Automatic switching control system and method for thermocouples of brazing furnace

Abstract

The invention provides a brazing furnace thermocouple automatic switching control system and method, and relates to the field of brazing furnaces, and the brazing furnace thermocouple automatic switching control system comprises a main thermocouple T1, a standby thermocouple T2, a thermocouple signal input module, a relay switching module and a PLC control unit; the main thermocouple T1 is in communication connection with the standby thermocouple T2 through the relay switching module; the main thermocouple T1 and the standby thermocouple T2 are connected with the input end of the PLC control unit through the thermocouple signal input module. The output end of the PLC control unit is in communication connection with the relay switching module. The output end of the PLC control unit is in communication connection with the alarm unit, the recording unit and the display unit. According to the invention, full-automatic redundancy protection is realized, the system reliability is greatly improved, the continuity of temperature monitoring signals is ensured, process out-of-control and equipment risks caused by temperature measurement interruption are avoided, and the system is simple in structure, low in cost and easy to implement and popularize.

Description

Technical Field

[0001] This invention relates to the field of brazing furnaces, and more specifically, to an automatic thermocouple switching control system and method for brazing furnaces. Background Technology

[0002] Brazing furnaces are key equipment in industries such as aerospace, automotive manufacturing, and precision electronics. Precise temperature control within the furnace directly determines the connection quality, microstructure, and product yield of brazed workpieces. Temperature control relies heavily on thermocouple sensors, which collect furnace temperature data in real time and feed it back to a temperature controller or PLC, forming a closed-loop control system to adjust the power output of the heating elements. However, in the harsh working environment of brazing furnaces—long-term operation at high temperatures, sometimes accompanied by protective atmospheres or vacuum—the main thermocouple, as the primary temperature sensing element, faces multiple failure risks: 1) Aging and deterioration of the thermocouple wire: Long-term high temperatures cause coarse grains and compositional segregation in the thermocouple material, leading to drift in thermoelectric properties and inaccurate temperature measurement; 2) Deterioration of insulation performance: The insulating material (such as magnesium oxide) inside the thermocouple protective sheath is prone to moisture absorption or deterioration at high temperatures, causing short circuits to ground or interference; 3) Physical damage: Workpiece movement, vibration, or installation stress within the furnace can cause thermocouple wire breakage and damage to the protective sheath; 4) Loosening or oxidation of connection points: Poor contact of compensating wires or terminals. If the main thermocouple fails, its output temperature signal will deviate significantly from the true value, potentially causing the control system to make completely erroneous adjustments: if the feedback temperature is lower than the actual value, it will trigger continuous overheating, causing the workpiece to overheat, melt, develop coarse grains, or even damage the furnace equipment (such as a vacuum furnace tube bursting); if the feedback temperature is higher than the actual value, it will result in insufficient heating, preventing the brazing filler metal from flowing and wetting sufficiently, leading to defects such as incomplete soldering and slag inclusions, causing the entire batch of workpieces to be scrapped.

[0003] Currently, the industry's response to thermocouple failures mainly relies on manual inspection and manual switching. A common practice is to install a backup thermocouple on the furnace body, but the two are usually connected to different temperature controllers or selected via a manual switch. The drawbacks of this approach are obvious: 1) Delayed response: Operators cannot monitor the status of the main thermocouple in real time and continuously. There is a significant time delay from the occurrence of a failure to its detection and manual switching, during which time production is already out of control; 2) Reliance on operator experience: Judging whether a thermocouple is faulty requires highly experienced operators, making misjudgment easy; 3) Increased labor intensity and risk of human error; 4) Inability to record the failure process: This hinders quality traceability and equipment maintenance analysis. Summary of the Invention

[0004] The present invention aims to solve the problems of existing brazing furnace main thermocouple failures, which rely on manual intervention, have delayed response, and lack reliability.

