Calibration device and method for tunnel carbon monoxide content detector based on infrared absorption method

Abstract

A calibration device and method for a tunnel carbon monoxide content detector based on an infrared absorption method belongs to the field of carbon monoxide gas concentration detection in a tunnel environment, and includes a carbon monoxide standard gas cylinder, an exhaust bag, and a support device, wherein the carbon monoxide standard gas cylinder includes a calcium fluoride window, a quartz glass tube, a sealing ring, an air valve, and a flexible tube; the exhaust bag includes a bag body, a sealing clamping device, and an inlet and outlet; the support device includes a linear guide rail, a mounting support, and an adjustable support; and the design of a carbon monoxide standard. The present invention selects the window glass at both ends of the standard to ensure that the infrared light in the corresponding band has the greatest possible transmittance; and eliminates the influence of other gases and dust particles in the air. In the present invention, there may be other gases and dust particles in the space between the two ends of the standard and the transmitter and receiver that absorb the infrared light in the corresponding band. In order to eliminate such influence, a nitrogen blowing method is adopted to solve the problem.

Description

Technical Field

[0001] The invention relates to equipment and a method for detecting carbon monoxide gas concentration in a tunnel environment. Background Art

[0002] Tunnel carbon monoxide content detector: a device that can be used to detect carbon monoxide gas concentration in a tunnel environment, generally including a sensor, an analysis device, a display or transmission device, etc.

[0003] Infrared absorption: When the inherent vibration frequency and rotation frequency of a molecule are the same as the frequency of a certain band of infrared radiation, the molecule absorbs the infrared radiation in this band, converting the infrared radiation energy into molecular vibration and rotational kinetic energy.

[0004] With the continuous development of highway transportation in my country, tunnels are increasingly being used in highway construction, and the maximum length of a single tunnel is constantly breaking records. However, as a relatively closed space, tunnels lack sufficient air flow and exchange, which can easily lead to the accumulation of vehicle exhaust, causing elevated carbon monoxide concentrations, which seriously endangers pedestrian and vehicle safety. Therefore, the detection and alarm of carbon monoxide concentrations in tunnels has become extremely necessary.

[0005] At present, tunnel carbon monoxide concentration detection usually uses tunnel carbon monoxide content detectors, which are divided into non-dispersive infrared absorption method and electrochemical method according to their technical principles. The working principle of the carbon monoxide content detector based on the electrochemical method determines that it has a long reaction time. In addition, because its working process will cause the carbon monoxide concentration in the vicinity to decrease, if relatively accurate carbon monoxide concentration detection is to be achieved, measures should be taken to speed up the circulation of nearby air. At present, pumping is generally adopted. However, this brings a further problem, which is the accelerated accumulation of dust particles in the air at the air inlet. Measures must be taken to filter them. For electrochemical carbon monoxide content detectors that have been used for a long time, the filter device must be replaced regularly, which greatly limits the use of electrochemical carbon monoxide content detectors.

[0006] Carbon monoxide content detectors based on the non-dispersive infrared absorption method have the advantages of relatively high sensitivity and accuracy, fast response, good selectivity, high reliability, and long life. In addition, because they can share the optical path and optical device with visibility detection, they have a strong advantage in detecting carbon monoxide concentrations in tunnels. However, similar verification procedures already exist for electrochemical tunnel carbon monoxide content detectors, and their market is relatively standardized. However, non-dispersive infrared absorption carbon monoxide content detectors have no corresponding verification procedures to refer to, let alone mature calibration devices. In order to standardize the use of non-dispersive infrared absorption tunnel carbon monoxide content detectors, it is urgent to develop corresponding calibration devices to calibrate them regularly to promote the improvement of related industry standards.

[0007] Currently, there are no calibration devices for infrared absorption tunnel carbon monoxide detectors in China. However, there are calibration devices for other gas detectors based on infrared absorption methods, such as an infrared absorption methane gas detection alarm calibration device. This device uses a methane gas cylinder with a specific standard value (LEL*m) as a standard to test and verify infrared absorption methane gas detection alarms. The calibration device has been proven to be accurate and effective and has been recognized by CNAS. However, due to differences in the calibration environment, the composition of the gas being calibrated, and the structure of the product being calibrated, this device cannot be used directly to calibrate infrared absorption tunnel carbon monoxide content detectors. A specialized calibration device must be designed for this purpose.

