Motor diagnostic device

Abstract

The present invention provides a motor diagnostic device for diagnosing motor abnormalities using only motor current information. The device includes a current input unit for inputting motor current value data, an FFT analysis unit for performing FFT analysis on the current value data to obtain power spectrum data, a normalized current calculation unit for calculating a normalized current based on the current value data, a load factor calculation unit for determining a load factor corresponding to the normalized current, a correction value data recording unit for recording, in a database, correction values ​​corresponding to the load factors, to adjust the effect of the difference between a reference value of the power spectrum data and the load factor of the power spectrum data during diagnosis, an FFT analysis result correction value selection unit for selecting a correction value based on the load factor during diagnosis and the database, an FFT analysis result correction unit for correcting the power spectrum data during diagnosis using the correction value, and a motor abnormality diagnosis unit for calculating the difference in current signal strength at the power supply frequency and the rotation frequency for the corrected power spectrum data during diagnosis and the reference value, and comparing the differences to diagnose motor abnormalities.

Description

Technical Field

[0001] The present application relates to a diagnostic device for an electric motor. Background Art

[0002] Electric motors, used to power equipment and machinery that make up production lines, such as pumps, compressors, fans, and industrial robots, have become indispensable in industry. Therefore, they are required to operate continuously and safely at all times.

[0003] Therefore, a motor diagnostic device has been proposed that collects and analyzes current information, voltage information, and zero-phase current information during motor operation to thereby diagnose abnormalities (for example, Patent Document 1).

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: WO2017 / 102545 Summary of the Invention

[0007] Technical problem to be solved by the invention

[0008] This diagnostic method based on the motor's current information, voltage information, and zero-phase current information requires a large number of sensors to be installed in the diagnostic device, resulting in a problem of increased equipment size and increased costs for motor abnormality diagnosis.

[0009] The present application is completed to solve the above-mentioned problems, and its purpose is to obtain a diagnostic device that can diagnose abnormalities of a motor without obtaining multiple information of the motor.

[0010] Technical means for solving technical problems

[0011] The diagnostic device for the electric motor of the present application includes: a current input unit, which inputs the current value data of the electric motor; an FFT analysis unit, which performs FFT analysis on the current value data to obtain power spectrum data; a normalized current calculation unit, which calculates the normalized current based on the current value data; a load factor calculation unit, which uses the normalized current-load factor curve obtained from the setting information of the electric motor to calculate the load factor corresponding to the normalized current calculated by the normalized current calculation unit; a correction value data recording unit, which is used to adjust the reference value and diagnostic value of the power spectrum data. a correction value for the influence caused by the difference in the load rate of the power spectrum data at the time of diagnosis, and recorded in a database corresponding to the load rate; an FFT analysis result correction value selection unit, which selects the correction value based on the load rate at the time of diagnosis obtained by the load rate calculation unit and the database; an FFT analysis result correction unit, which corrects the power spectrum data at the time of diagnosis using the correction value; and an abnormality diagnosis unit, which calculates the difference in the current signal strength of the power supply frequency and the rotation frequency respectively for the corrected power spectrum data at the time of diagnosis and the reference value, and diagnoses the motor by comparing them with each other.

[0012] Effects of the Invention

[0013] The motor diagnostic device of the present application can diagnose the motor using only the current information of the motor, and can diagnose abnormalities of the motor at a low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a schematic configuration diagram of the electric motor diagnostic device in the first embodiment.

[0015] Figure 2 This is a block diagram of the calculation processing unit of the electric motor diagnostic device in the first embodiment.

[0016] Figure 3 This is a diagram showing a normalized current-load factor curve in the first embodiment.

[0017] Figure 4A This is a diagram illustrating correction of the power spectrum in the first embodiment.

[0018] Figure 4B This is a diagram illustrating correction of the power spectrum in the first embodiment.

[0019] Figure 5 This is a diagram for explaining the diagnostic method in the first embodiment.

[0020] Figure 6 This is a flowchart illustrating the operation of the diagnostic device in the first embodiment.

[0021] Figure 7 This is a flowchart illustrating the operation in the FFT analysis step in the first embodiment.

[0022] Figure 8 This is a hardware diagram of the electric motor diagnostic device in the first embodiment. DETAILED DESCRIPTION

[0023] In the description of the embodiments and the drawings, parts denoted by the same reference numerals represent the same or corresponding parts.

[0024] Implementation method 1.

[0025] Next, use Figures 1 to 8 Implementation 1 will be described.