[0005] To address the aforementioned problems, this invention provides an automatic thermocouple switching control system for brazing furnaces, comprising a main thermocouple T1, a standby thermocouple T2, a thermocouple signal input module, a relay switching module, and a PLC control unit. The main thermocouple T1 is communicatively connected to the standby thermocouple T2 via the relay switching module. Both the main thermocouple T1 and the standby thermocouple T2 are connected to the input terminals of the PLC control unit via the thermocouple signal input module. The output terminal of the PLC control unit is communicatively connected to the relay switching module. The output terminal of the PLC control unit is communicatively connected to an alarm unit, a recording unit, and a display unit.

[0006] The present invention provides an automatic thermocouple switching control system and method for brazing furnaces, which, compared with the prior art, has the following beneficial effects, but is not limited to: This invention achieves fully automatic redundant protection, greatly improving system reliability: through PLC-based intelligent logic judgment, it automates the entire process from fault detection and decision-making to execution switching, with a response time in the second range, completely eliminating the delay and uncertainty of manual intervention. When the main thermocouple fails, the system can seamlessly switch to the backup thermocouple in a very short time, ensuring the continuity of temperature monitoring signals and avoiding process control failures and equipment risks caused by temperature measurement interruptions.

[0007] This invention features comprehensive diagnostic, recording, and alarm functions, enhancing maintainability: the system is not merely a switchover execution tool, but a complete diagnostic tool. By recording switchover events, fault data, and alarm history, it provides equipment maintenance personnel with clear clues for problem localization, facilitating preventative maintenance and root cause analysis. Audible and visual alarms immediately alert operators to abnormalities, complying with industrial safety regulations.

[0008] This invention features a simple structure, low cost, and ease of implementation and promotion: the core of the system uses standard industrial PLCs, relays, and thermocouples, eliminating the need for expensive triple redundancy hardware or complex fault-tolerant controllers. Its logic is clear, program development is simple, and it can be easily integrated into existing brazing furnace electrical control cabinets, resulting in low retrofit and upgrade costs, making it suitable for a wide range of industrial users.

[0009] This invention ensures product quality and production safety: it fundamentally avoids the scrapping of batches of workpieces due to overheating or underheating caused by thermocouple failure, protecting the valuable workpiece materials and the value of previous processes. Simultaneously, by preventing furnace overheating, it effectively ensures the safety of the heating elements, furnace lining materials, vacuum system, and other equipment, avoiding potential production accidents.

[0010] Furthermore, the main thermocouple T1 and the backup thermocouple T2 are dual-core temperature probe thermocouples of the same model.

[0011] Furthermore, the main thermocouple T1 and the standby thermocouple T2 are thermocouples of the same type; the main thermocouple T1 and the standby thermocouple T2 are installed in adjacent positions inside the brazing furnace.

[0012] Furthermore, the relay switching module is a single-pole double-throw signal relay, whose common terminal is connected to the output terminal of the PLC control unit, whose normally closed contact is connected to the main thermocouple T1, and whose normally open contact is connected to the spare thermocouple T2.

[0013] Furthermore, the alarm unit is an audible and visual alarm, which includes a flashing light and a buzzer.

[0014] Furthermore, the recording unit is communicatively connected to the data backup center.

[0015] An automatic thermocouple switching control method for a brazing furnace, comprising the following steps: S1. Temperature signal acquisition and monitoring: The main thermocouple T1 is connected through a relay switching module, and the first temperature value fed back by it is continuously acquired. S2. Temperature difference calculation and deviation analysis: Calculate the absolute value of the first temperature difference ΔT1 between the first temperature value and the preset process setting temperature value; S3. Preliminary fault diagnosis: Determine whether the absolute value of the first temperature difference ΔT1 is greater than the preset temperature difference threshold. If ΔT1 is less than or equal to the temperature difference threshold, return to step S1; If ΔT1 is greater than the temperature difference threshold, then proceed to step S4; S4. Automatic switching execution: Control the relay switching module to disconnect the connection with the main thermocouple T1 and connect the connection with the standby thermocouple T2. S5. Post-switching verification and secondary confirmation: Collect the second temperature value fed back by the backup thermocouple T2 after switching within a stable time, and determine whether it is stable and within a reasonable range. If so, then the main thermocouple T1 is confirmed to be faulty, and the backup thermocouple T2 should be used continuously for temperature monitoring. If not, proceed to step S6; S6. Abnormal handling, recording and alarm: If an abnormality is repeatedly detected within a set time period and a switch is triggered to reach a preset number of times, the alarm unit will be triggered to sound an alarm, and the fault information will be recorded by the recording unit and displayed on the display unit.

