Control circuit for relay life test and control method thereof

Abstract

This application discloses a control circuit and control method for relay life testing. The control circuit includes a relay, an AC power supply connected to the relay, a transformer connected to the relay, a controller coupled to the relay, and a load connected to the transformer. The AC power supply is configured to output an AC signal to the relay. The controller is configured to control the relay to close once after the start time of each cycle and at a preset time interval from the start time of each cycle. Wherein, when N≤T / n, t=N*n; when N>T / n, t=(N-T*[N / T])*n, where t is the preset time interval, N is the number of cycles, n is the preset time, T is the time of one cycle, and [N / T] is the integer part of the ratio of the number of cycles to the time of one cycle. The preset time is less than or equal to one-tenth of the cycle of the AC signal. This allows for more accurate prediction of relay life and improves the reliability of the control circuit.

Description

Technical Field

[0001] This application relates to the field of voltage regulator control, specifically to a control circuit and control method for relay life testing. Background Technology

[0002] Relays, as indispensable key components in electrical engineering and electronic technology, are widely used in various control systems and power equipment. Their core function is to automatically switch circuits on and off. Because relays are frequently subjected to electrical and mechanical stresses during operation, the performance of their contacts gradually degrades, eventually leading to failures such as adhesion, burning, or poor contact, directly affecting the reliability and safety of the entire system. Therefore, to accurately assess the lifespan of relays, predict their failure modes, and ensure their stable operation throughout their entire lifespan, rigorous and comprehensive lifespan testing is essential. This testing simulates the long-term, high-frequency operation of relays under controlled conditions to accelerate their aging process and obtain crucial lifespan data. A prerequisite for achieving this goal is the construction of a dedicated control circuit for relay lifespan testing.

[0003] In existing relay life testing practices, the commonly used control circuit structure is relatively straightforward, directly connecting the relay to the real or simulated load. While this direct-load connection method is simple in structure, it exposes a series of inherent technical defects in practical applications. First, it lacks flexibility and versatility, requiring the relay's rated voltage and current to be strictly matched with the load's electrical parameters. If the load changes, the entire test platform may need to be redesigned, limiting the applicability of the test circuit and increasing costs. Second, because the control circuit is directly connected to the high-voltage or high-current load circuit, electromagnetic interference such as voltage surges, current inrushes, or grounding faults on the load side can easily trace back to the precision control unit, threatening not only the stability of the control system but also posing safety hazards to operators. Furthermore, the relay contacts directly bear all the electrical stress from the load, especially the huge transient impacts generated when switching inductive or capacitive loads, which significantly accelerates the wear of the contact material and may not accurately reflect the relay's true lifespan in optimized real-world application circuits.

[0004] Besides limitations in circuit structure, current life testing methods also have shortcomings in control approach, especially for AC circuits. Traditional testing methods typically control relays to close at arbitrary points in time with the AC signal, using random or unpredictable methods. However, the electrical stress experienced by the relay contacts at the moment of contact closure, especially the magnitude of surge current and arc energy, is closely related to the instantaneous phase of the AC voltage. For example, the impact of closing a resistive load at the voltage peak is drastically different from that of closing an inductive load at the voltage zero crossing. Due to its randomness, random closure testing strategies may not be able to fully cover all phases within a finite test period, especially the worst-case scenarios that would cause extreme impacts. This randomness leads to two main problems: first, poor repeatability of test results, resulting in a lack of reliable comparability between different batches or designs; second, potential omission of critical design weaknesses in the relay, making the test conclusions less objective and comprehensive, thus affecting the accurate prediction of its lifespan and targeted design improvements. Summary of the Invention

[0005] One advantage of this application is that it provides a control circuit and control method for relay life testing, wherein the control circuit and control method for relay life testing can improve the accuracy of relay life prediction and improve the reliability of the control circuit to a certain extent.

