Marine fire alarm system ground fault detection method

Abstract

The invention discloses a ground fault detection method for a marine fire alarm system, and relates to the technical field of fault detection, a controller periodically applies alternating detection signals with preset frequency and amplitude between a signal bus and a ground wire of the fire alarm system, samples and obtains a real-time voltage value of the signal bus to the ground in real time, and sends the real-time voltage value to the ground; a dynamic reference voltage is calculated and updated according to the real-time voltage value, the dynamic reference voltage is used for tracking changes of the real-time voltage value in a fault-free state, the real-time voltage value is compared with the dynamic reference voltage, an absolute difference value is calculated, a first time delay threshold value and a second time delay threshold value are set, and the first time delay threshold value and the second time delay threshold value are set. And automatically generating a corresponding fault detection strategy according to the sent primary alarm or secondary alarm. The accuracy and reliability of ground fault detection are effectively improved by periodically applying an alternating detection signal, sampling the voltage to ground of a signal bus in real time, dynamically tracking the reference voltage and carrying out multi-stage comparison and delay judgment.

Description

Technical Field

[0001] This invention relates to the field of fault detection technology, and specifically to a method for detecting grounding faults in a marine fire alarm system. Background Technology

[0002] Ship fire alarm system is one of the core systems to ensure the safety of ship navigation. Its reliability is directly related to the life and property safety of crew and ship. Due to the humid environment, severe salt spray corrosion, large vibration and confined space of the ship, its cables and electrical equipment are very prone to grounding failure due to insulation aging, mechanical damage and other reasons. Currently, common fire alarm system grounding fault detection methods mostly employ DC balanced bridge method or simple threshold comparison method. The sensitivity of DC balanced bridge method decreases when the system has a large capacitance to ground and is easily affected by changes in ambient temperature. The simple threshold comparison method is prone to false alarms due to instantaneous fluctuations in the ship's electrical grid (such as the start-up and shutdown of high-power equipment) and lacks anti-interference capability. In addition, most existing methods can only detect the existence of faults but cannot quickly and accurately locate the specific branch where the fault occurred, which brings great difficulties to subsequent maintenance and troubleshooting.

[0003] Therefore, there is an urgent need for a grounding fault detection method that can adapt to the complex and harsh environment of ships, has high reliability and high sensitivity, and can achieve accurate fault location. Summary of the Invention

[0004] The purpose of this invention is to provide a grounding fault detection method for marine fire alarm systems. This method can effectively distinguish between transient interference and real faults, improve the accuracy and reliability of detection, and quickly locate the fault point.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for detecting grounding faults in a marine fire alarm system, the detection method comprising the following steps: S1: The controller periodically applies an alternating detection signal with a preset frequency and amplitude between the signal bus and ground wire of the fire alarm system; S2: Real-time sampling and acquisition of the real-time voltage value of the signal bus relative to ground; S3: Calculate and update the dynamic reference voltage based on the real-time voltage value, the dynamic reference voltage being used to track the change of the real-time voltage value under fault-free conditions; S4: Compare the real-time voltage value with the dynamic reference voltage and calculate the absolute difference; S5: Set the first delay threshold T1 and the second delay threshold T2, where T1 <T2; S6: When the absolute difference exceeds the first preset voltage threshold for a period of time T1, it is determined that a transient grounding fault has occurred in the fire alarm system, and a level one alarm is issued. S7: When the absolute difference exceeds the second preset voltage threshold for a period of time T2, it is determined that the fire alarm system has a continuous grounding fault and a level 2 alarm is issued. S8: Automatically generate corresponding fault detection strategies based on the issued Level 1 or Level 2 alarms.

[0006] In a preferred embodiment, step S8 involves automatically generating a corresponding fault detection strategy based on the issued Level 1 or Level 2 alarm, including the following steps: S81a: The controller sends a self-test command to all connected detectors via the signal bus; S82a: After receiving the self-test command, each detector connects a known diagnostic resistor between its internal circuit and ground; S83a: The controller detects sudden changes in bus-to-ground voltage caused by the connection of the diagnostic resistor; S84a: Identify detectors whose voltage change characteristics match the expectations, determine them as faulty branches, and report their address codes.

