Three-phase meter relay state detection circuit, method and electric energy meter

Abstract

The application discloses a three-phase meter relay state detection circuit, wherein the three-phase meter relay state detection circuit comprises a microswitch circuit, a transistor multi-state conversion circuit, a unidirectional power maintaining circuit and an I / O conversion circuit; the I / O conversion circuit is connected with the unidirectional power maintaining circuit, the transistor multi-state conversion circuit and an MCU respectively; the unidirectional power maintaining circuit is connected with the microswitch circuit and the transistor multi-state conversion circuit respectively; and the microswitch circuit is connected with the transistor multi-state conversion circuit. The application further discloses a three-phase meter relay state detection method and an electric energy meter. The application solves the technical problems of the existing three-phase split type relay state detection, such as too many wire harnesses, the incapability of being compatible with the 2-wire detection interface of the integrated relay, the high cost of the existing 2-wire scheme, the existence of a detection blind area and the incapability of being completely compatible with the 2-wire scheme using only the digital I / O port to detect the level state.

Description

Technical Field

[0001] This invention relates to the field of electricity metering equipment technology, and in particular to a three-phase meter relay status detection circuit, method, and electricity meter. Background Technology

[0002] Three-phase energy meters with built-in three-phase relays (also known as three-phase built-in load switches or three-phase load switches) are generally divided into two types: one is a three-phase integrated relay with a linkage mechanism, which has only one set of drive coils and operating mechanisms inside, and the A, B, and C phase contacts can operate synchronously; the other is a three-phase combined relay or a three-phase separate relay assembled from three single-phase relays (separate phase relays).

[0003] Three-phase integrated relays are typically designed with auxiliary contacts (microswitches) to indicate the status of the main contacts. The auxiliary contacts are linked to the main contacts and are executed by the same actuating mechanism. Relay status detection only requires two wires (signal line and signal ground). The signal line is connected to a digital I / O port of the MCU and pulled up to the peripheral power supply through an external resistor. The relay status can be determined by detecting the high or low level of the I / O port. The circuit is simple and inexpensive.

[0004] Three-phase split-type relays have independent drive coils and operating mechanisms for each phase. The actions of the A, B, and C phase contacts can have time differences, and even inconsistent states. Therefore, it is necessary to provide separate status signals for each phase relay to detect and identify abnormal contact states. Existing technologies for status detection in three-phase split-type relays have the following problems: First, while detecting the status by detecting the electrical signal of the relay's output copper bar is compatible with existing two-wire solutions, it involves many components, is costly, and has a detection blind spot. When the relay's input copper bar is de-energized, the output copper bar is also de-energized regardless of the situation, and the detected state always indicates the main contact is open, failing to accurately reflect the relay's state. Second, when providing status signals through microswitches linked within each phase relay, three sets of status signals are needed to represent the main contact states of phases A, B, and C. If the three I / O pins of an MCU are used… If each phase is detected separately using the I / O ports, at least four wires are required (signal line A, signal line B, signal line C, and signal ground). This results in a large wiring harness, consumes more I / O resources, and is incompatible with the original two-wire detection interface of the three-phase integrated relay. If only two wires (signal line and signal ground) are used, simply connecting the output contacts of each microswitch in parallel or series has serious drawbacks: In parallel mode, if the microswitch contact of one phase relay is closed, it is impossible to identify whether the microswitch contact of other phase relays is open; in series mode, if the microswitch contact of one phase relay is open, it is impossible to identify whether the microswitch contact of other phase relays is closed. Thirdly, the existing two-wire scheme that uses resistors of different resistance values ​​to divide the voltage in series (e.g., 1kΩ for phase A, 2kΩ for phase B, and 4kΩ for phase C), although it can distinguish the phase sequence, requires an additional ADC detection voltage, increasing costs, and is not fully compatible with the two-wire scheme that only uses digital I / O ports to detect the level status.

[0005] Therefore, in order to solve the above problems, it is urgent to propose a three-phase meter relay status detection circuit, method, and energy meter. Summary of the Invention

[0006] The main objective of this invention is to propose a three-phase meter relay status detection circuit, method, and energy meter, aiming to solve the technical problems of existing three-phase split relay status detection requiring multiple wiring harnesses, incompatibility with integrated relay 2-wire detection interfaces, high cost of existing 2-wire solutions, existence of detection blind spots, or incompatibility with 2-wire solutions that only use digital I / O ports to detect level status.

[0007] To achieve the above objectives, the present invention provides a three-phase meter relay status detection circuit, wherein the three-phase meter relay status detection circuit includes: a micro switch circuit, a transistor multi-state conversion circuit, a unidirectional power supply sustaining circuit, and an I / O conversion circuit;

[0008] The micro switch circuit includes three phase relay status indication micro switches: phase A, phase B, and phase C. Each micro switch includes a common contact, a normally open contact, and a normally closed contact. The common contact of the three micro switches is connected to the power supply terminal.

[0009] The transistor multi-state switching circuit includes a first transistor and a second transistor. The base of the first transistor is resistively connected to the normally closed contacts of three microswitches, and the base of the second transistor is resistively connected to the normally open contacts of three microswitches. The collector of the first transistor serves as the output terminal of the transistor multi-state switching circuit and is resistively connected to a unidirectional power supply sustaining circuit and an I / O conversion circuit, respectively. The collector of the second transistor is resistively connected to the power supply terminal.

[0010] The input terminal of the unidirectional power supply sustaining circuit is connected to the I / O conversion circuit, and the output terminal of the unidirectional power supply sustaining circuit is connected to the micro-switch circuit and the transistor multi-state conversion circuit, respectively.

[0011] The I / O conversion circuit is connected to the bidirectional I / O port of the MCU. The MCU controls the I / O port to switch between output high level and input state to realize the periodic detection of the relay state.

[0012] In one preferred embodiment, the micro-switch circuit includes:

[0013] Phase A relay status indicator micro switch SW1 and its corresponding common contact COM1, normally open contact NO1 and normally closed contact NC1;

[0014] B-phase relay status indicator micro switch SW2 and its corresponding common contact COM2, normally open contact NO2 and normally closed contact NC2;

[0015] C-phase relay status indicator micro switch SW3 and its corresponding common contact COM3, normally open contact NO3 and normally closed contact NC3.

[0016] In one preferred embodiment, the first transistor and the second transistor in the transistor multi-state switching circuit are both NPN type transistors;

[0017] The emitter of the first transistor and the emitter of the second transistor are grounded;

[0018] The base of the first transistor is connected to capacitor C2, resistor R4, resistor R5 and resistor R6 respectively. The other end of capacitor C2 is connected to resistor R7 and the collector of the second transistor respectively. The other end of resistor R7 is connected to the power supply terminal.