[0016] Furthermore, the temperature difference threshold in step S3 is 100°C; Furthermore, the stabilization time in step S5 is 5-15 seconds.

[0017] Furthermore, in step S6, the time interval is set to 3-5 minutes, and the preset number of times is 3-5. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the framework of the automatic thermocouple switching control system for brazing furnace according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the automatic switching control method for thermocouples in a brazing furnace according to an embodiment of the present invention. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings showing multiple embodiments according to this application. It should be understood that the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments described in this application without creative effort will fall within the scope of protection of this application.

[0020] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in the description of this application is for the purpose of describing specific embodiments only and is not intended to limit this application; the terms "comprising," "including," "having," "containing," etc., in the description, claims, and accompanying drawings of this application are open-ended terms. Therefore, "comprising," "including," or "having" refers to, for example, a method or apparatus having one or more steps or elements, but is not limited to having only these one or more elements. The terms "first," "second," etc., in the description, claims, or accompanying drawings of this application are used to distinguish different objects, not to describe a specific order or hierarchy. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0021] In the description of this invention, it should be understood that the terms "upper", "lower", "left", "right", "front", "rear", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0022] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "attachment" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0023] It should be emphasized that when the term "comprising / including" is used in this specification, it is used to explicitly indicate the presence of the stated feature, integer, step, or component, but does not exclude the presence or addition of one or more other features, integers, steps, parts, or groups of features, integers, steps, or parts.

[0024] In this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, in this application, the character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0025] See Figure 1 An embodiment of the present invention provides an automatic thermocouple switching control system for a brazing furnace, comprising a main thermocouple T1, a standby thermocouple T2, a thermocouple signal input module, a relay switching module, and a PLC control unit. The main thermocouple T1 is communicatively connected to the standby thermocouple T2 via the relay switching module. Both the main thermocouple T1 and the standby thermocouple T2 are connected to the input terminals of the PLC control unit via the thermocouple signal input module. The output terminal of the PLC control unit is communicatively connected to the relay switching module. The output terminal of the PLC control unit is communicatively connected to an alarm unit, a recording unit, and a display unit.

[0026] The main thermocouple T1 and the backup thermocouple T2 convert the physical quantity of temperature inside the furnace into a weak millivolt-level potential signal, i.e., the thermoelectric effect. The main thermocouple T1 serves as the default working sensor, while the backup thermocouple T2 serves as a cold backup. The two provide physical and electrical backup for each other, forming the basis of system reliability.

[0027] The main thermocouple T1 and the backup thermocouple T2 achieve seamless fault takeover: When the main thermocouple T1 fails, the backup thermocouple T2 can immediately take over the temperature measurement function, ensuring uninterrupted temperature signal transmission. This is the physical prerequisite for automatic switching and ensuring production continuity. The consistent characteristics allow the PLC to directly compare and switch without complex signal calibration or compensation, reducing the complexity of the control algorithm and improving system stability and response speed.

[0028] The thermocouple signal input module performs cold junction compensation (compensating for the influence of ambient temperature at the junction box) on the weak, nonlinear analog signal output by the thermocouple, amplifies and filters it, and finally converts it into a digital signal that the PLC can process via an analog-to-digital converter (ADC). Thermocouple signal input modules typically have isolation functions to prevent high-temperature and high-potential interference from the furnace side from entering the low-voltage control side, protecting core equipment such as the PLC. Thermocouple signal input modules provide high-quality input signals: processing the raw, easily interfered thermocouple signals into stable and accurate digital quantities provides the data foundation for the PLC to make correct logical judgments. Without accurate signals, no intelligent judgment can be achieved. Thermocouple signal input modules enhance the system's anti-interference capability: filtering and isolation designs effectively suppress electromagnetic interference common in industrial environments, ensuring the stability of temperature measurement signals in complex electrical environments and avoiding false triggering caused by signal noise. As a bridge between the PLC control unit and field sensors, it simplifies system integration, allowing thermocouples of different brands and types to be connected to the control system through a standard interface.

