An Automatic Calibration Method for Temperature Sensors in Aqueous Film-Forming Foam Extinguishing Agents

Abstract

The present invention discloses an automatic calibration method for temperature sensors in an aqueous film-forming fire extinguishing agent. Three temperature sensors are used to respectively transmit the temperatures inside the storage tank, on the outer wall of the storage tank, and of the air to a microcontroller. Under certain conditions, the heat transfer inside and outside the storage tank will temporarily stop periodically and make the three transmitted temperatures equal. Based on this, a program is designed at the microprocessor end to achieve the automatic calibration of the temperature sensors in the aqueous film-forming fire extinguishing agent.

Description

Technical Field

[0001] The present invention relates to the field of sensors, and more specifically, to a method for automatically calibrating a temperature sensor in a solution on a storage tank of a high-concentration sol solution, especially a method for automatically calibrating a temperature sensor in an aqueous film-forming fire extinguishing agent storage tank. Background Art

[0002] Aqueous film-forming fire extinguishing agent is a high-concentration fire extinguishing agent concentrate, which contains about 70% water and about 30% surfactants, foaming agents, foam stabilizers, etc., and belongs to a sol concentrated solution containing a large amount of macromolecular substances. Its specific heat capacity and heat transfer performance are both between water and solid solutes. Aqueous film-forming fire extinguishing agent is generally stored in a stainless steel tank for a long time for standby. To increase stability, stainless steel storage tanks generally have multiple adjustable feet to support the tank body.

[0003] The effectiveness of aqueous film-forming fire extinguishing agent is directly related to the reliability of the fire extinguishing system, and its storage life is directly related to the storage temperature (Yuan Yubin, Xie Xianjun, Han Yonghe, etc. Determination method for storage life of new aqueous film-forming fire extinguishing agent [J]. Fire Science and Technology, 2008, 27(5):3). In order to estimate the remaining life of aqueous film-forming fire extinguishing agent, it is necessary to obtain its accurate temperature at any time, which is generally achieved by setting a temperature sensor in the center of the storage tank. Since aqueous film-forming fire extinguishing agent contains a large amount of corrosive substances, the temperature sensor is easily eroded and undergoes zero drift, resulting in inaccurate readings. To identify zero drift, the simplest method is to set at least 3 temperature sensors in the tank and compare their readings at any time. However, due to the strong corrosiveness of aqueous film-forming fire extinguishing agent, the temperature sensors are easily damaged and need to be replaced. Placing at least 3 temperature sensors in it requires frequent replacement of sensors, which not only is not conducive to maintaining the stable storage state of aqueous film-forming fire extinguishing agent, but also causes certain waste.

[0004] The present invention aims at the problems of reliability monitoring and calibration of temperature sensors placed in aqueous film-forming fire extinguishing agent, and proposes a method for calibrating temperature sensors placed in aqueous film-forming fire extinguishing agent inside the tank body by using the readings of the outer wall of the tank and external air temperature sensors. Summary of the Invention

[0005] Aiming at the problem that the temperature sensor placed in aqueous film-forming fire extinguishing agent is easily corroded and undergoes zero drift, a method for calibrating the temperature sensor placed in aqueous film-forming fire extinguishing agent inside the storage tank by using the outer wall of the tank and external air temperature sensors is proposed.

[0006] The object of the present invention is achieved by the following scheme: An automatic calibration method for a temperature sensor in aqueous film-forming fire extinguishing agent, which is realized by connecting 3 temperature sensors placed at different positions to a microprocessing unit MCU, and is carried out according to the following steps:

[0007] (1) Place three calibrated temperature sensors inside the liquid level, on the inner and outer walls, and in the external air of the stainless-steel storage tank for aqueous film-forming foam extinguishing agent, and connect them to the MCU. The temperature data generated by the three sensors are respectively recorded as the internal temperature, external temperature, and air temperature. The MCU collects data every 10 minutes and synchronously plots the temperature curves generated by the three sensors. From evening to early morning the next day, the air temperature and external temperature will enter the downward range and intersect with the internal temperature curve. When the temperature sensors are all working properly, the three temperature curves will intersect at a point, which is called the alignment point.