[0007] In a preferred embodiment, step S8, which involves automatically generating a corresponding fault detection strategy based on the issued Level 1 or Level 2 alarm, further includes the following steps: S81b: The controller issues a global self-test command; S82b: The controller selects the first detector in a preset order; S83b: Sends a command to the selected detector to close its internal switch and connect the diagnostic resistor between its circuit and ground; S84b: The controller monitors the amplitude and waveform of sudden changes in bus voltage; S85b: Determine whether the magnitude of the sudden change matches the expected characteristics of the connected diagnostic resistor, and identify whether there are any abnormal characteristics based on the matching results; S86b: If an abnormal feature is detected, the branch where the detector is located is determined to be a faulty branch. The controller records its address code and displays the positioning result on the human-machine interface. S87b: After polling all devices, the positioning process ends.

[0008] In a preferred embodiment, the resistance value of the diagnostic resistor is calibrated so that the voltage fluctuation amplitude generated after its connection is greater than the normal fluctuation range of the system.

[0009] In a preferred embodiment, step S85b, identifying whether there are feature anomalies based on the matching results, includes the following steps: If a match is found, the detector branch is normal, and the controller commands it to disconnect the diagnostic resistor and select the next detector. If a match is not found, it indicates that there is a ground fault point in the branch, and the fault current is shunted, resulting in abnormal voltage change characteristics.

[0010] In a preferred embodiment, the dynamic reference voltage is calculated using a first-order digital low-pass filtering algorithm, with the formula: V_ref(n)=α*V_sense(n)+(1-α)*V_ref(n-1), where α is a filtering coefficient between 0 and 1, V_ref(n) is the current dynamic reference voltage, V_ref(n-1) is the previous dynamic reference voltage, and V_sense(n) is the current voltage value.

[0011] In a preferred embodiment, the frequency of the alternating detection signal is between 0.1 Hz and 10 Hz, and the amplitude is a non-dangerous voltage within the safe voltage range.

[0012] In a preferred embodiment, the first delay threshold T1 is 100ms to 500ms, and the second delay threshold T2 is 2s to 10s.

[0013] The technical effects and advantages provided by the present invention in the above technical solution are as follows: This invention accurately identifies abnormal voltage deviations caused by grounding faults by comparing real-time voltage with a dynamic reference voltage and calculating the absolute difference, providing a quantitative basis for subsequent fault determination. Based on this, by setting two different delay thresholds (T1 and T2) and corresponding first and second preset voltage thresholds, it achieves graded determination of transient and persistent grounding faults: when the voltage anomaly continuously exceeds the first threshold for a short time T1, the system determines it as a transient fault and issues a level-one alarm, which helps to promptly detect occasional or minor grounding anomalies; while when the voltage anomaly continuously exceeds the higher second threshold for a longer time T2, it is determined as a more serious persistent grounding fault and issues a level-two alarm, facilitating rapid location and handling of serious problems that may pose fire safety hazards.

[0014] This invention, by periodically applying an alternating detection signal with a preset frequency and amplitude between the signal bus and the ground wire, can actively stimulate potential ground fault characteristics without affecting the normal communication of the system, so that the grounding problem that might have been hidden will appear in the form of voltage changes, thereby achieving active detection of the fault.

[0015] This invention samples the voltage to ground of the signal bus in real time and dynamically calculates and updates the reference voltage, enabling the system to adaptively track the normal voltage fluctuation range under fault-free conditions. This effectively eliminates voltage drift caused by non-fault factors such as environmental interference, line aging, or temperature changes, and improves the robustness of detection.

[0016] This invention automatically generates corresponding fault detection strategies based on different alarm levels, guiding maintenance personnel to take targeted troubleshooting and repair measures, thereby significantly improving fault response efficiency, shortening maintenance time, and ensuring the stable operation of the ship's fire alarm system and the overall fire safety of the ship. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0018] Figure 1 This is a schematic diagram of the topology of an existing marine fire alarm system.

[0019] Figure 2 This is the main flowchart of the grounding fault detection method according to an embodiment of the present invention.

[0020] Figure 3 This is a schematic diagram illustrating the dynamic reference voltage update and fault diagnosis principle of an embodiment of the present invention.

[0021] Figure 4 This is a flowchart of the fault location method according to an embodiment of the present invention. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] like Figure 1 As shown, a typical marine fire alarm system includes a controller, a signal bus as a communication medium, and various detectors (such as smoke detectors and heat detectors) and modules (such as manual alarm buttons, monitoring modules, and other devices) connected to the bus. The controller integrates the detection circuit of this invention, including a programmable detection signal source V_test and its internal resistance R_test.