[0026] <Structure of the Motor Diagnostic Device>

[0027] Figure 1 A schematic diagram showing the structure of a motor diagnostic device used in a control center such as a closed switchboard to diagnose whether the motor has abnormalities.

[0028] Figure 1 A main circuit 1 introduced from the power system is provided with a wiring circuit breaker 2, an electromagnetic contactor 3, a current detector 4 for detecting the load current of the main circuit 1, and is connected to a motor 5 such as a three-phase induction motor.

[0029] The electric motor 5 is connected to mechanical equipment 6 constituting a production line or the like and drives the same to operate.

[0030] The diagnostic device 100 for the motor 5 includes a current input unit 7 that inputs current value data detected by the current detector 4 , and a processing unit 8 performs arithmetic processing for diagnosing the motor 5 based on the input current value data.

[0031] The diagnostic device 100 is provided with a rated information setting unit 10, which pre-inputs rated information of the motor 5, such as the power supply frequency, rated output, rated current, number of poles, and rated speed. This rated information input from the rated information setting unit 10 is stored in the rated information recording unit 9 and, as needed, transmitted to the calculation processing unit 8 for processing.

[0032] Here, the rated information refers to basic information about the motor 5 as described in the manufacturer's catalog, the nameplate of the motor 5, the instruction manual, and the like. When multiple motors 5 are to be diagnosed, the rated information corresponding to each motor 5 can be stored in the rated information recording unit 9 and used. Furthermore, in this first embodiment, for simplicity of description, the case where a single motor 5 is to be diagnosed will be described.

[0033] The display unit 11, contactor drive unit 12, output unit 13 and communication unit 14 are connected to the operation processing unit 8. When an abnormality of the motor 5 is detected based on the operation results in the operation processing unit 8, the display unit 11 displays the detected current value data, and displays abnormal status and alarms, etc.

[0034] Furthermore, the contactor driving unit 12 outputs a control signal for opening and closing the electromagnetic contactor 3 , and the output unit 13 outputs abnormal conditions, alarms, and the like to a management department of the production line and the like.

[0035] The communication unit 14 transmits data to an external monitoring device 200 such as a personal computer via a wired or wireless network.

[0036] <Structure of the Arithmetic Processing Unit>

[0037] Figure 2 1 is a block diagram of the arithmetic processing unit 8 of the diagnostic device 100 , and shows the configuration of the arithmetic processing unit 8 for performing a diagnosis of the motor 5 using the current value data input from the current input unit 7 .

[0038] Here, the roles and functions of each part constituting the arithmetic processing unit 8 are described, and the following uses Figure 6 and Figure 7 The flowchart shown describes the steps of calculation and determination, etc., for diagnosing abnormality of the electric motor 5 .

[0039] In the normalized current calculation unit 110, the normalized current value is calculated using formula (1) based on the current value data (measured current) input from the current input unit 7, the current value data at the rated load (rated current) recorded in the rated information recording unit 9, and the current value data at no load (no-load current).

[0040] Normalized current = ((measured current - no-load current) / (rated current - no-load current)) × 100

[0041] ···(1)

[0042] The measured current, which is current value data measured by the motor 5, changes within a limited range according to the state of the motor 5. Therefore, it may be difficult to detect a change in the state of the motor 5 based on the change in the measured current.

[0043] Therefore, the measured current is normalized based on the difference from the no-load current for evaluation.

[0044] By using the normalized current, changes in the measured current corresponding to the state of the motor 5 can be expressed with emphasis.

[0045] In the first embodiment, the normalization method shown in equation (1) is used, but the present invention is not limited thereto. As long as the change in current value data can be emphasized by normalization, normalized current obtained by various normalization methods that easily grasp the change can be used.

[0046] The load factor calculation unit 111 uses Figure 3 The normalized current-load rate curve shown is generated in advance based on the rated current and other rated information of the motor 5. Figure 3 The normalized current-load rate curve shown is stored in the rated information recording unit 9.

[0047] According to the normalized current value ( Figure 3 (black triangle in the figure) and extrapolate the normalized current-load factor curve as indicated by the arrow to find the corresponding load factor (×). The load factor used in this first embodiment represents the ratio of the load torque of the motor 5 during driving to the rated load torque.

[0048] The diagnostic current value data of the motor 5 to be diagnosed is subjected to FFT (Fast Fourier Transform) analysis, which will be described later, to obtain an FFT analysis result. The FFT analysis result correction value selection unit 112 selects a correction value for adjusting the FFT analysis result.