[0006] According to one aspect of this application, a control circuit for relay life testing is provided, comprising: Relay; The AC power supply connected to the relay is configured to output an AC signal to the relay; A transformer connected to a relay; The load connected to the transformer; The controller coupled to the relay is configured to control the relay to close once after the start time of each cycle and at a preset time interval from the start time of each cycle, until the relay fails. The preset time interval is calculated according to the following formula: when N≤T / n, t=N*n; when N>T / n, t=(NT*[N / T])*n, where t is the preset time interval, N is the number of cycles, n is the preset time, T is the time of one cycle, and [N / T] is the integer part of the ratio of the number of cycles to the time of one cycle. The preset time is less than or equal to one-tenth of the cycle of the AC signal.

[0007] In one embodiment of the control circuit for relay life testing according to this application, the preset time is 1 millisecond and the period of the AC signal is 20 milliseconds.

[0008] According to another aspect of this application, a control method for a control circuit used in relay life testing is provided, comprising: The relay is controlled to close once after the start time of each cycle and at a preset time interval from the start time of each cycle, until the relay fails. The preset time interval is calculated according to the following formula: when N≤T / n, t=N*n; when N>T / n, t=(NT*[N / T])*n, where t is the preset time interval, N is the number of cycles, n is the preset time, T is the time of one cycle, and [N / T] is the integer part of the ratio of the number of cycles to the time of one cycle. The preset time is less than or equal to one-tenth of the cycle of the AC signal.

[0009] In one embodiment of the control method for the control circuit used for relay life testing according to this application, the preset time is 1 millisecond and the period of the AC signal is 20 milliseconds.

[0010] In one embodiment of the control method for a control circuit for relay life testing according to this application, the relay is controlled to close once after the start time of each cycle and at a preset time interval from the start time of each cycle until the relay fails, including: controlling the relay to close once after the start time of each cycle and at a preset time interval from the start time of each cycle until the relay sticks and fails.

[0011] In one embodiment of the control method for a control circuit used for relay life testing according to this application, the transformer includes a primary coil and a secondary coil configured to sense the primary coil, the secondary coil being connected to at least one load; controlling the relay to close once after the start time of each cycle and at a preset time interval from the start time of each cycle until the relay fails due to sticking, including: measuring the primary current in the primary circuit where the primary coil and the relay are located; comparing the primary current with a preset current threshold, and determining that the relay has failed due to sticking in response to the primary current being greater than the preset current threshold.

[0012] In one embodiment of the control method for a control circuit for relay life testing according to this application, the preset current threshold is equal to 5% to 20% of the average current in the primary circuit when the relay is operating normally and the transformer is not connected to a load.

[0013] In one embodiment of the control method for a control circuit used for relay life testing according to this application, the primary circuit includes a current sampling resistor connected in series between the primary coil and the relay; calculating the primary current in the primary circuit containing the primary coil and the relay includes: measuring the voltage across the current sampling resistor; and calculating the primary current in the primary circuit according to Ohm's law.

[0014] In one embodiment of the control method for a control circuit used for relay life testing according to this application, the transformer includes a primary coil and a secondary coil configured to sense the primary coil, the secondary coil being connected to at least one load; the primary circuit containing the relay includes a current sampling resistor connected in series between the primary coil and the relay; controlling the relay to close once after the start time of each cycle and at a preset time interval from the start time of each cycle until the relay fails due to sticking, including: measuring the voltage across the current sampling resistor within a specified time window; calculating the root mean square (RMS) value of the voltage across the current sampling resistor within the specified time window; comparing the RMS value of the voltage with a preset voltage threshold, and determining that the relay has failed due to sticking if the RMS value of the voltage is greater than the preset voltage threshold.

[0015] In one embodiment of the control method for a control circuit used for relay life testing according to this application, the specified time window is greater than or equal to one cycle of the AC signal.

[0016] The further objectives and advantages of this application will become fully apparent from the following description and accompanying drawings. Attached Figure Description

[0017] The above and other objects, features, and advantages of this application will become more apparent from the more detailed description of the embodiments of this application in conjunction with the accompanying drawings. The drawings are provided to further illustrate the embodiments of this application and form part of the specification. They are used together with the embodiments of this application to explain this application and do not constitute a limitation thereof. In the drawings, the same reference numerals generally represent the same components or steps.

