A method for field calibration of a refrigerator thermometer

Abstract

This invention discloses a method for on-site calibration of refrigerator thermometers. The method involves placing the refrigerator thermometer to be calibrated and a standard platinum resistance thermometer within the temperature equalization chamber of a refrigerator thermometer calibration device. The device is controlled to reach and maintain a stable preset calibration temperature point. The readings of both the standard platinum resistance thermometer and the refrigerator thermometer to be calibrated are simultaneously collected. The temperature reading error of the refrigerator thermometer to be calibrated is calculated based on the collected data. For refrigerators with multiple temperature sensors, temperature reading consistency is calculated based on multiple sets of data collected simultaneously. This method utilizes a portable refrigerator thermometer calibration device and a standard platinum resistance thermometer to calibrate refrigerator thermometers on-site without disassembling the main equipment or interrupting monitoring. By simultaneously collecting data, it calculates temperature reading error and temperature reading consistency evaluation indicators to quantitatively assess data coordination capabilities.

Description

Technical Field

[0001] This invention relates to the field of temperature calibration technology, and in particular to a method for on-site calibration of a refrigerator thermometer. Background Technology

[0002] Currently, the calibration of refrigerator thermometers mostly involves disassembling them or removing them from the refrigerator or freezer and sending them to a metrology institution for calibration. This is problematic because the refrigeration environment is unmonitored during the calibration process, and some situations require real-time network monitoring. There are two methods for sending them to the laboratory for testing: one is to place them in a liquid environment, where the temperature field is provided by media such as alcohol or refrigerant, which can cause corrosion and contamination to liquid column thermometers, or require cleaning after calibration; the other is to place them in an air environment, using a dew point meter as a standard. However, using a dew point meter as a standard lacks theoretical support, as dew point temperature and temperature are two different concepts. Using a standard platinum resistance thermometer is more reasonable, as it is much more stable. Some customers, unable to disassemble the refrigerator, request on-site comparison, placing a standard platinum resistance thermometer and the refrigerator thermometer side-by-side to observe their readings. This method provides a rough on-site performance verification, but it is greatly affected by ambient temperature, wind speed, and other conditions, and cannot accurately determine the refrigerator thermometer's performance, especially in situations where performance is critical, potentially leading to misjudgment and misuse.

[0003] For the reasons mentioned above, there is an urgent need for a method that can efficiently calibrate refrigerator thermometers on-site without disassembling the main body of the equipment or affecting normal monitoring. Summary of the Invention

[0004] The purpose of this invention is to address the numerous shortcomings of existing technologies, such as the difficulty in sending refrigerator thermometers for calibration and testing due to the need for disassembly, low calibration efficiency, and lack of unified standards and consistency evaluation. To this end, this invention proposes an on-site calibration method for refrigerator thermometers, enabling on-site traceability of measurement values ​​for various types of refrigerator thermometers. It also innovatively proposes an evaluation index and calculation method for temperature indication consistency, solving the problem of on-site calibration of thermometers in networked and multi-sensor systems.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for on-site calibration of a refrigerator thermometer includes the following steps:

[0007] Place the refrigerator thermometer to be calibrated and the standard platinum resistance thermometer into the temperature equalization chamber of the refrigerator thermometer calibration device;

[0008] The refrigerator thermometer calibration device is controlled to reach and maintain a stable preset calibration temperature point.

[0009] The readings of the standard platinum resistance thermometer and the refrigerator thermometer to be calibrated are collected simultaneously.

[0010] Calculate the temperature reading error of the refrigerator thermometer to be calibrated based on the collected data;

[0011] For a refrigerator containing multiple temperature sensors, the consistency of temperature readings is calculated based on multiple sets of data collected at the same time.

[0012] Furthermore, the temperature indication error is defined as: the average value of the temperature readings of the refrigerator thermometer being calibrated obtained by repeated measurements at a certain calibration temperature point, minus the average value of the temperature readings of the standard platinum resistance thermometer.

[0013] Furthermore, the temperature indication consistency is defined as follows: in a set of data collected at the same calibration temperature point and at the same time, the absolute value of the difference between the maximum temperature indication error and the minimum temperature indication error is taken as the maximum value of the absolute value among all calibration temperature points and all measurement times as the temperature indication consistency.

[0014] Furthermore, the steps to obtain the consistency of the temperature readings are as follows:

[0015] Confirm the serial number of the refrigerator thermometer that needs to be calibrated, and whether the central control system, refrigerator thermometer calibration device, and standard platinum resistance thermometer of the corresponding refrigerator are functioning properly.

[0016] Place the refrigerator thermometer calibration device in a location easily accessible to the refrigerator thermometer sensor, and place the external temperature sensor of each refrigerator thermometer and the standard platinum resistance thermometer inside the temperature equalization chamber of the refrigerator thermometer calibration device.

[0017] Set the refrigerator thermometer calibration device to the calibration temperature point. Once the temperature of the refrigerator thermometer calibration device stabilizes, record the reading of the standard platinum resistance thermometer according to the recording interval and recording time set by the central control system. Set the refrigerator thermometer calibration device to different temperature points in sequence and repeat the recording.

[0018] The data recorded by the central control system is copied, the average value of the readings at each calibration point of each refrigerator thermometer is calculated, and the difference is made with the average value of the readings of the standard platinum resistance thermometer to obtain the temperature reading error of each refrigerator thermometer.