[0019] The collector of the first transistor is connected to capacitor C1, resistor R8 and resistor R9 respectively. The other end of capacitor C1 is connected to resistor R1, resistor R2, resistor R3 and the base of the second transistor respectively. The other end of resistor R8 is connected to the unidirectional power supply sustaining circuit. The other end of resistor R9 is connected to the unidirectional power supply sustaining circuit and the I / O conversion circuit respectively.

[0020] The other ends of resistors R1, R2, and R3 are respectively connected to the normally open contacts of the microswitches indicating the status of the three phase-separated relays for phases A, B, and C. The other ends of resistors R4, R5, and R6 are respectively connected to the normally closed contacts of the microswitches indicating the status of the three phase-separated relays for phases A, B, and C.

[0021] In one preferred embodiment, the resistance ratio of resistors R1, R2, and R3 is set to 3:4:6, and the resistance ratio of resistors R4, R5, and R6 is set to 3:4:6.

[0022] In one preferred embodiment, the unidirectional power supply sustaining circuit includes a diode D1, a resistor R10, and a capacitor C3; the anode of the diode D1 is connected to both the transistor multi-state switching circuit and the I / O switching circuit, the cathode of the diode D1 is connected to the power supply terminal, the transistor multi-state switching circuit, and the resistor R10, the other end of the resistor R10 is connected to the capacitor C3, and the other end of the capacitor C3 is grounded.

[0023] In one preferred embodiment, the I / O conversion circuit includes resistor R11, resistor R12, capacitor C4, and capacitor C5; one end of resistor R12 is connected to capacitor C5 and the bidirectional I / O port of the MCU, the other end of resistor R12 is connected to resistor R11 and capacitor C4, the other end of resistor R11 is connected to the power supply, and the other ends of capacitors C4 and C5 are grounded.

[0024] A detection method for a three-phase meter relay status detection circuit includes the following steps:

[0025] S1. During power-on initialization, the MCU control status detection I / O port outputs a high level, which supplies power to the micro-switch circuit and transistor multi-state conversion circuit through the unidirectional power supply maintenance circuit.

[0026] S2. During detection, the MCU switches the I / O port to the input state and collects the level signal of the I / O port within a preset time window;

[0027] S3. Determine the state of the three-phase split relays based on the characteristics of the acquired level signals; when all three-phase relays A, B, and C are closed, the transistor multi-state conversion circuit outputs a stable low level; when all three-phase relays A, B, and C are tripped, the transistor multi-state conversion circuit outputs a stable high level; when the states of the three-phase relays A, B, and C are inconsistent, the transistor multi-state conversion circuit outputs an oscillation signal.

[0028] S4. After the test is completed, the MCU controls the I / O port to output a high level again to power the unidirectional power supply circuit, and repeats steps S2-S4 for periodic testing.

[0029] One preferred embodiment, step S3, specifically includes:

[0030] The I / O port is sampled multiple times for level signals. The proportion of low-level sampling times to the total number of sampling times is used as the low-level duty cycle. A first threshold and a second threshold are set.

[0031] When the low-level duty cycle is less than or equal to the first threshold, it is determined that all three-phase relays A, B, and C are in a tripped state.

[0032] When the low-level duty cycle is greater than or equal to the second threshold, it is determined that all three-phase relays A, B, and C are in the closed state.

[0033] When the low-level duty cycle is between the first threshold and the second threshold, it is determined that the states of the three-phase relays A, B, and C are inconsistent, indicating a single-phase or two-phase abnormality.

[0034] One preferred embodiment is that when the states of the three-phase relays A, B, and C are inconsistent, a preset correspondence is matched based on the specific value of the low-level duty cycle to determine the specific abnormal phase sequence, specifically as follows:

[0035] When the low-level duty cycle is greater than the first threshold and less than or equal to the third threshold, it is determined that the C-phase relay is closed, and the A-phase relay and the B-phase relay are tripped.

[0036] When the low-level duty cycle is greater than the third threshold and less than or equal to the fourth threshold, it is determined that the B-phase relay is closed, and the A-phase relay and the C-phase relay are tripped.

[0037] When the low-level duty cycle is greater than the fourth threshold and less than or equal to the fifth threshold, it is determined that the A-phase relay is closed, and the B-phase relay and the C-phase relay are tripped.

[0038] When the low-level duty cycle is greater than the fifth threshold and less than or equal to the sixth threshold, it is determined that the A-phase relay trips and the B-phase relay and C-phase relay close.

[0039] When the low-level duty cycle is greater than the sixth threshold and less than or equal to the seventh threshold, it is determined that the B-phase relay trips and the A-phase and C-phase relays close.

[0040] When the low-level duty cycle is greater than the seventh threshold and less than the second threshold, it is determined that the C-phase relay trips, and the A-phase relay and B-phase relay close.

[0041] An electricity meter, the electricity meter including the aforementioned three-phase meter relay status detection circuit.

[0042] In the above technical solution of the present invention, the three-phase meter relay status detection circuit includes: a micro-switch circuit, a transistor multi-state conversion circuit, a unidirectional power supply sustaining circuit, and an I / O conversion circuit; the micro-switch circuit includes three phase relay status indicating micro-switches for phase A, phase B, and phase C, each micro-switch including a common contact, a normally open contact, and a normally closed contact, the common contact of the three micro-switches being connected to the power supply terminal; the transistor multi-state conversion circuit includes a first transistor and a second transistor, the base of the first transistor being resistively connected to the normally closed contacts of the three micro-switches respectively, and the base of the second transistor being resistively connected to the normally closed contacts of the three micro-switches respectively. The normally open contact of the transistor is resistively connected. The collector of the first transistor, serving as the output terminal of the transistor multi-state conversion circuit, is resistively connected to both the unidirectional power supply sustaining circuit and the I / O conversion circuit. The collector of the second transistor is resistively connected to the power supply terminal. The input terminal of the unidirectional power supply sustaining circuit is connected to the I / O conversion circuit, and the output terminal of the unidirectional power supply sustaining circuit is connected to both the micro-switch circuit and the transistor multi-state conversion circuit. The I / O conversion circuit is connected to the bidirectional I / O port of the MCU. The MCU controls the I / O port to switch between output high level and input state, thereby achieving periodic detection of the relay state. This invention solves the technical problems of existing three-phase split relay state detection requiring multiple wiring harnesses, incompatibility with integrated relay 2-wire detection interfaces, high cost of existing 2-wire solutions, detection blind spots, or incompatibility with 2-wire solutions that only use digital I / O ports to detect level states.

