Device and method for measuring abrupt change current of motor

Abstract

The invention discloses a device and a method for measuring abrupt change current of a motor. Comprising a current transformer used for collecting motor operation real-time current, a three-phase rectification amplification circuit used for amplifying signals collected by the current transformer, a differential amplification circuit and an integral amplification circuit which are arranged at the output end of the three-phase rectification amplification circuit, and an alarm circuit arranged at the output end of the differential amplification circuit. Motor operation real-time current is amplified through the three-phase rectification amplification circuit and subjected to three-phase half-wave rectification to become a direct-current voltage signal, the direct-current voltage signal is divided into two paths, one path of direct current enters the differential amplification circuit to be amplified, and the other path of direct current enters the differential amplification circuit to be amplified again after entering the integral amplification circuit to be amplified. And an abrupt change current value is formed through a difference value of the two paths of DC voltages, and the alarm circuit is used for measuring the abrupt change current value and sending out an abrupt change alarm. The current stability of the mechanical equipment in operation can be measured, so that the sudden change current condition is found, and the equipment is prevented from running with diseases for a long time.

Description

Technical Field

[0001] The present invention relates to the technical field of current measurement circuits, and in particular to a device and method for measuring sudden change current of a motor. Background Art

[0002] At present, in industrial and mining enterprises, rotating mechanical equipment such as conveyor belts, mixers, scrapers, etc. often experience discontinuous mechanical shocks during operation due to abnormal conditions such as mechanical damage and material jamming. Since the impact time is too short, it is difficult to monitor it through general current display and current recording. The usual method of measuring current is to measure the absolute value of the current. If the absolute value of the current does not exceed the alarm value, the sudden change of current cannot be detected, causing the equipment to run with problems for a long time, resulting in equipment damage and failure to stop, causing significant losses to production. Summary of the invention

[0003] In order to solve one or some technical problems existing in the prior art, one of the purposes of the present application is to provide a measuring device for sudden current of a motor, which can timely monitor and record the sudden current generated during the operation of the motor, so as to intuitively reflect abnormal conditions such as mechanical damage, material jamming, etc. in the motor transmission, and provide dynamic data for analyzing the operating status of the mechanical transmission, so as to take targeted preventive measures, eliminate faults, and avoid damage to the motor and transmission machinery caused by impact loads.

[0004] The second purpose of the present application is to provide a device and method for measuring sudden current changes in a motor, which can measure the current stability of mechanical equipment during operation, thereby discovering sudden current changes and preventing the equipment from running with problems for a long time.

[0005] In order to solve the above existing technical problems, one of the purposes of this application is achieved by adopting the following technical solution: A device for measuring sudden current of a motor comprises a current transformer for collecting real-time current of the motor, a three-phase rectifier amplifier circuit for amplifying the signal collected by the current transformer, a differential amplifier circuit and an integral amplifier circuit arranged at the output end of the three-phase rectifier amplifier circuit, and an alarm circuit arranged at the output end of the differential amplifier circuit, wherein the output end of the integral amplifier circuit is connected to the differential amplifier circuit, and the real-time current of the motor collected by each current transformer is amplified by the three-phase rectifier amplifier circuit and converted into a DC voltage signal after three-phase half-wave rectification, and the DC voltage signal is divided into two paths, one of which enters the differential amplifier circuit for amplification, and the other enters the integral amplifier circuit for amplification, and then enters the differential amplifier circuit for further amplification, and a sudden current value is formed by the difference between the two DC voltages, and the alarm circuit measures the unstable load of the mechanical equipment in operation through the sudden current value and issues a sudden alarm; and measures the sudden current value of the DC voltage signal to measure the unstable load of the mechanical equipment in operation.

[0006] Preferably, the three-phase rectifier amplifier circuit includes 12 resistors R1~R12, three three-phase operating amplifiers A1, A2, A3, three rectifier diodes D1, D2, D3 and a voltage follower, the resistors R1~R3 ​​are load resistors, and the voltage follower is composed of an amplifier A4 and a resistor R21.

