A data recorder for temperature rise of transformer for intrinsic safety circuit

Abstract

The application discloses a kind of intrinsically safe circuit transformer temperature rise data recorder, it is related to transformer winding temperature rise resistance measurement technical field.The recorder includes central processing unit, resistance measurement module and voltage drop detection circuit, voltage drop detection circuit is connected at the output terminal of power module, for detecting the output voltage drop of power module and when voltage drop is below preset threshold, trigger signal is sent to central processing unit;Central processing unit records power-off time in response to trigger signal, and controls resistance measurement module to start collecting the resistance value of transformer winding with first collection interval;Central processing unit is also configured to calculate the resistance value change rate of adjacent two times collection, when change rate is less than preset threshold, collection interval is switched to second collection interval greater than first collection interval.The application realizes the hardware synchronous trigger of power-off instant and variable interval adaptive collection, improves the precision and degree of automation of winding temperature rise resistance measurement.

Description

Technical Field

[0001] This invention relates to the field of transformer winding temperature rise resistance measurement technology, specifically to a transformer temperature rise data recorder for intrinsically safe circuits, which is particularly suitable for automatically recording the winding resistance during temperature rise tests of intrinsically safe transformers in accordance with GB / T 3836.4-2021 "Explosive Atmospheres Part 4: Devices Protected by Intrinsically Safe 'i'" standard. Background Technology

[0002] Transformers are widely used in electronic products, electrical appliances, lighting fixtures, power tools, industrial automation control, and other fields. Testing the temperature rise of transformer windings using the resistance method is a crucial aspect of electrical product safety testing. For intrinsically safe transformers, according to GB / T 3836.4-2021, power transformers must meet structural design requirements, as well as routine and type tests. Type tests require the transformer to undergo a temperature rise test for at least 6 hours under appropriate test conditions to verify that the winding temperature rise meets the requirements.

[0003] The core principle of the resistance method for measuring winding temperature rise is to calculate the temperature rise by measuring the resistance values ​​of the winding in both cold and hot states, using the direct proportionality between resistance and temperature. Accurately obtaining the hot-state resistance (i.e., the winding resistance value at the instant of power failure) is a key technical challenge. Due to the effects of the equivalent inductance and capacitance of the transformer winding, directly testing the resistance at the exact moment of power failure is impractical. Relevant standards stipulate that the resistance values ​​are typically measured as soon as possible after power failure, at short intervals, to plot a curve of resistance change over time, thereby determining the resistance value at the moment of power failure.

[0004] To address the aforementioned technical needs, several solutions have been proposed in the existing technology. Patent application CN1888919A discloses a method for dynamically and synchronously testing the winding resistance value after power failure. This method uses a computer to retrieve and store the resistance data measured by the resistance measuring device at intervals after power failure, thereby obtaining the winding resistance value at each interval. This method achieves an accurate correspondence between the intervals after power failure and the resistance data at that moment, and eliminates the need for manual observation and recording of the power failure delay time and resistance readings. However, this method uses a fixed-interval acquisition method, which fails to optimize the data acquisition density according to the actual change law of the winding resistance. Fixed-interval acquisition either collects too much redundant data in the later stages or insufficient data in the initial stages, affecting the fitting accuracy. Furthermore, the timing of the power failure delay time in this method is implemented by computer software, and its timing start depends on the software response speed, resulting in an uncertain delay. Patent CN103954872B discloses a transformer temperature rise measuring device. It obtains the resistance value at the moment of power failure by continuously measuring 10 to 30 resistance values ​​and using a trend graph function formula to deduce the resistance value. However, it also employs a fixed number of data acquisitions, failing to resolve the contradiction between data acquisition density and winding temperature field interference. Patent CN114113836B discloses a temperature rise experimental device and method for isolation transformers. It controls the test time by automatically switching between power-on and power-off measurements of the isolation transformer's winding internal resistance using a timed method. Although it achieves automatic measurement, its data acquisition method is still timed.

[0005] In summary, the existing technology lacks a transformer temperature rise data logger for intrinsically safe circuits that can adaptively adjust the acquisition interval according to the winding resistance change law, realize hardware synchronous triggering at the moment of power failure, and automatically complete independent optimized acquisition of multiple windings. Summary of the Invention

[0006] This invention addresses the aforementioned deficiencies in existing methods for acquiring winding resistance data during temperature rise tests of intrinsically safe transformers. It provides a temperature rise data recorder for intrinsically safe transformers, aiming to solve the following technical problem: how to acquire the winding resistance change curve after power failure with optimal data acquisition density without increasing human error or additional interference to the winding temperature field during temperature rise tests according to GB / T3836.4-2021 standards, thereby improving the accuracy of resistance value fitting and estimation at the moment of power failure.

[0007] To achieve the above objectives, the present invention provides a transformer temperature rise data logger for intrinsically safe circuits, employing the following technical solution: A transformer temperature rise data logger for intrinsically safe circuits, comprising: The central processing unit is configured to perform data acquisition control and data processing. The resistance measurement module is communicatively connected to the central processing unit and configured to measure the resistance value of the transformer windings. A voltage drop detection circuit is connected to the output terminal of the power module that powers the recorder, and is configured to detect a voltage drop in the output voltage of the power module and send a trigger signal to the central processing unit when the voltage drops below a preset threshold. The central processing unit responds to the trigger signal to record the power outage time and controls the resistance measurement module to start collecting the resistance value of the transformer winding at a first acquisition interval; The central processing unit is also configured to calculate the rate of change of resistance value between two adjacent acquisitions in real time, and when the rate of change is less than a preset threshold, switch the acquisition interval to a second acquisition interval that is greater than the first acquisition interval.