[0008] (2) The MCU continuously tracks the alignment point through comparison logic. When three consecutive alignment points deviate, that is, the three curves cannot intersect at a point within the error range, start the calibration program to achieve automatic calibration or guide the staff to perform the calibration operation and determine whether the internal temperature sensor needs to be replaced.

[0009] Further, the process of the MCU performing the main sensor calibration is as follows:

[0010] S1. The MCU continues to collect the internal temperature, external temperature, and air temperature data. The temperature data collected at regular time intervals form the internal temperature, external temperature, and air temperature curves.

[0011] S2. Determine whether the alignment point is abnormal. If not, the sensor is normal; if yes, correct the internal temperature offset value to make the alignment point achieve three-line unification and continue to collect data.

[0012] S3. After correcting the internal temperature offset value, continue to determine whether the alignment point is abnormal. If not, set a new offset value for the internal temperature sensor; if yes, request re-calibration or replacement of the external temperature and air temperature sensors and continue to collect temperature data.

[0013] S4. For the case of re-calibrating or replacing the external temperature and air temperature sensors, determine whether the alignment point is abnormal. If yes, request replacement of the internal temperature sensor, and then the MCU continues to collect the internal temperature, external temperature, and air temperature data; if not, it means the sensors are normal.

[0014] Preferably, the time intervals for data collection and comparison in step (2) are both 10 minutes, and the required temperature accuracy for comparison is 0.1 °C, that is, at the alignment point determined by the program, the difference between any two of the internal temperature, external temperature, and air temperature data does not exceed 0.1 °C.

[0015] Preferably, the storage tank for aqueous film-forming foam extinguishing agent is made of stainless steel, stands on the ground with feet, and is not directly irradiated by sunlight. The external temperature sensor is installed below the liquid level and is covered by a heat-insulating block.

[0016] The aqueous film-forming foam extinguishing agent is a high-concentration sol solution with 70% water and 30% solute.

[0017] The storage tank contains enough aqueous film-forming fire extinguishing agent, and a short-term thermal equilibrium can be achieved inside and outside the storage tank during the day-night alternation process, so that the inner temperature, outer temperature and air temperature curves periodically intersect at a point, namely the reference point.

[0018] Preferably, DS18B20 series low-cost temperature sensors are adopted, and their temperature measurement accuracy is 0.1 °C.

[0019] Experiments show that when the stainless steel storage tank has feet, and the liquid stored in it is high-concentration sol, and the storage position is not directly irradiated by sunlight, due to meeting the following 4 characteristics: (1) High-concentration sol has a high specific heat capacity and good heat transfer performance; (2) The stainless steel tank body itself has good heat transfer performance and low specific heat capacity; (3) The stainless steel storage tank has feet, so the contact area with the ground is small; (4) It is not directly irradiated by sunlight, the inner temperature of the tank will be mainly affected by the air temperature. The inner temperature will follow the air temperature and fluctuate gently repeatedly with a cycle of one day and night. The outer temperature is always between the air temperature and the inner temperature, indicating that it undertakes the heat exchange between the liquid in the tank and the outside air.

[0020] The reference point is a special case formed by heat transfer phenomena under certain conditions. Specifically, it requires: (1) The storage tank body basically exchanges heat only with the air and cannot be directly irradiated by sunlight; (2) The tank body needs to have good heat transfer ability and small heat capacity; (3) The liquid in the tank has a large heat capacity and good heat transfer performance. The aqueous film-forming fire extinguishing agent storage tank meets the above conditions, so the reference point can be used to check whether the inner temperature sensor (main sensor) has zero drift.