[0008] If the existing calibration device is used to calibrate the infrared absorption tunnel carbon monoxide content detector, the following disadvantages will occur:

[0009] Reduce infrared transmittance. The materials used in the standard instruments of existing calibration devices will significantly reduce the transmittance of carbon monoxide gas in the infrared band.

[0010] Interference from other gases. Since the two ends of the standard device of the calibration device have not been treated accordingly, other gases and dust particles near the two ends of the standard device will cause interference during on-site calibration in the tunnel, affecting the detection accuracy of carbon monoxide;

[0011] Causes material waste. Affected by the working principle, the calibration device should have sufficient length, which will undoubtedly increase material waste and other measures should be taken to solve it;

[0012] Improper inlet and outlet design: Affected by the density of the test gas, the inlet and outlet design of the existing calibration device will become unreasonable and should be redesigned based on the gas density relationship. Summary of the Invention

[0013] The calibration device of the tunnel carbon monoxide content detector based on the infrared absorption method described in this patent is mainly composed of a carbon monoxide standard gas cylinder, an exhaust bag and a support device. The structural design of the carbon monoxide standard gas cylinder and the exhaust bag is proposed for the first time in the relevant field of this patent. The carbon monoxide standard gas cylinder is a unique design of this patent, consisting of a calcium fluoride window, a quartz glass tube, a sealing ring, an air valve, and a flexible tube. The exhaust bag is a structure specially designed to achieve the discharge of interstitial impurity gas, consisting of a bag body, a sealing clamping device, an air inlet and an air outlet. The support device is composed of a linear guide rail, a mounting support and an adjustable support. The overall hardware connection diagram of the calibration device is shown as follows: Figure 1 shown.

[0014] A calibration device for a tunnel carbon monoxide content detector based on an infrared absorption method, characterized by:

[0015] It includes a carbon monoxide standard gas cylinder, an exhaust bag and a supporting device, wherein the carbon monoxide standard gas cylinder includes a calcium fluoride window, a quartz glass tube, a sealing ring, an air valve, and a flexible tube; the exhaust bag includes a bag body, a sealing clamping device, an air inlet, and an air outlet; and the supporting device includes a linear guide rail, a mounting support, and an adjustable support;

[0016] The middle section of the carbon monoxide standard gas cylinder is a flexible tube with two openings at both ends. The flexible tube with two openings at both ends is bonded to the outer edge of the sealing ring to ensure complete airtightness between the two. The sealing ring is sleeved on one end of the quartz glass tube to form a seal, while the other end of the quartz glass tube is tightly bonded to the calcium fluoride window piece. An air inlet is provided in the middle section of the flexible tube, and an air outlet is provided in the middle section of the quartz glass tube. Air valves are installed at the air inlet and outlet.

[0017] The exhaust bag is ellipsoidal in shape, with openings at both ends of the short axis. One end is connected to the device under test, and the other end is connected to the quartz glass tube of the carbon monoxide standard cylinder. The exhaust bag is provided with an air inlet and an exhaust port.

[0018] When assembling the carbon monoxide standard cylinder and the exhaust bag, keep the center lines aligned;

[0019] The linear guide is fixed on a flat workbench with four sliders on it. The two sliders at both ends of the guide are used to fix the mounting supports, and the two sliders in the middle of the guide are used to fix the adjustable supports, all of which can slide and lock on the linear guide.