[0049] This correction value is obtained by performing FFT analysis on the current value data of the electric motor 5 for a certain period before diagnosis, and accumulating and learning the analysis results.

[0050] The correction value is recorded in the correction value data recording unit 113 as a database in combination with the load factor when the current value data is acquired.

[0051] As an example, the load rate of 0% to 100% is divided into 20 equal parts at intervals of 5%. When the load rate is between 0% and below 5%, correction value A is taken, and when the load rate exceeds 5% and is below 10%, correction value B is taken. In this way, the load rate and the correction value corresponding to the load rate are combined and recorded as a database. By using this database, an appropriate correction value corresponding to the load rate calculated by the above-mentioned load rate calculation unit 111 is selected.

[0052] use Figure 4A 、 Figure 4B , further explaining the correction value used in this embodiment 1.

[0053] In the first embodiment, before the diagnosis of the motor 5 is performed, the FFT analysis is repeatedly performed for a certain period of time on the current value data of the motor 5 during normal operation, and a plurality of power spectrum data as the analysis results are stored. In these power spectrum data, the load factor varies depending on the use status of the motor 5, so as to Figure 4A As shown, the power spectrum data appearing at the highest frequency is used as a reference value, and the power spectrum data changes when the load factor of the motor 5 is high or low.

[0054] Therefore, in order to make the power spectrum data at high load rate and low load rate consistent with the reference value, the influence of the different load rates on the power spectrum data of the motor 5 is eliminated. Figure 4B As schematically shown by arrows in FIG. 1 , the current signal strength is increased or decreased. The adjustment value of this increase or decrease is the correction value.

[0055] This correction value is combined with the load factor of the motor 5 when the corresponding power spectrum data was generated and recorded in a database. Based on the load factor obtained by normalizing the current value data during diagnosis using the current-load factor curve, an appropriate correction value can be selected, thereby improving the accuracy of power spectrum data analysis.

[0056] The current fluctuation calculation unit 114 determines whether the current value data measured for the motor 5 has fluctuated, and detects whether the current value data is in a stable state.

[0057] The current variation calculation unit 114 performs statistical variation analysis on the current value data, for example, by calculating the standard deviation and Mahalanobis distance of the current value data to analyze the variation.

[0058] The FFT analysis interval determination unit 115 extracts a stable interval from the measured current value data to determine the FFT analysis interval. Specifically, the interval in which the statistical variation calculated by the current variation calculation unit 114 is below a predetermined threshold is defined as a stable interval.

[0059] Typically, when the load torque of motor 5 fluctuates, the current value data also fluctuates. When FFT analysis is performed using this current value data, the current signal strength increases in the frequency range centered on the power supply frequency, making peak detection difficult. Therefore, by providing FFT analysis range determination unit 115, a stable range is extracted and used for FFT analysis, making peak detection easier.

[0060] The FFT analysis unit 116 performs FFT analysis on the interval determined by the FFT analysis interval determination unit 115 , and the peak detection calculation unit 117 identifies the peak position included in the determined power spectrum data.

[0061] The peak detection calculation unit 117 detects peak values ​​corresponding to the power supply frequency and the rotational frequency of the motor 5 based on the power spectrum data. Peak values ​​are detected by extracting the portion where the steep slope reverses through first-, second-, and third-order differential calculations. Performing differential calculations up to the third order enables peak value detection at even lower current signal strengths.

[0062] The rotation frequency band determination unit 118 specifies the peak position caused by the rotation frequency based on the peak value detected by the peak detection calculation unit 117 .

[0063] The rotation frequency is obtained from the rated rotation speed stored in the rated information recording unit 9 , and peaks having the same current signal strength are extracted that differ from the power supply frequency by the rotation frequency toward the high-frequency side and the low-frequency side.

[0064] Since the rotation speed of the motor 5 varies depending on the load torque, the peak value due to the rotation frequency may vary. The rotation frequency band determination unit 118 determines the rotation frequency band including the peak position within the frequency band taking this variation into consideration.

[0065] The frequency axis conversion calculation unit 119 calculates conversion axes for aligning the rotation frequency bands of the repeatedly measured power spectrum data, and the averaging calculation unit 120 accumulates the power spectrum data to which these conversion axes are applied multiple times and performs averaging processing.

[0066] The frequency axis conversion calculation unit 119 is necessary for the accurate implementation of the averaging calculation unit 120 .

[0067] As described above, the rotation frequency band varies depending on the load torque of motor 5. Therefore, to accurately overlap and average multiple FFT analysis results, the frequency axes of the power spectrum data must be aligned. Specifically, when the rotation frequency band is varied by multiplying the conversion factor α based on the load torque of motor 5, accurate averaging can be achieved by multiplying the conversion factor α by the frequency axis.