[0008] Furthermore, it also includes an analog switch matrix connected between the resistance measurement module and the transformer winding. The analog switch matrix is ​​controlled by the central processing unit to switch the measurement channel between the primary winding and the secondary winding.

[0009] Furthermore, the first acquisition interval is 2 to 5 seconds, the second acquisition interval is 10 to 30 seconds, and the preset threshold is 0.3% / second to 1.0% / second.

[0010] Furthermore, the voltage drop detection circuit includes a voltage comparator and a reference voltage source. The inverting input of the voltage comparator is connected to the output of the power supply module, the non-inverting input is connected to the output of the reference voltage source, and the output of the voltage comparator is connected to the interrupt pin of the central processing unit.

[0011] Furthermore, the preset threshold of the voltage drop detection circuit is 5% to 15% of the rated output voltage of the power module.

[0012] Furthermore, the analog switch matrix is ​​composed of relays with low contact resistance, and the central processing unit controls the on / off state of the relays through a general-purpose input / output interface.

[0013] Furthermore, it also includes a timing module, a storage module, a display module, and an input module connected to the central processing unit. The timing module is used to record a timestamp for each acquisition, the storage module is used to store the acquired data, the display module is used to display the acquisition results in real time, and the input module is used to set the acquisition parameters.

[0014] Furthermore, the central processing unit maintains independent historical data on the resistance change rate for the primary winding and the secondary winding respectively, and controls the switching of their respective acquisition intervals.

[0015] This invention achieves hardware-level synchronous triggering at the moment of power failure through a voltage drop detection circuit, eliminating time delay errors from software or manual timing. It dynamically adjusts the acquisition interval based on the actual rate of change of winding resistance using a variable-interval adaptive acquisition algorithm built into the central processing unit. Furthermore, it utilizes an analog switch matrix to achieve automatic switching and independent variable-interval acquisition of multiple windings. Compared with existing technologies, this invention offers the following advantages: (1) The hardware synchronous triggering at the moment of power failure is realized by the voltage drop detection circuit, which eliminates the time delay error of software timing or manual timing in the traditional method, and makes the determination accuracy of the moment of power failure reach the microsecond level.

[0016] (2) By using the variable interval adaptive acquisition algorithm, more dense data points are obtained in the early stage of power failure when the resistance change rate is the fastest, which improves the accuracy of the resistance value fitting and estimation at the moment of power failure, and avoids data redundancy in the later stage.

[0017] (3) The variable interval strategy adopts a long interval in the later stage, which reduces the interference of the additional heat that may be introduced by frequent switching of measurement circuits on the winding temperature field.

[0018] (4) By automatically switching the analog switch matrix, the manual operation of changing the measurement wiring is eliminated, avoiding wiring errors and time delays.

[0019] (5) By independently maintaining the historical data of the rate of change and the status of the acquisition interval for each winding, each winding can obtain the optimal data distribution according to its own temperature change law. Attached Figure Description

[0020] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0021] Figure 1 This is a structural principle block diagram of the transformer temperature rise data recorder for intrinsically safe circuits of the present invention; Figure 2 This is a circuit diagram of the voltage drop detection circuit of the present invention; Figure 3 This is a flowchart illustrating the variable interval adaptive acquisition algorithm of the present invention; Figure 4 This is a circuit diagram of the analog switch matrix of the present invention; Figure 5 This is a timing diagram of the independent variable-interval acquisition of dual windings according to the present invention. Detailed Implementation

[0022] 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 a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0023] As described in the background section, the core defects in the existing technology can be summarized in three aspects: First, the existing solutions (such as CN1888919A, CN103954872B, CN114113836A, etc.) all adopt a fixed interval or fixed number of acquisition strategies, which cannot dynamically adjust the acquisition density according to the actual changes in winding resistance; Second, the determination of the power outage time of the above solutions all rely on software timing, and the timing accuracy is limited by the program response speed, resulting in uncertain delays; Third, for transformers with multiple windings, the existing technology lacks an automated channel switching and independent optimization mechanism, and still requires manual intervention.

[0024] To address the aforementioned three shortcomings, this invention employs innovative design from three interrelated technical dimensions.

[0025] First, a variable interval adaptive acquisition mechanism is set up to dynamically adjust the acquisition interval by calculating the resistance change rate in real time. Second, a voltage drop detection circuit is set up to achieve synchronous acquisition start-up at the moment of power failure through hardware triggering. Third, an analog switch matrix is ​​set up to realize automatic switching and independent variable interval control of multiple winding channels.

[0026] It should be noted that the three technical methods mentioned above do not operate in isolation, but rather form a functional coupling relationship through the unified coordination of the central processing unit. The precise power-off moment provided by the voltage drop detection circuit serves as the time zero point for the variable interval algorithm, ensuring the accuracy and reliability of the timing reference for the acquired data. The variable interval algorithm uses this zero point as a reference to perform dynamic acquisition, ensuring the accuracy of the time coordinates of each data point. Under the control of the variable interval algorithm, the analog switch matrix switches between winding channels in an interleaved mode and independently maintains the variable interval state for each winding, enabling each winding to obtain the optimal data distribution that matches its thermal characteristics. The three are interdependent and mutually reinforcing, forming a synergistic effect of "precise time reference + optimized data distribution + fully automatic independent switching".

[0027] The following detailed description of the specific implementation of the present invention, in conjunction with the accompanying drawings, covers both system structure and operational logic.