[0007] Preferably, the integration amplifier circuit is composed of an operational amplifier A5, three resistors R22, R23, R24 and a capacitor C1.

[0008] Preferably, the differential amplifier circuit is composed of an operational amplifier A6 and three resistors R25, R26, and R27.

[0009] Preferably, the alarm circuit includes an increasing comparison circuit, a decreasing comparison circuit and an alarm relay. When the sudden current value output by the differential amplifier circuit is too large or too small, an alarm is sounded through the alarm relay connected to the increasing comparison circuit or the decreasing comparison circuit respectively.

[0010] Preferably, the increasing comparison circuit is composed of an increasing comparator C1 and resistors R31 to R35.

[0011] Preferably, the decreasing comparison circuit is composed of a decreasing comparator C2 and resistors R41-R45.

[0012] Preferably, the output end of the differential amplifier circuit is also provided with a detachable digital display.

[0013] Preferably, the current transformer is composed of three-phase current transformers CT1, CT2, and CT3. The real-time current of the motor collected by the three-phase current transformers CT1, CT2, and CT3 is 0-5A, and the resistance of the load resistors R1, R2, and R3 is 0.1Ω. The real-time current flows through the load resistors R1, R2, and R3 of 0.1Ω and is converted into an AC voltage signal of 0-0.5V.

[0014] The second purpose of this application is achieved by the following technical solution: A method for measuring a sudden change in current of a motor, comprising a device for measuring a sudden change in current of a motor, the method comprising: S1, respectively collect three sets of real-time AC currents of the three-phase motor through current transformers CT1, CT2, and CT3; S2, three sets of real-time AC currents are respectively passed through three load resistors R1, R2, and R3, and the current signals are converted into voltage signals through the load resistors; S3, the three groups of voltage signals are amplified by three three-phase operating amplifiers A1, A2, and A3 in the three-phase rectifier amplifier circuit respectively; S4, the three groups of amplified AC voltage signals are converted into DC voltage signals after three-phase half-wave rectification through three rectifier diodes D1, D2, and D3, and then converge into the voltage follower, and the DC voltage signals are amplified again through the amplifier A4 in the voltage follower; S5, one channel of the DC voltage signal output by the amplifier A4 enters the differential amplifier circuit for amplification, and the other channel enters the integral amplifier circuit for amplification and then enters the differential amplifier circuit for further amplification, and the real-time current relative values ​​of the two DC voltages are calculated by the differential amplifier circuit; S6. The real-time current relative values ​​calculated by the differential amplifier circuit are compared. When the relative values ​​of the two real-time currents are within the set range, the alarm circuit is in standby mode. When the relative values ​​of the two real-time currents exceed the set range, it is determined to be a sudden change in current value, triggering the alarm circuit to generate an alarm signal, display sudden change data or record sudden change information.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The integral amplifier circuit is used to calculate the average current of the previous period in real time, and provide a reference value for the mutation current value; the differential amplifier circuit compares and amplifies the difference between the real-time value of the current and the average value, and its output value is the mutation current value measured based on the average value. When the two are equal, the integral amplifier circuit outputs 0, that is, the mutation current is 0. When the real-time value is twice the average value, the output is 5V, corresponding to a mutation current of 100%; conversely, when the real-time value is twice the average value, the output is -5V, corresponding to a mutation current of -100%, that is, the mutation current value can reflect the change in the mutation current.

[0016] The introduction of mutation current provides an intuitive and quantitative measurement method for monitoring transmission mechanical equipment. The mutation current is used to measure the fluctuation of motor current, the change amount and speed of AC current, and the mutation current generated during the operation of the motor can be monitored and recorded in time, so as to intuitively reflect the abnormal conditions such as mechanical damage and material jamming in the motor transmission, and provide dynamic data for analyzing the operating status of mechanical transmission, so that targeted preventive measures can be taken to eliminate faults and avoid damage to motors and transmission machinery caused by impact loads. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a structural schematic diagram of the present invention; Figure 2 It is the circuit principle diagram of the present invention; DETAILED DESCRIPTION

[0018] Below, the present application is further described in conjunction with the accompanying drawings and specific implementation methods. It should be noted that, under the premise of no conflict, the various embodiments or technical features described below can be arbitrarily combined to form a new embodiment.