[0068] The FFT analysis result correction unit 121 uses the correction value selected by the FFT analysis result correction value selection unit 112 according to the load factor of the motor 5 to correct the diagnostic power spectrum data of the motor 5. The correction value information of the FFT analysis result is stored in the rated information recording unit 9 when the motor 5 is started and is retained even after the motor 5 stops.

[0069] In the first embodiment, the correction value is assigned by dividing the load factor into 20 equal parts, but the present invention is not limited thereto. The number of divisions and the like can be changed in the adjustment and setting of the diagnostic device 100 for the electric motor 5 .

[0070] The abnormality diagnosis unit 122 performs diagnosis on the motor 5 based on the corrected power spectrum data. Figure 5 The abnormality detection in the abnormality diagnosis unit 122 is described below. Figure 5 In FIG. 1 , a solid line indicates power spectrum data (diagnostic value) during diagnosis, and a difference value D between the current signal intensities of the power spectrum data at the power supply frequency and the power spectrum data at the rotation frequency is obtained.

[0071] The dotted line indicates Figure 4B This reference value is used to perform FFT analysis on the current value data of motor 5 for a certain period before diagnosis to determine a correction value corresponding to the load factor. Similarly, the difference in current signal intensity between the power spectrum data at the power supply frequency and the power spectrum data at the rotational speed frequency is calculated for the reference value and recorded as the difference value D′.

[0072] The difference value D' is the difference value obtained when the motor 5 is operating normally before the diagnosis. Therefore, if the motor 5 is operating normally during the diagnosis, the difference value D during the diagnosis and the difference value D' are approximately equal. Conversely, if the difference value D during the diagnosis and the difference value D' differ by a predetermined value or more, it is determined that an abnormality has occurred in the motor 5 during the diagnosis.

[0073] Despite Figure 5 In FIG. 4 , the difference value D′ is depicted as being larger than the difference value D, but this is for the sake of convenience and does not reflect actual data.

[0074] <Motor Diagnosis Flowchart>

[0075] use Figure 6 and Figure 7 The steps of performing calculations and determinations for diagnosing the motor 5 will be described with reference to the flowchart of FIG.

[0076] The diagnostic process of motor 5 is as follows Figure 6 As shown, it includes steps S101 to S109, wherein, regarding the FFT analysis shown in step S107, by executing Figure 7 The process is performed as shown in steps S201 to S208.

[0077] The diagnostic device 100 of the motor 5 is started at a predetermined time interval and performs Figure 6 and Figure 7 The processing shown.

[0078] In step S101, information about the motor 5 is input from the rated information setting unit 10 and recorded in the rated information recording unit 9. The information about the motor 5 includes rated information such as the number of poles, rated output, power supply frequency, rated voltage, and current values ​​at no load and rated current, and can be obtained from the catalog, test report, nameplate, etc. of the motor 5.

[0079] The rated information recording unit 9 also records the Figure 3 The normalized current-load factor curve showing the relationship between the normalized current and the load factor of the motor 5 is obtained in step S102 from the rated information recording unit 9 .

[0080] In step S103, the current value data of the motor 5 to be diagnosed is acquired by the current detector 4 and input into the current input unit 7. In step S104, the normalized current calculation unit 110 calculates the normalized current using equation (1) based on the current value data to be diagnosed input into the current input unit 7 and the motor information of the motor 5 recorded in the rated information recording unit 9.

[0081] In step S105, Figure 3 As shown by the arrow, the normalized current of the motor 5 calculated in step S104 is applied to the normalized current-load factor curve obtained from the rated information recording unit 9 in step S102, and in the load factor calculation unit 111, the load factor value (×) corresponding to the value of the normalized current of the motor 5 (black triangle) is obtained.

[0082] In step S106, a previously determined database is used. The database is recorded in the correction value data recording unit 113 and records the load factor and the correction value of the power spectrum data obtained as a result of the FFT analysis of the current value data in combination.

[0083] The FFT analysis result correction value selection unit 112 acquires the correction value of the FFT analysis result corresponding to the load factor of the motor 5 obtained in step S105 based on the database.

[0084] In step S107, the FFT analysis unit 116 performs FFT analysis on the current value data as the diagnostic target acquired by the current detector 4. In addition, in the FFT analysis of step S107, the following is performed. Figure 7 Steps S201 to S208 are shown.