[0028] like Figure 1 As shown, it is a schematic diagram of the intrinsically safe circuit transformer temperature rise data recorder provided by the present invention.

[0029] Based on the illustration, the intrinsically safe circuit transformer temperature rise data recorder of the present invention mainly includes a central processing unit 100, a resistance measurement module 200, a voltage drop detection circuit 300, an analog switch matrix 400, a timing module 500, a storage module 600, a display module 700, an input module 800, and a power supply module 900.

[0030] The central processing unit 100 serves as the control core of the recorder, responsible for executing the variable interval adaptive acquisition algorithm, controlling the coordinated operation of various modules, and performing data processing and storage.

[0031] The resistance measurement module 200 is configured to communicate with the central processing unit 100 to measure the DC resistance value of the transformer winding under the control of the central processing unit 100 and transmit the measurement result to the central processing unit 100.

[0032] The voltage drop detection circuit 300 is configured to be connected to the output terminal of the power module 900 to monitor the output voltage of the power module 900 in real time, and to send a trigger signal to the central processing unit 100 when the voltage drops below a preset threshold.

[0033] The analog switch matrix 400 is configured to connect the resistance measurement module 200 and the transformer winding, and is controlled by the central processing unit 100 to switch the measurement channel between the primary winding and the secondary winding.

[0034] The timing module 500 is configured to connect to the central processing unit 100 to record precise timestamps for each acquisition.

[0035] The storage module 600 is configured to be connected to the central processing unit 100 and is used to store the collected data and configuration parameters.

[0036] The display module 700 is configured to be connected to the central processing unit 100 for real-time display of acquisition results and system status.

[0037] The input module 800 is configured to be connected to the central processing unit 100 and is used to receive user input of the acquisition parameter settings.

[0038] The power module 900 is configured to provide operating power to the above modules.

[0039] In the intrinsically safe circuit transformer temperature rise data logger thus formed, the power supply module 900 supplies power to the entire system; the voltage drop detection circuit 300 continuously monitors the power supply status and sends a trigger signal to the central processing unit 100 at the moment of power failure; after the central processing unit 100 responds to the trigger, it controls the analog switch matrix 400 to switch to the target winding, controls the resistance measurement module 200 to perform the measurement, and records the timestamp through the timing module 500; the measurement data is processed by the central processing unit 100 and stored in the storage module 600 and displayed in real time on the display module 700; the user sets the acquisition parameters through the input module 800.

[0040] Based on an understanding of the overall structure, functions, and interrelationships of the intrinsically safe transformer temperature rise data recorder provided by this invention, the specific implementation schemes of each component in this recorder are further described below.

[0041] As a specific example of an implementable configuration, the central processing unit 100 in this recorder preferably employs a microcontroller with an ARM Cortex-M4 core (such as an STM32F407), whose built-in floating-point unit can efficiently perform real-time rate-of-change calculations in the variable-interval adaptive acquisition algorithm. The central processing unit 100 receives trigger signals from the voltage drop detection circuit 300 via an external interrupt pin, communicates with the resistance measurement module 200 via the SPI bus, controls the analog switch matrix 400 via a general-purpose input / output interface, communicates with the timing module 500 and the storage module 600 via an integrated circuit bus or serial peripheral interface, connects to the display module 700 via a flexible static storage controller interface, and connects to the input module 800 via a matrix scanning method.

[0042] Furthermore, the central processing unit 100 internally incorporates a variable-interval adaptive acquisition algorithm module, which is configured to execute the following logic: Let the resistance value of the nth sampling be R. n The resistance value collected in the (n-1)th time is R. n ₋1, The time interval between the two data collections is Δt n ₋1, then the rate of change of resistance γ n = (R n - R n ₋1) / (Δt n ₋1 · R n ₋1). When γ n When the absolute value of γ is greater than the preset threshold γ0, the first acquisition interval T1 is used; when γ n When the absolute value is less than or equal to γ0, switch to the second acquisition interval T2.

[0043] Unlike existing technologies where the acquisition interval is preset and fixed, the acquisition interval of the variable interval adaptive acquisition algorithm module embedded in this central processing unit 100 is dynamically and adaptively adjusted according to the real-time measured resistance change rate.

[0044] As a specific example of an implementable configuration, the resistance measurement module 200 in this recorder employs a four-wire measurement method with a range of 0.01Ω to 200Ω and a measurement accuracy of 0.05% of the reading ± 0.01% of the range. The four-wire measurement method eliminates the influence of lead resistance on the measurement results through independent current and voltage terminals, making it suitable for precision measurements of small resistances such as transformer windings. The resistance measurement module 200 receives measurement commands from the central processing unit 100 via the SPI bus and returns the digitized resistance value through the same bus after completing the measurement.

[0045] As a specific description of an implementable form, such as Figure 2 As shown, the voltage drop detection circuit 300 in this recorder consists of a voltage comparator 310 (such as an LM339) and a reference voltage source 320 (such as a TL431). The output voltage of the power supply module 900 is divided by a voltage divider network composed of voltage divider resistors R1 and R2 and then connected to the inverting input terminal of the voltage comparator 310; the reference voltage source 320 generates a stable reference voltage and is connected to the non-inverting input terminal of the voltage comparator 310. The output terminal of the voltage comparator 310 is connected to the external interrupt pin of the central processing unit 100 through a pull-up resistor.