[0019] In the description of the present application, it should be understood that the terms "up", "down", "left", "right", etc., indicating directions or positional relationships are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore should not be understood as a limitation on the present application.

[0020] The terms "first", "second", etc. in this application are used to distinguish similar objects, and are not used to describe a specific order or sequence. It should be understood that the data used in this way can be interchangeable where appropriate, so that the embodiments of the present application can be implemented in an order other than those illustrated or described here, and the objects distinguished by "first", "second", etc. are generally of one type, and the number of objects is not limited. For example, the first object can be one or more. In addition, "and / or" in the specification and claims represents at least one of the connected objects, and the character " / " generally indicates that the objects associated with each other are in an "or" relationship.

[0021] Embodiment 1: like Figure 1 and Figure 2As shown, a device for measuring sudden current of a motor comprises a current transformer for collecting real-time current of the motor, a three-phase rectifying and amplifying circuit for amplifying the signal collected by the current transformer, a differential amplifying circuit and an integral amplifying circuit arranged at the output end of the three-phase rectifying and amplifying circuit, and an alarm circuit arranged at the output end of the differential amplifying circuit, wherein the output end of the integral amplifying circuit is connected to the differential amplifying circuit, and the real-time current of the motor collected by each current transformer is amplified by the three-phase rectifying and amplifying circuit, and becomes a DC voltage signal after three-phase half-wave rectification, and the DC voltage signal is divided into two paths, one DC enters the differential amplifying circuit for amplification, and the other enters the integral amplifying circuit for amplification, and then enters the differential amplifying circuit for further amplification, and a sudden current value is formed by the difference between the two DC voltages, and the alarm circuit measures the unstable load of the mechanical equipment in operation and issues a sudden current alarm through the sudden current value.

[0022] When detecting the real-time current of the motor, the real-time current of the motor is collected by the current transformer and input into the three-phase rectifier amplifier circuit for amplification. After three-phase half-wave rectification, it becomes a DC voltage signal. The DC voltage signal is divided into two paths. One path enters the differential amplifier circuit for amplification, and the other path enters the integral amplifier circuit for amplification, and then enters the differential amplifier circuit for further amplification. In the differential amplifier circuit, the difference between the two DC voltages forms a sudden current value. When the difference in the sudden current value reaches a certain value, the alarm circuit measures the sudden current generated and issues a sudden alarm, so as to facilitate the subsequent processing of the unstable load of the mechanical equipment in operation. Among them, the AC current measured by the current transformer is not directly used for display and alarm, but is converted into a DC signal after rectification and amplification. The DC signal is then amplified by integration and real-time amplification to obtain the average current and real-time current. The two current signals are differentially amplified to obtain the sudden current. The integral amplifier circuit is used to calculate the average current of the previous period in real time, and provide a reference value for the mutation current value; the differential amplifier circuit compares and amplifies the difference between the real-time value of the current and the average value, and its output value is the mutation current value measured based on the average value. When the two are equal, the integral amplifier circuit outputs 0, that is, the mutation current is 0. When the real-time value is twice the average value, the output is 5V, corresponding to a mutation current of 100%; conversely, when the real-time value is twice the average value, the output is -5V, corresponding to a mutation current of -100%, that is, the mutation current value can reflect the change in the mutation current.

[0023] Mutation current is a relative value, which is the percentage of instantaneous change based on the average current value in the previous few seconds. The larger the mutation current, the greater the mechanical impact force, and the more dangerous it is to the transmission machinery and equipment. The introduction of mutation current provides an intuitive and quantitative measurement method for the monitoring of transmission machinery and equipment. Mutation current is used to measure the fluctuation of motor current, to measure the change amount and speed of AC current, that is, to reflect abnormal conditions such as mechanical damage and material jamming in motor transmission, and to provide dynamic data for analyzing the operating status of mechanical transmission, so as to take targeted preventive measures to eliminate faults and avoid damage to motors and transmission machinery caused by impact loads.