[0024] Example: This example provides a method for detecting grounding faults in a marine fire alarm system. The detection method includes the following steps: S1: The system controller periodically applies an alternating detection signal (V_test) with a preset frequency and amplitude between the signal bus (BUS) and ground (GND) of the fire alarm system; the frequency of the alternating detection signal (V_test) is between 0.1 Hz and 10 Hz, and the amplitude is a non - dangerous low voltage within the system safety voltage range. S2: Real - time sample and obtain the real - time voltage value (V_sense) of the signal bus to ground. S3: Calculate and update a dynamic reference voltage (V_ref) based on the real - time voltage value (V_sense). The dynamic reference voltage (V_ref) tracks the slow change of the real - time voltage value (V_sense) in a fault - free state. In step S3, the calculation of the dynamic reference voltage (V_ref) uses a first - order digital low - pass filtering algorithm, and its formula is: V_ref(n)=α*V_sense(n)+(1 - α)*V_ref(n - 1), where α is a filtering coefficient between 0 and 1. S4: Compare the real - time voltage value (V_sense) with the dynamic reference voltage (V_ref) and calculate their absolute difference (|ΔV|). S5: Set a first delay threshold (T1) and a second delay threshold (T2), where T1 < T2. The first delay threshold (T1) is between 100 ms and 500 ms, and the second delay threshold (T2) is between 2 s and 10 s. S6: When the time that the absolute difference (|ΔV|) continuously exceeds the first preset voltage threshold (V_th1) reaches T1, it is determined that the system has a transient ground fault and a first - level alarm is issued. S7: When the time that the absolute difference (|ΔV|) continuously exceeds the second preset voltage threshold (V_th2) reaches T2, it is determined that the system has a continuous ground fault and a second - level alarm is issued, where V_th2 ≤ V_th1.

[0025] S8: Automatically generate corresponding fault detection strategies according to the issued first - level or second - level alarm.

[0026] It further includes a fault location step: S81a: The controller sends a self - test instruction to all detectors connected through the signal bus. S82a: After each detector receives the self - test instruction, a known diagnostic resistor (R_diag) is connected between its internal loop and ground. S83a: The controller detects the mutation of the bus - to - ground voltage caused by the connection of the diagnostic resistor (R_diag). The resistance value of the diagnostic resistor (R_diag) is calibrated so that the voltage mutation amplitude generated after its connection is significantly greater than the normal fluctuation range of the system. S84a: Identify detectors whose voltage change characteristics match the expectations, determine them as faulty branches, and report their address codes.

[0027] like Figure 4 As shown, after the level 2 alarm is triggered: S81b: The controller issues a global self-test command.

[0028] S82b: The controller selects the first detector in a preset order (e.g., address codes from smallest to largest).

[0029] S83b: Sends a command to the selected detector to close its internal switch and connect the diagnostic resistor R_diag between its loop and ground.

[0030] S84b: The controller monitors the amplitude and waveform of sudden changes in the bus voltage V_sense.

[0031] S85b: Determine if the sudden change matches the expected characteristics of the connected R_diag (e.g., voltage drop to a specific value). If it matches, the detector branch is normal, the controller commands it to disconnect R_diag, and selects the next detector. If it does not match (e.g., no voltage change or minimal change), it indicates that there is a low-resistance path (i.e., a ground fault point) in the branch, and the fault current is shunted, resulting in abnormal voltage change characteristics.

[0032] S86b: Once an abnormal feature is detected, the branch where the detector is located is determined to be a faulty branch. The controller records its address code and displays the positioning result on the human-machine interface.

[0033] S87b: After polling all devices, the positioning process ends.