[0020] The method of using the device is characterized by:

[0021] Separately, tightly bond the calcium fluoride window piece, the quartz glass tube, and the sealing ring to the flexible tube to ensure airtightness; rotate the gas valve knob to close the two gas outlets; open the air inlet valve, suck out the gas inside the standard gas cylinder, and then close the air inlet valve; connect the carbon monoxide standard gas cylinder to the air inlet, open the air inlet valve at the same time, and inject carbon monoxide standard gas. After the flexible tube bulges, stop injecting carbon monoxide standard gas and suck out the gas inside the carbon monoxide standard gas cylinder. Repeat this 3 to 5 times to improve the purity of the gas inside the standard gas cylinder. After the last injection of carbon monoxide standard gas, close the air inlet valve after the gas injection is completed, and then stop injecting gas to prevent gas backflow;

[0022] The production process of standard carbon monoxide and nitrogen cylinders with different concentrations is carried out in the same way until all standard cylinders are completed;

[0023] Install the calibration device so that the center line of the device under test is parallel to the linear guide rail; install the nitrogen cylinder on the adjustable support and adjust the support height so that the center line of the nitrogen cylinder is parallel to the center line of the device under test and at the same height;

[0024] Input nitrogen into the exhaust bag and perform nitrogen blowing operation before calibration. The purpose of this operation is to eliminate the interference of impurity gases at both ends of the standard gas cylinder;

[0025] Replace the nitrogen cylinder with a standard carbon monoxide cylinder. During this process, impurity gas will enter the exhaust bag, so perform nitrogen blowing again and test the readings. Then use other standard carbon monoxide cylinders with different concentrations to replace them, perform nitrogen blowing and test the readings in the same way until the test is completed.

[0026] Design of a carbon monoxide standard. The window glass at each end of the standard is selected to maximize infrared transmittance in the corresponding wavelength band. While increasing the standard's size, the middle section is designed to be flexible, reducing material consumption and improving portability.

[0027] Eliminate the influence of other gases and dust particles in the air. In the space between the transmitter and receiver at both ends of the standard, there may be other gases and dust particles that absorb infrared rays of the corresponding band. In order to eliminate such influence, nitrogen blowing is used to solve the problem. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Hardware connection diagram of the calibration device of the tunnel carbon monoxide content detector based on infrared absorption method

[0029] Figure 1 In the figure, 1 is the device under test, 2 is the air inlet of the exhaust bag, which is used to input high-purity nitrogen with a nitrogen content greater than 99% into the exhaust bag, 3 is the air inlet, which is used to input carbon monoxide standard gas, with an adjusting air valve, 4 is a quartz glass tube, 5 is a calcium fluoride window, 6 is a flexible tube, whose length can be customized according to different installation distances of different detectors, 7 is a sealing ring, 8 is the air outlet, which is used to discharge impurities when making carbon monoxide standard cylinders, with an adjusting air valve, 9 is the air outlet of the exhaust bag, which is used to discharge impurities inside the exhaust bag, 10 is a mounting bracket, which is used to install the device under test, 11 is a linear guide rail, and 12 is an adjustable bracket, which is used to adjust and position the vertical position of the standard cylinder.

[0030] Figure 2 Production flow chart of carbon monoxide standard gas cylinder

[0031] Figure 3 Calibration device installation flow chart

[0032] Figure 4 Nitrogen blowing operation flow chart before calibration

[0033] Figure 5 Nitrogen blowing operation flow chart of the embodiment DETAILED DESCRIPTION

[0034] The calibration device of the tunnel carbon monoxide content detector based on the infrared absorption method described in this patent is a split assembly type, which is easy to disassemble and assemble.

[0035] The infrared light source of the tunnel carbon monoxide content detector based on infrared absorption method is generally emitted through a cylindrical light-shielding tube, such as Figure 1 The device under test is shown.

[0036] The middle section of the carbon monoxide standard cylinder is a flexible tube with two open ends. This tube is bonded to the outer edge of a sealing ring to ensure a complete airtight seal between the two. The sealing ring is fitted over one end of the quartz glass tube, forming a static seal. The other end of the quartz glass tube is tightly bonded to a calcium fluoride window. Additionally, an air inlet and outlet are located in the middle sections of the flexible tube and quartz glass tube, respectively. These inlet and outlet ports are equipped with valves, and when closed, they should provide a Class III airtight seal or higher.

[0037] Calcium fluoride windows have a low absorption coefficient and achieve a transmittance exceeding 90% in the infrared absorption band corresponding to carbon monoxide gas. One calcium fluoride window is located at each end of the carbon monoxide standard cylinder. The mounting surface must be perpendicular to the cylinder axis. The calcium fluoride window is circular and 2 mm thick.

