature error of the calibration device should be controlled within ±0.5°C of the target specified temperature, and the temperature fluctuation should not exceed 0.5°C / h; when it is necessary to calibrate an instrument with a refractive index nominal indication error not exceeding ±0.0002 or a concentration nominal indication error not exceeding ±0.1%, the temperature error of the calibration device should be controlled within ±0.2°C of the target specified temperature, and the temperature fluctuation should not exceed 0.2°C / h.

[0042] Preferably, the stable homogeneous liquid with a known specific refractive index or concentration in the standard calibration method (S1) and the stable homogeneous liquid with a refractive index or concentration in the standard calibration method (S2) include water of grade 2 or higher in GB / T 6682.

[0043] Preferably, the specified temperature includes 20°C.

[0044] Due to the adoption of the above technical solution, the present invention has the following technical advances compared with the prior art:

[0045] (1) It includes two methods: standard condition calibration and operating condition calibration. The standard condition calibration method is suitable for detachable instruments, or when the measurement accuracy is high and the instrument can be used as a reference instrument; the operating condition calibration method is suitable for instruments that cannot be disassembled, or when the instrument needs to be corrected for operating condition parameters.

[0046] (2) Standard condition calibration can calibrate the instrument being calibrated, correct the built-in measurement parameters of the instrument being calibrated, and reduce the indication error of the instrument being calibrated; working condition calibration is not used to calibrate the built-in measurement parameters of the instrument being calibrated, but to obtain the measurement error of the instrument being calibrated for the actual working medium under working conditions, correct process measurement data, and guide enterprise production.

[0047] (3) A mobile online refractometer calibration device is used to achieve dynamic calibration of the online refractometer under working conditions at the user's site. There is no need to disassemble the online refractometer and then send it to a metrology and testing agency, thus avoiding data deviation caused by factors such as temperature and flow of the liquid medium in offline static calibration. At the same time, it can better meet the user's on-site online calibration needs. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 It is a schematic diagram of the calibration process of the standard condition calibration method (S1) of the present invention;

[0049] Figure 2 Schematic diagram of the calibration process of the standard condition calibration method (S2) of the present invention;

[0050] Figure 3 It is a schematic diagram of the calibration process of the working condition calibration method (S3) of the present invention;

[0051] Figure 4 This is a calibration flow chart of the present invention. DETAILED DESCRIPTION

[0052] The following embodiments may help those skilled in the art to more fully understand the present invention, but shall not limit the present invention in any way.

[0053] An online refractometer calibration method includes a standard condition calibration method and a working condition calibration method.

[0054] For detachable online refractometers that have high requirements for measurement accuracy and can be used as reference instruments, the standard calibration method (S1) is applicable, including the following steps:

[0055] S101 (Preparation): Install the calibrated online refractometer on the working position of a fixed online refractometer calibration device, inject water into the liquid storage tank of the calibration device, set the control temperature of the calibration device to 20°C, start the circulation, allow water to continuously flow through the measuring sensor surface of the calibrated online refractometer, and gradually keep the temperature constant at 20°C.

[0056] S102 (calibration of temperature indication error): immerse the temperature sensor of the standard thermometer near the measuring sensor of the calibrated online refractometer, record the temperature measurement value of the standard thermometer as the temperature standard value after it stabilizes, and read the temperature measurement value of the calibrated online refractometer for comparison, the difference between the two is the temperature indication error of the calibrated online refractometer at 20°C; obtain the indication error data three times in succession, and take the arithmetic mean of the three data as the temperature indication error calibration result of the calibrated online refractometer at 20°C;

[0057] S103 (calibration of temperature indication error): setting the control temperature of the calibration device to 30°C, repeating step S102, and obtaining the temperature indication error calibration result of the calibrated online refractometer at 30°C. Similarly, the temperature indication error calibration results at other temperatures can also be obtained;