[0019] The data recorded by the central control system is copied, and a set of data from several refrigerator thermometers collected simultaneously at each moment is calculated. The maximum temperature indication error is subtracted from the minimum temperature indication error, and the absolute value is taken to obtain the temperature indication consistency at that moment.

[0020] Furthermore, the reliability of the on-site calibration method for the refrigerator thermometer was verified using expanded uncertainty, wherein the expanded uncertainty... Calculate using the following formula:

[0021]

[0022] In the formula, For factor coefficients, Indicates the combined standard uncertainty;

[0023] Evaluation of measurement uncertainty of temperature indication error:

[0024]

[0025]

[0026]

[0027]

[0028] In the above formula, This represents the maximum of the uncertainty introduced by resolution and the standard uncertainty introduced by repeatability. This represents the standard uncertainty introduced by repeatability; Indicates refrigerator thermometer The standard deviation of the measurement results This indicates the number of times the average value of the measurements was selected as the measurement result. This indicates the calibration temperature point of the refrigerator thermometer being calibrated. The temperature value measured this time, This represents the average value of multiple measurements taken at a specific calibration temperature point on the refrigerator thermometer being calibrated. This indicates the measurement uncertainty of the temperature reading error. This represents the standard uncertainty component introduced by the temperature indication error;

[0029] For the assessment of measurement uncertainty regarding the consistency of temperature readings:

[0030]

[0031] In the formula, This represents the standard uncertainty component introduced by the consistency of temperature readings.

[0032] Furthermore, the refrigerator thermometer calibration device includes an upper compartment and a lower compartment. The upper compartment is equipped with a temperature control chamber with a uniform temperature cavity, and an insert plate for placing the thermometer is also provided in the temperature control chamber. The lower compartment is equipped with a refrigeration compressor that supplies cold air medium to the temperature control chamber.

[0033] Furthermore, the temperature control chamber is equipped with multiple viewing windows around it for observing the readings of each thermometer. A guide fan is also installed on one side of the temperature control chamber, with the fan blades inside the temperature control chamber and the motor of the guide fan located outside the temperature control chamber.

[0034] Furthermore, the temperature value and the number of correction points in the refrigerator thermometer calibration device are corrected using either system default correction or manual correction.

[0035] The system defaults to correcting the number of correction points by subtracting the maximum and minimum values ​​from the maximum number of correction points set by the system, and the corrected temperature value is 0℃ by default.

[0036] The number of correction points for manual correction is the maximum number of correction points set by the system, and the temperature value for manual correction is entered manually.

[0037] Furthermore, apart from the maximum and minimum correction points, the segmentation interval of the correction points is calculated as follows:

[0038] δ=ROUND[(t 上 -t 下 ) / (20-1)1]

[0039] In the formula, δ represents the segmented interval, and t 上 This indicates the upper temperature limit of the refrigerator thermometer calibration device, t 下 This indicates the lower limit of the refrigerator thermometer calibration device; ROUND indicates rounding, and the number 1 means to retain one decimal place.

[0040] Furthermore, the corrected temperature value The calculation method is as follows:

[0041]

[0042] In the formula, This represents the average value of multiple measurements taken at a specific calibration temperature point on the refrigerator thermometer being calibrated. This indicates the temperature value measured by the refrigerator's multi-channel temperature data acquisition instrument. This indicates the temperature data recorded by the refrigerator's multi-channel temperature data acquisition device;

[0043]

[0044] In the formula, This indicates the correction value of the refrigerator thermometer calibration device. This indicates the temperature setpoint of the refrigerator thermometer calibration device. This indicates the temperature data recorded by the multi-channel temperature data acquisition instrument within 10 minutes.

[0045] Compared with existing technologies, the advantages of this invention are as follows: This invention can simultaneously calibrate multiple refrigerator thermometers, improving calibration efficiency. The calibration device is visualized for easy observation and can meet the on-site calibration needs of refrigerator thermometers with built-in sensors, external sensors, or slightly larger sizes. It also enables non-destructive on-site calibration of thermometers, eliminating the need to disassemble the refrigerator thermometer main unit or interrupt the central control system; calibration is completed simply by moving the sensor probe into the calibration device, ensuring the continuity of refrigerator cold chain monitoring. This invention employs a multi-dimensional evaluation of calibration results, not only assessing the temperature indication error of a single thermometer but also innovatively introducing a temperature indication consistency index, effectively evaluating the collaborative working capability of the multi-sensor network system, and better meeting the needs of practical application scenarios. Attached Figure Description

[0046] Figure 1 This is a flowchart of the on-site calibration method for a refrigerator thermometer proposed in an embodiment of the present invention; Figure 2 This is a flowchart illustrating the acquisition and calculation of temperature indication error and temperature indication consistency in an embodiment of the present invention; Figure 3 This is a schematic diagram of the overall appearance of the refrigerator thermometer calibration device in an embodiment of the present invention; Figure 4 This is a schematic diagram of the refrigerator thermometer calibration device with the door open in an embodiment of the present invention; Figure 5 This is a schematic diagram of the interior of the upper and lower compartments of the refrigerator thermometer calibration device in an embodiment of the present invention; Figure 6 This is a schematic diagram showing the placement of the sensors of each channel in the temperature control chamber of the multi-channel temperature data acquisition instrument in an embodiment of the present invention.

