A method and apparatus for calibrating a heat flux sensor

Abstract

The present application relates to a kind of heat flux sensor calibration method and device, belong to sensor calibration technical field.The present application when heat flux sensor needs to be calibrated, only need to heat it, do not need to take out sensor from soil, by determining the heat flux information of heat flux sensor caused by heating and the output voltage pressure difference of heat flux sensor heating and not heating can calculate calibration coefficient, without the aid of external calibration equipment, and calculation is simple, calibration process does not need to spend too long time, greatly improve the calibration efficiency.

Description

Technical Field

[0001] This invention relates to a method and apparatus for calibrating a heat flux sensor, belonging to the field of sensor calibration technology. Background Technology

[0002] The heat flux sensor utilizes the thermopile sensor principle to measure the energy balance and heat flux of soil. It primarily employs a thermopile to measure the temperature gradient. This thermopile is composed of two different metallic materials, generating a thermoelectric potential through the temperature difference between its cold and hot ends, which is output as a voltage. The sensor's output voltage is directly proportional to the heat flux, representing a constant heat flux coefficient. Calibration of the heat flux sensor essentially involves determining its heat flux coefficient. Since the heat flux sensor operates in a real-world environment, its internal materials experience some wear, directly affecting the heat flux coefficient. Therefore, periodic calibration is necessary. Existing calibration techniques involve placing a standard material with known thermal conductivity and a material of the same thickness and thermal conductivity as the sensor between hot and cold plates, comparing their properties. This method has significant drawbacks: it requires specialized equipment, is costly, and complex to operate. Furthermore, removing the sensor from frozen soil is cumbersome, resulting in low calibration efficiency and the inability to perform real-time or long-term calibration. Summary of the Invention

[0003] The purpose of this invention is to provide a method and apparatus for calibrating a heat flux sensor, so as to solve the problem of low calibration efficiency in the current calibration process of heat flux sensors.

[0004] To solve the above-mentioned technical problems, the present invention provides a calibration method for a heat flux sensor, the calibration method comprising the following steps:

[0005] 1) Heating the heat flux sensor that needs to be calibrated, and obtaining the heat flux information of the heat flux sensor caused by heating;

[0006] 2) Obtain the voltage output value of the heat flux sensor when it is not heated;

[0007] 3) Determine the coefficient based on the voltage difference between the heated and unheated output voltages of the heat flux sensor and the heat flux information obtained in step 1). This coefficient is the calibration coefficient.

[0008] When a heat flux sensor needs calibration, this invention only requires heating it; the sensor does not need to be removed from the soil. The calibration coefficient can be calculated by determining the heat flux information of the heat flux sensor caused by heating and the voltage difference between the heated and unheated output voltages. This eliminates the need for external calibration equipment, and the calculation is simple and the calibration process does not take too long, greatly improving calibration efficiency.

[0009] Furthermore, the heating in step 1) is achieved by attaching an additional thermal film to the surface of the heat flux sensor.

[0010] Furthermore, the heat flux information from the heat flux sensor caused by heating is half of the heat flux generated by the heated thin film.

[0011] The heating film is attached to the upper surface of the heat flux sensor, making it easier for heat flux to be transferred to the heat flux sensor. Part of the heat flux from the heating film is transferred downwards to the heat flux sensor, and part of it diffuses upwards. Only half of the heat flux is transferred to the heat flux sensor. Therefore, accurate heat flux information of the heat flux sensor can be obtained by measuring the heating film.

[0012] Furthermore, the heat flux sensor that needs to be calibrated refers to any one of the calibration conditions, which are that the heat flux information exceeds the set range and the maintenance cycle is reached.

[0013] By setting calibration conditions, the heat flux sensor will not be calibrated frequently, which would affect normal use, or it will not cause measurement errors due to problems caused by not being calibrated for a long time.

[0014] Furthermore, the voltage output value of the unheated heat flux sensor is the output voltage value before heating, the voltage output value after heating and settling, or the average of the output voltage before heating and the output voltage after heating and settling.

[0015] This invention provides three methods for measuring the voltage output value of an unheated heat flux sensor: the output voltage value before heating, the output voltage value after heating and settling, or the average of the output voltage before heating and the output voltage after heating and settling. These three methods can be flexibly selected according to actual needs. To improve measurement accuracy, the average of the output voltage before heating and the output voltage after settling can be used; to save calibration time, either the output voltage value before heating or the output voltage value after heating and settling can be selected.