[0058] S104 (calibration of refractive index indication error): inject a certified standard substance of pure water refractive index into the liquid storage tank of the calibration device, set the control temperature of the calibration device to 20°C, start the cycle, and after the refractive index measurement value of the calibrated online refractometer is stabilized, read the refractive index measurement value of the calibrated online refractometer and compare it with the refractive index standard value of the certified standard substance of pure water refractive index, and the difference between the two is the refractive index indication error data of the calibrated online refractometer at 20°C; obtain the indication error data three times in succession, and take the arithmetic mean of the three data as the calibration result of the refractive index indication error of the calibrated online refractometer at 20°C;

[0059] S105 (calibration of refractive index indication error): replace the certified standard material of pure water refractive index with other stable homogeneous liquids with known specific refractive index, such as certified standard material of isooctane liquid refractive index, repeat step S104, and obtain the indication error calibration results of other different refractive index measurement points of the calibrated online refractometer at 20°C;

[0060] S106 (calibration of refractive index repeatability): select one of the stable homogeneous liquids with a known specific refractive index, such as a certified standard material of pure water refractive index, repeat step S104, continuously obtain a group of no less than 6 refractive index measurement data of the calibrated online refractometer, calculate the standard deviation of the group of measurement data using the Bessel formula, and use it as the refractive index repeatability calibration result of the calibrated online refractometer;

[0061] S107 (calibration of refractive index stability): select one of the stable homogeneous liquids with a known specific refractive index, such as a certified standard substance of pure water refractive index, repeat step S104, obtain the refractive index measurement data of the calibrated online refractometer every 15 minutes, and measure continuously for 1 hour, and take the ratio of the difference between the maximum and minimum values ​​of the obtained refractive index measurement data and the initial measurement value as the refractive index stability calibration result of the calibrated online refractometer;

[0062] S108 (calibration or data correction of the calibrated online refractometer): calibrate the calibrated online refractometer or correct the temperature measurement value according to the calibration or data correction method in the manual of the calibrated online refractometer and use one or more temperature indication error calibration results obtained in step S102 or S103;

[0063] S109 (calibration or data correction of the calibrated online refractometer): calibrate the calibrated online refractometer or correct the refractive index measurement value according to the calibration or data correction method in the manual of the calibrated online refractometer and use one or more refractive index indication error calibration results obtained in step S104 or S105;

[0064] For detachable online refractometers that do not require high measurement accuracy and are not used as reference instruments, the standard calibration method (S2) is applicable, including the following steps:

[0065] S201 (Preparation): Install the calibrated online refractometer on the working position of a fixed online refractometer calibration device, inject water into the liquid storage tank of the calibration device, set the control temperature of the calibration device to 20°C, start the circulation, let the water continuously flow through the measuring sensor surfaces of the calibrated online refractometer and the reference online refractometer, and gradually keep the temperature constant at 20°C.

[0066] S202 (calibration of temperature indication error): immerse the temperature sensor of the standard thermometer near the measuring sensor of the calibrated online refractometer, record the temperature measurement value of the standard thermometer as the temperature standard value after it stabilizes, and read the temperature measurement value of the calibrated online refractometer for comparison, the difference between the two is the temperature indication error of the calibrated online refractometer at 20°C; obtain the indication error data three times in a row, and take the arithmetic mean of the three data as the temperature indication error calibration result of the calibrated online refractometer at 20°C;

[0067] S203 (calibration of temperature indication error): setting the control temperature of the calibration device to 30°C, repeating step S202, and obtaining the temperature indication error calibration result of the calibrated online refractometer at 30°C. Similarly, the temperature indication error calibration results at other temperatures can also be obtained;

[0068] S204 (calibration of refractive index indication error): set the control temperature of the calibration device to 20°C, keep the water in the calibration device at a constant temperature of 20°C, and after the refractive index measurement values ​​of the reference online refractometer and the calibrated online refractometer are stable, read the refractive index measurement value of the reference online refractometer as the standard value, and read the refractive index measurement value of the calibrated online refractometer for comparison, the difference between the two is the refractive index indication error data of the calibrated online refractometer at 20°C; obtain the indication error data three times in succession, and take the arithmetic mean of the three data as the calibration result of the refractive index indication error of the calibrated online refractometer at 20°C;