[0024] Further improved, the three-phase rectifier amplifier circuit includes 12 resistors R1~R12, three three-phase operating amplifiers A1, A2, A3, three rectifier diodes D1, D2, D3 and a voltage follower, the resistors R1~R3 ​​are load resistors, and the voltage follower is composed of an amplifier A4 and a resistor R21.

[0025] Three-phase rectifier amplifier circuit: Resistors R1, R2, and R3 are the load resistors of the three-phase current transformer, which are used to convert the 0~5A current signal of the current transformer into a 0~0.5V voltage signal; A1, A2, and A3 are three-phase operational amplifiers, which are used to synthesize the three phase voltage signals into one voltage signal. The amplification factor of the operational amplifier is determined by its respective peripheral resistors. The amplification factor = feedback resistor value / negative input resistance value, that is, the amplification factor of A1 = R10 / R4. Similarly, the amplification factors of A2 and A3 are R11 / R5 and R12 / R6 respectively; D1, D2, and D3 are rectifier diodes, which play a role of rectification. A4 and its peripheral resistor R21 constitute a voltage follower, which plays an isolation role. The DC voltage signal output from the voltage follower is divided into two paths, one of which enters the differential amplifier circuit for amplification, and the other enters the integral amplifier circuit. After amplification by the integral amplifier circuit, it enters the differential amplifier circuit for amplification. The DC signal is then amplified by the integral amplifier circuit and the real-time amplification to obtain the average current and the real-time current.

[0026] As a further improvement, the integration amplifier circuit is composed of an operational amplifier A5, three resistors R22, R23, R24 and a capacitor C1.

[0027] The function of the integral amplifier circuit is to calculate the average value of the voltage signal in the previous few seconds. It is a relatively stable dynamic value that changes slowly with the change of real-time current.

[0028] A further improvement is that the differential amplifier circuit is composed of an operational amplifier A6 and three resistors R25, R26, and R27.

[0029] When the difference between the real-time value and the average value of the current is compared and amplified, the output value is the sudden change current value measured based on the average value. When the two are equal, for example, the output of the integral amplifier circuit is 0, that is, the sudden change current is 0; when the real-time value is twice the average value, the output is 5V, corresponding to the sudden change current of 100%; conversely, when the real-time value is twice the average value, the output is -5V, corresponding to the sudden change current of -100%. Since the current transformer and each amplifier are linear, the sudden change current value can reflect the change in the sudden change current.

[0030] A further improvement is that the alarm circuit includes an increasing comparison circuit, a decreasing comparison circuit and an alarm relay. When the sudden current value output by the differential amplifier circuit is too large or too small, an alarm is sounded through the alarm relay connected to the increasing comparison circuit or the decreasing comparison circuit respectively.

[0031] After the signal output by the differential amplifier circuit A6 is amplified and enters the alarm circuit, the DC signal is then integrated and amplified in real time to obtain the average current and the real-time current. The average current and the real-time current can then be compared through two comparison circuits. When the output mutation current value is greater than or less than the set value, an alarm will be issued through the alarm relay, thereby realizing the measurement of the current stability of the equipment during operation.

[0032] A further improvement is that the increasing comparison circuit is composed of an increasing comparator C1 and resistors R31-R35; the decreasing comparison circuit is composed of a decreasing comparator C2 and resistors R41-R45.

[0033] The alarm circuit is a combination of two comparators and two alarm relays, among which the increasing comparator C1 is an alarm for increasing current, and the decreasing comparator C2 is an alarm for decreasing current. The alarm value is obtained by the voltage division of resistors R33 and R34, which is set to 2V in the figure, and the corresponding sudden current alarm value is 20%. When the sudden current is greater than 20% of the average current, the increasing comparator C1 outputs a high level, the alarm relay K1 is energized, and the K1 passive contact outputs an alarm for increasing sudden current; conversely, when the sudden current is less than 20% of the average current, the alarm relay K2 is energized, and the K2 passive contact outputs an alarm for decreasing sudden current.