[0046] Furthermore, to improve the reliability of power failure detection, the voltage comparator 310 may be equipped with a hysteresis comparator circuit (such as introducing a positive feedback resistor) to suppress signal jitter during power supply voltage drops; or the central processing unit 100 may perform software de-jitter processing after interrupt response. Both the hysteresis comparator circuit and the software de-jitter processing are well-known techniques in the art.

[0047] Furthermore, under normal operating conditions, the power module 900 outputs a stable voltage, and the voltage after voltage division is higher than the reference voltage, causing the voltage comparator 310 to output a low level. When the power supply to the transformer input side is disconnected, the output voltage of the power module 900 drops rapidly, and the voltage after voltage division falls below the reference voltage. The voltage comparator 310 then flips to a high level, sending a rising edge interrupt trigger signal to the central processing unit 100. This triggering method has a response time in the microsecond range (the typical flip delay of the voltage comparator 310 is 1.3 μs), significantly improving accuracy compared to existing software timing methods.

[0048] The preset threshold for voltage drop detection is set to 5% to 15% of the rated output voltage of the power module 900. This threshold range is chosen to consider two factors: a threshold that is too low may cause a delay in power-off detection (requiring waiting for the voltage to drop to a lower level), while a threshold that is too high may cause false triggering (caused by power fluctuations). By appropriately setting the ratio of the voltage divider resistors R1 and R2, the voltage comparator 310 can be made to flip at a specific percentage of the rated output voltage.

[0049] As a specific description of an implementable form, such as Figure 4 As shown, the analog switch matrix 400 in this recorder consists of multiple low-contact-resistance electromagnetic relays 410. For example, it can be composed of low-contact-resistance electromagnetic relays 410a and 410b. Each relay corresponds to a measurement channel, with relay 410a connected to the primary winding and relay 410b connected to the secondary winding. The selection of relays 410a and 410b is based on the following considerations: the contact resistance of the electromagnetic relays (typically in the milliohm range) is much smaller than the on-resistance of the MOSFET switch, and the contact resistance has good long-term stability, having minimal impact on small-signal precision measurements.

[0050] The central processing unit 100 controls the energizing state of the coils of each relay 410 through a general-purpose input / output interface, thereby realizing the switching of measurement channels. Between the primary and secondary windings, the central processing unit 100 switches channels in an alternating pattern of "primary side → secondary side → primary side → secondary side". The advantage of this alternating switching method is that it ensures that the acquisition time points of the two windings are staggered, providing balanced data points for subsequent separate fitting, and avoiding sparse data points in the other winding due to continuous acquisition of the same winding.

[0051] As a specific example of an implementable form, the timing module 500 in this recorder utilizes the real-time clock unit inside the central processing unit 100, and can continue running time after a power outage when powered by battery backup. When the central processing unit 100 receives a trigger signal from the voltage drop detection circuit 300, it immediately reads the current value of the real-time clock as the timestamp of the power outage.

[0052] As a specific example of an implementable configuration, the storage module 600 in this recorder uses an external Flash memory with a capacity of 16MB or more to store acquired data and system configuration parameters. Each measurement's data record includes a timestamp, winding identifier, resistance value, and the current acquisition interval status.

[0053] As a specific example of an implementable form, the display module 700 in this recorder uses a color TFT LCD screen to display the currently acquired resistance value, acquisition interval status, number of acquired data points, and power-off timestamp in real time.

[0054] As a specific example of an implementable form, the input module 800 in this recorder uses a matrix keypad or touch screen for inputting initial acquisition parameters before the experiment.

[0055] As a specific example of an implementable configuration, the power module 900 in this recorder receives AC220V AC mains power as input and outputs DC5V / 2A (powering the digital circuits such as the central processing unit 100, timing module 500, storage module 600, and display module 700) and DC±12V / 0.5A (powering the analog circuits of the resistance measurement module 200). The output of the power module 900 also serves as a monitoring point for the voltage drop detection circuit 300.

[0056] Based on an understanding of the above system composition and the specific structure of each part, the overall operating logic of the recorder of this invention will be explained below. This operating logic is built on the core architecture of "event-driven adaptive acquisition"—using a power outage event as the trigger to start the acquisition process, the resistance change rate as the dynamic adjustment basis of the acquisition strategy, and the time series as the logical main line for data organization.

[0057] From a functional perspective, the recorder's operational logic sequentially includes the pre-configuration phase, standby monitoring phase, event triggering and data acquisition initiation phase, variable interval adaptive acquisition loop phase, and acquisition termination and data output phase. These five phases are interconnected, forming a complete operational loop from setup to completion. The following section combines... Figure 3 The flowchart shown provides a detailed explanation of each stage.

[0058] 1. Pre-configuration phase Before the temperature rise test begins, the user writes the parameter configuration of the acquisition strategy to the central processing unit 100 through the input module 800, including the first acquisition interval T1, the second acquisition interval T2, the rate of change threshold γ0, and the total acquisition time T_total. After receiving the input, the central processing unit 100 performs a validity check, checking whether T1 is less than T2, whether γ0 is within the valid range, and whether T_total is a positive number. After the check passes, the parameters are permanently stored in the configuration area of ​​the storage module 600.

[0059] Subsequently, the central processing unit 100 controls the analog switch matrix 400 through the general purpose input / output interface, setting the measurement channel to the preset starting winding (usually the primary winding). This initial state ensures that the first measurement after a power outage trigger does not experience a channel switching delay. The central processing unit 100 executes a system self-test sequence: verifying the communication link with the resistance measurement module 200, reading the current value of the timing module 500 to verify the normal operation of the real-time clock, and checking whether the available space of the storage module 600 meets the expected data volume requirements. After all self-tests pass, the recorder enters standby monitoring mode.