[0043] In this invention, the transistor multi-state switching circuit generates astable multivibration when the three-phase states are inconsistent. By distinguishing the states through the duty cycle, it can not only determine "all closed / all open" but also accurately identify which phase is abnormal (such as phase A sticking, phase B not engaging, etc.), solving the problem that traditional two-wire parallel / series schemes cannot locate the specific faulty phase. At the same time, in the steady state of full tripping or full closing, the circuit outputs a fixed high and low level, which is minimally affected by temperature. In the oscillating state, the RC time constant that determines the duty cycle changes synchronously with the temperature, ensuring that the duty cycle remains stable under different temperatures and reducing the misjudgment rate. Attached Figure Description

[0044] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0045] Figure 1 This is a first schematic diagram of a three-phase meter relay status detection circuit according to an embodiment of the present invention;

[0046] Figure 2 This is a second schematic diagram of a three-phase meter relay status detection circuit according to an embodiment of the present invention;

[0047] Figure 3 This is a schematic diagram of a three-phase meter relay status detection method according to an embodiment of the present invention.

[0048] The realization of the objective, functional characteristics and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0049] 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. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0050] Furthermore, in this invention, descriptions involving "first," "second," etc., are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of that feature.

[0051] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0052] See Figures 1-2 According to one aspect of the present invention, the present invention provides a three-phase meter relay state detection circuit, wherein the three-phase meter relay state detection circuit includes: a micro switch circuit, a transistor multi-state conversion circuit, a unidirectional power supply sustaining circuit, and an I / O conversion circuit;

[0053] The micro switch circuit includes three phase relay status indication micro switches: phase A, phase B, and phase C. Each micro switch includes a common contact, a normally open contact, and a normally closed contact. The common contact of the three micro switches is connected to the power supply terminal.

[0054] The transistor multi-state switching circuit includes a first transistor and a second transistor. The base of the first transistor is resistively connected to the normally closed contacts of three microswitches, and the base of the second transistor is resistively connected to the normally open contacts of three microswitches. The collector of the first transistor serves as the output terminal of the transistor multi-state switching circuit and is resistively connected to a unidirectional power supply sustaining circuit and an I / O conversion circuit, respectively. The collector of the second transistor is resistively connected to the power supply terminal.

[0055] The input terminal of the unidirectional power supply sustaining circuit is connected to the I / O conversion circuit, and the output terminal of the unidirectional power supply sustaining circuit is connected to the micro-switch circuit and the transistor multi-state conversion circuit, respectively.

[0056] The I / O conversion circuit is connected to the bidirectional I / O port of the MCU. The MCU controls the I / O port to switch between output high level and input state to realize the periodic detection of the relay state.

[0057] Specifically, in this embodiment, the three-phase meter relay status detection circuit includes a micro switch circuit, a transistor multi-state conversion circuit, a unidirectional power supply sustaining circuit, and an I / O conversion circuit; the I / O conversion circuit is connected to the unidirectional power supply sustaining circuit, the transistor multi-state conversion circuit, and the MCU respectively; the unidirectional power supply sustaining circuit is connected to the micro switch circuit and the transistor multi-state conversion circuit respectively; and the micro switch circuit is connected to the transistor multi-state conversion circuit.

[0058] Specifically, in this embodiment, the micro-switch circuit includes:

[0059] Phase A relay status indicator micro switch SW1 and its corresponding common contact COM1, normally open contact NO1 and normally closed contact NC1;

[0060] B-phase relay status indicator micro switch SW2 and its corresponding common contact COM2, normally open contact NO2 and normally closed contact NC2;

[0061] C-phase relay status indicator micro switch SW3 and its corresponding common contact COM3, normally open contact NO3 and normally closed contact NC3;

[0062] Three microswitches indicate the status of phase A relay, phase B relay, and phase C relay, respectively; the common contact of all three microswitches is connected to the power supply.

[0063] Specifically, in this embodiment, both the first transistor and the second transistor in the transistor multistate conversion circuit are NPN type transistors;

[0064] The emitter of the first transistor and the emitter of the second transistor are grounded;

[0065] The base of the first transistor is connected to capacitor C2, resistor R4, resistor R5 and resistor R6 respectively. The other end of capacitor C2 is connected to resistor R7 and the collector of the second transistor respectively. The other end of resistor R7 is connected to the power supply terminal.

[0066] The collector of the first transistor is connected to capacitor C1, resistor R8 and resistor R9 respectively. The other end of capacitor C1 is connected to resistor R1, resistor R2, resistor R3 and the base of the second transistor respectively. The other end of resistor R8 is connected to the unidirectional power supply sustaining circuit. The other end of resistor R9 is connected to the unidirectional power supply sustaining circuit and the I / O conversion circuit respectively.

[0067] The other ends of resistors R1, R2, and R3 are respectively connected to the normally open contacts of the microswitches indicating the status of the three phase-separated relays in phases A, B, and C. The other ends of resistors R4, R5, and R6 are respectively connected to the normally closed contacts of the microswitches indicating the status of the three phase-separated relays in phases A, B, and C.

[0068] The first transistor is an NPN transistor Q1, and the second transistor is an NPN transistor Q2.

[0069] Specifically, in this embodiment, the resistance ratio of resistors R1, R2 and R3 is set to 3:4:6, and the resistance ratio of resistors R4, R5 and R6 is set to 3:4:6.

[0070] Specifically, in this embodiment, the unidirectional power supply sustaining circuit includes a diode D1, a resistor R10, and a capacitor C3; the anode of the diode D1 is connected to the transistor multi-state switching circuit and the I / O switching circuit respectively, the cathode of the diode D1 is connected to the power supply terminal, the transistor multi-state switching circuit and the resistor R10 respectively, the other end of the resistor R10 is connected to the capacitor C3, and the other end of the capacitor C3 is grounded.

[0071] Specifically, in this embodiment, the I / O conversion circuit includes resistor R11, resistor R12, capacitor C4, and capacitor C5; one end of resistor R12 is connected to capacitor C5 and the bidirectional I / O port of the MCU, the other end of resistor R12 is connected to resistor R11 and capacitor C4, the other end of resistor R11 is connected to the power supply terminal, and the other ends of capacitor C4 and capacitor C5 are grounded.

[0072] See Figure 3 According to another aspect of the present invention, a method for detecting the state of a three-phase meter relay is provided, wherein the method for detecting the state of a three-phase meter relay includes the following steps:

[0073] S1. During power-on initialization, the MCU control status detection I / O port outputs a high level, which supplies power to the micro-switch circuit and transistor multi-state conversion circuit through the unidirectional power supply maintenance circuit.

[0074] S2. During detection, the MCU switches the I / O port to the input state and collects the level signal of the I / O port within a preset time window;

[0075] S3. Determine the state of the three-phase split relays based on the characteristics of the acquired level signals; when all three-phase relays A, B, and C are closed, the transistor multi-state conversion circuit outputs a stable low level; when all three-phase relays A, B, and C are tripped, the transistor multi-state conversion circuit outputs a stable high level; when the states of the three-phase relays A, B, and C are inconsistent, the transistor multi-state conversion circuit outputs an oscillation signal.

[0076] S4. After the test is completed, the MCU controls the I / O port to output a high level again to power the unidirectional power supply circuit, and repeats steps S2-S4 for periodic testing.