[0047] The following are the labels in the diagram: 1. Upper compartment; 2. Lower compartment; 11. Temperature-controlled compartment; 12. Viewing window; 13. Insert plate; 14. Flow fan; 21. Refrigeration compressor. Detailed Implementation

[0048] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0049] Reference Figure 1 The on-site calibration method for refrigerator thermometers proposed in this embodiment mainly includes the following steps:

[0050] Place the refrigerator thermometer to be calibrated and the standard platinum resistance thermometer into the temperature equalization chamber of the refrigerator thermometer calibration device;

[0051] The refrigerator thermometer calibration device is controlled to reach and maintain a stable preset calibration temperature point.

[0052] The readings of the standard platinum resistance thermometer and the refrigerator thermometer to be calibrated are collected simultaneously.

[0053] Calculate the temperature reading error of the refrigerator thermometer to be calibrated based on the collected data;

[0054] For a refrigerator containing multiple temperature sensors, the consistency of temperature readings is calculated based on multiple sets of data collected at the same time.

[0055] In this scheme, two quantitative indicators are defined to measure the performance of refrigerator thermometers: one is temperature indication error, and the other is temperature indication consistency.

[0056] Temperature indication error is the average value of the refrigerator thermometer being calibrated minus the average value of the standard platinum resistance thermometer, obtained by repeatedly measuring at a certain calibration temperature point.

[0057] Temperature indication consistency refers to the absolute value of the difference between the maximum and minimum temperature indication errors among a set of data collected by multiple refrigerator thermometers at the same calibration temperature point and at the same time. The maximum value of the absolute value among all calibration temperature points and all measurement times is taken as the temperature indication consistency.

[0058] Temperature indication error: The formula for calculating the temperature indication error of a refrigerator thermometer is as follows:

[0059]

[0060] In the formula, This indicates the reading error of the refrigerator thermometer at a certain calibration temperature point, in °C. This represents the average value (°C) of multiple measurements taken at a specific calibration temperature point on the calibrated refrigerator thermometer. This represents the average value (°C) of multiple measurements taken at a calibrated temperature point using a standard platinum resistance thermometer.

[0061] When the data system of the refrigerator or cold storage being calibrated contains multiple refrigerator thermometers, external probes or recorders, the consistency of temperature readings at each temperature calibration point for a set of data collected at the same time is an important parameter that customers reflect or that affects the actual environmental temperature of the cold storage, and it is also a performance that users care about.

[0062] Temperature indication consistency is defined as the absolute value of the difference between the maximum and minimum temperature indication errors in a set of data collected at the same temperature calibration point at the same time. Multiple measurements are taken at each calibration point, and the maximum absolute value of the difference between the maximum and minimum temperature indication errors in the measured data is taken as the temperature indication consistency for that calibration point. The maximum value of the temperature indication consistency across all temperature calibration points is taken as the temperature indication consistency of the data system; therefore, its calculation formula is:

[0063]

[0064] δ t =δ ti max

[0065] In the formula, This indicates that the temperature readings of the i-th group of collected data are consistent, in °C. This represents the maximum sensor temperature error, expressed in °C, from the data collected in the i-th group. δ represents the minimum sensor temperature error in the i-th data set, expressed in °C. t Indicates the consistency of the system's temperature readings, in °C; δ ti max This represents the maximum temperature reading consistency across all temperature calibration points, expressed in °C.

[0066] Based on the above principles, the following explains the on-site calibration method for refrigerator thermometers.

[0067] like Figure 2 As shown, the implementation steps for on-site calibration of a refrigerator thermometer regarding temperature indication error and temperature indication consistency are as follows:

[0068] Step 1: Confirm the serial number of the refrigerator thermometer to be calibrated, the corresponding channel in the refrigerator's central control system, and whether the central control system displays and records data normally. Confirm the recording interval and recording time points of the central control system. Check that the refrigerator thermometer calibration device and the standard platinum resistance thermometer are functioning normally.

[0069] Step 2: Determine the lead length of the external sensor of each refrigerator thermometer and place the refrigerator thermometer calibration device in a location that is easily accessible to the refrigerator thermometer sensor.

[0070] Step 3: Place the external temperature sensor of each refrigerator thermometer into the temperature equalization chamber of the refrigerator thermometer calibration device.

[0071] Step 4: Place the standard platinum resistance thermometer in the temperature equalization chamber of the refrigerator thermometer calibration device. The standard platinum resistance thermometer and the external sensor of the refrigerator thermometer under test should be placed on the same horizontal plane as much as possible, or placed in the central area of ​​the refrigerator thermometer calibration device. Then, use a plug to seal the test hole.

[0072] Step 5: Power on the standard platinum resistance thermometer and the refrigerator thermometer calibration device. Set the refrigerator thermometer calibration device to the calibration temperature point (e.g., -18℃). Wait until the refrigerator thermometer calibration device reaches a stable calibration temperature point (-18℃ ± 0.2℃). This indicates the refrigerator thermometer calibration device has reached a stable state. If the refrigerator thermometer calibration device has not reached a stable state, return to Step 4 and reposition it. After the refrigerator thermometer calibration device has stabilized for 15 minutes, start recording the reading of the standard platinum resistance thermometer according to the recording interval and recording time set by the central control system. Repeat the recording multiple times.