[0029] The relay switching module enables fast and reliable physical switching: its response speed is as fast as milliseconds, allowing for the switching of temperature measurement channels in an extremely short time, minimizing the fault window period. With its simple structure, compared to complex electronic switches or multiplexers, electromagnetic relays are technologically mature, have high contact isolation, and low on-resistance. They exhibit extremely high reliability and robustness in high-temperature, high-electromagnetic-interference industrial environments, and are also inexpensive.

[0030] The PLC control unit now features intelligent automatic control: transforming traditional "human experience-based judgment" and "manual operation" into fully automatic, rule-based intelligent decision-making, which is the core of this system's "automatic switching." Advanced diagnostic logic is introduced: It can not only perform simple over-limit judgments but also implement complex diagnostic logic such as "delayed confirmation to prevent false alarms," ​​"secondary verification after switching," and "multiple loop attempts," significantly improving the accuracy of fault identification and the system's intelligence level, far exceeding simple hardware comparison circuits. High flexibility and scalability: Through software programming, parameters such as thresholds, delay times, and number of loops can be easily adjusted to adapt to different process requirements. Functionality can also be easily expanded, such as adding more thermocouples or communicating with the upper-level MES system, making the system highly adaptable and easy to upgrade and modify.

[0031] Alarm units immediately attract the operator's attention: In noisy industrial sites with multiple devices, audible and visual alarms are the most direct and effective way to notify operators of abnormal conditions, ensuring that faults are not overlooked.

[0032] The recording unit enables fault traceability: when a quality accident occurs or equipment performance needs to be analyzed, the recorded data can completely reconstruct the process before and after the fault occurred, providing tamper-proof data for root cause analysis.

[0033] The display unit enhances the intuitiveness and convenience of operation: it centrally and user-friendly displays all key information, greatly reducing the difficulty for operators to monitor and control the system.

[0034] This invention achieves fully automatic redundant protection, greatly improving system reliability: through PLC-based intelligent logic judgment, it automates the entire process from fault detection and decision-making to execution switching, with a response time in the second range, completely eliminating the delay and uncertainty of manual intervention. When the main thermocouple fails, the system can seamlessly switch to the backup thermocouple in a very short time, ensuring the continuity of temperature monitoring signals and avoiding process control failures and equipment risks caused by temperature measurement interruptions.

[0035] This invention employs a dual thermocouple configuration of "same model, adjacent installation" to ensure accurate judgment: the primary and backup thermocouples are of the same model and installed in adjacent positions, guaranteeing that the temperatures sensed by both are highly consistent under normal operating conditions. This provides a physical basis for fault judgment based on the "deviation between set temperature and actual temperature," making the PLC's logic judgment simple and effective, and avoiding erroneous switching caused by different temperature measurement points or differences in thermocouple characteristics.

[0036] This invention introduces a "secondary confirmation" mechanism to effectively prevent malfunctions: after automatic switching, a verification step is added to check the stability and rationality of the backup thermocouple readings. This mechanism can effectively distinguish between "primary thermocouple individual failure," "actual furnace temperature anomaly," or "common channel failure," greatly reducing the probability of false alarms and erroneous switching, and improving the intelligence and accuracy of control decisions.

[0037] This invention features comprehensive diagnostic, recording, and alarm functions, enhancing maintainability: the system is not merely a switchover execution tool, but a complete diagnostic tool. By recording switchover events, fault data, and alarm history, it provides equipment maintenance personnel with clear clues for problem localization, facilitating preventative maintenance and root cause analysis. Audible and visual alarms immediately alert operators to abnormalities, complying with industrial safety regulations.

[0038] This invention features a simple structure, low cost, and ease of implementation and promotion: the core of the system uses standard industrial PLCs, relays, and thermocouples, eliminating the need for expensive triple redundancy hardware or complex fault-tolerant controllers. Its logic is clear, program development is simple, and it can be easily integrated into existing brazing furnace electrical control cabinets, resulting in low retrofit and upgrade costs, making it suitable for a wide range of industrial users.