[0077] Specifically, in this embodiment, step S3 is as follows:

[0078] The I / O port is sampled multiple times for level signals. The proportion of low-level sampling times to the total number of sampling times is used as the low-level duty cycle. A first threshold and a second threshold are set.

[0079] When the low-level duty cycle is less than or equal to the first threshold, it is determined that all three-phase relays A, B, and C are in a tripped state.

[0080] When the low-level duty cycle is greater than or equal to the second threshold, it is determined that all three-phase relays A, B, and C are in the closed state.

[0081] When the low-level duty cycle is between the first threshold and the second threshold, it is determined that the states of the three-phase relays A, B, and C are inconsistent, indicating a single-phase or two-phase abnormality.

[0082] Specifically, in this embodiment, when the states of the three-phase relays A, B, and C are inconsistent, a preset correspondence is matched according to the specific value of the low-level duty cycle to determine the specific abnormal phase sequence, specifically as follows:

[0083] When the low-level duty cycle is greater than the first threshold and less than or equal to the third threshold, it is determined that the C-phase relay is closed, and the A-phase relay and the B-phase relay are tripped.

[0084] When the low-level duty cycle is greater than the third threshold and less than or equal to the fourth threshold, it is determined that the B-phase relay is closed, and the A-phase relay and the C-phase relay are tripped.

[0085] When the low-level duty cycle is greater than the fourth threshold and less than or equal to the fifth threshold, it is determined that the A-phase relay is closed, and the B-phase relay and the C-phase relay are tripped.

[0086] When the low-level duty cycle is greater than the fifth threshold and less than or equal to the sixth threshold, it is determined that the A-phase relay trips and the B-phase relay and C-phase relay close.

[0087] When the low-level duty cycle is greater than the sixth threshold and less than or equal to the seventh threshold, it is determined that the B-phase relay trips and the A-phase and C-phase relays close.

[0088] When the low-level duty cycle is greater than the seventh threshold and less than the second threshold, it is determined that the C-phase relay trips, and the A-phase relay and B-phase relay close.

[0089] Specifically, in this embodiment, after power-on, during MCU initialization, the corresponding state detection I / O port RELAY_STATE outputs a high level, which is then supplied to the unidirectional power supply sustaining circuit via resistor R12. Due to the forward conduction of diode D1 in the unidirectional power supply sustaining circuit, capacitor C3 begins to charge. Current-limiting resistor R10 is used to limit the charging current to prevent excessive charging current from affecting the normal operation of the MCU's I / O port. Simultaneously, the transistor multi-state conversion circuit is powered on and begins to operate. When it is necessary to detect the relay status, the I / O port RELAY_STATE is set to the input state, and the MCU can then perform relay status detection. At this time, due to the reverse cutoff of diode D1 in the unidirectional power supply sustaining circuit, the charge stored in capacitor C3 can still sustain the transistor multi-state conversion circuit for a short period of time. The level of I / O port RELAY_STATE is determined by the pull-up resistor R11 and the output state of the transistor multi-state conversion circuit, and within the preset time range T1, the output level of the three-phase meter relay status detection meets the requirements of the MCU. The MCU completes the signal integrity test of the I / O port during this period. After the test is completed, the MCU sets the I / O port RELAY_STATE to output high level and continues to supply power to the unidirectional power supply maintenance circuit. After a preset time T2, the I / O port RELAY_STATE is set to input state again to start detecting the relay state. This process is repeated to complete the timed detection of the relay state.

[0090] Specifically, in this embodiment, when the MCU needs to drive the relay to trip or close, the two I / O ports connected to the three-phase meter relay drive circuit of the MCU will send drive signals to the three-phase meter relay drive circuit, causing the three-phase meter relay drive circuit to send a drive pulse with a time width of T3 to drive the relay to trip or close. The relay in the energy meter is generally a magnetic latching relay or a motor relay, which only needs a short pulse to complete the state switching and does not need to provide drive current continuously. When the MCU starts to drive the relay, the MCU's state detection I / O port should be controlled to output a high level to supply power to the unidirectional power supply maintenance circuit. The time from the moment the relay drive pulse is issued until the relay state changes is completed is called the relay action time. The MCU should delay for a preset time T4 from the moment the relay drive pulse is issued before setting the state detection I / O port to the input state to perform relay state detection. This time should be greater than the relay action time, so that the relay completes the action and is in a stable state before performing relay state detection.

[0091] Specifically, in this embodiment, when all three relays are closed, the normally open contact of the microswitch is open to the common contact, and the normally closed contact is closed to the common contact. When all three relays are tripped, the normally open contact of the microswitch is closed to the common contact, and the normally closed contact is open to the common contact. The common contact of the microswitch is connected to power supply VCC3, and can provide drive to the base of transistor Q1 or transistor Q2 in the transistor multi-state conversion circuit through its normally open or normally closed contact. The microswitch, in conjunction with the transistor multi-state conversion circuit, can perform relay status detection. When all three relays are closed, the normally closed contacts of the three microswitches are connected to the common contact, connected to power supply VCC3, and after passing through current-limiting resistors R4, R5, and R6, drive the VBE of transistor Q1 to be forward biased, and the CE terminal of transistor Q1 is turned on, while the normally open contacts of the three microswitches are open to the common contact. When the circuit is in the off state, no driving current can be provided to turn on transistor Q2. At this time, transistor Q1 is turned on and transistor Q2 is turned off in the transistor multi-state conversion circuit. The circuit is in a steady state, and the MCU status detection I / O port RELAY_STATE can detect that the output of the transistor multi-state conversion circuit is a stable low level. When all three relays are tripped, the normally open contacts of the three microswitches are connected to the common contact, and the power supply VCC3 is connected. After passing through the current limiting resistors R1, R2 and R3, the VBE of transistor Q2 is forward biased, and the CE terminal of transistor Q2 is turned on. However, the normally closed contacts of the three microswitches are in the off state with the common contact, and no driving current can be provided to turn on transistor Q1. At this time, transistor Q2 is turned on and transistor Q1 is turned off in the transistor multi-state conversion circuit. The circuit is in a steady state, and the MCU status detection I / O port RELAY_STATE can detect that the output of the transistor multi-state conversion circuit is a stable high level.

[0092] Specifically, in this embodiment, when the three relays are in inconsistent states, there are two scenarios: one is that one is in a closed state while the other two are in a tripped state; the other is that two are in a closed state while the other is in a tripped state. For example, if phase A relay is in a closed state, and phase B and phase C relays are in a tripped state, then the normally open contact of the microswitch of phase A relay is open with respect to the common contact, and the normally closed contact is closed with respect to the common contact. Similarly, the normally open contact of the microswitch of phase B and phase C relays is closed with respect to the common contact, and the normally closed contact is open with respect to the common contact. State: The normally closed contact of the microswitch of phase A relay is connected to the common contact. Power supply VCC3 drives the base of transistor Q1 through the common contact, normally closed contact and resistor R4. The normally open contact of the microswitch of phase B relay and phase C relay is connected to the common contact. Power supply VCC3 drives the base of transistor Q2 through the common contact, normally open contact and resistors R2 and R3. The remaining normally open contacts and normally closed contacts are disconnected from the common contact and are in a floating state. Resistors R1, R5 and R6 have no effect on the circuit. At this time, the transistor multi-state switching circuit enters the astable multivibrator state in which the two transistors conduct alternately.