[0038] The quartz glass tube has a fixed length of 60mm and is provided with an exhaust port with an inner diameter of 3mm for exhausting impurities. The exhaust port is equipped with a regulating valve, which is opened and closed when making a carbon monoxide standard cylinder, and ensures that it has an airtightness of level three or above in the closed state.

[0039] Flexible tubes are generally made of flexible materials such as soft plastic or soft rubber to facilitate the discharge of impurities. Their length can be customized according to the installation distance of the equipment being tested. An air inlet with an inner diameter of 6~10mm is provided in the middle to form positive pressure to prevent gas backflow. An regulating air valve is provided on the air inlet, which is also used for switching operations when making carbon monoxide standard cylinders to ensure that the air tightness is above level three in the closed state.

[0040] The bladder is ellipsoidal in shape, with circular openings at either end of its short axis. One end connects to the device under test, and the other end connects to the quartz glass tube of a carbon monoxide standard cylinder. Made of a flexible material such as rubber, the bladder's openings are elastic. Depending on the needs of the device under test, its elasticity should be designed to be between 1.2 and 1.5 to accommodate connections with devices of varying diameters. Airtightness requirements are not stringent at the connection. The bladder features an inlet with an inner diameter of 6-8mm and an outlet with an inner diameter of 3-4mm. The inner diameters are designed to create positive pressure and prevent gas backflow at the outlet. When setting the inlet and outlet, the relationship between air and nitrogen densities should be considered. Since the density of air is similar, with air density slightly greater than nitrogen, the inlet should be located at the top, while the outlet should be located at the bottom. This allows for rapid evacuation of the internal air and achieves a high-purity nitrogen atmosphere.

[0041] In order to facilitate the coaxial installation of the device to be tested, the carbon monoxide standard cylinder and the exhaust bag, the calibration device of the tunnel carbon monoxide content detector based on the infrared absorption method also includes a set of supporting devices.

[0042] Linear guides are typically fixed to a flat workbench and equipped with four sliders: two at each end of the rail are used to secure mounting brackets, and two in the middle are used to secure adjustable brackets. Each slider can slide and lock onto the rail. Linear guides are used to keep related equipment on the same mounting surface. Their length is generally greater than the installation distance of the equipment being inspected, typically greater than 3 meters. To ensure rigidity, linear guides with a grooved cross-section are recommended.

[0043] The purpose of the mounting bracket is to fix the device under test so that the optical axis of the device under test is on the mounting plane. In addition, the mounting bracket should also have the function of micro-adjusting the angle so that the optical axis of the device under test is parallel to the linear guide.

[0044] The adjustable support mainly realizes two functions: one is to realize fixed installation with the quartz glass tube, and the other is to realize the parallelism of the installation axis of the entire carbon monoxide standard cylinder and the linear guide rail by adjusting the vertical position.

[0045] After clarifying the various components of the calibration device and its installation process, the following work mainly includes the production of carbon monoxide standard gas cylinders, nitrogen blowing operation before calibration, and assembly of the calibration device. After that, the prepared carbon monoxide standard gas cylinders can be used for calibration work.

[0046] The calibration device of the infrared absorption tunnel carbon monoxide content detector described in this patent includes 3 carbon monoxide standard gas cylinders and 1 high-purity nitrogen gas cylinder. The production process of the carbon monoxide standard gas cylinder is as follows: Figure 2 , the production process of high-purity nitrogen cylinders can be used as a reference.

[0047] Tightly bond the calcium fluoride window to the quartz glass tube, and the sealing ring to the flexible tube to ensure airtightness. Then, connect the sealing ring to the quartz glass tube. The sealing ring should be made of a material with a smooth inner surface and an elastic expansion / contraction ratio of 1.2 to 1.5 to ensure airtightness at the connection.