[0060] In the above configuration process, compared with the existing technology that only sets a single fixed interval parameter, the present invention provides an adjustable control dimension for subsequent adaptive acquisition by introducing a configuration mechanism of change rate threshold and dual interval parameters. Users can flexibly configure the acquisition strategy according to the thermal characteristics of different transformers.

[0061] 2. Standby monitoring phase After pre-configuration, the recorder enters a low-power standby state. During this stage, the central processing unit 100 suspends active operation and enters sleep mode, retaining only the external interrupt wake-up function to reduce power consumption. Power-consuming components such as the resistance measurement module 200, the display module 700 backlight, and the analog switch matrix 400 coil are all in standby or low-power states.

[0062] Meanwhile, the voltage drop detection circuit 300 continues to operate after the recorder is powered on, unaffected by the operating state of the central processing unit 100. Figure 2 Taking the circuit shown as an example, the DC 5V output of the power supply module 900 is divided by voltage divider resistors R1 and R2 and then connected to the inverting input of the voltage comparator 310. The reference voltage generated by the reference voltage source 320 is connected to the non-inverting input. Under normal operating conditions, the voltage after voltage division (e.g., approximately 0.45V) is lower than the reference voltage (2.5V), and the comparator outputs a low level. The external interrupt pin of the central processing unit 100 is configured in rising edge trigger mode and is kept in a high-level standby state through a pull-up resistor. The low-level output of the comparator pulls the interrupt pin low.

[0063] The standby monitoring phase is designed to ensure that the recorder can remain on standby for extended periods during the test preparation phase without concern for power consumption, while the monitoring behavior is continuous and real-time, ensuring that the system can respond immediately in the event of a power outage.

[0064] 3. Event Triggering and Data Acquisition Initiation Phase When the power supply to the transformer input side is disconnected, the output voltage of the power module 900 begins to drop. When the output voltage drops below a preset threshold (5% to 15% of the rated value), the output of the voltage comparator 310 flips from low to high, and the external interrupt pin of the central processing unit 100 detects the rising edge and immediately triggers the external interrupt service routine.

[0065] The interrupt service routine executes the following sequence of atomic operations, which must be performed sequentially to ensure that the time window from the power outage to the first data acquisition is minimized: The first step is to read the current count value of the timing module 500 and store it in the register as the timestamp T0 of the power failure moment. This operation is completed within the first clock cycle of the interrupt response, ensuring that the delay between the timestamp and the power failure event is compressed to the nanosecond level.

[0066] The second step involves controlling the analog switch matrix 400 via the general-purpose input / output interface to switch the measurement channel to the preset starting winding. Specifically, the central processing unit 100 outputs a high-level signal to the control pin of the relay 410 corresponding to the winding, energizing the relay 410 coil and closing the contacts to complete the channel connection. The typical operating time of the relay 410 is 5–10 ms. Although this delay is unavoidable, it does not affect the accurate recording of the power-off moment because it is executed after the timestamp is locked.

[0067] The third step is to send the first measurement command to the resistance measurement module 200. The resistance measurement module 200 initiates a four-wire measurement sequence: applying a constant test current to the winding under test through the current terminal, measuring the potential difference at the voltage terminal, calculating the resistance value using Ohm's law, and then returning the digitized resistance value to the central processing unit 100 via the SPI bus.

[0068] After receiving the first measured resistance value, the central processing unit 100 generates the first data record (containing three fields: timestamp, winding identifier, and resistance value), writes it to the storage module 600, and transmits it to the display module 700 in real time to refresh the display.

[0069] The hardware interrupt triggering method described above has significant advantages over the existing software timing method. In existing technologies, there is an operator reaction time (typically 3-5 seconds) or a software polling cycle delay between the power outage and the initial data acquisition, leading to the loss of critical data points in the initial stage of a power outage. This invention, through a hardware interrupt triggering mechanism, compresses the start time of the initial acquisition to the millisecond level, significantly improving the integrity of data acquisition in the initial stage of a power outage.

[0070] 4. Variable Interval Adaptive Acquisition Cycle Stage After data acquisition begins, the central processing unit (CPU) 100 exits the interrupt service routine and enters the main loop to execute the continuous data acquisition task. For example... Figure 3 The diagram clearly illustrates the overall operation process of this stage. The following section explains the operation mechanism of this stage from three aspects: cyclic control structure, variable interval decision algorithm, and multi-winding independent variable interval control.

[0071] (1) Framework structure of the main acquisition loop - top-level scheduling layer.

[0072] The loop control structure is responsible for the timing and flow jump of the main loop. Its specific functions include: starting a timer to wait for the currently effective acquisition interval T_current; after the timer arrives, calling the analog switch matrix 400 to switch the measurement channel and sending a measurement command to the resistance measurement module 200; after obtaining the measurement value, passing the winding identifier and resistance value of this measurement to the multi-winding independent variable interval control layer; receiving the updated acquisition interval returned by the layer, updating T_current and entering the next loop.

[0073] In this invention, the main loop adopts a state machine architecture, and performs the following operation sequence in each loop cycle: ① Interval Waiting: The central processing unit 100 reads the currently effective acquisition interval T_current (initial value is T1), starts the internal timer, and triggers the timer interrupt after waiting for T_current time.

[0074] ② Channel switching and measurement execution: After the timer interrupt is triggered, the central processing unit 100 controls the analog switch matrix 400 to switch to the target winding through the general input / output interface according to the preset channel switching mode. Then, it sends a measurement command to the resistance measurement module 200, waits for the measurement to be completed, and reads the resistance value R_new.