[0093] If phase A and phase B relays are in the closed state, and phase C relay is in the tripped state, then the normally open contacts and common contacts of the microswitches of phase A and phase B relays are open, and the normally closed contacts and common contacts are closed. Similarly, the normally open contacts and common contacts of the microswitches of phase C relays are closed, and the normally closed contacts and common contacts are open. The normally closed contacts and common contacts of the microswitches of phase A and phase B relays are connected, and power supply VCC3 flows through the common contact... The common contact, normally closed contact, and resistors R4 and R5 drive the base of transistor Q1. The normally open contact of the micro switch of the C-phase relay is connected to the common contact. Power supply VCC3 drives the base of transistor Q2 through the common contact, normally open contact, and resistor R3. The remaining normally open or normally closed contacts are disconnected from the common contact and are in a floating state. Resistors R1, R2, and R6 have no effect on the circuit. At this time, the transistor multi-state switching circuit enters an astable multivibrator state in which the two transistors alternately conduct.

[0094] If initially all three relays are in a steady state with all switches closed, the pull-up terminals of resistors R1, R2, and R3 are left floating, while resistors R4, R5, and R6 are pulled up to power supply VCC3. Transistor Q1 is turned on, and transistor Q2 is turned off. Figure 2In the circuit, the potential at point A is approximately 0V, the potential at point B is 0.7V, the potential at point C is approximately 0V, and the potential at point D is pulled up to the power supply VCC3. The voltage across capacitor C2 is (VCC3 - 0.7V). Then, the B-phase relay and the C-phase relay trip, resistors R1, R5, and R6 are pulled up and left floating, while resistors R2, R3, and R4 are pulled up to the power supply VCC3. The power supply VCC3 begins to charge capacitor C1 through resistors R2 and R3, and the potential at point C begins to rise. When it rises to 0V... At 0.7V, transistor Q2 is turned on, and the potential at point D becomes approximately 0. Since the voltage across capacitor C2 cannot change abruptly, the potential at point B becomes (0.7V - VCC3). The base and emitter terminals of transistor Q1 are reverse biased, and transistor Q1 is turned off. Power supply VCC3 charges capacitor C1 in reverse through pull-up resistor R8 (assuming I / O port RELAY_STATE is input at this time). The potential at point A gradually rises to power supply VCC3. At the same time, power supply VCC3 charges capacitor C2 through resistor R4, and the potential at point B... As the voltage at point B gradually rises, when it reaches 0.7V, transistor Q1 turns on, and the voltage at point A becomes approximately 0. Since the voltage across capacitor C1 cannot change abruptly, the voltage at point C becomes (0.7V - VCC3). The base and emitter terminals of transistor Q2 are reverse biased, and transistor Q2 is turned off. Power supply VCC3 charges capacitor C2 in reverse through pull-up resistor R7, and the voltage at point D gradually rises to the level of power supply VCC3. Simultaneously, power supply VCC3 charges capacitor C1 through pull-up resistors R2 and R3, and the voltage at point C gradually rises. When the voltage at point C reaches 0.7V, transistor Q2 turns on again, and the voltage at point D becomes approximately 0. Since the voltage across capacitor C2 cannot change abruptly, the voltage at point B becomes (0.7V - VCC3), and the base and emitter terminals of transistor Q1 are reverse biased, and transistor Q1 is turned off again. This cycle repeats, and the circuit enters an astable multivibrator state where two transistors alternately conduct. The same logic applies to other inconsistent states, where the circuit is also in an astable multivibrator state where two transistors alternately conduct.

[0095] Specifically, in this embodiment, in this invention, resistors R7 and R8 are set to be one to two orders of magnitude smaller than resistors R1 to R6; capacitors C1 and C2 are equal; resistors R1 and R4 are equal; resistors R2 and R5 are equal; and resistors R3 and R6 are equal. If resistors R1 to R6 are connected to power supply VCC3 through microswitch contacts, they are considered effective resistors; if resistors R1 to R6 are disconnected from power supply VCC3, they are considered ineffective resistors. The parallel resistance of the effective resistors R1 to R3 is considered as Ra. The parallel resistance of resistor R6 is considered as Rb. The RC time constant formed by resistor R7 and capacitor C2 is one to two orders of magnitude smaller than that formed by resistor Rb and capacitor C2. The RC time constant formed by resistor R8 and capacitor C1 is one to two orders of magnitude smaller than that formed by resistor Ra and capacitor C1. The circuit oscillation period is determined by resistor Ra, resistor Rb, capacitor C1, and capacitor C2. The circuit oscillation period is approximately (0.7 × Rb × C2 + 0.7 × Ra × C1). The ratio of low level to high level is (Ra × C1) / (Rb × C2). When capacitor C1 and capacitor C2 are equal, the ratio of low level to high level is Ra / Rb.

[0096] Specifically, in this embodiment, the resistance values ​​of resistors R1 to R6 are all equal, and the capacitance values ​​of capacitors C1 and C2 are equal. Thus, when all phase relays are tripped, the low-level duty cycle should be 0%; when all phase relays are closed, the low-level duty cycle should be 100%. When the phase relay states are inconsistent, there are only two possible low-level duty cycles: one is 1 / 3, representing that one phase relay is closed while the other two are tripped; the other is 2 / 3, representing that one phase relay is tripped while the other two are closed. See Table 1 for the various states.

[0097] Table 1 Status of Relays in Each Phase

[0098] Tripping Tripping Tripping 1:∞ 0.00% Tripping Tripping Closing the circuit breaker 1:2 33.33% Tripping Closing the circuit breaker Tripping 1:2 33.33% Closing the circuit breaker Tripping Tripping 1:2 33.33% Tripping Closing the circuit breaker Closing the circuit breaker 2:1 66.67% Closing the circuit breaker Tripping Closing the circuit breaker 2:1 66.67% Closing the circuit breaker Closing the circuit breaker Tripping 2:1 66.67% Closing the circuit breaker Closing the circuit breaker Closing the circuit breaker ∞:1 100%

[0099] Specifically, in this embodiment, the present invention can preset multiple duty cycle thresholds, including a first threshold Dth1 and a second threshold Dth2, where Dth1 < Dth2. When a low-level duty cycle D ≤ the first threshold Dth1 is detected, it is determined that the phase relays have all tripped. When a low-level duty cycle D ≥ the second threshold Dth2 is detected, it is determined that the phase relays have all closed. When the first threshold Dth1 < the low-level duty cycle D < the second threshold Dth2, it is determined that the phase relays are in an inconsistent state, i.e., in an abnormal state, and corresponding processing can be performed, such as attempting to restore the state to the normal state or the state before the trip / close command, or reporting a fault.