[0069] S205 (calibration of refractive index indication error): replace other liquids with different refractive indexes, such as isooctane refractive index liquid, repeat step S204, and obtain indication error calibration results of other different refractive index measurement points of the calibrated online refractometer at 20°C;

[0070] S206 (calibration of refractive index repeatability): when performing step S204, continuously obtain a set of no less than 6 refractive index measurement data of the calibrated online refractometer, and use the Bessel formula to calculate the standard deviation of the set of measurement data as the refractive index repeatability calibration result of the calibrated online refractometer;

[0071] S207 (calibration of refractive index stability): when performing step S204, the refractive index measurement data of the calibrated online refractometer is obtained every 15 minutes, and the measurement is continuously performed for 1 hour, and the ratio of the difference between the maximum and minimum values ​​of the obtained refractive index measurement data and the initial measurement value is used as the refractive index stability calibration result of the calibrated online refractometer;

[0072] S208 (calibration or data correction of the calibrated online refractometer): calibrate the calibrated online refractometer or correct the temperature measurement value according to the calibration or data correction method in the manual of the calibrated online refractometer and use one or more temperature indication error calibration results obtained in step S202 or S203;

[0073] S209 (calibration or data correction of the calibrated online refractometer): according to the calibration or data correction method in the manual of the calibrated online refractometer, use one or more refractive index indication error calibration results obtained in step S204 or S205 to calibrate the calibrated online refractometer or correct the refractive index measurement value.

[0074] For online refractometers that cannot be disassembled or require working condition parameter calibration, the working condition calibration method (S3) is applicable, including the following steps:

[0075] S301 (preparation): using an online refractometer calibrated by the standard condition calibration method (S1) as a reference online refractometer, and installing it on a working position of a mobile online refractometer calibration device containing a standard thermometer;

[0076] S302 (preparation): connecting the above-mentioned mobile online refractometer calibration device to the working pipeline installed with the online refractometer to be calibrated through the bypass interface, so that the liquid working medium flows through the reference online refractometer and the online refractometer to be calibrated at the same time;

[0077] S303 (calibration of temperature indication error): after the temperature measurement value of the standard thermometer is stabilized, it is recorded as the temperature standard value, and the temperature measurement value of the calibrated online refractometer is read and compared with it. The difference between the two is the temperature indication error data of the calibrated online refractometer under the working condition; the temperature indication error data is obtained three times continuously, and the arithmetic mean of the three data is taken as the temperature indication error calibration result of the calibrated online refractometer under the working condition;

[0078] S304 (calibration of refractive index or concentration indication error): after the refractive index or concentration measurement values ​​of the reference online refractometer and the calibrated online refractometer are stable, read the refractive index or concentration measurement value of the reference online refractometer as the standard value, and read the refractive index or concentration measurement value of the calibrated online refractometer for comparison, the difference between the two is the refractive index or concentration indication error data of the calibrated online refractometer under the working medium and working conditions; obtain the indication error data three times in succession, and take the arithmetic mean of the three data as the calibration result of the refractive index or concentration indication error of the calibrated online refractometer under the working medium and working conditions;

[0079] S305 (calibration of refractive index or concentration repeatability): Keep the liquid working medium stable, continuously obtain a set of no less than 6 refractive index or concentration measurement data of the calibrated online refractometer, and use the Bessel formula to calculate the standard deviation of the set of measurement data as the refractive index or concentration repeatability calibration result of the calibrated online refractometer;

[0080] S306 (calibration of refractive index or concentration stability): keep the liquid working medium stable, obtain the refractive index or concentration measurement data of the calibrated online refractometer every 15 minutes, and measure continuously for 1 hour, and take the ratio of the difference between the maximum and minimum values ​​of the obtained refractive index or concentration measurement data and the initial measurement value as the calibration result of the refractive index or concentration stability of the calibrated online refractometer;

[0081] S307 (data correction of the calibrated online refractometer): according to the correction method in the manual of the calibrated online refractometer, the temperature measurement value of the calibrated online refractometer is corrected using the temperature indication error calibration result obtained in step S303;

[0082] S308 (data correction of the calibrated online refractometer): according to the correction method in the manual of the calibrated online refractometer, the refractive index or concentration measurement value of the calibrated online refractometer is corrected using the refractive index or concentration indication error calibration result obtained in step S304.