[0016] This invention also provides a heat flux sensor calibration device, including a heater, a processor, a data acquisition unit, and a power supply module. The heater heats the heat flux sensor to be calibrated and transmits the heating information to the processor via the data acquisition unit. The power supply module supplies power to the processor and the heater. The processor controls the heater to heat the heat flux sensor, calculates the heat flux information of the sensor caused by heating based on the received heating information, and calculates coefficients based on the calculated heat flux information and the voltage difference between the heated and unheated output voltages of the heat flux sensor. The calculated coefficients are the calibration coefficients.

[0017] This calibration device includes a heater, processor, data acquisition unit, and power supply module, all of which are readily available and commercially available. The absence of expensive specialized equipment saves on costs. During calibration, the processor controls the heater to heat the heat flux sensor to be calibrated. Based on the received heating information, it calculates the heat flux information of the sensor caused by heating. Then, based on the calculated heat flux information and the voltage difference between the heated and unheated output voltages, it calculates coefficients to complete the calibration. The entire calibration process requires no manual operation, saving labor costs. Furthermore, the power supply module powers the processor and heater, ensuring that the device can perform calibration tasks for extended periods.

[0018] Furthermore, the heater is a heating film attached to the upper surface of the heat flux sensor.

[0019] Since the heating film can be attached to the surface of the heat flux sensor, part of the heat flux from the heater is transferred downwards to the heat flux sensor, part is diffused upwards, and only half is transferred to the heat flux sensor. Therefore, by measuring the heating film, accurate heat flux information of the heat flux sensor can be obtained.

[0020] Furthermore, the power supply module is a solar power generation device.

[0021] Since heat flux sensors are generally buried in outdoor environments without mains power, the power supply module of this invention uses a solar power generation device to power the equipment used in the entire calibration process, enabling long-term calibration.

[0022] Furthermore, the processor determines whether the heat flux sensor needs to be calibrated by judging whether the heat flux sensor meets the calibration conditions. The calibration conditions include the heat flux information exceeding the set range and reaching the maintenance cycle. If either one is met, it means that the heat flux sensor needs to be calibrated.

[0023] By having the processor determine whether the heat flux sensor meets the pre-set calibration conditions, it is possible to effectively avoid the impact of frequent calibration on normal use of the heat flux sensor and the measurement error caused by problems due to prolonged lack of calibration.

[0024] Furthermore, the voltage output value of the unheated heat flux sensor used by the processor in calculating the calibration coefficient is the output voltage value before heating, the voltage output value after heating and settling, or the average of the output voltage before heating and the output voltage after heating and settling.

[0025] When calculating the calibration coefficients, the processor provides three methods for the voltage output value of the unheated heat flux sensor. The method of using the average of the output voltage before heating and the output voltage after resting can improve the accuracy of the measurement; the method of selecting the output voltage value before heating or the voltage output value after heating and resting can save calibration time. The processor can flexibly select these three methods according to actual needs. Attached Figure Description

[0026] Figure 1 This is a schematic block diagram of the structure of the invention heat flux sensor calibration device;

[0027] Figure 2 This is a flowchart of the invention of a calibration method for a permafrost heat flux sensor;

[0028] Figure 3 This is a schematic diagram of the calibration device structure in an embodiment of the invention;

[0029] Wherein: 1 is a lightning rod; 2 is a pole; 3 is a chassis; 4 is a solar power generation device; 5 is a heater; 6 is a heat flux sensor; 7 is a second heat flux sensor. Detailed Implementation

[0030] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0031] Examples of calibration methods

[0032] This invention first acquires the current heat flux information, then judges whether the acquired heat flux information exceeds the normal range or is due to periodic maintenance. Automatic calibration is initiated, interrupting normal soil heat flux measurement. Next, the sensor output voltage before heating is acquired. The heater is then turned on to heat the sensor for a period of time, after which heating is stopped, and the sensor output voltage and the current flowing through the heater before heating is stopped are collected. After a period of rest, the sensor output voltage is collected again. A new heat flux coefficient is calculated according to the heat flux coefficient calculation formula, and the new heat flux coefficient is stored, completing the sensor calibration. The implementation flow of this method is as follows: Figure 2 As shown, the specific steps for this example are as follows:

[0033] First, determine whether the heat flux sensor needs to be calibrated.