[0021] The present invention uses 3 temperature sensors to respectively transmit the temperatures inside the storage tank, on the outer wall of the storage tank and in the air to the microcontroller. Under certain conditions, the heat transfer inside and outside the storage tank will temporarily stop periodically and make the 3 transmitted temperatures equal. Based on this, a program is designed at the microprocessor end to realize the automatic calibration of the temperature sensor in the aqueous film-forming fire extinguishing agent. Its advantages are as follows:

[0022] The advantages of using the reference point are: (1) Only the temperature sensors set on the outer wall and in the air are needed to check the working condition of the main sensor in the fire extinguishing agent liquid. Since the aqueous film-forming fire extinguishing agent is corrosive, the expected service lives of the former two are much higher than that of the main sensor, which saves costs compared with setting multiple main sensors in the tank; (2) The MCU only needs simple cyclic comparison operations to judge faults and guide disposal, without having to process complex heat transfer formulas with a large number of parameters. Description of the Drawings

[0023] Figure 1: Schematic diagram of the setting method of the sensor;

[0024] Appendix Figure 2 : Variation rules of a typical inner temperature, outer temperature and air temperature curve;

[0025] AppendixFigure 3 : Attachment Figure 2 Partial enlargement, highlighting the watch alignment point at 4780 minutes;

[0026] Attachment Figure 4 : Logic block diagram of the MCU for main sensor calibration;

[0027] Description of the reference numerals in the figure:

[0028] 1 - Aqueous film-forming foam extinguishing agent storage tank; 2 - Inner aqueous film-forming foam extinguishing agent liquid level;

[0029] 3 - Inner temperature sensor; 4 - Outer temperature sensor; 5 - Air temperature sensor; respectively connected to the microprocessing unit 6 - MCU;

[0030] 7 - Thermal insulation block; 8 - Support leg. Specific implementation manner

[0031] It is realized by the inner temperature sensor 3 placed below the inner aqueous film-forming foam extinguishing agent liquid level 2 in the aqueous film-forming foam extinguishing agent storage tank 1, the outer temperature sensor 4 on the outer wall of the aqueous film-forming foam extinguishing agent storage tank 1, and the air temperature sensor 5 respectively connected to the microprocessing unit MCU. Among them, the inner temperature sensor 3 is placed inside the aqueous film-forming foam extinguishing agent storage tank body 1 as the main sensor, and the automatic calibration of this main sensor is jointly realized by 1 air temperature sensor 5 placed outside the storage tank and 1 outer temperature sensor placed on the storage tank wall. The specific setting method of the above hardware is shown in the attachment Figure 1 .

[0032] Among them, the aqueous film-forming foam extinguishing agent storage tank 1 is a stainless steel storage tank, stands on the ground with support legs 8, and is not directly irradiated by sunlight. The outer temperature sensor 4 is set below the aqueous film-forming foam extinguishing agent liquid level 2 and is covered by the thermal insulation block 7.

[0033] By continuously monitoring the temperature data transmitted back by the 3 temperature sensors through the MCU, 3 temperature curves are obtained, which are respectively recorded as the inner temperature curve (corresponding to the main sensor), the outer temperature curve (corresponding to the outer wall sensor), and the air temperature curve (corresponding to the sensor placed in the air). When the above series of conditions are met, the fluctuation laws of the inner temperature, outer temperature, and air temperature curves are as shown in the attachment Figure 2As shown. Its greatest feature lies in that starting from every evening (around 17:00), the temperature curve and the outside temperature curve will rapidly decline until early the next morning (around 7:00). During this period (around 21:00 in the evening), they will cross the internal temperature curve at an angle greater than 45°. Experiments show that within the error range of the temperature sensor, the internal temperature, outside temperature, and temperature curves will intersect at one point at this time. The physical meaning of this point is that when the internal temperature is equal to the air temperature, the heat exchange on the surface of the aqueous film-forming fire extinguishing agent storage tank 1 temporarily stops, so the outside temperature will also be equal to the internal temperature and the air temperature. Because the phenomenon of the three lines intersecting at one point fixedly appears at around 21:00 every evening, just like the three sensors perform a "time alignment" operation every day to verify each other's working status, so we define this phenomenon as "time alignment", and the common intersection point of the three temperature curves is called the "time alignment point", attached Figure 3 is attached Figure 2 For partial enlargement, a time alignment point located at 4780 minutes is marked. Attached Figure 2 The arrow also marks each time alignment point in the figure.