[0083] In one embodiment of the present invention, the concentration refers to a concentration scale converted by refractive index, including sucrose concentration (Brix), fructose concentration, glucose concentration, sodium chloride concentration, calcium chloride concentration, ethanol concentration, urea concentration, ethylene glycol concentration, propylene glycol concentration, isopropanol concentration, polyvinyl alcohol concentration, hydrogen peroxide concentration, ammonia concentration, sodium hydroxide concentration, N-methylpyrrolidone concentration, and dimethylformamide concentration.

[0084] In one embodiment of the present invention, in order to ensure metrological traceability, the homogeneous liquid with stable properties and known specific refractive index or concentration in the standard condition calibration method (S1) adopts a certified standard material with a corresponding refractive index or concentration scale, and the expanded uncertainty of the certified standard material should not be greater than 1 / 2 of the expected indication error of the refractive index or concentration of the calibrated online refractometer; if a certified standard material with a corresponding refractive index or concentration scale is not available, a homogeneous liquid with stable properties, whose refractive index or concentration value is determined by a desktop refractometer with a higher traceability level or is obtained by precise preparation of pure substances, can also be used, and the expanded uncertainty of the refractive index or concentration value should not be greater than 1 / 2 of the expected indication error of the refractive index or concentration of the calibrated online refractometer.

[0085] In one embodiment of the present invention, in order to ensure metrological traceability, the reference online refractometer of the standard condition calibration method (S2) and the working condition calibration method (S3) should be calibrated by the standard condition calibration method (S1), and its refractive index or concentration value should be traced back using a certified standard material of the corresponding refractive index or concentration scale, and the refractive index or concentration indication error should be corrected using the traceability result, and the expanded uncertainty of the correction value or correction factor should not be greater than 1 / 2 of the expected indication error of the refractive index or concentration of the calibrated online refractometer; if a certified standard material of the corresponding refractive index or concentration scale cannot be obtained, it can also be traced back to the refractive index or concentration value of a reliably quantified homogeneous liquid with stable properties, and the refractive index or concentration indication error should be corrected using the traceability result, and the expanded uncertainty of the correction value or correction factor should not be greater than 1 / 2 of the expected indication error of the refractive index or concentration of the calibrated online refractometer.

[0086] In one embodiment of the present invention, in order to ensure metrological traceability, the temperature expansion uncertainty of the standard thermometer should not be greater than 1 / 3 of the expected indication error of the temperature of the calibrated online refractometer.

[0087] In one embodiment of the present invention, during the standard condition calibration method, in order to achieve continuous flow of water at a specified temperature on the surface of the measuring sensor of the calibrated online refractometer or the reference online refractometer, a fixed online refractometer calibration device is used. The calibration device is provided with working positions for the calibrated online refractometer and the reference online refractometer, a constant temperature liquid storage tank and a circulation pipeline, and the liquid medium can be dynamically circulated at a specified temperature; during the standard condition calibration method (S1), the calibration device is not provided with a reference online refractometer, and during the standard condition calibration method (S2), the calibration device is provided with a reference online refractometer.

[0088] In one embodiment of the present invention, when a fixed online refractometer calibration device is used for standard condition calibration, since the refractive index is a parameter closely related to temperature, in order to ensure the accuracy of the calibration result of the refractive index indication error, the temperature error of the calibration device should be controlled within ±0.5°C of the target specified temperature, and the temperature fluctuation should not exceed 0.5°C / h; when it is necessary to calibrate an instrument with a refractive index nominal indication error not exceeding ±0.0002 or a concentration nominal indication error not exceeding ±0.1%, the temperature error of the calibration device should be controlled within ±0.2°C of the target specified temperature, and the temperature fluctuation should not exceed 0.2°C / h.