[0073] Step 6: Adjust the calibration temperature points. Set the refrigerator thermometer calibration device to 2℃, 5℃, and 8℃ in sequence. The temperature points can also be set according to the customer's actual needs. Repeat Step 5.

[0074] Step 7: Copy the data recorded by the central control system (or export and print the data and attach it to the original calibration record), calculate the average temperature reading of each refrigerator thermometer at each calibration point, and subtract the average temperature reading of the standard platinum resistance thermometer to obtain the temperature reading error of each refrigerator thermometer.

[0075] Step 8: Copy the data recorded by the central control system (or export and print the data and attach it to the original calibration record), calculate a set of data from several refrigerator thermometers collected at the same time, subtract the minimum temperature indication error from the maximum temperature indication error, and take the absolute value to obtain the temperature indication consistency data at that time; the maximum value of the temperature indication consistency at all times of each calibration temperature point in the calibration process can be taken as the temperature indication consistency of the refrigerator thermometer in the central control system.

[0076] By using the above steps, the temperature indication error of a single thermometer and the temperature indication consistency of the hollow system can be calculated. Using temperature indication error and temperature indication consistency as evaluation indicators, the data collaboration capability of a multi-sensor networked system at the same time can be scientifically quantified and evaluated.

[0077] The refrigerator thermometer calibration device used in this embodiment, such as Figures 3-5 Its structure is as follows:

[0078] The refrigerator thermometer calibration device consists of two compartments: an upper compartment 1 and a lower compartment 2, both of which have doors.

[0079] The upper compartment 1 contains a temperature-controlled compartment 11 with a uniform temperature chamber, and the outer perimeter of the temperature-controlled compartment 11 is covered with insulation material. Multiple viewing windows 12 are provided around the temperature-controlled compartment 11 to facilitate observation of the thermometer readings inside; one of the viewing windows 12 is located on the door of the upper compartment 1. Furthermore, to facilitate the placement of the thermometers, an insert plate 13 is provided inside the temperature-controlled compartment 11 for inserting and placing the thermometers. In this embodiment, the insert plate 13 can hold a standard platinum resistance thermometer and various refrigerator thermometers to be calibrated.

[0080] To facilitate uniform temperature distribution within the temperature control chamber 11, a guide fan 14 is installed on one side of the temperature control chamber 11. The fan blades of the guide fan 14 are located inside the temperature control chamber 11, while the motor of the guide fan 14 is located outside the temperature control chamber 11. By installing the guide fan 14, the temperature inside the temperature control chamber 11 is stabilized, ensuring that the uniformity is no greater than 0.3℃ and the temperature fluctuation is no greater than ±0.2℃.

[0081] The lower compartment 2 is the equipment compartment, housing a refrigeration compressor 21 and related equipment. This compressor supplies cold air to the temperature-controlled compartment 11, bringing the temperature within 11 to the calibration point. Refrigeration and the supply of cold air to the temperature-controlled compartment 11 are mature technologies in the industry and will not be elaborated upon in this embodiment. For ease of use, casters are installed at the bottom of the lower compartment 2, allowing the device to be easily moved to the location of the refrigerator requiring calibration.

[0082] By using a portable refrigerator thermometer calibration device and a standard platinum resistance thermometer, the refrigerator thermometer can be calibrated on-site without disassembling the main body of the equipment or interrupting temperature monitoring, which greatly improves the calibration efficiency of the refrigerator thermometer.

[0083] Commonly used refrigerator thermometers include liquid column refrigerator thermometers, digital refrigerator thermometers (with external temperature probes), and refrigerator thermometers or temperature recorders with built-in sensors. Refrigerator thermometers or temperature recorders with built-in sensors can export data via USB, have built-in printing functions, can connect to Wi-Fi for storage, or display stored data through a central control system for use in cold chain or refrigerator applications.

[0084] In another implementation scenario of the present invention, taking the on-site calibration of an externally mounted digital temperature sensor refrigerator thermometer used in a biopharmaceutical plant as an example, the reliability of the on-site calibration method for the refrigerator thermometer is verified.

[0085] Scenario Description: This pharmaceutical factory has 10 medical refrigerators, each equipped with an external digital temperature sensor. All sensors are connected to the same central control system for real-time monitoring. Due to GSP certification requirements, the system needs to be calibrated on-site.

[0086] Equipment preparation: Select a refrigerator thermometer on-site calibration device, with a standard platinum resistance thermometer and matching electrical measuring instruments as the standard.

[0087] The parameters of the standard instrument, calibration device, and environmental conditions used to calibrate the above-mentioned refrigerator thermometer are as follows.

[0088] Standard instrument, standard platinum resistance thermometer, measuring range (-80~419.527)℃, maximum permissible error (MPE): ±0.05℃;

[0089] On-site calibration device for refrigerator thermometers, temperature range (-20~50)℃, temperature uniformity: 0.3℃, temperature fluctuation: ±0.2℃.

[0090] Environmental conditions: Temperature: (15~25)℃, Relative humidity: ≤85%.