[0034] The specific implementation method is as follows:

[0035] (1) The MCU6 synchronously plots the internal temperature, outside temperature, and temperature curves, as shown in attached Figure 2 and attached Figure 3 shown, and identifies the time alignment points among them through comparison operations.

[0036] When the time alignment point deviates, that is, when the three temperature curves cannot intersect at one point within the error range, start the calibration program. First, automatically calibrate the zero point of the main sensor and determine whether time alignment can be achieved again. If not, guide the staff to perform calibration operations and determine whether the main sensor needs to be replaced. The specific execution logic is as shown in attached Figure 4 shown.

[0037] In this embodiment, the DS18B20 series of low-cost sensors are selected as the temperature sensors.

[0038] The sampling data interval of the MCU is 10 minutes, and the determination criterion for the time alignment point is that each curve allows ±0.1 °C. If the three temperature curves can intersect, it is determined that the main sensor is working normally.

[0039] Install this system on the aqueous film-forming fire extinguishing agent storage tank 1 and continuously track:

[0040] (1) Fill a rectangular vertical stainless steel storage tank with legs, with a length of 40 cm, a width of 20 cm, and a height of 40 cm, with the aqueous film-forming fire extinguishing agent. Among them, the composition ratio of the aqueous film-forming fire extinguishing agent is: 70% water, 12% urea, 7% CAB, 9% APG0810, 1% JR-400, and 1% FC-134.

[0041] (2) According to attachedFigure 1 Three DS18B20 type temperature sensors are installed on the aqueous film forming foam fire extinguishing agent storage tank 1 and connected to the micro control unit MCU6.

[0042] (3)At the MCU end, continuously record the feedback data of the three temperature sensors according to the set program. The time periods for recording data and processing data are both 10 minutes. Identify the "clock calibration point" through cyclic comparison to obtain the internal temperature, external temperature and air temperature data, and plot them as shown in Appendix Figure 2 Appendix Figure 3 .

[0043] (4)When the clock calibration point is abnormal, that is, at the clock calibration point determined by the program, if the difference between any two of the internal temperature, external temperature and air temperature data exceeds 0.1 °C, start the automatic calibration program. The working logic is as shown in Appendix Figure 4 :

[0044] S1. The MCU continues to collect the internal temperature, external temperature and air temperature data. The temperature data collected at regular time intervals form the internal temperature, external temperature and air temperature curves;

[0045] S2. Determine whether the clock calibration point is abnormal. If not, the sensor is normal; if yes, correct the internal temperature offset value to make the clock calibration point achieve three-line unification and continue to collect data;

[0046] S3. After correcting the internal temperature offset value, continue to determine whether the clock calibration point is abnormal. If not, set a new offset value for the internal temperature sensor; if yes, request re-calibration or replacement of the external temperature and air temperature sensors and continue to collect temperature data;

[0047] S4. For the case of re-calibrating or replacing the external temperature and air temperature sensors, determine whether the clock calibration point is abnormal. If yes, request replacement of the internal temperature sensor, and then the MCU continues to collect the internal temperature, external temperature and air temperature data; if not, it means the sensor is normal.

[0048] The advantages of using the clock calibration point are as follows: (1) Only the temperature sensors set on the outer wall and in the air are needed to check the working condition of the main sensor in the fire extinguishing agent liquid. Since the aqueous film forming foam fire extinguishing agent is corrosive, the expected service lives of the former two are much higher than that of the main sensor, thus saving costs compared with setting multiple main sensors in the tank; (2) The MCU only needs simple cyclic comparison operations to judge faults and guide the disposal, without having to process complex heat transfer formulas with a large number of parameters.