[0039] This invention ensures product quality and production safety: it fundamentally avoids the scrapping of batches of workpieces due to overheating or underheating caused by thermocouple failure, protecting the valuable workpiece materials and the value of previous processes. Simultaneously, by preventing furnace overheating, it effectively ensures the safety of the heating elements, furnace lining materials, vacuum system, and other equipment, avoiding potential production accidents.

[0040] Furthermore, the main thermocouple T1 and the backup thermocouple T2 are dual-core temperature probe thermocouples of the same model.

[0041] Because the same type of dual-core temperature probe thermocouple is used, the temperatures measured by the two should be highly consistent under normal circumstances, providing a reliable physical and logical reference for the PLC to judge single-point faults.

[0042] Furthermore, the main thermocouple T1 and the standby thermocouple T2 are thermocouples of the same type; the main thermocouple T1 and the standby thermocouple T2 are installed in adjacent positions inside the brazing furnace.

[0043] Similarly, since they are installed in adjacent configurations with the same model, the temperatures measured by both should be highly consistent under normal circumstances, providing a reliable physical and logical reference for the PLC to judge single-point faults.

[0044] Furthermore, the relay switching module is a single-pole double-throw signal relay, whose common terminal is connected to the output terminal of the PLC control unit, whose normally closed contact is connected to the main thermocouple T1, and whose normally open contact is connected to the spare thermocouple T2.

[0045] The relay switching module acts as a controlled single-pole double-throw switch, determining which thermocouple signal to connect to the subsequent signal input module based on PLC instructions. Electrical isolation and power drive are achieved between the control signal (PLC low voltage, low current) and the measurement signal (thermocouple return). The system automatically returns to the state using the main thermocouple, or at least maintains a defined and predictable state, conforming to safety design principles.

[0046] Furthermore, the alarm unit is an audible and visual alarm, which includes a flashing light and a buzzer; The audible and visual alarm indicates that when a thermocouple switch occurs or a serious fault is diagnosed in the system, it immediately emits a strong visual signal (flashing red light) and an audible signal (buzzer sound). This complies with industrial safety regulations: it mandates that operators or maintenance personnel respond to abnormalities, improving the safety of the entire production system and preventing secondary accidents caused by delayed fault detection. Through the alarm mode, operators can remotely assess the nature and urgency of the fault, facilitating a rapid response.

[0047] Furthermore, the recording unit is communicatively connected to the data backup center.

[0048] The recording unit records all key events chronologically, such as the time of main thermocouple temperature anomaly, the time of switching action, the temperature value after switching, and the alarm trigger time and type. This creates a historical archive of system operation, which is transmitted to the data backup center for easy fault traceability. By analyzing long-term recorded thermocouple performance data, such as drift trends and switching frequency, sensor lifespan can be predicted in advance, enabling the development of scientific preventative maintenance plans and transforming reactive maintenance into proactive maintenance.

[0049] like Figure 2 As shown, an automatic thermocouple switching control method for a brazing furnace is described, and the method steps are as follows: S1. Temperature signal acquisition and monitoring: The main thermocouple T1 is connected through a relay switching module, and the first temperature value fed back by it is continuously acquired. Specifically, after the system is powered on and initialized, the PLC control unit, by default, continuously collects and monitors the real-time temperature value T_act fed back by the main thermocouple T1 channel connected through the relay switching module; S2. Temperature difference calculation and deviation analysis: Calculate the absolute value of the first temperature difference ΔT1 between the first temperature value and the preset process setting temperature value; Specifically, the PLC control unit reads the preset process set temperature value T_s and calculates the absolute difference between the current actual temperature and the set temperature, i.e., temperature difference ΔT=|T_s-T_act|; S3. Preliminary fault diagnosis: Determine whether the absolute value of the first temperature difference ΔT1 is greater than the preset temperature difference threshold. If ΔT1 is less than or equal to the temperature difference threshold, return to step S1; If ΔT1 is greater than the temperature difference threshold, then proceed to step S4; Specifically, the calculated ΔT is compared with a pre-set temperature difference threshold, which serves as a fault criterion, and is denoted as ΔT_threshold. If ΔT ≤ ΔT_threshold, the main thermocouple T1 is determined to be working normally. The system maintains the current state and returns to step S1 to continue monitoring. If ΔT > ΔT_threshold, it is determined that the main thermocouple T1 may have a significant fault (such as open circuit, short circuit, severe drift), triggering the switching preparation and proceeding to step S4; S4. Automatic switching execution: Control the relay switching module to disconnect the connection with the main thermocouple T1 and connect the connection with the standby thermocouple T2. Specifically, the PLC control unit outputs a switching control signal to the relay switching module, driving the relay to operate and physically disconnect the connection with the main thermocouple T1, while simultaneously connecting the connection with the backup thermocouple T2; at this point, the signal source input to the thermocouple signal input module is switched to T2.