[0091] Confirm that the sensor number of the digital refrigerator thermometer corresponds correctly with the central control channel.

[0092] Place the refrigerator thermometer field calibration device next to the refrigerator group, and put the sensor probe of the digital refrigerator thermometer and the standard platinum resistance thermometer into the refrigerator thermometer field calibration device to ensure that the depth is consistent.

[0093] Set the temperature of the refrigerator thermometer's on-site calibration device to -18℃. Wait 15 minutes until the temperature stabilizes (fluctuation less than ±0.2℃).

[0094] Read the 10 values ​​displayed on the central control system and the values ​​from the standard platinum resistance thermometer, record them once every minute, and record them for a total of 3 times.

[0095] Set the temperature of the refrigerator thermometer field calibration device to -18℃, 2℃, 5℃, and 8℃ in sequence, and repeat the above recording process.

[0096] Using the measurement of a digital refrigerator thermometer at 5℃ by the refrigerator thermometer field calibration device as an example, 10 repeated measurements were performed. The test data are shown in Table 1, unit: ℃.

[0097] Table 1 Repeated measures data

[0098]

[0099] Data processing:

[0100] Temperature indication error calculation: The average value of a standard platinum resistance thermometer is 4.48℃, and the average value of a digital refrigerator thermometer is 4.61℃. Therefore, the indication error at this point is +0.13℃.

[0101] Temperature reading consistency calculation: The errors of the digital refrigerator thermometer in 10 measurements were -0.40℃, -0.2℃, -0.5℃, ..., -0.3℃. The maximum error was -0.6℃, and the minimum error was -0.2℃. The temperature reading consistency is:

[0102] |-0.6-(-0.2)|=0.4℃.

[0103] The system iterates through the measured temperatures at all times and takes the maximum value as the consistency index of the system.

[0104] If the reading error of the digital refrigerator thermometer is within the allowable range (±0.5℃) and the system consistency meets the user's requirements (≤0.5℃), then the digital refrigerator thermometer is deemed to be calibrated successfully.

[0105] Furthermore, the reliability of the on-site calibration method for the refrigerator thermometer will be verified based on the uncertainty.

[0106] Evaluation of measurement uncertainty of temperature indication error:

[0107] Calculate the standard deviation of 10 measurements taken by the refrigerator thermometer using the following formula. :

[0108]

[0109] In the above formula, This indicates the calibration temperature point of the refrigerator thermometer being calibrated. Temperature value measured, unit: ℃.

[0110] The standard deviation of a single measurement at 5℃ is s=0.13. In actual measurements, the measurand is repeatedly measured multiple times, and the average of the three measurements is taken as the measurement result. The standard uncertainty introduced by repeatability is:

[0111] ℃

[0112] The uncertainty u2 introduced by the resolution of the digital refrigerator thermometer is given by the fact that the resolution of the calibrated digital refrigerator thermometer at 5℃ is 0.1℃. The resulting half-interval of uncertainty is 0.05℃, following a uniform distribution. Therefore, the uncertainty introduced by the resolution of the digital refrigerator thermometer is:

[0113] ℃

[0114] The uncertainty introduced by the resolution of the digital refrigerator thermometer is less than the standard uncertainty introduced by repeatability, so the standard uncertainty u2 introduced by the resolution is discarded.

[0115] Uncertainty u3 introduced by standard platinum resistance thermometer:

[0116] The maximum uncertainty of a standard platinum resistance thermometer is 20 mK, or 0.02℃, and the coverage factor k = 2.58. Therefore, the uncertainty of the standard platinum resistance thermometer is:

[0117] ℃

[0118] The standard uncertainty u4 introduced by the matching electrical measuring instruments:

[0119] The maximum permissible temperature error of the electrical measuring instrument at 5℃ is ±0.0044℃. This distribution follows a uniform pattern, therefore:

[0120] ℃

[0121] Standard uncertainty u5 introduced by non-uniformity in refrigerator thermometer calibration device:

[0122] If the uniformity of the refrigerator thermometer calibration device is 0.3℃, then the half-width of the uncertainty interval is 0.15℃. This distribution follows a uniform distribution. Therefore:

[0123] ℃

[0124] Standard uncertainty u6 introduced by the fluctuation of the refrigerator thermometer calibration device:

[0125] The refrigerator thermometer calibration device has a fluctuation of ±0.2℃, and its uncertainty interval half-width is 0.2℃. This distribution follows a uniform distribution, therefore:

[0126] ℃

[0127] If u3, u4, u5, and u6 are mutually uncorrelated, then:

[0128] ℃

[0129] Combined uncertainty u c :

[0130] Independent and uncorrelated, combined standard uncertainty u c :

[0131] ℃

[0132] Expanded uncertainty U:

[0133] Expanded uncertainty Let the coverage factor coefficient k=2;

[0134] Uncertainty of measurement results of digital refrigerator thermometer at 5.0℃:

[0135] U = 2 × 0.168 ≈ 0.4℃ (k = 2)

[0136] According to the temperature range of the digital refrigerator thermometer under test, the calibrated temperature points are -18.0℃, 2.0℃, 5.0℃, and 8.0℃. The measurement uncertainty is shown in Table 2 below.