[0034] A further improvement is that the output end of the differential amplifier circuit is also provided with a detachable digital display.

[0035] The sudden current can be connected to a universal digital display recording alarm meter for display.

[0036] Further improvement: the current transformer is composed of three-phase current transformers CT1, CT2, and CT3. The real-time current of the motor collected by the three-phase current transformers CT1, CT2, and CT3 is 0-5A, the resistance of the load resistors R1, R2, and R3 is 0.1Ω, and the real-time current flows through the load resistors R1, R2, and R3 of 0.1Ω and is converted into a 0-0.5V AC voltage signal.

[0037] When the three-phase motor is running, the current transformers CT1, CT2, and CT3 collect the 0-5A real-time current of the motor. After the current flows through the 0.1Ω load resistor, it is converted into a 0-0.5V AC voltage signal. This AC voltage signal is amplified by the A1, A2, and A3 precision rectifier circuits and becomes a 0-5V DC voltage signal after three-phase half-wave rectification. This DC voltage signal passes through the A4 voltage follower to obtain a real-time DC signal isolated from the rectifier circuit. This DC voltage signal is divided into two paths, one DC enters the differential amplifier circuit A6, and the other enters the integral amplifier circuit A5. After amplification by A5, A6 compares and amplifies the difference between the real-time value of the current and the average value. Its output value is the sudden change current value measured based on the average value. When the two are equal, A5 outputs 0, that is, the sudden change current is 0. When the real-time value is twice the average value, the output is 5V, corresponding to the sudden change current of 100%. Conversely, when the real-time value is twice the average value, the output is -5V, corresponding to the sudden change current of -100%. Since the current transformer and each amplifier are linear, the mutation current value can reflect the change in the mutation current.

[0038] When the real-time current of the motor is collected through the three-phase current transformers CT1, CT2, and CT3, A1, A2, and A3 in the precision rectifier circuit are three-phase operation amplifiers, which are used to synthesize the three-phase voltage signals into one voltage signal. The amplification factor of the operational amplifier is determined by its respective peripheral resistance. Among them, the AC current measured by the three-phase current transformers CT1, CT2, and CT3 is not directly used for display and alarm, but is rectified by the precision rectifier circuits A1, A2, A3 and the rectifier diodes D1, D2, and D3 to form a DC signal. The real-time DC signal is then passed through the operational amplifier to obtain the average current and the real-time current. The two current signals are differentially amplified to obtain the mutation current. The average current is a dynamic current that changes with the change of the real-time current. The mutation current is the change relative to the average current. The greater the current fluctuation, the greater the mutation current change. This can well reflect the change amount and change speed of the AC current, and indirectly reflect abnormal conditions such as mechanical damage and material jamming in the motor transmission.

[0039] Embodiment 2: A method for measuring a sudden change in current of a motor, comprising a device for measuring a sudden change in current of a motor, the method comprising: S1, respectively collect three sets of real-time AC currents of the three-phase motor through current transformers CT1, CT2, and CT3; S2, three sets of real-time AC currents are respectively passed through three load resistors R1, R2, and R3, and the current signals are converted into voltage signals through the load resistors; S3, the three groups of voltage signals are amplified by three three-phase operating amplifiers A1, A2, and A3 in the three-phase rectifier amplifier circuit respectively; S4, the three groups of amplified AC voltage signals are converted into DC voltage signals after three-phase half-wave rectification through three rectifier diodes D1, D2, and D3, and then converge into the voltage follower, and the DC voltage signals are amplified again through the amplifier A4 in the voltage follower; S5, one channel of the DC voltage signal output by the amplifier A4 enters the differential amplifier circuit for amplification, and the other channel enters the integral amplifier circuit for amplification and then enters the differential amplifier circuit for further amplification, and the real-time current relative values ​​of the two DC voltages are calculated by the differential amplifier circuit; S6. The real-time current relative values ​​calculated by the differential amplifier circuit are compared. When the relative values ​​of the two real-time currents are within the set range, the alarm circuit is in standby mode. When the relative values ​​of the two real-time currents exceed the set range, it is determined to be a sudden change in current value, triggering the alarm circuit to generate an alarm signal, display sudden change data or record sudden change information.