[0018] Figure 1 The figure shows a schematic block diagram of a control circuit for relay life testing according to an embodiment of this application.

[0019] Figure 2 The figure shows a flowchart illustrating a control method for a control circuit used in relay life testing according to an embodiment of this application.

[0020] Figure 3 The illustration shows a flowchart of one step of a control method for a control circuit used in relay life testing according to an embodiment of this application.

[0021] Figure 4 The illustration shows another flowchart of a step in a control method for a control circuit used for relay life testing according to an embodiment of this application. Detailed Implementation

[0022] Hereinafter, exemplary embodiments according to this application will be described in detail with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of this application, and not all embodiments of this application. It should be understood that this application is not limited to the exemplary embodiments described herein.

[0023] It is understood that the term "a" should be understood as "at least one" or "one or more," meaning that in one embodiment, the number of an element can be one, while in another embodiment, the number of the element can be multiple. The term "a" should not be construed as a limitation on the quantity. "Multiple" means two or more.

[0024] While ordinal numbers such as “first,” “second,” etc., will be used to describe various components, there is no limitation on those components herein. The term is used only to distinguish one component from another; for example, a first component may be referred to as a second component, and similarly, a second component may be referred to as a first component, without departing from the teachings of this application. The term “and / or” as used herein includes any and all combinations of one or more of the associated listed items.

[0025] The terminology used herein is for the purpose of describing various embodiments only and is not intended to be limiting. As used herein, the singular form also includes the plural form, unless the context clearly indicates otherwise. It will also be understood that the terms “comprising” and / or “having” as used in this specification specify the presence of the described features, numbers, operations, components, elements or combinations thereof, without excluding the presence or addition of one or more other features, numbers, operations, components, elements or combinations thereof.

[0026] As mentioned above, in existing relay life testing practices, the control circuit structure is usually quite straightforward, directly connecting the relay to a real or simulated load. While this direct-load connection method is simple in structure, it exposes a series of inherent technical defects in practical applications.

[0027] Traditional testing methods typically employ random or unpredictable methods to control the relay to close at arbitrary points in time with an AC signal. This randomness leads to two main problems: first, the repeatability of test results is poor, resulting in a lack of reliable comparability between different batches or designs; second, it may overlook critical design weaknesses of the relay, making the test conclusions less objective and comprehensive, thus affecting the accurate prediction of its lifespan and targeted design improvements.

[0028] Based on this, this application makes fundamental improvements at both the circuit structure and control strategy levels. In terms of circuit structure, this application changes the traditional mode of directly connecting the relay to the load, introducing a transformer as a coupling medium between the relay and the final load. By placing the relay in the primary circuit of the transformer, instead of directly driving the load, and utilizing the inherent voltage / current transformation, electrical isolation, and impedance matching characteristics of the transformer, the application fundamentally solves the problems of poor applicability, low safety, and susceptibility to shock damage to relay contacts caused by the mismatch between load and relay parameters in traditional circuits. Based on this optimized circuit architecture, the application further proposes to precisely control the relay's closing action using a controller with a preset time much shorter than the AC signal cycle (e.g., a 1ms interval for a 20ms cycle AC current at 50Hz). This high-frequency step-by-step control strategy aims to ensure that within one or several AC cycles, the relay's closing operation can systematically and comprehensively cover almost all phase points on the AC waveform, thereby exposing the relay to various transient electrical stresses.