[0048] Rotate the air valve knob to close the two air outlets. Open the air inlet, and use a pump or other suction method to suck out the gas inside the standard gas cylinder. At the same time, close the air inlet valve. Connect the carbon monoxide standard gas cylinder to the air inlet, open the air inlet valve at the same time, inject carbon monoxide standard gas, and stop injecting carbon monoxide standard gas after the flexible tube bulges. Use a pump or other method to suck out the gas inside the standard gas cylinder. Repeat this 3 to 5 times to ensure that the gas inside the standard gas cylinder is as close to the carbon monoxide standard gas as possible. After the last injection of carbon monoxide standard gas, close the air inlet valve while injecting gas, and then stop injecting gas. The process is as follows Figure 2 shown.

[0049] The production process of standard carbon monoxide cylinders and high-purity nitrogen cylinders with different concentrations is carried out in the same way until the production of all standard cylinders is completed.

[0050] The installation of the calibration device should follow the installation order from bottom to top and from both sides to the middle, and each component should be installed firmly and accurately.

[0051] To ensure the horizontal installation of the linear guide, a flat workbench should be selected for calibration in indoor environments, and a horizontal bracket should be selected for assistance in calibration in outdoor environments. After the horizontal installation of the linear guide is completed, fix the installation support according to the installation distance required by the equipment, and install the equipment to be tested on it. Install the adjustable support according to the installation distance of the equipment to be tested to ensure uniform force. Fix the quartz glass tube to the adjustable support, and adjust the height of the adjustable support to make the optical axis of the standard gas cylinder and the equipment to be tested coincide. Finally, install the exhaust bag. The exhaust bag is made of elastic material, and the diameter of its two ends can vary in the range of 0.8 to 1.2 times the diameter of the tube protruding from the equipment to be tested. One end of the exhaust bag should be connected to the standard gas cylinder, and the other end should be connected to the equipment to be tested. The installation flow chart is as follows Figure 3 shown.

[0052] High-purity nitrogen is injected into the exhaust bag from the air inlet. At the same time, the exhaust bag is squeezed to exhaust the air inside as much as possible. When the squeezing reaches the limit, the air outlet is blocked to restore the exhaust bag to its inflated state under the action of the incoming air. Then, the bag is squeezed again. After 3 to 5 times, it can be considered that the gas inside the exhaust bag has reached 99.999% high-purity nitrogen. The flow chart is shown in the figure. Figure 4 shown.

[0053] First, prepare a carbon monoxide standard gas cylinder and a high-purity nitrogen gas cylinder according to the method described above for later use.

[0054] Install the calibration device according to the calibration environment requirements, making sure the optical axis of the device under test is parallel to the linear guide rail. Install the high-purity nitrogen cylinder on the adjustable support, and adjust the support height so that the axis of the standard cylinder and the optical axis of the device under test are parallel and approximately at the same height.

[0055] High-purity nitrogen is introduced into the exhaust bag to perform nitrogen blowing operation before calibration.

[0056] Take test readings, read a value every five seconds, a total of five readings, and make a record.

[0057] Replace the high-purity nitrogen cylinder with carbon monoxide standard cylinder 1, perform nitrogen purge operation and test readings. Then replace carbon monoxide standard cylinder 1 with carbon monoxide standard cylinder 2 and carbon monoxide standard cylinder 3 in sequence, perform nitrogen purge operation and test readings in the same way until the test is completed.

[0058] The calibration device of the tunnel carbon monoxide content detector based on the infrared absorption method described in this patent provides a solution for the calibration of related products.

[0059] This patent reduces the consumption of carbon monoxide standard gas by setting up flexible tubes and inlet and outlet designs, reduces the workload of waste disposal, and minimizes pollution to the environment as much as possible. At the same time, flexible tubes are cheaper than quartz glass, reducing material waste, and reducing size for easy transportation.

[0060] This patent uses high-transmittance windows and can customize the length of standard gas cylinders according to the instrument design and installation distance, thereby improving calibration accuracy.

[0061] This patent eliminates the interference of other gases or smoke in the air, further promoting the improvement of detection accuracy.

[0062] The calibration device described in this patent can realize on-site calibration of the equipment under inspection, avoiding the trouble caused by disassembling the equipment.

[0063] The overall design scheme and component design concepts of the calibration device for the infrared absorption method tunnel carbon monoxide content detector are as follows:

[0064] The standard gas cylinder in the calibration device adopts a design that combines quartz glass tube and flexible tube, which reduces material waste, reduces component size, and facilitates transportation and storage.