[0034] The steps for this application are explained in detail below: When the absolute difference (|ΔV|) exceeds the first preset voltage threshold (V_th1) for a duration of T1, a transient ground fault is determined to have occurred in the system, and a Level 1 alarm is issued. Based on the issued Level 1 alarm, the corresponding fault detection strategy is automatically generated as follows: Furthermore, when the system detects that the absolute difference between the signal bus voltage and ground (|ΔV|) exceeds the first preset voltage threshold (V_th1) for a duration exceeding the first delay threshold T1, it indicates a short-term or intermittent abnormal offset in the signal bus voltage to ground. This abnormality is usually caused by non-continuous factors such as transient interference, brief grounding, or poor line contact. Therefore, the system determines that a transient grounding fault has occurred and triggers a Level 1 alarm. The Level 1 alarm serves as an early warning of the fault, indicating that the system may have a temporary grounding abnormality. Although it has not yet constituted a serious safety hazard, it requires attention. Based on this Level 1 alarm, the system can automatically generate corresponding fault detection strategies, such as suggesting prioritizing checks on the connection status between the signal bus and ground wire, investigating for partial short circuits or poor contact, and confirming whether surrounding equipment is generating electromagnetic interference. This guides maintenance personnel to conduct targeted preliminary diagnosis and troubleshooting, thereby quickly locating possible transient fault sources and preventing them from developing into persistent grounding faults.

[0035] like Figure 2 As shown, the detection process of the ground fault detection method in this embodiment of the invention is as follows: Step A: Power on and initialize the system, set the parameters as follows: V_test is 1Hz, 5V square wave; α=0.01; V_th1=1.5V, T1=200ms; V_th2=0.5V, T2=5s.

[0036] Step B: The controller applies an alternating detection signal V_test to the bus.

[0037] Step C: The ADC module samples the bus-to-ground voltage V_sense in real time.

[0038] Step D: Update the dynamic reference voltage according to the formula V_ref(n)=0.01*V_sense(n)+0.99*V_ref(n-1).

[0039] Step E: Calculate |ΔV| = |V_sense - V_ref|.

[0040] Step F: Determine if |ΔV|>V_th1. If yes, start timer T1_cnt; otherwise, clear T1_cnt and proceed to step H.

[0041] Step G: Determine if T1_cnt >= T1? If yes, determine it as a transient fault and execute step J (Level 1 alarm); otherwise, proceed to step H.

[0042] Step H: Determine if |ΔV| > V_th2. If yes, start timer T2_cnt; otherwise, clear T2_cnt.

[0043] Step I: Determine if T2_cnt >= T2. If yes, determine it as a persistent fault and execute step K (level 2 alarm); otherwise, return to step C and continue the loop.

[0044] Step J: Issue a transient fault warning (such as a panel indicator light flashing), record the log, and return to the previous step.

[0045] Step K: Issue a continuous fault alarm (audio-visual alarm) and optionally initiate the fault location process.

[0046] Figure 3 The discrimination process is illustrated visually. At time t1, a short-duration pulse interference causes |ΔV| to exceed V_th1, but since the duration does not reach T1, the system does not alarm. At time t2, a real ground fault occurs, and |ΔV| initially exceeds V_th1. Due to the persistence of the fault, |ΔV| subsequently stabilizes at a level higher than V_th2, and after reaching time T2, the system confirms and alarms.

[0047] Example 1: Further, when the absolute difference (|ΔV|) exceeds the second preset voltage threshold (V_th2) for a period of time T2, it is determined that a continuous ground fault has occurred in the system, and a secondary alarm is issued. When the secondary alarm is issued, the fault location steps are as follows: S81a: The controller sends a self-test command to all connected detectors via the signal bus; S82a: After receiving the self-test command, each detector connects a known diagnostic resistor (R_diag) between its internal circuit and ground. S83a: The controller detects sudden changes in bus-to-ground voltage caused by the connection of a diagnostic resistor (R_diag). The resistance value of the diagnostic resistor (R_diag) is calibrated so that the voltage change amplitude generated after its connection is significantly greater than the normal fluctuation range of the system. S84a: Identify detectors whose voltage change characteristics match the expectations, determine them as faulty branches, and report their address codes.

[0048] In marine fire alarm systems, when the absolute difference in signal bus voltage to ground (|ΔV|) exceeds the second preset voltage threshold (V_th2) for an extended period, reaching a longer second delay threshold T2, it indicates a significant and prolonged abnormal voltage deviation in the bus to ground voltage. This situation is often not caused by momentary interference or accidental factors, but rather by a persistent grounding fault in the line. For example, a detector or line in a signal branch may experience a stable leakage or short-circuit path to ground due to insulation aging, damage, or moisture. To quickly and accurately identify the specific faulty detector or branch, the system automatically triggers a secondary alarm and initiates a series of fault location steps.