[0029] The introduction of a transformer significantly enhances the flexibility and safety of the test circuit. It not only effectively blocks electrical noise and faults from the load side from interfering with the control system through electrical isolation, ensuring the safety of equipment and personnel, but also allows the same test system to be easily adapted to various loads with different voltage and current levels by replacing transformers of different specifications, significantly improving its versatility. More importantly, the high-precision, full-phase control strategy completely changes the randomness and unreliability of traditional testing methods. By ensuring that the relay inevitably experiences all harsh conditions during life testing, including voltage peaks, current peaks, and voltage zero crossings, this application can comprehensively and quickly induce and expose the relay's potential failure modes, especially key weaknesses such as contact adhesion, thereby obtaining a more accurate life assessment in a shorter time. This deterministic testing method guarantees high repeatability and comparability of test results, providing a solid data foundation for performance comparison and design optimization between different products, making the test conclusions no longer fuzzy statistical probabilities, but an objective evaluation that accurately reflects the relay's intrinsic physical characteristics.

[0030] Accordingly, such as Figures 1 to 4 As shown, a control circuit and control method for life testing of a relay 10 according to an embodiment of this application are illustrated. Figure 1As shown, the control circuit for life testing of relay 10 includes relay 10, AC power supply 20 connected to relay 10, transformer 30 connected to relay 10, load 40 connected to transformer 30, and controller 50 coupled to relay 10. The AC power supply 20 is configured to output an AC signal to relay 10; the controller 50 is configured to control relay 10 to close once after the start time of each cycle and at a preset time interval from the start time of each cycle, until relay failure. The preset time interval is calculated according to the following formula: when N≤T / n, t=N*n; when N>T / n, t=(NT*[N / T])*n, where t is the preset time interval, N is the number of cycles, n is the preset time, T is the time of one cycle, and [N / T] is the integer part of the ratio of the number of cycles to the time of one cycle. The preset time is less than or equal to one-tenth of the cycle of the AC signal.

[0031] Specifically, the relay 10 is an electronic device that uses the principle of electromagnetic induction to control the on / off state of a circuit. The relay 10 mainly includes a magnet, a coil wound around the magnet, an armature, a spring, a moving contact formed on the armature, and two stationary contacts (a normally open contact and a normally closed contact). When a certain voltage is applied across the coil, current flows through the coil, thereby generating electromagnetic induction, attracting the moving contact on the armature towards the normally open contact until the moving contact contacts the normally open contact, completing the engagement process. When the coil is de-energized, the magnetic force of the magnet disappears, and the armature returns to its original position under the reaction force of the spring. The moving contact on the armature then contacts the normally closed contact, completing the release process.

[0032] In one embodiment of this application, the transformer 30 includes a primary coil and a secondary coil configured to sense the primary coil, the secondary coil being connected to at least one load 40. The primary coil, the relay 10, the AC power supply 20, and the controller 50 form a primary circuit.

[0033] The controller 50 is a microcontroller unit (MCU) or a digital signal processor (DSP). The controller 50 controls the relay 10 to close once after the start time of each cycle and at a preset time interval. This ensures that the relay 10 will inevitably experience all harsh operating conditions, including voltage peaks, current peaks, and voltage zero crossings, during the life test. Therefore, the preset time is set according to the length of the AC signal cycle. When the AC signal cycle is long, the preset time can be less than one-tenth of the AC signal cycle, for example, one-fifteenth or one-twentieth.

[0034] In one example of this application, the period of the AC signal is 20 milliseconds, and the preset time is 1 millisecond. Thus, the relay 10 is controlled to close once at the start time interval of 1*1 milliseconds with the first cycle, once at the start time interval of 2*1 milliseconds with the second cycle, once at the start time interval of 3*1 milliseconds with the third cycle, once at the start time interval of (21-20*[21 / 20])*1=1 milliseconds with the start time interval of (21-20*[41 / 20])*1=1 milliseconds with the start time interval of (41-20*[41 / 20])*1=1 milliseconds with the start time of the forty-first cycle.

[0035] The key to determining whether to stop the life test lies in determining whether relay 10 has failed and when it has failed.

[0036] In theory, it is possible to determine whether the relay 10 is faulty by checking the structure of the relay 10 itself or the load 40 connected to the relay 10.

[0037] Preferably, for relay 10 connected to load 40 via transformer 30, this application shifts the monitoring point for monitoring whether relay 10 is malfunctioning from the secondary (load 40) side of transformer 30 to the primary (relay 10) side.