[0137] Table 2. Uncertainty of each temperature

[0138]

[0139] As shown in the table above, the refrigerator thermometer with a scale of 0.1℃ is the best refrigerator thermometer that this calibration device can calibrate. Therefore, the temperature calibration and measurement capability of this project is: (-18~8)℃, U=0.4℃; k=2.

[0140] The same method was used to evaluate the measurement uncertainty of temperature indication consistency.

[0141] Uncertainty introduced by repeated measurements:

[0142] At 5°C, the data recorded by the refrigerator's central control system was obtained from 10 repeated measurements:

[0143]

[0144] This represents the average value indicating the consistency of temperature readings.

[0145] In actual calculations, the average of three measurements is taken. Therefore, the standard uncertainty introduced by repeatability is:

[0146]

[0147] Standard uncertainty introduced by the resolution of the central control system of the inspected refrigerator:

[0148] If the temperature resolution of the refrigerator's central control system is typically 0.1℃, and we estimate it to be half the reading and assume a uniform distribution, then:

[0149]

[0150] If the temperature resolution of the refrigerator's central control system is 1℃, and we estimate it to be half the temperature, assuming a uniform distribution, we get:

[0151]

[0152] The uncertainty introduced by the resolution of the central control system of the refrigerator under test, with a resolution of 0.1℃, is greater than the uncertainty introduced by repeatability. Therefore, the uncertainty introduced by repeatability is discarded.

[0153] Uncertainty component introduced by temperature hysteresis of the sensor in the central control system of the refrigerator thermometer being calibrated:

[0154] Compared to a standard platinum resistance thermometer, the temperature lag of the sensor in the control system of the refrigerator thermometer being calibrated is set to 0.1℃, and its half-width is 0.05℃. Assuming a uniform distribution, then:

[0155]

[0156] Standard uncertainty introduced by non-uniformity of the refrigerator thermometer calibration device:

[0157] The internal temperature uniformity of the refrigerator thermometer calibration device is 0.3℃, and its half-width is 0.15℃. Assuming a uniform distribution, then:

[0158]

[0159] Combined standard uncertainty:

[0160] The above standard uncertainty components are uncorrelated, so the combined standard uncertainty is:

[0161]

[0162] Calculation of expanded uncertainty:

[0163] Its distribution can be considered as a normal distribution. Therefore, when P = 95%, the coverage factor coefficient k = 2 can be taken. Then the expanded uncertainty is: U = k × u c =0.2℃, (k=2).

[0164] According to the temperature range of the central control system of the refrigerator under test, the calibration temperature points are -18.0℃, 2.0℃, 5.0℃, and 8.0℃. The measurement uncertainty is shown in Table 3 below.

[0165] Table 3 Measurement Uncertainty Table

[0166]

[0167] The temperature measurement range of the refrigerator thermometer control system is (-18~8)℃, and the measurement uncertainty evaluation values ​​for all calibration points are: U=0.2℃, k=2.

[0168] When the scale division values ​​of the sensors in the central control system of the refrigerator thermometer being calibrated are different, the u1 and u3 components in the uncertainty will change. Therefore, when calibrating a temperature and humidity sensor with a scale division value of 1℃, the measurement uncertainty is shown in Table 4.

[0169] Table 4. Overview of Uncertainty at 1℃

[0170]

[0171] The consistency of the readings of the central control system of the refrigerator being calibrated with a 0.1℃ scale is the best temperature and humidity sensor that this calibration device can calibrate. Therefore, the temperature calibration and measurement capability of this project is: (-18~8)℃, U=0.2℃; k=2.

[0172] The results of the above uncertainty assessment show that this method has high metrological reliability.

[0173] To improve the accuracy of the refrigerator thermometer calibration device, this embodiment also proposes a method for correcting the refrigerator thermometer calibration device.

[0174] The correction principle is as follows:

[0175] According to Taylor polynomials:

[0176]

[0177] Near the point x=a, construct a polynomial for the approximation function f(x):

[0178]

[0179] According to the Lagrange remainder, let:

[0180]

[0181] but:

[0182] ,

[0183] m is a constant, that is:

[0184] ,make =0

[0185] We get: f(x) = f(a) + m, x = a

[0186] Then at a certain temperature point At this point, the actual value is f(x), the nominal value is f(a), and m is the correction value.

[0187] Based on the above principles, for a refrigerator thermometer field calibration device ranging from -20°C to 50°C, a multi-segment correction method is used to ensure the accuracy of the device, approximating the true curve of the entire temperature range using multiple points. The entire temperature range is corrected using a 20-point correction method.

[0188] As shown in the above formula, two parameters need to be confirmed to correct the refrigerator thermometer calibration device: one is the temperature point to be corrected. The other is the m-value. Correcting the refrigerator thermometer calibration device requires confirming the temperature point. The specific temperature correction value and the number of temperature points.

[0189] There are two correction modes. One mode allows you to manually input the correction value and the number of temperature points to be corrected, with a maximum of 20 points. The other mode is the system default, which sets the number of correction points to 20. In addition to the minimum and maximum values, the system automatically sets 18 temperature points, requiring you to manually input the correction values ​​for all 20 temperature points. If no correction is input, the system default correction value is 0℃.