[0049] The specific fault location process is as follows: The system's controller sends a self-test command to all connected fire detectors via the signal bus. This command triggers each detector to enter fault diagnosis mode. Upon receiving the command, each detector actively connects a diagnostic resistor (R_diag) of known resistance value between its internal circuit and ground. This resistor is precisely calibrated, designed to cause a significant and identifiable voltage spike in the bus-to-ground voltage when connected to the bus system. This spike is significantly larger than the voltage fluctuation range under normal operating conditions, ensuring the controller monitors the voltage changes on the signal bus in real time. By comparing the voltage data before and after connecting the diagnostic resistor, the controller identifies detectors whose voltage spike characteristics match the expected values. In other words, the controller detects that one or more detectors, after connecting the diagnostic resistor, experience a voltage spike in the bus that matches the calibrated expectation in terms of magnitude and direction. This indicates that the branch containing these detectors is the one currently experiencing a ground fault. Once identified, the system records and reports the detector's address code, clearly indicating which detector or branch is experiencing a persistent ground fault.

[0050] Example: Suppose a ship's fire alarm system has 30 detectors, numbered from 001 to 030. When the system detects a prolonged abnormality in the bus-to-ground voltage and triggers a level-two alarm, the controller immediately sends a self-test command to each detector from address 001 to 030. Upon receiving the command, detector 012 connects a 1kΩ diagnostic resistor R_diag between its internal circuit and ground according to a preset program. Because this detector actually has insulation damage, creating a continuous leakage path between it and ground, when R_diag is connected, the bus-to-ground voltage experiences a sudden drop of approximately 1.5V. This drop is far beyond the normal fluctuation range and perfectly matches the voltage drop characteristics of the faulty branch as pre-defined by the system. Through real-time monitoring and comparison, the controller quickly identifies that this voltage drop originates from detector 012, marks it as a faulty branch, and reports address 012 as fault information to maintenance personnel. In this way, maintenance personnel can directly focus on inspecting and repairing the detector at address 012 and its connecting lines, significantly shortening the troubleshooting time, improving system repair efficiency, and ensuring the safe and reliable operation of the ship's fire alarm system.

[0051] Example 2: As Figure 4 As shown, when the absolute difference (|ΔV|) exceeds the second preset voltage threshold (V_th2) for a duration of T2, a persistent ground fault is determined to have occurred in the system, and a secondary alarm is issued. After the secondary alarm is triggered: S81b: The controller issues a global self-test command.

[0052] S82b: The controller selects the first detector in a preset order (e.g., address codes from smallest to largest).

[0053] S83b: Sends a command to the selected detector to close its internal switch and connect the diagnostic resistor R_diag between its loop and ground.

[0054] S84b: The controller monitors the amplitude and waveform of sudden changes in the bus voltage V_sense.

[0055] S85b: Determine if the sudden change matches the expected characteristics of the connected R_diag (e.g., voltage drop to a specific value). If it matches, the detector branch is normal, the controller commands it to disconnect R_diag, and selects the next detector. If it does not match (e.g., no voltage change or minimal change), it indicates that there is a low-resistance path (i.e., a ground fault point) in the branch, and the fault current is shunted, resulting in abnormal voltage change characteristics.

[0056] S86b: Once an abnormal feature is detected, the branch where the detector is located is determined to be a faulty branch. The controller records its address code and displays the positioning result on the human-machine interface.

[0057] S87b: After polling all devices, the positioning process ends.

[0058] In marine fire alarm systems, when the absolute difference in signal bus voltage to ground (|ΔV|) exceeds the second preset voltage threshold (V_th2) for a duration exceeding a set long delay threshold T2, it indicates a significant and prolonged abnormal voltage deviation in the bus to ground voltage. This is usually not caused by transient interference or accidental factors, but rather by a persistent grounding fault in the connection lines of one or more detectors within the system. Examples include aging and damaged insulation, accidental short circuits between the detector's internal circuitry and ground, or leakage due to moisture in the wiring terminals. In this situation, the system will automatically trigger a level-two alarm, indicating a serious grounding anomaly that requires prompt location and troubleshooting to prevent disruption to the normal operation of the entire fire alarm system and the ship's fire safety.