[0034] Heat flux sensors are typically buried in permafrost to measure the permafrost layer. Frequent calibration will inevitably affect the normal operation of the heat flux sensor. If it is not calibrated for a long time or if the heat flux sensor suddenly malfunctions, the measurement results will be unreliable.

[0035] Therefore, this invention sets two conditions, and calibration is required if either condition is met.

[0036] Condition 1: Heat flux information exceeds the set range;

[0037] Condition 2: The maintenance cycle has been reached (the working time of the heat flux sensor after the last calibration).

[0038] Obtain the output voltage U of the heat flux sensor C Based on the fact that the sensor's output voltage is proportional to the heat flux, and using the stored heat flux coefficient K1, the current soil heat flux information Ф=U is obtained. C / K1 compares the current heat flux information obtained by the sensor with a set range. If it exceeds the set range, it indicates that the heat flux information detected by the sensor is abnormal and needs to be recalibrated. The set range here can be determined by the maximum and minimum values ​​of heat flux information in the area over a recent period. If it exceeds the maximum value or is less than the minimum value, it is considered to be out of range. As another implementation method, the set range here can also be determined in other ways, such as the heat flux information of the area during the same historical period.

[0039] Record the time of each calibration and compare the current time with the most recent calibration time. If the calibration exceeds the maintenance cycle, calibration is also required. The maintenance cycle can be determined based on the actual situation of the sensor.

[0040] 2. Heat the heat flux sensor that needs to be calibrated and determine the amount of heat flux generated by the heating.

[0041] 1) Interrupt the normal measurement of soil heat flux.

[0042] When the heat flux sensor needs to be calibrated, in order to improve the accuracy of the calibration, the normal measurement of soil heat flux should be interrupted, that is, the heat flux sensor should be turned off, for example, the sensor can be turned off for at least 360 seconds.

[0043] 2) Heat the heat flux sensor to obtain the heat flux information of the sensor.

[0044] This invention heats the heat flux sensor by placing a heater on its surface. In this embodiment, the heater, a heating film, is located on the upper surface of the heat flux sensor. The heating film is attached to the upper surface of the heat flux sensor, and after a set time when the heat flux sensor is turned off, the heater is turned on to heat it. During heating, the heater attached to the sensor continuously heats the sensor. A portion of the heat flux from the heater is transferred downwards to the heat flux sensor, while a portion diffuses upwards. Therefore, only half of the heat flux is transferred to the heat flux sensor. The heat flux information of the sensor can then be calculated from the power of the heater. The specific calculation process is as follows:

[0045] To ensure effective heating, this invention requires a specific heating time when heating the heat flux sensor, ensuring the heating process lasts for a certain duration, such as 180 seconds. During the heating process, the voltage U of the heater is measured. T1 The heating current is calculated based on the known resistance of the resistor connected in series with the heater, and thus the heating power of the heater can be calculated. In this embodiment, the heating current is calculated by taking the current value of a resistor with a known resistance connected in series with the heater, and then calculating the current value of the heater. For example, if the resistance of the resistor is R1, the voltage across the resistor is measured to be U1, and the current value of the heater is U1 / R1.

[0046] Since the heater in this embodiment uses a heating film that is attached to the surface of the heat flux sensor, the area of ​​the heating film can be determined. Based on the area of ​​the heating film and the heating power, the heat flux information of the heater can be obtained. The specific calculation formula is as follows:

[0047] The formula for the heat flux generated by the heater is Φ = P 加热器 / S 加热器 Where P is the heat transferred per unit time (W), and S is the heat transfer area, the heat generated by the heater per unit time when using a heater is:

[0048] P = I 2 *R 加热器 =(U1 / R1) 2 *R 加热器

[0049] Ф=(U1 2 *R 加热器 ) / (R1 2 *S)

[0050] Since half of the heater's heat flux is transferred to the heat flux sensor, the heat flux sensor detects heat flux information as 1 / 2Ф during the heating process.

[0051] To avoid environmental impact, multiple sets of heating measurements can be used, for example, by installing the same set of sensor devices 5m away from the heat flux sensor.

[0052] 3. Determine the heat flux coefficient based on the heat flux sensor values ​​before and after heating to calibrate the heat flux sensor.