[0038] Furthermore, in the life test of relay 10, the main reason for relay 10 failure is structural adhesion. Theoretically, whether relay 10 has failed due to adhesion can be monitored manually. However, considering that manual monitoring of relay 10 failure is labor-intensive and time-consuming, and has a significant degree of judgment error or delay, this application determines whether relay 10 contacts have failed due to adhesion by accurately measuring the primary coil current flowing through the contacts of relay 10 (meaning that the stationary and movable contacts of relay 10 are stuck together due to melting or welding, resulting in inability to control normally). Here, in the ideal relay 10-transformer 30-load 40 circuit, the state of relay 10 directly determines the energizing state of the primary coil of transformer 30. During the normal disconnection of relay 10, controller 50 instructs relay 10 to disconnect, its moving and stationary contacts physically separate, cutting off the primary circuit, resulting in no current flowing through the secondary coil of transformer 30, and load 40 is de-energized. In the case of relay 10 failure due to contact adhesion, if the moving or stationary contacts of relay 10 become welded together due to electric arc, high temperature, or other reasons, the contacts will remain physically connected even if the controller 50 issues a disconnect command. At this time, the AC power supply 20 continues to supply power to the primary coil of transformer 30. Even if the secondary side is not connected to load 40 (or load 40 is damaged), the primary coil itself will still experience a non-zero current, known as the excitation current or no-load current, as it needs to establish a magnetic field. Therefore, detecting whether there is an excitation current greater than a preset threshold in the primary circuit when the controller 50 commands relay 10 to disconnect is the most direct and clear evidence for determining whether the relay 10 contacts are stuck.

[0039] To implement the above logical judgment, a failure judgment threshold current needs to be set first, that is, a preset current threshold Ith, which serves as a reference threshold and should be much greater than the noise current of the circuit, but much less than the normal minimum excitation current of transformer 30. For example, it can be calibrated by performing a no-load test on a normal transformer 30, for example, setting Ith to 10% of the normal excitation current.

[0040] Then, a low-resistance, high-precision current sampling resistor (Rsense) needs to be connected in series between relay 10 and the primary coil of transformer 30. By measuring the voltage Vsense(t) across this resistor, the primary current Iprimary(t) is calculated in real time according to Ohm's law. Specifically, the controller 50 is connected to the current sampling resistor. Within a specified time window after the controller 50 issues a disconnect command, the primary current Iprimary(t) = Vsense(t) / Rsense is determined by high-frequency sampling of the voltage Vsense(t) across Rsense.

[0041] Furthermore, since the signal being processed is AC, directly comparing instantaneous values ​​is susceptible to noise and phase effects. Therefore, the root mean square (RMS) value of the sampled voltage can be calculated within a preset time window, for example, one or more complete cycles (e.g., 20 ms), and compared with a preset voltage threshold Vth calculated based on a preset current threshold Ith. Here, the preset voltage threshold Vth is equal to the product of the set current threshold Ith and the known sampling resistance Rsense, Vth = Ith × Rsense. Then, within the time window, the sampled voltage sequence Vsense(t) is processed to calculate its RMS value.

[0042] Finally, the root mean square value of the calculated sampling voltage is compared with the preset voltage threshold Vth. If it is greater than Vth, it is determined that the contacts of relay 10 are stuck and have failed to disconnect normally. If it is less than Vth, it is determined that relay 10 disconnects normally.

[0043] Here, since the test is on the lifespan of relay 10, and its failure mode is contact adhesion, monitoring the current flowing through the contacts is a direct physical quantity. Compared to the indirect monitoring of the voltage / current at the load 40 terminal, the judgment logic is directly linked to the physical state of the relay 10 contacts, eliminating misjudgments caused by load 40 faults or problems on the secondary side of transformer 30. The directness and clarity of the judgment can improve the accuracy of failure detection.