[0075] ③ Data recording: Read the current value of timing module 500, calculate the relative time Δt, combine (Δt, winding identifier, R_new) into a data record, write it to storage module 600 and update the display.

[0076] ④ Rate of change calculation and interval decision: Read the last measured resistance value R_old and the corresponding timestamp T_old from memory, and calculate the rate of change γ = (R_new - R_old) / [(T_current - T_old) · R_old]. Compare |γ| with the preset threshold γ0: if |γ| > γ0, set T_current = T1; if |γ| ≤ γ0, set T_current = T2.

[0077] ⑤ Termination Judgment: Determine whether the current relative time has reached the preset total acquisition time T_total, or check whether the user has issued a stop command through input module 800. If either termination condition is met, exit the main loop; otherwise, return to the interval and wait to continue to the next loop.

[0078] (2) Multi-winding independent variable interval control - intermediate routing and state management.

[0079] The multi-winding independent variable interval control layer is responsible for isolating and maintaining the acquisition status of each winding. Its functions include: extracting the historical resistance value R_old and the current acquisition interval T_current (stored independently for each winding) of the current winding from the storage module 600; passing the extracted exclusive data along with the newly measured R_new to the variable interval decision algorithm; and updating the interval decision result output by the algorithm only to the exclusive status area of ​​the current winding.

[0080] Specifically, for transformers with primary and secondary windings, this invention uses an analog switch matrix 400 to achieve interleaved acquisition and independent variable interval control of the dual windings.

[0081] like Figure 5 As shown, the timing logic of interleaved acquisition is as follows: the central processing unit 100 independently maintains the most recent acquisition time, the most recent resistance value, and the current acquisition interval for each winding. In each measurement of the main cycle, the central processing unit 100 switches channels according to a fixed pattern of "primary side → secondary side → primary side → secondary side" to ensure that the windings on both sides receive a balanced sampling opportunity.

[0082] The logic of independent interval switching is as follows: when switching to a certain winding for measurement, the central processing unit 100 only updates the state variable of that winding and determines whether to switch its acquisition interval based solely on the resistance change rate of that winding itself. Therefore, the two windings may be in different acquisition interval states—for example, the primary winding temperature is still dropping rapidly and maintaining a short interval, while the secondary winding temperature has slowed down and switched to a long interval—each independently following its temperature change pattern.

[0083] Since the thermal time constants of the primary winding and the secondary winding may differ, and their respective resistance change rate curves are different, this control method uses independent variable intervals so that each winding can obtain the optimal data distribution according to its own change law, effectively avoiding the problem of one winding being compatible while the other is mismatched when using a uniform interval.

[0084] (2) Variable interval decision algorithm - underlying computation layer.

[0085] The variable interval decision algorithm receives data (R_new, R_old, time difference dt) transmitted from the multi-winding control layer, performs the calculation of the rate of change γ and compares it with the threshold, and outputs the acquisition interval decision result (T1 or T2).

[0086] The specific calculation of the rate of change γ and its comparison with a threshold are key aspects of this variable interval decision algorithm. The physical meaning of γ is the relative change in winding resistance per unit time, and its magnitude directly reflects the rate of decrease in winding temperature. In the initial stage of power outage, the winding temperature drops rapidly, and the absolute value of γ is relatively large; as time progresses, the winding temperature gradually approaches the ambient temperature, the resistance change slows down, and the absolute value of γ gradually decreases until it approaches zero.

[0087] The algorithm compares |γ| with a preset threshold γ0, thereby automatically adjusting the sampling density. When |γ| > γ0, it indicates that the winding temperature is still in a rapid change phase, and dense sampling is required to capture the detailed features of the temperature curve. Therefore, a short interval T1 is used. When |γ| ≤ γ0, it indicates that the winding temperature has entered a slow change stage. Sparse sampling can accurately describe the overall trend of the temperature curve, so switch to long interval T2.

[0088] In this algorithm, the timing of the switching of the acquisition interval depends on the comparison between the real-time calculated rate of change and the threshold. Therefore, the switching time dynamically shifts later as the rate of change of winding temperature slows down, rather than switching at a preset fixed time point. This adaptive switching method based on real-time data can adapt to the differentiated temperature drop curves of transformers with different thermal characteristics and has wide applicability.

[0089] The following section uses a typical sampling sequence to explain the coordination process of the three levels in actual operation from a mechanistic perspective. For ease of understanding, the recorder is configured with a first acquisition interval T1 (short interval) and a second acquisition interval T2 (long interval), the rate of change threshold is γ0, and the initial measurement channel is the primary winding.

[0090] At the moment of power failure, the cyclic control structure first responds to the trigger signal of the voltage drop detection circuit 300, completes the first resistance measurement in the interrupt service routine, records the power failure time T0, and uses the preset short interval T1 as the current acquisition interval. At this time, the multi-winding control layer does not yet have complete historical data, and the variable interval decision algorithm does not perform interval switching judgment.

[0091] When the cyclic control structure enters its first normal acquisition cycle, the timer overflows at a short interval T1, controlling the analog switch matrix 400 to switch to the secondary winding and perform resistance measurement. The multi-winding independent variable interval control layer identifies the current winding as the secondary side. Since no historical data records have been established for this winding, this measurement is only used as the initial data for this winding and stored in its dedicated state area, without triggering the variable interval decision algorithm.