[0053] Step two yields the heat flux information from the heat flux sensor caused by heating. This heat flux information is proportional to the voltage difference of the heat flux sensor before and after heating. The unheated output voltage can be the output voltage information collected after turning the heat flux sensor off and on again, or the output voltage information after heating and resting for a period of time. To improve accuracy, this invention uses the average of the output voltage before heating and the output voltage after resting. Therefore, the heater needs to be turned off, the sensor needs to be left to rest for a period of time, and then the output voltage U of the sensor after resting needs to be collected. T1+T2 The difference U between the sensor's output voltage before and after heating is obtained.

[0054] The formula for the difference U between the output voltage of the heat flux sensor before and after heating is:

[0055] U = U T1 -0.5*(U0+U T1+T2 )

[0056] The new heat flux coefficient K2 is calculated based on the fact that the difference U between the sensor's output voltage before and after heating is proportional to the sensor's heat flux 1 / 2Ф.

[0057] K2=2*U / Ф=2*U*R1 2 *S / (U1 2 *R 加热器 )

[0058] The new heat flux coefficient K2 is stored to complete the calibration of the sensor.

[0059] Through the above process, this invention only requires heating the heat flux sensor, acquiring valid data, and analyzing it to complete calibration. The calibration process is simple, saves calibration time, and effectively improves calibration efficiency. Simultaneous heating and measurement of multiple heat flux sensors in the same area avoids environmental influences, reduces measurement errors, and effectively improves calibration accuracy. The heat flux sensor only needs to be placed in the soil, and calibration can be completed with only simple auxiliary equipment such as a heater and processor, effectively saving costs.

[0060] Examples of calibration devices

[0061] The calibration device for the heat flux sensor of the present invention includes a heater 5 disposed on the heat flux sensor 6, a processor, and auxiliary equipment. The auxiliary equipment includes a power supply module, a data acquisition unit, a memory, and a communication module. Figure 1As shown, the processor connects to the heat flux sensor and heater via a data acquisition unit to collect information from the heat flux sensor and heater, and controls the heat flux sensor and heater. The power supply module supplies power to the processor, heater, and other devices. The memory, connected to the processor, stores all collected heat flux information and calibrated heat flux coefficients. It can store information for a long time and generate historical data, which is beneficial for the processor to compare and analyze the current heat flux information when determining whether the calibration conditions are met. The communication module, which can be a wired or wireless communication module, is used to transmit the collected heat flux information and data generated during the calibration process to the cloud platform via the network, facilitating remote data monitoring.

[0062] The heater is used to provide heat flux information for the heat flux sensor to be calibrated. In order to accurately determine that the heater provides heat flux information for the heat flux sensor, the heater 5 in this invention is a thin-film heater. When in use, the thin-film heater can be attached to the upper surface of the heat flux sensor to be calibrated. Since the thin-film heater is very thin, the heat generated by it can be assumed that it is only transferred along the upper and lower surfaces of the film. Therefore, half of the heat generated is transferred downward to the heat flux sensor and half diffuses upward. By calculating the heat flux of the heater, the heat flux detected by the heat flux sensor can be accurately obtained.

[0063] The processor determines whether the heat flux sensor needs calibration based on the collected heat flux sensor data and the previous calibration time. If calibration is required, it runs the calibration program: it controls the heat flux sensor to interrupt measurement and, after a set interruption time, controls the heater to start; it calculates the heat flux generated by the heater to obtain the heat flux sensor's data; based on the proportional relationship between the output voltage difference before and after heating and the heat flux of the heat flux sensor, it determines the coefficients of the heat flux sensor to be calibrated. This system then stores these coefficients in memory, completing the calibration process. The specific calibration procedure is as follows: Figure 2 As shown in the method embodiments, detailed descriptions have been provided and will not be repeated here.

[0064] To further improve the accuracy of calibration, this invention allows for two or more calibrations during the calibration process, for example, such as... Figure 3 As shown, when it is necessary to calibrate the heat flux sensor 6, another heat flux sensor can be selected, referred to as the second heat flux sensor 7. The second heat flux sensor 7 and the heat flux sensor 6 are buried in the soil at the same depth (e.g., 5cm), and the second heat flux sensor 7 is close to the heat flux sensor 6 (e.g., 5m). By simultaneously heating and measuring the second heat flux sensor 7 and the heat flux sensor 6, and comparing and analyzing the results, the accuracy can be improved.