[0089] In one embodiment of the present invention, in step S302, when the mobile online refractometer calibration device is connected to the working pipeline installed with the calibrated online refractometer through the bypass interface, the reference online refractometer and the calibrated online refractometer are connected to the working pipeline in parallel.

[0090] See also Figure 4 , select the appropriate calibration method according to the situation of the calibrated online refractometer and user needs. If the calibrated online refractometer is detachable and has high requirements for measurement accuracy and can be used as a reference instrument, the standard calibration method (S1) is used. If the calibrated online refractometer is detachable, but has low requirements for measurement accuracy and is not used as a reference instrument, the standard calibration method (S2) is used. If the calibrated online refractometer cannot be disassembled or requires working condition parameter calibration, the working condition calibration method (S3) is used. The calibration items include temperature indication error, refractive index or concentration indication error, refractive index or concentration repeatability, and refractive index or concentration stability.

[0091] The standard condition calibration method is calibrated under specific refractive index or concentration and specified temperature conditions. A fixed online refractometer calibration device can be used to achieve dynamic calibration under specified temperature conditions through a constant temperature liquid storage tank and a circulating pipe in the device. The temperature indication error of the calibrated online refractometer is calibrated with the temperature measurement value of the standard thermometer as the standard value, and the refractive index or concentration indication error, repeatability, and stability of the calibrated online refractometer are calibrated with the certified value of the refractive index or concentration certified standard material, or the refractive index or concentration value of a stable homogeneous liquid whose refractive index or concentration value is determined by a desktop refractometer with a higher traceability level, or obtained by precise preparation of pure substances, or the refractive index or concentration measurement value of the online refractometer as the reference value. Finally, the calibrated online refractometer is calibrated according to the calibration results, or the refractive index or concentration and temperature measurement values ​​of the calibrated online refractometer are corrected.

[0092] The working condition calibration method is calibrated under the working medium and working conditions. A mobile online refractometer calibration device can be used. The online refractometer calibrated by the standard condition calibration method (S1) is first installed as a reference online refractometer on a working position of a mobile online refractometer calibration device containing a standard thermometer. The calibration device is then connected to the working condition pipeline installed with the calibrated online refractometer through a bypass interface. The temperature measurement value of the standard thermometer is used as the standard value to calibrate the temperature indication error of the calibrated online refractometer. The refractive index or concentration measurement value of the reference online refractometer is used as the standard value to calibrate the refractive index or concentration indication error, repeatability and stability of the calibrated online refractometer. Finally, the refractive index or concentration and temperature measurement value of the calibrated online refractometer are corrected according to the calibration results.

[0093] The above generally describes the present invention in detail, but it is obvious to a person skilled in the art that some modifications or improvements can be made to the present invention. Therefore, modifications or improvements that do not depart from the spirit of the present invention are within the scope of protection of the present invention.