[0059] After the level 2 alarm is triggered, the system immediately enters the fault location process to accurately identify the specific detector or branch with the grounding fault. The specific steps are as follows: In step S81b, the controller issues a global self-test command to notify all detectors connected to the signal bus to prepare to enter fault diagnosis mode. Next, in step S82b, the controller selects the first detector from all detectors in a pre-set order (e.g., selecting detectors in ascending order of their address codes) as the current target to be tested.

[0060] In step S83b, the controller sends a dedicated command to the selected detector (e.g., address 001), triggering the closure of an internal control switch. This connects a diagnostic resistor R_diag with a known resistance value between the detector's internal circuit and ground. This diagnostic resistor is precisely calibrated, and its connection will generate a specific voltage change on the signal bus. For example, the bus-to-ground voltage V_sense will show a expected decrease. This characteristic change is explicitly set and stored in the controller during the system design phase, serving as a basis for determining whether the detector branch is functioning correctly.

[0061] In step S84b, the controller monitors the voltage to ground V_sense on the signal bus in real time, focusing on capturing the voltage surge amplitude and waveform characteristics generated at the moment the diagnostic resistor is connected. Then, in step S85b, the controller compares the actual monitored voltage surge with the expected characteristics (e.g., the voltage should drop to a specific value) that should occur after the detector connects to the diagnostic resistor. If the monitored voltage change matches the expectation, for example, if the voltage does indeed drop to the predetermined amplitude, it indicates that the current path of the detector branch is normal after the diagnostic resistor is connected, and no abnormal current shunting has occurred. This means that the detector and its connected lines do not have a grounding fault and are considered a normal branch. In this case, the controller sends a command to the detector to disconnect the diagnostic resistor (i.e., the internal switch is reopened), and then selects the next detector (e.g., address 002) according to a preset sequence, repeating the above detection process.

[0062] If, in step S85b, it is found that after a diagnostic resistor is connected to a certain detector (e.g., address 015), the bus voltage V_sense monitored by the controller does not show the expected voltage drop, or the voltage change is very small, or even there is no obvious change, this indicates that the current loop that should have been formed after the diagnostic resistor is connected did not work as expected. The cause of the fault is likely that there is a low-resistance path (i.e., a ground fault point) in the branch where the detector is located, which causes the fault current to be diverted and cannot form the expected voltage change on the bus. In other words, the ground fault in this branch causes the diagnostic resistor to fail to produce the expected voltage change characteristics, which is inconsistent with the normal response preset by the system.

[0063] In this situation, the system will proceed to step S86b. Based on this, the controller will determine that the branch where the detector is located is a faulty branch and immediately record the address code of the detector (e.g., 015). At the same time, the location result of the faulty detector will be displayed intuitively on the human-machine interface of the system (e.g., touch screen or monitoring terminal), prompting maintenance personnel that the detector or its connection line corresponding to the address has a continuous grounding fault and needs to be inspected and repaired on-site as soon as possible.

[0064] Once the controller has completed the above detection steps for all detectors connected to the signal bus in address order (i.e., completed polling of all devices in step S87b), the entire fault location process ends. At this point, the system not only successfully identifies the specific detector branch with the persistent grounding fault, but also clearly displays the fault location through the human-machine interface, greatly facilitating subsequent maintenance work, effectively shortening fault diagnosis time, and improving the operational safety and reliability of the ship's fire alarm system.

[0065] Example: Suppose a ship's fire alarm system has 50 detectors, with addresses from 001 to 050. When the system detects an abnormal bus-to-ground voltage and triggers a level 2 alarm, the controller first issues a global self-test command, then sequentially checks starting from address 001. The first few detectors (e.g., 001 to 014) all produce the expected voltage drop (e.g., voltage drop to 2.5V) after connecting a diagnostic resistor. The controller determines that their branches are normal, disconnects the diagnostic resistors sequentially, and continues checking. When the detector at address 015 is detected, the controller finds that after connecting the diagnostic resistor, the bus voltage V_sense hardly changes (e.g., only drops by 0.1V, far below the expected 1.5V). The system determines that there is a low-resistance path in this branch, i.e., a ground fault, and records address 015 as the faulty branch and displays the faulty detector: address 015 on the screen. Subsequent detectors (e.g., 016 to 050) test normally. Finally, the system completes polling of all 50 detectors, accurately locating the only device with a persistent ground fault, providing maintenance personnel with a clear target for fault handling.