[0065] A solution for filling standard gas cylinders. By utilizing the flexible tube's ease of exhaust, the cylinders can be emptied without the need for vacuum, simplifying the process. This exhaust solution also offers the added benefit of reducing standard gas consumption.

[0066] The gas filling method and production process of standard gas cylinders are relatively scientific.

[0067] The exhaust bag used in the nitrogen blowing method is designed to be made of elastic material, easy to deform, and the openings at both ends have a tension of 1.2~1.5 times.

[0068] The size of the air inlet and outlet of the exhaust bag used in the nitrogen blowing method can maintain positive pressure inside the bag to prevent gas backflow.

[0069] Nitrogen blowing is a method to eliminate interference from other gases and smoke.

Claims

1. A calibration method for a tunnel carbon monoxide content detector based on infrared absorption method, the device used in this method is: It includes a carbon monoxide standard gas cylinder, an exhaust bag and a supporting device, wherein the carbon monoxide standard gas cylinder includes a calcium fluoride window, a quartz glass tube, a sealing ring, an exhaust port, and a flexible tube; the exhaust bag includes a bag body, a sealing clamping device, an exhaust bag air inlet and an exhaust bag air outlet; and the supporting device includes a linear guide rail, a mounting support and an adjustable support; The middle section of the carbon monoxide standard gas cylinder is a flexible tube with two openings at both ends. The flexible tube with two openings at both ends is bonded to the outer edge of the sealing ring to ensure complete airtightness between the two. The sealing ring is sleeved on one end of the quartz glass tube to form a seal, while the other end of the quartz glass tube is tightly bonded to the calcium fluoride window piece. An air inlet is provided in the middle section of the flexible tube, and an air outlet is provided in the middle section of the quartz glass tube. Air valves are installed at the air inlet and outlet. The exhaust bag is ellipsoidal in shape, with openings at both ends of the short axis of the ellipsoid. One end is connected to the device under test, and the other end is connected to the quartz glass tube of the carbon monoxide standard gas cylinder. The exhaust bag is provided with an air inlet and an exhaust port. When assembling the carbon monoxide standard cylinder and the exhaust bag, keep the center lines aligned; The linear guide is fixed on a flat workbench, on which there are 4 sliders. The two sliders at both ends of the guide are used to fix the mounting brackets, and the two sliders in the middle of the guide are used to fix the adjustable brackets. Both can slide and lock on the linear guide. The method is characterized by: Separately, tightly bond the calcium fluoride window piece, the quartz glass tube, and the sealing ring to the flexible tube to ensure air tightness; rotate the gas valve knob to close the two gas outlets; open the gas inlet valve, suck out the gas inside the standard gas cylinder, and then close the gas inlet valve; connect the carbon monoxide standard gas cylinder to the gas inlet, open the gas inlet valve at the same time, and inject carbon monoxide standard gas. After the flexible tube bulges, stop injecting carbon monoxide standard gas and suck out the gas inside the carbon monoxide standard gas cylinder. Repeat this 3 to 5 times to improve the purity of the gas inside the standard gas cylinder. After the last injection of carbon monoxide standard gas, close the gas inlet valve after the gas injection is completed, and then stop injecting gas to prevent gas backflow; The production process of standard carbon monoxide and nitrogen cylinders with different concentrations is carried out in the same way until all standard cylinders are completed; Install the calibration device so that the center line of the device under test is parallel to the linear guide rail; install the nitrogen cylinder on the adjustable support and adjust the support height so that the center line of the nitrogen cylinder is parallel to the center line of the device under test and at the same height; Input nitrogen into the exhaust bag and perform nitrogen blowing operation before calibration. The purpose of this operation is to eliminate the interference of impurity gases at both ends of the standard gas cylinder; Replace the nitrogen cylinder with a standard carbon monoxide cylinder. During this process, impurity gas will enter the exhaust bag, so perform nitrogen blowing again and test the readings. Then use other standard carbon monoxide cylinders with different concentrations to replace them, perform nitrogen blowing and test the readings in the same way until the test is completed.

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