[0190] Apart from the upper and lower limits, the interval calculation method for correction points is as follows:

[0191] δ=ROUND[(t 上 -t 下 ) / (20-1)1]

[0192] In the formula, δ represents the segmented interval, ℃; t 上 Indicates the upper temperature limit of the refrigerator thermometer calibration device, in °C; t 下 This indicates the lower limit of the refrigerator thermometer calibration device, in °C; ROUND indicates rounding, with the number 1 representing one decimal place.

[0193] Assume the temperature points to be corrected are t1, t2, ..., t 20 Each temperature point is as follows:

[0194] t1 = t 下 ;

[0195] t2 = ROUND[t1 + (2-1)*δ, 0] ;

[0196] …

[0197] t p =ROUND[t1+(p-1)*δ, 0], p=3, 4, 5,…, 19;

[0198] t 20 =t 上

[0199] In the formula, ROUND means rounding, and the number 0 represents keeping the integer.

[0200] The method for confirming the temperature point correction value m is as follows:

[0201] 1. Data point placement method: Use a multi-channel temperature data acquisition instrument (≥6 channels) to... Figure 6 The location diagram shows the placement of each channel sensor. Position 0 is the geometric center of the refrigerator thermometer calibration device. Figure 6All six points (0-5) are located in the middle layer of the refrigerator thermometer calibration device. Points 1-4 correspond to the four corners of the middle layer plane, each 3cm from one side. Point 5 is the temperature sensor integrated into the refrigerator thermometer calibration device. The channel relationships of the multi-channel temperature data acquisition instrument corresponding to points 0-5 are shown in Table 5 below:

[0202] Table 5. Correspondence between location and multi-channel temperature data acquisition instrument

[0203]

[0204] Fix the probes of the multi-channel temperature data acquisition instrument in each position according to the correspondence in Table 5.

[0205] 2. Calculation method

[0206] The CH1~CH6 channels of the multi-channel temperature data acquisition instrument are configured according to Table 5 and... Figure 6 After fixing the position, power on the refrigerator thermometer calibration device, set the temperature point, and start operation. Once the device stabilizes at the set temperature, typically displaying a value within ±0.2℃ / 10min of the set value, it is considered to have reached a stable operating state. Turn on the multi-channel temperature data acquisition device to record data, recording one data point per minute for 10 minutes, for a total of 11 sets of data. Calculate the average value of all points over 10 minutes.

[0207]

[0208] In the formula, This represents the average value (°C) of multiple measurements taken at a specific calibration temperature point on the calibrated refrigerator thermometer. This represents the temperature values ​​measured by the CH1~CH6 channels of the multi-channel temperature data acquisition instrument, in °C. This represents the temperature data (°C) recorded by the multi-channel temperature data acquisition instrument within 10 minutes.

[0209]

[0210] In the formula, This indicates the correction value, expressed in °C, for the refrigerator thermometer calibration device. This indicates the temperature setting value of the refrigerator thermometer calibration device, in °C. This represents the temperature data (°C) recorded by the multi-channel temperature data acquisition instrument within 10 minutes. The value is the correction value for the temperature point that needs to be corrected, which is manually entered.

[0211] By selecting whether to manually correct or use the default system program to correct, input the correction value obtained from the above measurement and calculation for the temperature point to be corrected.

[0212] The above-described on-site calibration method for refrigerator thermometers of this invention utilizes a portable refrigerator thermometer calibration device and a standard platinum resistance thermometer to calibrate the refrigerator thermometer on-site without disassembling the main equipment or interrupting monitoring. By placing the sensor to be calibrated and the standard platinum resistance thermometer in the same uniform temperature field, data is collected synchronously, and the temperature indication error of a single thermometer is calculated. Specifically, a temperature indication consistency evaluation index is used to quantitatively assess the data collaboration capability of a multi-sensor networked system at the same time. This method solves the problem of monitoring interruption caused by traditional inspection methods, improves calibration efficiency, and provides a scientific basis for the quality evaluation of refrigerator cold chain monitoring systems.

[0213] It should be noted that any parts not covered in this invention are the same as or can be implemented using existing technology. The above description is merely a preferred embodiment of this invention, but the scope of protection of this invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in this invention, based on the technical solution and inventive concept of this invention, should be covered within the scope of protection of this invention.

Claims

1. A method for on-site calibration of a refrigerator thermometer, characterized in that, Includes the following steps: Place the refrigerator thermometer to be calibrated and the standard platinum resistance thermometer into the temperature equalization chamber of the refrigerator thermometer calibration device; The refrigerator thermometer calibration device is controlled to reach and maintain a stable preset calibration temperature point. The readings of the standard platinum resistance thermometer and the refrigerator thermometer to be calibrated are collected simultaneously. Calculate the temperature reading error of the refrigerator thermometer to be calibrated based on the collected data; For a refrigerator containing multiple temperature sensors, the consistency of temperature readings is calculated based on multiple sets of data collected at the same time.

2. The on-site calibration method for a refrigerator thermometer according to claim 1, characterized in that, The temperature indication error is defined as: the average value of the temperature readings of the refrigerator thermometer being calibrated, obtained by repeated measurements at a certain calibration temperature point, minus the average value of the temperature readings of the standard platinum resistance thermometer.

3. The on-site calibration method for a refrigerator thermometer according to claim 1, characterized in that, The temperature indication consistency is defined as follows: in a set of data collected at the same calibration temperature point and at the same time, the absolute value of the difference between the maximum temperature indication error and the minimum temperature indication error is taken as the maximum value of the absolute value among all calibration temperature points and all measurement times as the temperature indication consistency.