[0066] Example 3: The detection method can be widely applied to the daily monitoring and fault diagnosis of fire alarm systems on various types of ships, especially suitable for scenarios with high requirements for system safety, stability, and fault response timeliness. For example, in the engine room, cargo hold, passenger cabin corridors, and various equipment rooms of a large cargo ship or cruise ship, a large number of fire detectors are usually installed. These detectors are connected to the system controller via a signal bus (BUS) to monitor fire-related parameters such as smoke and temperature in the environment in real time. Due to the complex operating environment of ships, which are exposed to harsh conditions such as humidity, salt spray, vibration, and temperature changes for a long time, the signal bus and detector connection lines are prone to problems such as insulation aging, loose joints, wire damage, or moisture, which may lead to abnormal connection between the signal bus and ground (GND), i.e., grounding fault. If such faults are not detected and handled in time, they may affect the normal monitoring function of the fire alarm system, or even lead to false alarms or missed alarms, or even cause electrical safety hazards in extreme cases, threatening the safety of the ship and personnel.

[0067] In this application scenario, the system controller periodically (e.g., once per second or according to a set period) applies a low-voltage alternating detection signal (V_test) with a frequency of 0.1Hz to 10Hz and an amplitude within the system's safe range between the signal bus and ground, following the method described above. This signal will not interfere with normal fire detection signals and can effectively stimulate potential ground fault characteristics. The controller obtains the voltage value (V_sense) of the signal bus to ground through real-time sampling and uses a first-order digital low-pass filtering algorithm (e.g., formula V_ref(n)=α*V_sense(n)+(1-α)*V_ref(n-1)) to calculate and dynamically update a reference voltage (V_ref). This reference voltage can smoothly track the slow changes in bus voltage under fault-free conditions, such as small voltage drifts caused by fluctuations in ambient temperature and humidity or natural aging of the lines, thereby improving the accuracy of fault detection and anti-interference capability.

[0068] When the system detects that the absolute difference (|ΔV|) between the real-time voltage value (V_sense) and the dynamic reference voltage (V_ref) exceeds a lower first preset voltage threshold (V_th1) for a short period of time (e.g., 100ms to 500ms), it indicates that the bus voltage has an intermittent or short-term abnormality, which may be caused by transient factors such as transient interference, poor contact, or local leakage. At this time, the system determines it as a transient ground fault and automatically issues a level one alarm to prompt maintenance personnel to pay attention to possible temporary grounding anomalies. At the same time, it automatically generates corresponding fault detection strategies, such as suggesting checking the detector wiring terminals and checking for the presence of electromagnetic interference sources nearby.

[0069] When the system detects that the absolute difference (|ΔV|) exceeds a higher second preset voltage threshold (V_th2, and V_th2≤V_th1) for a prolonged period (e.g., 2s to 10s), it indicates a significant and continuous abnormal deviation in the bus voltage. This is highly likely due to a persistent low-resistance grounding fault in a detector branch, such as insulation damage leading to a short circuit to ground or internal circuit faults causing leakage. In this case, the system will classify it as a persistent grounding fault and trigger a secondary alarm, alerting relevant personnel to take immediate action. Simultaneously, the system can automatically generate detailed fault location and troubleshooting strategies based on the secondary alarm. For example, it can guide maintenance personnel to prioritize checking detectors in specific areas or branches, and even combine this with subsequent diagnostic resistor access methods to further locate the faulty detector, significantly improving fault troubleshooting efficiency and shortening system recovery time.

[0070] This solution is suitable for the following application scenarios: During ship navigation, the engine room environment is prone to interference and accelerated aging due to high temperatures, oil mist, and frequent vibrations, which can easily lead to grounding hazards. In areas with high humidity, such as cargo holds or refrigerated tanks, the insulation performance of the wiring deteriorates, significantly increasing the risk of grounding. After the ship docks in port or experiences severe sea conditions, electrical connection points may become faulty due to vibration or oxidation, inducing transient or persistent grounding faults. By implementing the above-mentioned grounding fault detection methods, the system can proactively and in real-time monitor changes in the signal bus voltage to ground without affecting normal fire monitoring functions. It can intelligently distinguish between transient and persistent faults, provide graded early warnings, and automatically generate response strategies. This effectively ensures the reliable operation of the ship's fire alarm system, improves the overall fire safety level, and provides strong technical support for safe ship navigation.