[0050] S5. Verification and secondary confirmation after switching: Collect the second temperature value fed back by the backup thermocouple T2 after switching, and determine whether it is stable and within a reasonable range. If so, then the main thermocouple T1 is confirmed to be faulty, and the backup thermocouple T2 should be used continuously for temperature monitoring. If not, proceed to step S6; Specifically, after the switch is completed, the PLC control unit immediately begins to collect the temperature value T_new fed back by the backup thermocouple T2; the system sets a short stabilization time, and then judges whether the reading of T2 is stable, and whether the difference between it and the set temperature ΔT'=|T_s-T_new| returns to a reasonable range, i.e., ΔT'≤ΔT_threshold; If the verification passes and it is confirmed that the main thermocouple T1 is indeed faulty, while the backup thermocouple T2 is working normally, the system will lock T2 as the current effective temperature sensing element and will display "Switched to backup thermocouple" on the display unit, and the process will end. If the verification fails, such as when the T2 reading is abnormal or unstable, or when ΔT' is still very large, it indicates that the problem may not be a single thermocouple failure, but rather other systemic issues such as input module failure, furnace overheating, or low-temperature accidents. In this case, the system proceeds to step S6. S6. Abnormal handling, recording and alarm: If an abnormality is repeatedly detected within a set time period and a switch is triggered to reach a preset number of times, the alarm unit will be triggered to sound an alarm, and the fault information will be recorded by the recording unit and displayed on the display unit.

[0051] Specifically, when step S5 fails verification, and the abnormality is repeatedly detected and the switching is triggered repeatedly within the set time period to reach the preset number of times, the PLC control unit determines that there is a serious abnormality in the system and implements an abnormality alarm.

[0052] The alarm unit is activated, triggering the audible and visual alarm, which includes a flashing red light and a buzzer, to send an emergency intervention signal to the operator.

[0053] The drive recording unit stores key information such as the time of the fault event, the temperature data at the time of triggering, and the number of switching actions into non-volatile memory or uploads it to the display unit to form a traceable maintenance log.

[0054] The drive display unit displays specific fault codes and prompts, such as "Thermocouples are all abnormal" or "System failure, please check," to guide maintenance.

[0055] Furthermore, the predetermined temperature difference threshold in step S3 is 100°C; This threshold is set based on a combination of the maximum allowable temperature fluctuation of the process, normal thermocouple error, and safety margin.

[0056] Furthermore, the stabilization time in step S5 is 5-15 seconds.

[0057] A 5-15 second settling time provides ample time for relay contacts to stabilize, loop current to build up, and signal noise to attenuate. Waiting for the signal loop to enter a stable and clean electrical state is a physical prerequisite for subsequent effective logical judgments.

[0058] Furthermore, in step S6, the time interval is set to 3-5 minutes, and the preset number of times is 3-5.

[0059] A 3-5 minute retry cycle allows the system to observe, within a limited time, whether the temperature control system can bring the actual furnace temperature back to the set range, using the T2 reading as the real input. If the furnace temperature begins to decrease and tends to normal within this time, it indicates that the historical overtemperature was caused by the T1 fault and the problem is being resolved; if the furnace temperature remains abnormal, it is confirmed as a serious system-level fault. This enables a deeper diagnosis of the root cause of the fault.