[0040] The specific principle of the above measurement method is as follows: operational amplifiers A1, A2, A3 and follower A4 are composed of four operational amplifier integrated circuits LM324 and their peripheral resistors, powered by a single 12V power supply, and their working principle is mainly based on negative feedback. By controlling the voltage difference between the input and feedback terminals, the voltage at the output terminal can be adjusted. Under the action of negative feedback, the LM324 operational amplifier can stably amplify the input AC and DC signals and output the corresponding amplified signals. The outputs of A1, A2, and A3 are the three-phase current signals of the motor A, B, and C respectively, and the output U04 of A4 is the total current signal after the rectification of the three-phase current signals of the motor. The resistance values ​​of resistors R10, R11, and R12 can be adjusted to calibrate the three-phase current values, and at the same time, the range of U04 is 0~5V, corresponding to the 0~5A of the transformer current.

[0041] The integral amplifier circuit A5 and the differential amplifier circuit A6 are composed of the integrated circuit LM358 of the dual operational amplifier and its peripheral resistors and capacitors, and are powered by ±12V dual power supplies. They include two independent, high-gain, low-power operational amplifiers. A5 is used for integral amplification, with the same-phase input, and the integral time constant is R23C21. Changing the value of R23 can adjust the integral time. Generally, the integral time is 2 to 5 seconds. The integral amplification factor is R24 / R23. Adjusting the resistance value of R24 can adjust the integral amplification factor. The output voltage signal U05 of A5 is the current signal after the integral operation, that is, the average current of the current signal in the previous period of time, and the voltage value is 0 to 5V. A6 is used for DC differential amplification. It uses U05 as a reference to calculate the relative value of the real-time current. When U04=U05, A6 outputs U06=0. When U04 is larger than U05, A6 outputs U06 as positive, otherwise it is negative. U06 is the sudden change current value. Adjust the amplification factor R26 of A6 to make: U06=U04-U05.

[0042] Since U04=0~5V, U05=0~5V, so U06=-5~+5V.

[0043] The sudden current signal U06 can be directly connected to the digital display, the value unit is %, the display range is -100%~+100%, and the corresponding signal voltage is -5~+5V. It can also be connected to the alarm circuit, such as Figure 2 As shown in the comparator C1 and C2, C1 is the current suddenly increased alarm circuit, C2 is the current suddenly decreased alarm circuit, the comparator can use a conventional dual comparator Figure 2 The alarm value is ±20%. The AC current measured by the current transformer is not used directly for display and alarm, but is converted into a DC signal after rectification and amplification. The DC signal is then amplified by integration and real-time amplification to obtain the average current and real-time current. The two current signals are differentially amplified to obtain the mutation current. The average current is a dynamic current that changes with the real-time current. The mutation current is the change relative to the average current. The greater the current fluctuation, the greater the mutation current change. This can well reflect the change amount and speed of the AC current, and indirectly reflect abnormal conditions such as mechanical damage and material jamming in the motor transmission.

[0044] The above-mentioned implementation modes are only preferred implementation modes of the present application and cannot be used to limit the scope of protection of the present application. Any non-substantial changes and substitutions made by technicians in this field on the basis of the present application shall fall within the scope of protection required by the present application.

Claims

1. A device for measuring sudden current of a motor, characterized in that: The invention comprises a current transformer for collecting real-time current of the motor, a three-phase rectifying and amplifying circuit for amplifying the signal collected by the current transformer, a differential amplifying circuit and an integral amplifying circuit arranged at the output end of the three-phase rectifying and amplifying circuit, and an alarm circuit arranged at the output end of the differential amplifying circuit. The output end of the integral amplifying circuit is connected to the differential amplifying circuit. The real-time current of the motor collected by each current transformer is amplified by the three-phase rectifying and amplifying circuit and converted into a DC voltage signal after three-phase half-wave rectification. The DC voltage signal is divided into two paths, one of which enters the differential amplifying circuit for amplification, and the other enters the integral amplifying circuit for amplification and then enters the differential amplifying circuit for further amplification. A sudden current value is formed by the difference between the two DC voltages. The alarm circuit measures the unstable load of the mechanical equipment in operation through the sudden current value and issues a sudden alarm. The sudden current value is measured on the DC voltage signal to measure the unstable load of the mechanical equipment in operation.