Claims

1. An online refractometer calibration method, characterized in that: The calibration methods include standard condition calibration method and working condition calibration method; For detachable online refractometers that have high requirements for measurement accuracy and can be used as reference instruments, the standard calibration method (S1) is applicable, including the following steps: S101: Using water at a specified temperature to continuously flow on the surface of the measuring sensor of the calibrated online refractometer, so that the measuring sensor of the calibrated online refractometer remains stable at the specified temperature; S102: Immerse the temperature sensor of the standard thermometer near the measuring sensor of the calibrated online refractometer, record the temperature measurement value of the standard thermometer as the temperature standard value after it stabilizes, and read the temperature measurement value of the calibrated online refractometer for comparison, the difference between the two is the temperature indication error of the calibrated online refractometer at the specified temperature; obtain the indication error data three times in a row, and take the arithmetic mean of the three data as the temperature indication error calibration result of the calibrated online refractometer at the specified temperature; S103: changing different designated temperatures, repeating step S102, and obtaining the temperature indication error calibration results of the calibrated online refractometer at different designated temperatures; S104: using a uniform liquid with a known specific refractive index or concentration to continuously flow on the surface of the measuring sensor of the calibrated online refractometer, and maintaining it at the same specified temperature as step S101, after the measured refractive index or concentration value of the calibrated online refractometer is stabilized, reading the measured refractive index or concentration value of the calibrated online refractometer and comparing it with the refractive index or concentration standard value of the liquid with the known specific refractive index or concentration, the difference between the two is the refractive index or concentration indication error data of the calibrated online refractometer at the specified temperature; continuously obtaining three indication error data, and taking the arithmetic mean of the three data as the calibration result of the refractive index or concentration indication error of the calibrated online refractometer at the specified temperature; S105: replacing a different stable homogeneous liquid with a known specific refractive index or concentration, repeating step S104, and obtaining the indication error calibration results of other different refractive index or concentration measurement points of the calibrated online refractometer at the specified temperature; S106: Select one of the stable homogeneous liquids with a known specific refractive index or concentration, repeat step S104, continuously obtain a set of no less than 6 refractive index or concentration measurement data of the calibrated online refractometer, and use the Bessel formula to calculate the standard deviation of the set of measurement data as the refractive index or concentration repeatability calibration result of the calibrated online refractometer; S107: Select one of the stable homogeneous liquids with a known specific refractive index or concentration, repeat step S104, obtain the refractive index or concentration measurement data of the calibrated online refractometer every 15 minutes, and measure continuously for 1 hour, and take the ratio of the difference between the maximum and minimum values ​​of the obtained refractive index or concentration measurement data and the initial measurement value as the refractive index or concentration stability calibration result of the calibrated online refractometer; S108: calibrating the online refractometer to be calibrated or correcting the temperature measurement value using one or more temperature indication error calibration results obtained in step S102 or S103 according to the calibration or data correction method in the manual of the online refractometer to be calibrated; S109: calibrating the online refractometer to be calibrated or correcting the refractive index or concentration measurement value using one or more refractive index or concentration indication error calibration results obtained in step S104 or S105 according to the calibration or data correction method in the manual of the online refractometer to be calibrated; For detachable online refractometers that do not require high measurement accuracy and are not used as reference instruments, the standard calibration method (S2) is applicable, including the following steps: S201: Continuously flowing water at a specified temperature on the surfaces of the measuring sensors of the calibrated online refractometer and the reference online refractometer, so that the measuring sensors of the calibrated online refractometer and the reference online refractometer remain stable at the specified temperature; S202: immerse the temperature sensor of the standard thermometer near the measuring sensor of the calibrated online refractometer, record the temperature measurement value of the standard thermometer as the temperature standard value after it stabilizes, and read the temperature measurement value of the calibrated online refractometer for comparison, the difference between the two is the temperature indication error of the calibrated online refractometer at the specified temperature; obtain the indication error data three times in a row, and take the arithmetic mean of the three data as the temperature indication error calibration result of the calibrated online refractometer at the specified temperature; S203: changing different designated temperatures, repeating step S202, and obtaining the temperature indication error calibration results of the calibrated online refractometer at different designated temperatures; S204: using a liquid with a stable refractive index or uniform concentration to continuously flow on the measuring sensor surfaces of the calibrated online refractometer and the reference online refractometer, and maintaining the liquid at the same designated temperature as step S201, after the refractive index or concentration measurement