[0060] 3-5 cycles is a proven best practice value in industrial control. It gives the system sufficient time for self-healing and diagnostics, while ensuring that in the event of a real crisis, a final safety decision can be made within a reasonable timeframe, keeping the risk within an acceptable range.

[0061] While the present invention has been disclosed above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention, and all such changes and modifications will fall within the scope of protection of the present invention.

Claims

1. An automatic thermocouple switching control system for a brazing furnace, characterized in that, It includes a main thermocouple T1, a backup thermocouple T2, a thermocouple signal input module, a relay switching module, and a PLC control unit. The main thermocouple T1 is communicatively connected to the backup thermocouple T2 via the relay switching module. Both the main thermocouple T1 and the backup thermocouple T2 are connected to the input terminals of the PLC control unit via the thermocouple signal input module. The output terminal of the PLC control unit is communicatively connected to the relay switching module. The output terminal of the PLC control unit is communicatively connected to the alarm unit, the recording unit, and the display unit.

2. The automatic thermocouple switching control system for brazing furnace according to claim 1, characterized in that, The main thermocouple T1 and the backup thermocouple T2 are dual-core temperature probe thermocouples of the same model.

3. The automatic thermocouple switching control system for brazing furnace according to claim 1, characterized in that, The main thermocouple T1 and the standby thermocouple T2 are thermocouples of the same type; the main thermocouple T1 and the standby thermocouple T2 are installed in adjacent positions inside the brazing furnace.

4. The automatic thermocouple switching control system for brazing furnaces according to claim 2 or 3, characterized in that, The relay switching module is a single-pole double-throw signal relay. Its common terminal is connected to the output terminal of the PLC control unit, its normally closed contact is connected to the main thermocouple T1, and its normally open contact is connected to the spare thermocouple T2.

5. The automatic thermocouple switching control system for brazing furnace according to claim 4, characterized in that, The alarm unit is an audible and visual alarm, which includes a flashing light and a buzzer.

6. The automatic thermocouple switching control system for brazing furnace according to claim 5, characterized in that, The recording unit is communicatively connected to the data backup center.

7. The control method of the automatic thermocouple switching control system for brazing furnaces according to any one of claims 1-6, characterized in that, The steps are as follows: S1. Temperature signal acquisition and monitoring: The main thermocouple T1 is connected through a relay switching module, and the first temperature value fed back by it is continuously acquired. S2. Temperature difference calculation and deviation analysis: Calculate the absolute value of the first temperature difference ΔT1 between the first temperature value and the preset process setting temperature value; S3. Preliminary fault diagnosis: Determine whether the absolute value of the first temperature difference ΔT1 is greater than the preset temperature difference threshold. If ΔT1 is less than or equal to the temperature difference threshold, return to step S1; If ΔT1 is greater than the temperature difference threshold, then proceed to step S4; S4. Automatic switching execution: Control the relay switching module to disconnect the connection with the main thermocouple T1 and connect the connection with the standby thermocouple T2. S5. Post-switching verification and secondary confirmation: Collect the second temperature value fed back by the backup thermocouple T2 after switching within a stable time, and determine whether it is stable and within a reasonable range. If so, then the main thermocouple T1 is confirmed to be faulty, and the backup thermocouple T2 should be used continuously for temperature monitoring. If not, proceed to step S6; S6. Abnormal handling, recording and alarm: If an abnormality is repeatedly detected within a set time period and a switch is triggered to reach a preset number of times, the alarm unit will be triggered to sound an alarm, and the fault information will be recorded by the recording unit and displayed on the display unit.

8. The control method of the automatic thermocouple switching control system for brazing furnace according to claim 7, characterized in that, The temperature difference threshold for step S3 is 100℃.

9. The control method of the automatic thermocouple switching control system for brazing furnace according to claim 8, characterized in that, The stabilization time in step S5 is 5-15 seconds.

10. The control method of the automatic thermocouple switching control system for brazing furnace according to claim 9, characterized in that, In step S6, the set time is 3-5 minutes and the preset number of times is 3-5.

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