[0044] Furthermore, since it is not affected by the state of the load 40 terminal, for example, if the load 40 burns out during the test, the monitoring on the load 40 side will misjudge that the relay 10 is normally disconnected because there is no current at the load 40 terminal. However, the monitoring method based on the primary side current will not be affected by this. As long as the contacts stick together, the primary excitation current will still exist, which can accurately capture the failure, thus making the test system more robust.

[0045] In addition, although the excitation current of transformer 30 is usually much smaller than the full-load current, it is a stable and measurable non-zero signal. This allows for the setting of a very sensitive detection threshold, which can reliably distinguish between adhesion failure (excitation current present) and normal disconnection (theoretically zero current, but actually extremely low noise). For example, it can detect soft failures caused by tiny weld points (i.e., weak conduction between contacts), thus improving sensitivity.

[0046] Based on the structure and working principle of the control circuit used for the life test of relay 10, as follows: Figure 2As shown, this application proposes a control method for a control circuit used in relay life testing, comprising: S1, controlling the relay 10 to close once after the start time of each cycle and at a preset time interval from the start time of each cycle, until the relay 10 fails, wherein the preset time interval is calculated according to the following formula: when N≤T / n, t=N*n; when N>T / n, t=(NT*[N / T])*n, where t is the preset time interval, N is the number of cycles, n is the preset time, T is the time of one cycle, [N / T] is the integer part of the ratio of the number of cycles to the time of one cycle, and the preset time is less than or equal to one-tenth of the cycle of the AC signal.

[0047] Specifically, in step S1, the relay 10 is controlled to close once after the start time of each cycle and at a preset time interval from the start time of each cycle, until the relay 10 fails. As described above, preferably, since the relay 10 is connected to the load 40 via the transformer 30, this application shifts the monitoring point for detecting whether the relay 10 has failed from the secondary (load 40) side of the transformer 30 to the primary (relay 10) side. Accordingly, in step S1, the relay 10 is controlled to close once after the start time of each cycle and at a preset time interval from the start time of each cycle, until the relay 10 fails due to adhesion.

[0048] More specifically, in one embodiment of this application, such as Figure 3 As shown, step S1 includes: S11, calculating the primary current in the primary circuit where the primary coil and the relay 10 are located; S12, comparing the primary current with a preset current threshold, and determining that the relay 10 has failed due to sticking if the primary current is greater than the preset current threshold. In one example of this application, the preset current threshold is equal to 5% to 20% of the average current in the primary circuit when the relay 10 is operating normally and the transformer 30 is not connected to the load 40. The average current refers to the average of multiple primary current values ​​calculated within a preset time window. It should be understood that other current statistics reflecting the average current level within the preset time window can be used, such as the median current value.

[0049] In step S11, the primary current in the primary circuit containing the primary coil and the relay 10 is calculated. Specifically, the voltage Vsense(t) across the current sampling resistor is first measured, and then the primary current Iprimary(t) = Vsense(t) / Rsense in the primary circuit is calculated according to Ohm's law.

[0050] In another embodiment of this application, such as Figure 4As shown, step S1 includes: S11A, measuring the voltage across the current sampling resistor within a specified time window; S12A, calculating the root mean square (RMS) value of the voltage across the current sampling resistor within the specified time window; S13A, comparing the RMS value of the voltage with a preset voltage threshold, and determining that the relay 10 has failed due to sticking if the RMS value of the voltage is greater than the preset voltage threshold. The preset voltage threshold is equal to the preset current threshold plus the resistance value of the current sampling resistor. In one example of this application, the specified time window is greater than or equal to one cycle of the AC signal.

[0051] In summary, the control circuit and control method for life testing of relay 10 have been explained. The control circuit and control method for life testing of relay 10 can improve the accuracy of relay 10 life prediction and enhance the reliability of the control circuit to a certain extent.

[0052] The present application and its embodiments have been described above. This description is not restrictive, and the accompanying drawings are only one embodiment of the present application. The actual structure is not limited to this. In conclusion, if a person skilled in the art is inspired by this description and designs a similar structure and embodiment without departing from the spirit of the present application, such design should fall within the protection scope of the present application.