values ​​of the reference online refractometer and the calibrated online refractometer are stable, reading the refractive index or concentration measurement value of the reference online refractometer as the standard value, and reading the refractive index or concentration measurement value of the calibrated online refractometer for comparison, the difference between the two is the refractive index or concentration indication error data of the calibrated online refractometer at the designated temperature; acquiring the indication error data three times continuously, and taking the arithmetic mean of the three data as the refractive index or concentration indication error calibration result of the calibrated online refractometer at the designated temperature; S205: replacing a different stable liquid with a uniform refractive index or concentration, and repeating step S204 to obtain the indication error calibration results of other different refractive index or concentration measurement points of the calibrated online refractometer at the specified temperature; S206: Select one of the stable liquids with uniform refractive index or concentration, repeat step S204, continuously obtain a set of no less than 6 refractive index or concentration measurement data of the calibrated online refractometer, and calculate the standard deviation of the set of measurement data using the Bessel formula as the refractive index or concentration repeatability calibration result of the calibrated online refractometer; S207: Select one of the stable liquids with uniform refractive index or concentration, repeat step S204, obtain the refractive index or concentration measurement data of the calibrated online refractometer every 15 minutes, and measure continuously for 1 hour, and take the ratio of the difference between the maximum and minimum values ​​of the refractive index or concentration measurement data and the initial measurement value as the calibration result of the refractive index or concentration stability of the calibrated online refractometer; S208: Calibrate the online refractometer to be calibrated or correct the temperature measurement value using one or more temperature indication error calibration results obtained in step S202 or S203 according to the calibration or data correction method in the manual of the online refractometer to be calibrated; S209: calibrating the online refractometer to be calibrated or correcting the refractive index or concentration measurement value using one or more refractive index or concentration indication error calibration results obtained in step S204 or S205 according to the calibration or data correction method in the manual of the online refractometer to be calibrated; For online refractometers that cannot be disassembled or require working condition parameter calibration, the working condition calibration method (S3) is applicable, including the following steps: S301: using an online refractometer calibrated by the standard condition calibration method (S1) as a reference online refractometer, and installing it on a working position of a mobile online refractometer calibration device containing a standard thermometer; S302: connecting the mobile online refractometer calibration device to a working pipeline installed with the online refractometer to be calibrated through a bypass interface, so that the liquid working medium flows through the reference online refractometer and the online refractometer to be calibrated at the same time; S303: After the temperature measurement value of the standard thermometer is stable, it is recorded as the temperature standard value, and the temperature measurement value of the calibrated online refractometer is read and compared with it. The difference between the two is the temperature indication error data of the calibrated online refractometer under the working condition; the temperature indication error data are obtained three times in succession, and the arithmetic mean of the three data is taken as the temperature indication error calibration result of the calibrated online refractometer under the working condition; S304: after the refractive index or concentration measurement values ​​of the reference online refractometer and the calibrated online refractometer are stable, the refractive index or concentration measurement value of the reference online refractometer is read as the standard value, and the refractive index or concentration measurement value of the calibrated online refractometer is read for comparison, and the difference between the two is the refractive index or concentration indication error data of the calibrated online refractometer under the working medium and working conditions; three indication error data are obtained continuously, and the arithmetic mean of the three data is taken as the refractive index or concentration indication error calibration result of the calibrated online refractometer under the working medium and working conditions; S305: Keeping the liquid working medium stable, continuously acquiring a set of no less than 6 refractive index or concentration measurement data of the calibrated online refractometer, and using the Bessel formula to calculate the standard deviation of the set of measurement data as the refractive index or concentration repeatability calibration result of the calibrated online refractometer; S306: Keep the liquid working medium stable, obtain the refractive index or concentration measurement data of the calibrated online refractometer every 15 minutes, and measure continuously for 1 hour, and use the ratio of the difference between the maximum and minimum values ​​of the obtained refractive index or concentration measurement data and the initial measurement value as the refractive index or concentration stability calibration result of the calibrated online refractometer; S307: Correcting the temperature measurement value of the calibrated online refractometer according to the correction method in the manual of the calibrated online refractometer using the temperature indication error calibration result obtained in step S303; S308: According to the correction method in the manual of the calibrated online refractometer, the refractive index or concentration measurement value of the calibrated online refractometer is corrected using the refractive index or concentration indication error calibration result obtained in step S304.