[0100] Specifically, in this embodiment, to determine whether a relay in one phase is closed while the other two phases are tripped, or a relay in one phase is tripped while the other two phases are closed, a third threshold Dth3 can be preset. When the first threshold Dth1 < low-level duty cycle D ≤ the third threshold Dth3, it is determined that a relay in one phase is closed while the other two phases are tripped. When the third threshold Dth3 < low-level duty cycle D < the second threshold Dth2, it is determined that a relay in one phase is tripped while the other two phases are closed. This setting can improve the fault tolerance and anti-interference capability of relay status detection.

[0101] Specifically, in this embodiment, when the MCU's status detection I / O performs relay status detection, the level of the status detection I / O can be sampled N times at fixed time intervals. A low threshold number of samplings (Nlow), a medium threshold number of samplings (Nmid), and a high threshold number of samplings (Nhigh) are set. When the number of zeros in the N samples (N0 ≤ Nlow) indicates that all phase relays are in a tripped state, when the number of zeros in the N samples (N0 ≥ Nhigh) indicates that all phase relays are in a closed state, and when the number of zeros in the N samples (N0) satisfies Nlow < N0 < Nhigh, it indicates that the phase relays are closed. The device exhibits an abnormal situation of inconsistent states. Furthermore, when the number of 0 values ​​N0 in N sampled values ​​satisfies Nlow<N0≤Nmid, it means that one phase relay is closed while the other two phase relays are tripped. When the number of 0 values ​​N0 in N sampled values ​​satisfies Nmid<N0<Nhigh, it means that one phase relay is tripped while the other two phase relays are closed. By setting it in this way, when there is a certain amount of external interference, if the level of the state detection I / O port experiences a short-term disturbance, causing the MCU to obtain a few incorrect sampled values, it will still not affect the actual state judgment of the relay, thus improving the system's anti-interference capability.

[0102] Specifically, in this embodiment, the resistance ratios of resistors R1, R2, and R3 are set in a 3:4:6 ratio, and the resistance ratios of resistors R4, R5, and R6 are also set in a 3:4:6 ratio. Furthermore, the resistance values ​​of resistors R1, R2, and R3 are set to be equal to those of resistors R4, R2, and R5, and R3 and R6, respectively. Simultaneously, the capacitance value of capacitor C1 is set to be equal to that of capacitor C2. This allows for the acquisition of low-level duty cycle data for the phase-separated relays under various conditions, as shown in Table 2. This enables accurate determination of which phase-separated relay is faulty based on the different low-level duty cycle sampling results.

[0103] Table 2 shows the states of the A, B, and C three-phase relays corresponding to different low-level duty cycles.

[0104] Tripping Tripping Tripping 1:∞ 0.00% Tripping Tripping Closing the circuit breaker 2:7 22.22% Tripping Closing the circuit breaker Tripping 1:2 33.33% Closing the circuit breaker Tripping Tripping 4:5 44.44% Tripping Closing the circuit breaker Closing the circuit breaker 5:4 55.56% Closing the circuit breaker Tripping Closing the circuit breaker 2:1 66.67% Closing the circuit breaker Closing the circuit breaker Tripping 7:2 77.78% Closing the circuit breaker Closing the circuit breaker Closing the circuit breaker ∞:1 100%

[0105] In this invention, the resistance of resistor R1 is 75KΩ or 150KΩ, the resistance of resistor R2 is 100KΩ or 200KΩ, the resistance of resistor R3 is 150KΩ or 300KΩ, etc., the capacitance of capacitor C1 is 0.022μF or 0.01μF, and the capacitance of capacitor C2 is 0.022μF or 0.01μF. This invention does not impose specific limitations, and the values ​​can be set as needed.

[0106] Specifically, in this embodiment, according to the above settings, when the MCU's state detection I / O performs relay state detection, the level of the state detection I / O can be sampled N times at fixed time intervals, and a first threshold number of times Nth1, a second threshold number of times Nth2, a third threshold number of times Nth3, a fourth threshold number of times Nth4, a fifth threshold number of times Nth5, a sixth threshold number of times Nth6, and a seventh threshold number of times Nth7 are set. When the number of 0 values ​​N0 in the N samples is ≤ Nth1, it means that all phase relays are in the tripped state. When the number of 0 values ​​N0 in the N samples is ≥ Nth7, it means that all phase relays are in the closed state. When the number of 0 values ​​N0 in the N samples satisfies Nth1 < N0 ≤ Nth2, it means that the C phase relay is closed while the other two phase relays are tripped. When the number of 0 values ​​N0 in the N samples satisfies Nth2 < N0 ≤ Nth3, it means that the B phase relay is closed while the other two phase relays are tripped. Tripping occurs when the number of zeros (N0) in N samples satisfies Nth3 < N0 ≤ Nth4, indicating that phase A relay is closed while the other two phase relays are closed. Similarly, when the number of zeros (N0) satisfies Nth4 < N0 ≤ Nth5, phase A relay is closed while the other two phase relays are closed. When the number of zeros (N0) satisfies Nth5 < N0 ≤ Nth6, phase B relay is closed while the other two phase relays are closed. Finally, when the number of zeros (N0) satisfies Nth6 < N0 < Nth7, phase C relay is closed while the other two phase relays are closed. This configuration ensures that even with short-term disturbances in the status detection I / O level due to external interference, causing the MCU to receive a few incorrect samples, the actual relay status judgment remains unaffected. This improves the system's anti-interference capability and allows for accurate identification of which phase relay is faulty.

[0107] Specifically, in this embodiment, the MCU's status detection I / O port can be a special I / O port with input capture function. This I / O port can first be set as a normal input port, and the level of the status detection I / O port can be sampled M times at a fixed sampling frequency fs. A low threshold number of samplings Mlow and a high threshold number of samplings Mhigh are set. When the number of zeros in the M samples M0 ≤ Mlow, it indicates that all phase relays are in a tripped state. When the number of zeros in the M samples M0 ≥ Mhigh, it indicates that all phase relays are in a closed state. When the number of zeros in the M samples M0 satisfies Mlow < M0 < Mhigh, it indicates that the phase relays have an inconsistent state. Then, this I / O port is set to input capture mode, and duty cycle detection is implemented as follows:

[0108] First, set up rising edge detection and clear the count value;

[0109] When the I / O port detects a rising edge, the current value of the counter is locked into the capture register, and an interrupt is generated;

[0110] The interrupt service routine saves the value of the capture register to CNT1, clears the interrupt flag, and then sets the capture to fall edge.