[0065] Since heat flux sensors are typically buried in outdoor environments without mains power, the power supply module of this invention uses a solar power generation device, such as... Figure 3 As shown, the solar panels of the solar power generation device 4 are installed on the pole 2, which is about 3m long. The pole is also equipped with a housing 3 and a lightning rod 1. The housing 3 houses the processor, data collector, memory and communication module. Since the housing 3 is a sealed space, it achieves good waterproof and windproof effects. The lightning rod is installed on the top of the pole to effectively prevent lightning from damaging the device.

Claims

1. A method of calibrating a heat flux sensor, the method comprising: The calibration method comprises the following steps: 1) heating the heat flux sensor in the soil that needs to be calibrated by a heater arranged on the surface of the heat flux sensor, and obtaining the heat flux information of the heat flux sensor caused by the heating; 2) obtaining the voltage output value of the heat flux sensor when not heated; 3) determining a coefficient according to the output voltage difference of the heat flux sensor when heated and when not heated and the sensor heat flux information obtained in step 1), wherein the coefficient is the calibration coefficient, and the calculation formula of the calibration coefficient is: K2 = 2*U / Φ Ф = (U1 2 *R 加热器 ) / (R1 2 *S) wherein K2 is the calibration coefficient, U is the output voltage difference of the heat flux sensor when heated and when not heated, Φ is the heat flux of the heater, R1 is the resistance value of the resistor in series with the heater, U1 is the voltage value on both sides of the resistor in series with the heater, and S is the heat transfer area.

2. The heat flux sensor calibration method of claim 1, wherein, The heater in step 1) is a heating film attached to the surface of the heat flux sensor.

3. The heat flux sensor calibration method of claim 2, wherein, The heat flux information of the heat flux sensor caused by the heating is half of the heat flux generated by the heating film.

4. The heat flux sensor calibration method according to claim 1 or 2, characterized in that, The heat flux sensor that needs to be calibrated refers to any one that meets the calibration condition, and the calibration condition is that the heat flux information exceeds the set range and reaches the maintenance period.

5. The heat flux sensor calibration method of claim 1 or 2, wherein The voltage output value of the heat flux sensor when not heated is the output voltage value before heating, the voltage output value after heating and resting, or the average of the output voltage before heating and the output voltage after heating and resting.

6. A heat flux sensor calibration device, characterized by The apparatus comprises a heater, a processor, a collector and a power supply module, the heater is arranged on the surface of the heat flux sensor and is used to heat the heat flux sensor in the soil that needs to be calibrated, and the heating information is transmitted to the processor through the collector; the power supply module is used to supply power to the processor and the heater; the processor is used to control the heater to heat the heat flux sensor that needs to be calibrated, calculate the heat flux information of the heat flux sensor caused by the heating according to the received heating information, and calculate a coefficient according to the calculated heat flux information of the heat flux sensor and the output voltage difference of the heat flux sensor when heated and when not heated, wherein the calculated coefficient is the calibration coefficient, and the calculation formula of the calibration coefficient is: K2 = 2*U / Φ Ф = (U1 2 *R 加热器 ) / (R1 2 *S) wherein K2 is the calibration coefficient, U is the output voltage difference of the heat flux sensor when heated and when not heated, Φ is the heat flux of the heater, R1 is the resistance value of the resistor in series with the heater, U1 is the voltage value on both sides of the resistor in series with the heater, and S is the heat transfer area.

7. The heat flux sensor calibration device of claim 6, wherein, The heater is a heating film attached to the upper surface of the heat flux sensor.

8. The heat flux sensor calibration device of claim 6, wherein, The power supply module is a solar power generation device.

9. The heat flux sensor calibration device of claim 6, wherein, The processor determines whether the heat flux sensor needs to be calibrated by judging whether the heat flux sensor meets the calibration condition, and the calibration condition comprises that the heat flux information exceeds the set range and reaches the maintenance period, and any one of the conditions means that the heat flux sensor needs to be calibrated.

10. The heat flux sensor calibration device of claim 6, wherein, The voltage output value of the heat flux sensor when not heated used by the processor when calculating the calibration coefficient is the output voltage value before heating, the voltage output value after heating and resting, or the average of the output voltage before heating and the output voltage after heating and resting.

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