[0092] The cyclic control structure continues to advance to the next acquisition with short intervals T1, controlling the analog switch matrix 400 to switch back to the primary winding to perform measurement. The multi-winding independent variable interval control layer identifies the current winding as the primary side and extracts the primary side's exclusive historical data from the storage module 600—that is, the previous resistance value and measurement time of the winding—and sends it along with the newly measured resistance value to the variable interval decision algorithm. The algorithm calculates the rate of change based on the two resistance values ​​and the time difference, and compares the calculation result with a preset threshold γ0. When the absolute value of the calculated rate of change is greater than the threshold, it indicates that the winding temperature is still in a rapid change phase, and the algorithm outputs a short interval T1; otherwise, it outputs a long interval T2, indicating that the temperature change has slowed down. The multi-winding independent variable interval control layer writes the algorithm's decision result into the dedicated state area of ​​the primary winding, updating its current acquisition interval.

[0093] After the multi-winding independent variable-interval control layer completes the primary winding state update, the cyclic control structure enters the next acquisition cycle. At this time, the currently effective acquisition interval has been determined by the multi-winding control layer based on the specific state of the next target winding—if the next target is a primary winding, the newly updated primary acquisition interval is used; if the next target is a secondary winding, the acquisition interval stored in the secondary winding's specific state area is used. As the acquisition cycle continues, each winding independently accumulates its own historical data sequence according to the above mechanism. After each measurement, its own rate of change calculation and interval switching judgment are triggered, and its acquisition interval is independently adjusted according to the dynamic changes in its own resistance rate.

[0094] The above example demonstrates that the cyclic control structure is only responsible for maintaining the acquisition rhythm and does not participate in state differentiation or interval decision-making; the multi-winding control layer performs state identification and distribution after each measurement to ensure that the data and states of each winding are not confused; the variable interval decision algorithm, as the invoked computational core, performs change rate calculation and threshold judgment on the specific data of the current winding. These three components sequentially perform their respective functions in each acquisition cycle, jointly maintaining independent variable interval adaptive acquisition of the two windings on the same time axis.

[0095] 5. Acquisition Termination and Data Output Stage The main loop performs a termination check after each measurement. When the current relative time is detected to be greater than or equal to T_total or the user presses the stop button, the central processing unit 100 executes the termination sequence: stops sending new measurement commands to the resistance measurement module 200; restores all relays 410 of the analog switch matrix 400 to the open state, disconnects the measurement circuit from the winding; and writes an end marker containing the termination time and the total number of acquisition points to the end of the data area of ​​the storage module 600.

[0096] Subsequently, the central processing unit 100 organizes the raw data records in the storage module 600: sorting by timestamp to ensure the correct temporal order of the data, and calculating and adding statistical information (total number of records, number of records for each winding, number of acquisition interval switching times, etc.). After organization, the data can be exported to an external device via USB interface in a standard file format (such as CSV or TXT) for subsequent curve fitting and temperature rise calculation.

[0097] In some implementations, the central processing unit 100 can also automatically perform a preliminary calculation of the resistance value at the moment of power failure: substitute the collected data into an exponential decay model or a polynomial model for curve fitting, extrapolate to the zero point of time to obtain an estimated value of the resistance value at the moment of power failure, which can be used as a reference for subsequent detailed analysis.

[0098] To enable those skilled in the art to better understand the present invention, the following description is provided in conjunction with two specific embodiments. Embodiment 1 is a basic embodiment, covering the basic technical features of the present invention; Embodiment 2 is a preferred embodiment, which further optimizes the independent variable-interval acquisition of dual windings based on Embodiment 1.

[0099] Example 1 This embodiment provides a specific implementation of a transformer temperature rise data logger for intrinsically safe circuits.

[0100] In terms of system composition, the housing is made of aluminum alloy and measures 200mm × 150mm × 80mm. The central processing unit 100 uses an STM32F407ZGT6 (ARM Cortex-M4 core, 168MHz clock speed, built-in floating-point unit). The resistance measurement module 200 uses a four-wire measurement method, with a range of 0.01Ω-200Ω and an accuracy of 0.05% of the reading ± 0.01% of the range. It communicates with the central processing unit 100 via the SPI bus. The voltage drop detection circuit 300 consists of a voltage comparator 310 LM339 and a reference voltage source 320TL431: the DC5V output of the power supply module 900 is divided by voltage divider resistors R1=10kΩ and R2=1kΩ and then connected to the inverting input of the LM339; the TL431 generates a 2.5V reference voltage which is connected to the non-inverting input; the output of the LM339 is connected to the EXTI interrupt pin of the central processing unit 100 through a 4.7kΩ pull-up resistor. When the DC5V drops below approximately 0.75V (corresponding to 15% of the rated voltage), the LM339 output toggles, triggering an interrupt. The analog switch matrix 400 consists of four low-contact-resistance relays 410 (contact resistance <50mΩ), with the four general-purpose input / output ports of the central processing unit 100 controlling the coils of each relay 410. The timing module 500 utilizes the internal real-time clock of the central processing unit 100, an external 32.768kHz crystal oscillator, and is powered by a backup battery. The storage module 600 uses an externally expanded SPI Flash (W25Q128, 16MB capacity). The display module 700 uses a 3.5-inch TFT color LCD screen (320×480 resolution), connected via a flexible static memory controller interface. The input module 800 uses a 4×4 matrix keypad. The power supply module 900 inputs AC220V and outputs DC5V / 2A and DC±12V / 0.5A.