[0049] The above embodiments are merely examples for clearly illustrating the present invention and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. An automatic calibration method for temperature sensors in aqueous film-forming fire extinguishing agents, characterized in that, it is realized by connecting three temperature sensors placed at different positions to a microprocessing unit MCU, and the steps are as follows: (1) Place three calibrated temperature sensors inside the liquid level, on the inner and outer walls, and in the external air of the stainless steel storage tank of the aqueous film-forming fire extinguishing agent respectively, and connect them to the MCU; the temperature data generated by the three are respectively recorded as internal temperature, external temperature and air temperature, and the MCU collects data every 10 minutes and synchronously plots the temperature curves generated by the three; from evening to early morning of the next day, the air temperature and external temperature will enter the descending range and intersect with the internal temperature curve; when the temperature sensors are all working properly, the three temperature curves will intersect at one point, which is called the alignment point; (2) The MCU continuously tracks the alignment point through comparison logic. When three consecutive alignment points deviate, that is, the three curves cannot intersect at one point within the error range, start the correction program to achieve automatic correction or guide the staff to perform the correction operation and determine whether the internal temperature sensor needs to be replaced.

2. The automatic calibration method for temperature sensors in aqueous film-forming fire extinguishing agents according to claim 1, characterized in that, the start of the correction program follows the following process: S1, the MCU continues to collect internal temperature, external temperature and air temperature data, and the temperature data collected at regular time intervals form internal temperature, external temperature and air temperature curves; S2, determine whether the alignment point is abnormal. If not, the sensor is normal; if so, correct the internal temperature offset value to make the alignment point achieve three-line unification and continue to collect data; S3, after correcting the internal temperature offset value, continue to determine whether the alignment point is abnormal. If not, set a new offset value for the internal temperature sensor; if so, request re-calibration or replacement of the external temperature and air temperature sensors and continue to collect temperature data; S4, for the re-calibration or replacement of the external temperature and air temperature sensors, determine whether the alignment point is abnormal. If so, request replacement of the internal temperature sensor, and then the MCU continues to collect internal temperature, external temperature and air temperature data; if not, it means the sensor is normal.

3. The automatic calibration method for temperature sensors in aqueous film-forming fire extinguishing agents according to claim 1 or 2, characterized in that, the time intervals for data collection and comparison in step (2) are both 10 minutes, and the required temperature accuracy for comparison is 0.1 °C, that is, at the alignment point determined by the program, the difference between any two of the internal temperature, external temperature and air temperature data does not exceed 0.1 °C.

4. The automatic calibration method for temperature sensors in aqueous film-forming fire extinguishing agents according to claim 1, characterized in that, the storage tank of the aqueous film-forming fire extinguishing agent is made of stainless steel, stands on the ground with feet, is not directly irradiated by sunlight, and the external temperature sensor is arranged below the liquid level and covered by a heat-insulating block.

5. The automatic calibration method for temperature sensors in aqueous film-forming fire extinguishing agents according to claim 1, characterized in that, the aqueous film-forming fire extinguishing agent described in step (1) is a high-concentration sol solution with 70% water and 30% solute.

6. The automatic calibration method for temperature sensors in aqueous film-forming fire extinguishing agents according to claim 1, characterized in that, The storage tank described in step (1) contains enough aqueous film-forming foam extinguishing agent, and short-term thermal equilibrium can be achieved inside and outside the storage tank during the day-night alternation process, so that the inner temperature, outer temperature and air temperature curves periodically intersect at one point, namely the reference point.

7. An automatic calibration method for a temperature sensor in an aqueous film-forming foam extinguishing agent according to claim 1, characterized in that in step (1), a DS18B20 series temperature sensor is used, and its temperature measurement accuracy is 0.1 °C.

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