4. The on-site calibration method for a refrigerator thermometer according to claim 1, characterized in that, The steps to obtain the consistency of the temperature readings are as follows: Confirm the serial number of the refrigerator thermometer that needs to be calibrated, and whether the central control system, refrigerator thermometer calibration device, and standard platinum resistance thermometer of the corresponding refrigerator are functioning properly. Place the refrigerator thermometer calibration device in a location easily accessible to the refrigerator thermometer sensor, and place the external temperature sensor of each refrigerator thermometer and the standard platinum resistance thermometer inside the temperature equalization chamber of the refrigerator thermometer calibration device. Set the refrigerator thermometer calibration device to the calibration temperature point. Once the temperature of the refrigerator thermometer calibration device stabilizes, record the reading of the standard platinum resistance thermometer according to the recording interval and recording time set by the central control system. Set the refrigerator thermometer calibration device to different temperature points in sequence and repeat the recording. The data recorded by the central control system is copied, the average value of the readings at each calibration point of each refrigerator thermometer is calculated, and the difference is made with the average value of the readings of the standard platinum resistance thermometer to obtain the temperature reading error of each refrigerator thermometer. The data recorded by the central control system is copied, and a set of data from several refrigerator thermometers collected simultaneously at each moment is calculated. The maximum temperature indication error is subtracted from the minimum temperature indication error, and the absolute value is taken to obtain the temperature indication consistency at that moment.

5. The on-site calibration method for a refrigerator thermometer according to claim 1, characterized in that, The reliability of the on-site calibration method for refrigerator thermometers was verified using expanded uncertainty. Calculate using the following formula: ； In the formula, For factor coefficients, Indicates the combined standard uncertainty; Evaluation of measurement uncertainty of temperature indication error: ； ； ； ； In the above formula, This represents the maximum of the uncertainty introduced by resolution and the standard uncertainty introduced by repeatability. This represents the standard uncertainty introduced by repeatability; Indicates refrigerator thermometer The standard deviation of the measurement results This indicates the number of times the average value of the measurements was selected as the measurement result. This indicates the calibration temperature point of the refrigerator thermometer being calibrated. The temperature value measured this time, This represents the average value of multiple measurements taken at a specific calibration temperature point on the refrigerator thermometer being calibrated. This indicates the measurement uncertainty of the temperature reading error. This represents the standard uncertainty component introduced by the temperature indication error; For the assessment of measurement uncertainty regarding the consistency of temperature readings: ； In the formula, This represents the standard uncertainty component introduced by the consistency of temperature readings.

6. The on-site calibration method for a refrigerator thermometer according to claim 1, characterized in that, The refrigerator thermometer calibration device includes an upper compartment (1) and a lower compartment (2). The upper compartment (1) is provided with a temperature control chamber (11) having a uniform temperature cavity. The temperature control chamber (11) is also provided with a plate (13) for placing the thermometer. The lower compartment (2) is provided with a refrigeration compressor (21) for supplying cold air medium to the temperature control chamber (11).

7. The on-site calibration method for a refrigerator thermometer according to claim 6, characterized in that, The temperature control chamber (11) is surrounded by multiple viewing windows (12) for observing the readings of each thermometer. A guide fan (14) is also provided on one side of the temperature control chamber (11). The fan blades of the guide fan (14) are located inside the temperature control chamber (11), and the motor of the guide fan (14) is located outside the temperature control chamber (11).

8. The on-site calibration method for a refrigerator thermometer according to claim 1 or 6, characterized in that, The temperature value and the number of correction points in the refrigerator thermometer calibration device are corrected using either the system default correction or manual correction methods. The system defaults to correcting the number of correction points by subtracting the maximum and minimum values ​​from the maximum number of correction points set by the system, and the corrected temperature value is 0℃ by default. The number of correction points for manual correction is the maximum number of correction points set by the system, and the temperature value for manual correction is entered manually.

9. The on-site calibration method for a refrigerator thermometer according to claim 8, characterized in that, Except for the maximum and minimum correction points, the segmented interval of the correction points is calculated as follows: δ=ROUND[(t 上 -t 下 ) / (20-1),1]; In the formula, δ represents the segmented interval, and t 上 This indicates the upper temperature limit of the refrigerator thermometer calibration device, t 下 This indicates the lower limit of the refrigerator thermometer calibration device; ROUND indicates rounding, and the number 1 means to retain one decimal place.

10. The on-site calibration method for a refrigerator thermometer according to claim 8, characterized in that, The corrected temperature value The calculation method is as follows: ； In the formula, This represents the average value of multiple measurements taken at a specific calibration temperature point on the refrigerator thermometer being calibrated. This indicates the channel number of the refrigerator's multi-channel temperature data acquisition instrument. This indicates the sequence number of the temperature data recorded by the refrigerator's multi-channel temperature data acquisition instrument. ； In the formula, This indicates the correction value of the refrigerator thermometer calibration device. This indicates the temperature setpoint of the refrigerator thermometer calibration device. This indicates the temperature measured by the refrigerator's multi-channel temperature data acquisition instrument during the acquisition time.

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