2. The device for measuring sudden change current of a motor according to claim 1, characterized in that: The three-phase rectifier amplifier circuit includes 12 resistors R1~R12, three three-phase operating amplifiers A1, A2, A3, three rectifier diodes D1, D2, D3 and a voltage follower. The resistors R1~R3 ​​are load resistors, and the voltage follower is composed of an amplifier A4 and a resistor R21.

3. The device for measuring sudden change current of a motor according to claim 2, characterized in that: The integral amplifier circuit is composed of an operational amplifier A5, three resistors R22, R23, R24 and a capacitor C1.

4. The device for measuring sudden current of a motor according to claim 3, characterized in that: The differential amplifier circuit is composed of an operational amplifier A6 and three resistors R25, R26, and R27.

5. A device for measuring sudden current of a motor according to any one of claims 1 to 4, characterized in that: The alarm circuit includes an increasing comparison circuit, a decreasing comparison circuit and an alarm relay. When the sudden current value output by the differential amplifier circuit is too large or too small, an alarm is sounded through the alarm relay connected to the increasing comparison circuit or the decreasing comparison circuit.

6. The device for measuring sudden current of a motor according to claim 5, characterized in that: The increasing comparison circuit is composed of an increasing comparator C1 and resistors R31-R35.

7. The device for measuring sudden change current of a motor according to claim 6, characterized in that: The decreasing comparison circuit is composed of a decreasing comparator C2 and resistors R41-R45.

8. The device for measuring sudden current of a motor according to claim 5, characterized in that: The output end of the differential amplifier circuit is also provided with a detachable digital display meter.

9. The device for measuring sudden change current of a motor according to claim 2, characterized in that: The current transformer is composed of three-phase current transformers CT1, CT2, and CT3. The real-time current of the motor collected by the three-phase current transformers CT1, CT2, and CT3 is 0-5A. The resistance of the load resistors R1, R2, and R3 is 0.1Ω. The real-time current flows through the load resistors R1, R2, and R3 of 0.1Ω and is converted into an AC voltage signal of 0-0.5V.

10. A method for measuring sudden current of a motor, characterized in that: The device for measuring sudden motor current as claimed in any one of claims 1 to 9, wherein the measuring method comprises: S1, respectively collect three sets of real-time AC currents of the three-phase motor through current transformers CT1, CT2, and CT3; S2, three sets of real-time AC currents are respectively passed through three load resistors R1, R2, and R3, and the current signals are converted into voltage signals through the load resistors; S3, the three groups of voltage signals are amplified by three three-phase operating amplifiers A1, A2, and A3 in the three-phase rectifier amplifier circuit respectively; S4, the three groups of amplified AC voltage signals are converted into DC voltage signals after three-phase half-wave rectification through three rectifier diodes D1, D2, and D3, and then converge into the voltage follower, and the DC voltage signals are amplified again through the amplifier A4 in the voltage follower; S5, one channel of the DC voltage signal output by the amplifier A4 enters the differential amplifier circuit for amplification, and the other channel enters the integral amplifier circuit for amplification and then enters the differential amplifier circuit for further amplification, and the real-time current relative values ​​of the two DC voltages are calculated by the differential amplifier circuit; S6. The real-time current relative values ​​calculated by the differential amplifier circuit are compared. When the relative values ​​of the two real-time currents are within the set range, the alarm circuit is in standby mode. When the relative values ​​of the two real-time currents exceed the set range, it is determined to be a sudden change in current value, triggering the alarm circuit to generate an alarm signal, display sudden change data or record sudden change information.

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