[0111] When the I / O port detects a falling edge, the current value of the counter is locked into the capture register, and an interrupt is generated;

[0112] The interrupt service routine saves the value of the capture register to CNT2, clears the interrupt flag, and then sets the rising edge capture.

[0113] When the I / O port detects a rising edge, the current value of the counter is locked into the capture register, and an interrupt is generated;

[0114] The interrupt service routine saves the value of the capture register to CNT3 and clears the interrupt flag.

[0115] Calculate the low-level duty cycle using the formula D=(CNT3-CNT2) / (CNT3-CNT1)×100%;

[0116] The duty cycle calculated using this method is more accurate. After the low-level duty cycle D is calculated, it is then determined which range the low-level duty cycle falls into based on a combination of preset thresholds, thereby determining the specific state of each phase relay.

[0117] Specifically, in this embodiment, in addition to the preset first threshold Dth1, second threshold Dth2, and third threshold Dth3, multiple duty cycle thresholds are preset for the low-level duty cycle, including a fourth threshold Dth4, a fifth threshold Dth5, a sixth threshold Dth6, and a seventh threshold Dth7, where 0 < Dth1 < 22.22%, 77.78% < Dth2 < 100%, 44.44% < Dth3 < 55.56%, 22.22% < Dth4 < 33.33%, 33.33% < Dth5 < 44.44%, 55.56% < Dth6 < 66.67%, and 66.67% < Dth7 < 77.78%. When D ≤ Dth1... This indicates that all phase relays are in the tripped state. When Dth1 < D ≤ Dth4, it means that the C phase relay is closed while the other two phase relays are tripped. When Dth4 < D ≤ Dth5, it means that the B phase relay is closed while the other two phase relays are tripped. When Dth5 < D ≤ Dth3, it means that the A phase relay is closed while the other two phase relays are tripped. When Dth3 < D ≤ Dth6, it means that the A phase relay is tripped while the other two phase relays are closed. When Dth6 < D ≤ Dth7, it means that the B phase relay is tripped while the other two phase relays are closed. When Dth7 < D < Dth2, it means that the C phase relay is tripped while the other two phase relays are closed. When D ≥ Dth2, it means that all phase relays are in the closed state.

[0118] Specifically, in this embodiment, when the phase relay uses only the normally open or normally closed contacts of the microswitch to indicate the status, the three-phase meter relay status detection circuit can also be slightly modified. If the microswitch contact is open, it means the corresponding phase relay main contact is closed. In this case, Rb can be replaced by a resistor, and Rb is fixedly connected to the power supply VCC3. In this way, when the phase relay is fully closed, the low-level duty cycle is still 100%. However, when the phase relay is fully tripped, the low-level duty cycle is not 0%, but a fixed value between 0% and 100%, determined by the resistance values ​​of Ra and Rb. If the microswitch contact is closed, it means the corresponding phase relay main contact is closed. In this case, Ra can be replaced by a resistor, and Ra is fixedly connected to the power supply VCC3. In this way, when the phase relay is fully tripped, the low-level duty cycle is still 0%. However, when the phase relay is fully closed, the low-level duty cycle is not 100%, but a fixed value between 0% and 100%, determined by the resistance values ​​of Ra and Rb.

[0119] Specifically, in this embodiment, in order to be compatible with the two-wire detection method of the integrated relay, a small circuit board is added to the relay body. The circuits of the three-phase meter relay status detection circuit introduced in this invention, except for the MCU and I / O conversion circuit, are placed on this small circuit board. With the MCU program modified, it can be made compatible with the three-phase integrated relay status detection interface without modifying the mainboard detection circuit.

[0120] Specifically, in this embodiment, the MCU can detect the accurate state of each phase relay in the three-phase split relay system, whether it is consistent or whether it is the desired state, and thus perform corresponding processing. For example, when a trip command is issued, all phase relays should be in the tripped state. However, if the state detection circuit detects that one or two phase relays are in the closed state, it means that the phase relay states are inconsistent. In this case, after detecting the inconsistency, the phase relays can be driven to be all closed, or after attempting to drive all phase relays to trip again, if it still cannot be in the closed state... If the circuit breaker trips, it will attempt to drive all phase relays to close again to prevent the safety hazard of single-phase operation. After a closing command is issued, all phase relays should be in the closed state. However, if the status detection circuit detects that one or two phase relays are in the tripped state, it means that the phase relay states are inconsistent. In this case, after detecting the inconsistency, the phase relays can be driven to trip all of them. Alternatively, after attempting to drive all phase relays to close again, if they still cannot be fully closed, it will attempt to drive all phase relays to trip again to prevent the safety hazard of single-phase operation.

[0121] Specifically, in this embodiment, the three-phase meter relay status detection circuit and method provided by the present invention, by adding a signal processing circuit to the relay body, can realize the detection of the status of the three microswitches of the three-phase split relay with two wires, and can identify whether there is an abnormal status of one or two phase relays. It is compatible with the status detection interface of the three-phase integrated relay, without modifying the mainboard detection circuit. The energy meter made according to this circuit and method has higher reliability. The main failure mode of conventional microswitches is poor contact. When all phase relays are closed, poor contact of the normally closed contact of any one or two microswitches will not affect the stable low level output of the transistor multi-state conversion circuit. Similarly, when all phase relays are tripped, poor contact of the normally open contact of any one or two microswitches will not affect the stable high level output of the transistor multi-state conversion circuit. Conversely, using three I / O ports The scheme of separately detecting the status of microswitches of phases A, B, and C relays has a drawback: any poor contact at any microswitch contact will affect the MCU's judgment of the relay status, leading to erroneous records of inconsistent phase relay statuses. For example, if the normally open contact of a microswitch in a split-type relay is open, it indicates that the main contact of the phase relay is closed. Therefore, when the main contact of the phase relay is open, the normally open contact of the microswitch should be closed. If a poor contact occurs when one microswitch contact is closed, the MCU will mistakenly identify it as an inconsistency in the phase relay status, which may affect the normal operation of the energy meter. Secondly, when all three-phase relays are tripped or fully closed, the circuit is in a steady state and is less affected by temperature. However, when the three-phase relays are inconsistent, the resistors and capacitors that determine the oscillation period in the circuit are simultaneously affected by temperature, and their RC time constants change synchronously. Therefore, the low-level duty cycle corresponding to various inconsistent states will not change with temperature, reducing the probability of misjudgment and improving detection accuracy.

[0122] According to another aspect of the present invention, the present invention provides an electricity meter, the electricity meter including the aforementioned three-phase meter relay status detection circuit.