[0101] During operation, before the test, the user sets T1=2 seconds, T2=15 seconds, γ0=0.5% / second, and total acquisition time=600 seconds via the keyboard, and the recorder enters standby mode. When the user disconnects the power supply to the transformer input side, the DC5V output of the power module 900 begins to drop. The voltage comparator 310 LM339 flips its output when the DC5V drops to approximately 0.75V, sending an external interrupt signal to the central processing unit 100. The central processing unit 100 responds to the interrupt (response time <1μs), reads the current value of the real-time clock as the timestamp of the power outage. Subsequently, it controls the relay 1 of the analog switch matrix 400 to close, connecting the primary winding and sending a measurement command to the resistance measurement module 200. The resistance measurement module 200 completes the measurement (measurement time approximately 200ms) and returns the resistance value via the SPI bus. Then, data is continuously collected at 2-second intervals. After each collection, the resistance change rate γ is calculated. When the absolute value of γ drops below 0.5% / second, the collection interval is automatically switched to 15 seconds. The collection continues until 600 seconds or is manually stopped by the user.

[0102] A comparative experiment was conducted using the recorder of this embodiment and the manual recording method (10 times each). The results showed that the average time delay of the manual recording was 3.2 seconds (standard deviation 0.8 seconds), while the time delay of the recorder was less than 0.05 seconds. The standard deviation of the resistance value at the moment of power failure calculated by the recorder was reduced by about 60% compared with the manual recording method.

[0103] Example 2 This embodiment further optimizes the variable interval acquisition algorithm based on embodiment 1, realizing independent variable interval acquisition for dual windings.

[0104] In terms of technical features, the central processing unit 100 maintains independent historical data on the rate of resistance change and interval switching states for the primary and secondary windings respectively. The central processing unit 100 maintains two sets of state variables: for the primary winding, it maintains its two most recent resistance values ​​R. 1p and R 2p Current acquisition interval T p , rate of change threshold γ 0p For the secondary winding, maintain its two most recent resistance values ​​R. 1s and R 2s Current acquisition interval T s , rate of change threshold γ 0s The analog switch matrix 400 switches in an alternating pattern of "primary side → secondary side → primary side → secondary side". Each time it switches to a certain winding for measurement, it only updates the state variable of that winding and determines whether the acquisition interval of that winding needs to be changed.

[0105] Because the thermal time constants of the primary and secondary windings may differ, their respective resistance change rate curves are different. Independent variable spacing allows each winding to obtain the optimal data distribution according to its own variation law, avoiding the problem of one winding being compatible while the other is mismatched when using a uniform spacing, and further improving the accuracy of fitting and extrapolation for each winding.

[0106] As can be seen from the above, the intrinsically safe transformer temperature rise data recorder of the present invention can be implemented using existing mature electronic components and manufacturing processes, and is suitable for intrinsically safe transformer temperature rise type tests conducted in accordance with GB / T 3836.4-2021 standard, and has clear industrial applicability.

[0107] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A transformer temperature rise data logger for intrinsically safe circuits, characterized in that, include: The central processing unit is configured to perform data acquisition control and data processing. The resistance measurement module is communicatively connected to the central processing unit and configured to measure the resistance value of the transformer windings. A voltage drop detection circuit is connected to the output terminal of the power module that powers the recorder, and is configured to detect a voltage drop in the output voltage of the power module and send a trigger signal to the central processing unit when the voltage drops below a preset threshold. The central processing unit responds to the trigger signal to record the power outage time and controls the resistance measurement module to start collecting the resistance value of the transformer winding at a first acquisition interval; The central processing unit is also configured to calculate the rate of change of resistance value between two adjacent acquisitions in real time, and when the rate of change is less than a preset threshold, switch the acquisition interval to a second acquisition interval that is greater than the first acquisition interval.

2. The transformer temperature rise data recorder for intrinsically safe circuits according to claim 1, characterized in that, It also includes an analog switch matrix connected between the resistance measurement module and the transformer winding. The analog switch matrix is ​​controlled by the central processing unit to switch the measurement channel between the primary winding and the secondary winding.

3. The transformer temperature rise data recorder for intrinsically safe circuits according to claim 1, characterized in that, The first acquisition interval is 2 to 5 seconds, the second acquisition interval is 10 to 30 seconds, and the preset threshold is 0.3% / second to 1.0% / second.

4. The transformer temperature rise data recorder for intrinsically safe circuits according to claim 1, characterized in that, The voltage drop detection circuit includes a voltage comparator and a reference voltage source. The inverting input of the voltage comparator is connected to the output of the power supply module, the non-inverting input is connected to the output of the reference voltage source, and the output of the voltage comparator is connected to the interrupt pin of the central processing unit.

5. The transformer temperature rise data recorder for intrinsically safe circuits according to claim 1, characterized in that, The preset threshold of the voltage drop detection circuit is 5% to 15% of the rated output voltage of the power module.

6. The transformer temperature rise data recorder for intrinsically safe circuits according to claim 2, characterized in that, The analog switch matrix is ​​composed of relays with low contact resistance, and the central processing unit controls the on / off state of the relays through a general-purpose input / output interface.

7. The transformer temperature rise data recorder for intrinsically safe circuits according to claim 1, characterized in that, It also includes a timing module, a storage module, a display module, and an input module connected to the central processing unit. The timing module is used to record a timestamp for each acquisition, the storage module is used to store the acquired data, the display module is used to display the acquisition results in real time, and the input module is used to set the acquisition parameters.

8. The transformer temperature rise data recorder for intrinsically safe circuits according to claim 1, characterized in that, The central processing unit maintains independent historical data on the resistance change rate for the primary winding and the secondary winding respectively, and controls the switching of their respective acquisition intervals.

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