2. The online refractometer calibration method according to claim 1, characterized in that: The concentration refers to a concentration scale converted by refractive index, including sucrose concentration (Brix), fructose concentration, glucose concentration, sodium chloride concentration, calcium chloride concentration, ethanol concentration, urea concentration, ethylene glycol concentration, propylene glycol concentration, isopropanol concentration, polyvinyl alcohol concentration, hydrogen peroxide concentration, ammonia concentration, sodium hydroxide concentration, N-methylpyrrolidone concentration, and dimethylformamide concentration.

3. The online refractometer calibration method according to claim 1, characterized in that: To ensure metrological traceability, the standard calibration method (S1) uses a certified reference material with a corresponding refractive index or concentration scale as the stable homogeneous liquid with a known specific refractive index or concentration, and the expanded uncertainty of the certified reference material should not be greater than 1 / 2 of the expected indication error of the refractive index or concentration of the calibrated online refractometer. If a certified reference material with a corresponding refractive index or concentration scale is not available, a stable homogeneous liquid whose refractive index or concentration is determined by a desktop refractometer with a higher traceability level or is obtained by precise preparation of pure substances may also be used, and the expanded uncertainty of the refractive index or concentration of the liquid should not be greater than 1 / 2 of the expected indication error of the refractive index or concentration of the calibrated online refractometer.

4. The online refractometer calibration method according to claim 1, characterized in that: To ensure metrological traceability, the reference online refractometer of the standard condition calibration method (S2) and the operating condition calibration method (S3) shall be calibrated by the standard condition calibration method (S1), and its refractive index or concentration value shall be traced back using certified standard materials of the corresponding refractive index or concentration scale, and the indication error of the refractive index or concentration shall be corrected using the traceability results, and the expanded uncertainty of the correction value or correction factor shall not be greater than 1 / 2 of the expected indication error of the refractive index or concentration of the calibrated online refractometer; if certified standard materials of the corresponding refractive index or concentration scale are not available, they may also be traced back to the refractive index or concentration value of a reliably quantified homogeneous liquid with stable properties, and the indication error of the refractive index or concentration shall be corrected using the traceability results, and the expanded uncertainty of the correction value or correction factor shall not be greater than 1 / 2 of the expected indication error of the refractive index or concentration of the calibrated online refractometer.

5. The online refractometer calibration method according to claim 1, characterized in that: To ensure metrological traceability, the temperature expansion uncertainty of the standard thermometer should not be greater than 1 / 3 of the expected indication error of the temperature of the calibrated online refractometer.

6. The online refractometer calibration method according to claim 1, characterized in that: When calibrating in the standard condition calibration method, in order to achieve continuous flow of water at a specified temperature on the surface of the measuring sensor of the calibrated online refractometer or the reference online refractometer, a fixed online refractometer calibration device can be used. The calibration device is provided with working positions for the calibrated online refractometer and the reference online refractometer, a constant temperature liquid storage tank and a circulation pipeline, and the liquid medium can be dynamically circulated at the specified temperature; when calibrating in the standard condition calibration method (S1), the calibration device is not provided with a reference online refractometer, and when calibrating in the standard condition calibration method (S2), the calibration device is provided with a reference online refractometer.

7. The online refractometer calibration method according to claim 6, characterized in that: The temperature error of the calibration device should be controlled within ±0.5℃ of the target specified temperature, and the temperature fluctuation should not exceed 0.5℃ / h; when it is necessary to calibrate an instrument with a refractive index nominal indication error not exceeding ±0.0002 or a concentration nominal indication error not exceeding ±0.1%, the temperature error of the calibration device should be controlled within ±0.2℃ of the target specified temperature, and the temperature fluctuation should not exceed 0.2℃ / h.

8. The online refractometer calibration method according to claim 1, characterized in that: The stable homogeneous liquid with a known specific refractive index or concentration in the standard calibration method (S1) and the stable homogeneous liquid with a known specific refractive index or concentration in the standard calibration method (S2) include water of grade 2 or higher in GB / T 6682.

9. The online refractometer calibration method according to claim 1, characterized in that: The specified temperature includes 20°C.

Images