Claims

1. A control circuit for relay life testing, characterized in that, include: Relay; The AC power supply connected to the relay is configured to output an AC signal to the relay; A transformer connected to a relay; The load connected to the transformer; The controller coupled to the relay is configured to control the relay to close once after the start time of each cycle and at a preset time interval from the start time of each cycle, until the relay fails. The preset time interval is calculated according to the following formula: when N≤T / n, t=N*n; when N>T / n, t=(NT*[N / T])*n, where t is the preset time interval, N is the number of cycles, n is the preset time, T is the time of one cycle, and [N / T] is the integer part of the ratio of the number of cycles to the time of one cycle. The preset time is less than or equal to one-tenth of the cycle of the AC signal.

2. The control circuit for relay life testing according to claim 1, characterized in that, The preset time is 1 millisecond, and the period of the AC signal is 20 milliseconds.

3. A control method of a control circuit for relay life test, characterized by, The control circuit used for relay life testing includes a relay, an AC power supply connected to the relay, a transformer connected to the relay, a load connected to the transformer, and a controller coupled to the relay. The AC power supply is configured to output an AC signal to the relay; The control methods used for control circuits in relay life testing include: The relay is controlled to close once after the start time of each cycle and at a preset time interval from the start time of each cycle, until the relay fails. The preset time interval is calculated according to the following formula: when N≤T / n, t=N*n; when N>T / n, t=(NT*[N / T])*n, where t is the preset time interval, N is the number of cycles, n is the preset time, T is the time of one cycle, and [N / T] is the integer part of the ratio of the number of cycles to the time of one cycle. The preset time is less than or equal to one-tenth of the cycle of the AC signal.

4. The control method of the control circuit for relay life test according to claim 3, characterized by, The preset time is 1 millisecond, and the period of the AC signal is 20 milliseconds.

5. The control method of the control circuit for relay life test according to claim 3, characterized by, The relay is controlled to close once after the start time of each cycle and at a preset time interval from the start time of each cycle, until the relay fails, including: The relay is controlled to close once after the start time of each cycle and at a preset time interval from the start time of each cycle, until the relay sticks and fails.

6. The control method of the control circuit for relay life test according to claim 3, characterized by, The transformer includes a primary coil and a secondary coil configured to induct the primary coil, the secondary coil being connected to at least one load; The relay is controlled to close once after the start time of each cycle and at a preset time interval from the start time of each cycle, until the relay fails due to sticking, including: Calculate the primary current in the primary circuit containing the primary coil and the relay; The primary current is compared with a preset current threshold. If the primary current is greater than the preset current threshold, the relay is determined to be stuck and failed.

7. The control method of the control circuit for a relay life test according to claim 6, characterized by, The preset current threshold is equal to 5% to 20% of the average current in the primary circuit when the relay is operating normally and the transformer is not connected to a load.

8. The control method of the control circuit for relay life test according to claim 6, characterized by, The primary circuit includes a current sampling resistor connected in series between the primary coil and the relay; Calculating the primary current in the primary circuit containing the primary coil and the relay includes: Measure the voltage across the current sampling resistor; The primary current in the primary circuit is calculated using Ohm's law.

9. The control method of the control circuit for a relay life test according to claim 3, characterized by, The transformer includes a primary coil and a secondary coil configured to sense the primary coil, the secondary coil being connected to at least one load; the primary circuit containing the relay includes a current sampling resistor connected in series between the primary coil and the relay; The relay is controlled to close once after the start time of each cycle and at a preset time interval from the start time of each cycle, until the relay fails due to sticking, including: The voltage across the current sampling resistor is measured within a specified time window. Calculate the root mean square value of the voltage across the current sampling resistor within a specified time window; The root mean square value of the voltage is compared with a preset voltage threshold. If the root mean square value of the voltage is greater than the preset voltage threshold, the relay is determined to be stuck and failed.

10. The control method of the control circuit for a relay life test according to claim 9, characterized by, The specified time window is greater than or equal to one cycle of the AC signal.

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