[0071] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0072] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to any specific implementation. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for detecting grounding faults in a marine fire alarm system, characterized in that: The detection method includes the following steps: S1: The controller periodically applies an alternating detection signal with a preset frequency and amplitude between the signal bus and ground wire of the fire alarm system; S2: Real-time sampling and acquisition of the real-time voltage value of the signal bus relative to ground; S3: Calculate and update the dynamic reference voltage based on the real-time voltage value, the dynamic reference voltage being used to track the change of the real-time voltage value under fault-free conditions; S4: Compare the real-time voltage value with the dynamic reference voltage and calculate the absolute difference; S5: Set the first delay threshold T1 and the second delay threshold T2, where T1 <T2; S6: When the absolute difference exceeds the first preset voltage threshold for a period of time T1, it is determined that a transient grounding fault has occurred in the fire alarm system, and a level one alarm is issued. S7: When the absolute difference exceeds the second preset voltage threshold for a period of time T2, it is determined that the fire alarm system has a continuous grounding fault and a level 2 alarm is issued. S8: Automatically generate corresponding fault detection strategies based on the issued Level 1 or Level 2 alarms.

2. The method for detecting grounding faults in a marine fire alarm system according to claim 1, characterized in that: In step S8: Based on the issued Level 1 or Level 2 alarm, automatically generate the corresponding fault detection strategy, including the following steps: S81a: The controller sends a self-test command to all connected detectors via the signal bus; S82a: After receiving the self-test command, each detector connects a known diagnostic resistor between its internal circuit and ground; S83a: The controller detects sudden changes in bus-to-ground voltage caused by the connection of the diagnostic resistor; S84a: Identify detectors whose voltage change characteristics match the expectations, determine them as faulty branches, and report their address codes.

3. The method for detecting grounding faults in a marine fire alarm system according to claim 1, characterized in that: In step S8: Based on the issued Level 1 or Level 2 alarm, the corresponding fault detection strategy is automatically generated, which also includes the following steps: S81b: The controller issues a global self-test command; S82b: The controller selects the first detector in a preset order; S83b: Sends a command to the selected detector to close its internal switch and connect the diagnostic resistor between its circuit and ground; S84b: The controller monitors the amplitude and waveform of sudden changes in bus voltage; S85b: Determine whether the magnitude of the sudden change matches the expected characteristics of the connected diagnostic resistor, and identify whether there are any abnormal characteristics based on the matching results; S86b: If an abnormal feature is detected, the branch where the detector is located is determined to be a faulty branch. The controller records its address code and displays the positioning result on the human-machine interface. S87b: After polling all devices, the positioning process ends.

4. The method for detecting grounding faults in a marine fire alarm system according to claim 2, characterized in that: The resistance value of the diagnostic resistor is calibrated so that the voltage fluctuation amplitude generated after its connection is greater than the normal fluctuation range of the system.

5. A method for detecting grounding faults in a marine fire alarm system according to claim 3, characterized in that: In step S85b, identifying whether there are feature anomalies based on the matching results includes the following steps: If a match is found, the detector branch is normal, and the controller commands it to disconnect the diagnostic resistor and select the next detector. If a match is not found, it indicates that there is a ground fault point in the branch, and the fault current is shunted, resulting in abnormal voltage change characteristics.

6. The method for detecting grounding faults in a marine fire alarm system according to claim 1, characterized in that: The dynamic reference voltage is calculated using a first-order digital low-pass filtering algorithm, with the formula: V_ref(n)=α*V_sense(n)+(1-α)*V_ref(n-1), where α is a filtering coefficient between 0 and 1, V_ref(n) is the current dynamic reference voltage, V_ref(n-1) is the previous dynamic reference voltage, and V_sense(n) is the current voltage value.

7. A method for detecting grounding faults in a marine fire alarm system according to claim 6, characterized in that: The frequency of the alternating detection signal is between 0.1 Hz and 10 Hz, and the amplitude is a non-dangerous voltage within the safe voltage range.

8. The method for detecting grounding faults in a marine fire alarm system according to claim 1, characterized in that: The first delay threshold T1 is 100ms to 500ms, and the second delay threshold T2 is 2s to 10s.

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