[0123] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made using the contents of the present invention's specification and drawings under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A three-phase meter relay status detection circuit, characterized in that, include: Micro-switching circuits, transistor multi-state switching circuits, unidirectional power supply sustaining circuits, and I / O conversion circuits; The micro switch circuit includes three phase relay status indication micro switches: phase A, phase B, and phase C. Each micro switch includes a common contact, a normally open contact, and a normally closed contact. The common contact of the three micro switches is connected to the power supply terminal. The transistor multi-state switching circuit includes a first transistor and a second transistor. The base of the first transistor is resistively connected to the normally closed contacts of three microswitches, and the base of the second transistor is resistively connected to the normally open contacts of three microswitches. The collector of the first transistor serves as the output terminal of the transistor multi-state switching circuit and is resistively connected to a unidirectional power supply sustaining circuit and an I / O conversion circuit, respectively. The collector of the second transistor is resistively connected to the power supply terminal. The base of the first transistor is connected to capacitor C2, resistor R4, resistor R5 and resistor R6 respectively. The other end of capacitor C2 is connected to resistor R7 and the collector of the second transistor respectively. The other end of resistor R7 is connected to the power supply terminal. The collector of the first transistor is connected to capacitor C1, resistor R8 and resistor R9 respectively. The other end of capacitor C1 is connected to resistor R1, resistor R2, resistor R3 and the base of the second transistor respectively. The other end of resistor R8 is connected to the unidirectional power supply sustaining circuit. The other end of resistor R9 is connected to the unidirectional power supply sustaining circuit and the I / O conversion circuit respectively. The other ends of resistors R1, R2, and R3 are respectively connected to the normally open contacts of the microswitches indicating the status of the three phase-separated relays in phases A, B, and C. The other ends of resistors R4, R5, and R6 are respectively connected to the normally closed contacts of the microswitches indicating the status of the three phase-separated relays in phases A, B, and C. The input terminal of the unidirectional power supply sustaining circuit is connected to the I / O conversion circuit, and the output terminal of the unidirectional power supply sustaining circuit is connected to the common contact of the micro switch circuit and the resistor R8 respectively. The I / O conversion circuit is connected to the bidirectional I / O port of the MCU. The MCU controls the I / O port to switch between output high level and input state to realize the periodic detection of the relay state.

2. The three-phase meter relay status detection circuit according to claim 1, characterized in that, The micro-switch circuit includes: Phase A relay status indicator micro switch SW1 and its corresponding common contact COM1, normally open contact NO1 and normally closed contact NC1; B-phase relay status indicator micro switch SW2 and its corresponding common contact COM2, normally open contact NO2 and normally closed contact NC2; C-phase relay status indicator micro switch SW3 and its corresponding common contact COM3, normally open contact NO3 and normally closed contact NC3.

3. A three-phase meter relay status detection circuit according to any one of claims 1-2, characterized in that, In the transistor multi-state conversion circuit, both the first transistor and the second transistor are NPN type transistors; The emitter of the first transistor and the emitter of the second transistor are grounded.

4. The three-phase meter relay status detection circuit according to claim 3, characterized in that, The resistance ratio of resistors R1, R2, and R3 is set to 3:4:6, and the resistance ratio of resistors R4, R5, and R6 is set to 3:4:

6.

5. A three-phase meter relay status detection circuit according to any one of claims 1-2, characterized in that, The unidirectional power supply sustaining circuit includes a diode D1, a resistor R10, and a capacitor C3; the anode of the diode D1 is connected to the resistor R9 and the I / O conversion circuit respectively, the cathode of the diode D1 is connected to the power supply terminal, the resistor R8, and the resistor R10 respectively, the other end of the resistor R10 is connected to the capacitor C3, and the other end of the capacitor C3 is grounded.

6. A three-phase meter relay status detection circuit according to any one of claims 1-2, characterized in that, The I / O conversion circuit includes resistors R11 and R12, capacitor C4 and capacitor C5; one end of resistor R12 is connected to capacitor C5 and the bidirectional I / O port of the MCU, the other end of resistor R12 is connected to resistor R11 and capacitor C4, the other end of resistor R11 is connected to the power supply, and the other ends of capacitors C4 and C5 are grounded.

7. A detection method applied to a three-phase meter relay state detection circuit according to any one of claims 1-6, characterized in that, Includes the following steps: S1. During power-on initialization, the MCU control status detection I / O port outputs a high level, which supplies power to the micro-switch circuit and transistor multi-state conversion circuit through the unidirectional power supply maintenance circuit. S2. During detection, the MCU switches the I / O port to the input state and collects the level signal of the I / O port within a preset time window; S3. Determine the state of the three-phase split relays based on the characteristics of the acquired level signals; when all three-phase relays A, B, and C are closed, the transistor multi-state conversion circuit outputs a stable low level; when all three-phase relays A, B, and C are tripped, the transistor multi-state conversion circuit outputs a stable high level; when the states of the three-phase relays A, B, and C are inconsistent, the transistor multi-state conversion circuit outputs an oscillation signal. S4. After the test is completed, the MCU controls the I / O port to output a high level again to power the unidirectional power supply circuit, and repeats steps S2-S4 for periodic testing.

8. The detection method for a three-phase meter relay status detection circuit according to claim 7, characterized in that, Step S3 specifically includes: The I / O port is sampled multiple times for level signals. The proportion of low-level sampling times to the total number of sampling times is used as the low-level duty cycle. A first threshold and a second threshold are set. When the low-level duty cycle is less than or equal to the first threshold, it is determined that all three-phase relays A, B, and C are in a tripped state. When the low-level duty cycle is greater than or equal to the second threshold, it is determined that all three-phase relays A, B, and C are in the closed state. When the low-level duty cycle is between the first threshold and the second threshold, it is determined that the states of the three-phase relays A, B, and C are inconsistent, indicating a single-phase or two-phase abnormality.

9. The detection method for a three-phase meter relay status detection circuit according to claim 8, characterized in that, When the states of the three-phase relays A, B, and C are inconsistent, a preset correspondence is matched according to the specific value of the low-level duty cycle to determine the specific abnormal phase sequence, specifically as follows: When the low-level duty cycle is greater than the first threshold and less than or equal to the third threshold, it is determined that the C-phase relay is closed, and the A-phase relay and the B-phase relay are tripped. When the low-level duty cycle is greater than the third threshold and less than or equal to the fourth threshold, it is determined that the B-phase relay is closed, and the A-phase relay and the C-phase relay are tripped. When the low-level duty cycle is greater than the fourth threshold and less than or equal to the fifth threshold, it is determined that the A-phase relay is closed, and the B-phase relay and the C-phase relay are tripped. When the low-level duty cycle is greater than the fifth threshold and less than or equal to the sixth threshold, it is determined that the A-phase relay trips and the B-phase relay and C-phase relay close. When the low-level duty cycle is greater than the sixth threshold and less than or equal to the seventh threshold, it is determined that the B-phase relay trips and the A-phase and C-phase relays close. When the low-level duty cycle is greater than the seventh threshold and less than the second threshold, it is determined that the C-phase relay trips, and the A-phase relay and B-phase relay close.

10. An electricity meter, characterized in that, The electricity meter includes a three-phase meter relay status detection circuit as described in any one of claims 1-6.

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