[0085] In step S108 , the FFT analysis result correction unit 121 corrects the FFT analysis result performed in step S107 using the correction value obtained from the database in step S106 in correspondence with the load factor.

[0086] In step S109, if Figure 5 As described, for the FFT analysis result obtained during diagnosis in step S108 after the influence caused by the difference in load rate is corrected using the correction value selected from the database, the difference value D of the current signal intensity of the power spectrum data at the power supply frequency and the power spectrum data at the rotation frequency is calculated.

[0087] Similarly, for the baseline value of the power spectrum data measured when the motor 5 is operating normally before diagnosis, the difference in current signal strength between the power spectrum data at the power supply frequency and the power spectrum data at the rotation frequency is calculated and used as the difference value D′.

[0088] When the difference value D′ obtained in advance during normal operation and the difference value D during diagnosis have a difference greater than a predetermined certain value, the abnormality diagnosis unit 122 can determine that an abnormality has occurred in the motor 5 .

[0089] use Figure 7 Flowchart Description Figure 6 Details of the FFT analysis step of step S107.

[0090] In step S201 , current value data of the motor 5 detected by the current detector 4 and serving as a diagnosis target is input to the current input unit 7 .

[0091] In step S202, the current fluctuation calculation unit 114 calculates the fluctuation of the input current value data, and the FFT analysis interval determination unit 115 determines whether the current value data is stable. If the fluctuation of the current value data is greater than a preset value, the system is determined to be unstable (No) and the process returns to step S201. If the current value data is stable (Yes), the process proceeds to step S203.

[0092] For example, current value data for multiple types of motors 5 can be acquired in advance, and a threshold value used to determine whether a stable state exists can be selected from a range smaller than the standard deviation of the current value data. Alternatively, current value data for the motor 5 to be evaluated can be collected over a certain period of time, and the threshold value can be set based on the standard deviation of the current value data during that period.

[0093] In step S203, FFT analysis unit 116 performs FFT analysis using the input current value data within a stable interval. As an example, FFT analysis is performed on the frequency range from 0 Hz to 120 Hz, which is twice the power supply frequency of 60 Hz. The analysis results are sent to peak detection operation unit 117.

[0094] In step S204 , the peak detection operation unit 117 extracts all peaks from the analysis result. In step S205 , the rotation frequency band determination unit 118 extracts peaks located in the rotation frequency band from the detected peaks and determines the rotation frequency band.

[0095] In step S206 , the frequency axis conversion calculation unit 119 converts the frequency axes of all peaks so as to eliminate the influence of the frequency deviation caused by the load torque and make the determined rotation frequency band the rotation frequency band under no-load conditions.

[0096] In step S207 , the operations from step S201 to step S206 are repeated multiple times to perform FFT analysis, and power spectrum data obtained by transforming the frequency axis is collected.

[0097] In step S208 , the averaging operation unit 120 performs averaging processing on the plurality of power spectrum data subjected to the FFT analysis, thereby eliminating the influence of noise on the power spectrum data.

[0098] Finally, return to Figure 6 In step S108 of the flowchart shown, correction and diagnosis of the analysis results are performed.

[0099] As described above, by generating a database for determining the relationship between the correction value required for power spectrum data and the load factor before diagnosis, and correcting the power spectrum data as the FFT analysis result of the motor 5, the motor 5 can be diagnosed with high accuracy.

[0100] Conventional diagnostic devices require multiple pieces of information, including current, voltage, and zero-phase current, to diagnose motor abnormalities. However, the motor diagnostic device described in Embodiment 1 achieves comparable high diagnostic accuracy using only current information. Consequently, the introduction of motor diagnostic devices is much easier than with conventional devices, enabling low-cost implementation.

[0101] In the embodiment of the present application, one of the hardware 151 that performs calculations in the calculation processing unit 8 of the diagnostic device 100 is, for example, Figure 8 shown.

[0102] As shown in the figure, hardware 151 includes a processor 152 and a storage device 153. Although the storage device is not shown, it includes a volatile storage device such as a random access memory and a non-volatile auxiliary storage device such as a flash memory. Alternatively, an auxiliary storage device such as a hard disk may be included instead of the flash memory. Processor 152 executes a program input from storage device 153. In this case, the program is input from the auxiliary storage device to processor 152 via the volatile storage device. In addition, processor 152 can output data such as calculation results to the volatile storage device of storage device 153, or save data to the auxiliary storage device via the volatile storage device.

[0103] This application describes exemplary embodiments, but the various features, aspects, and functions described in the embodiments are not limited to application to specific embodiments and can be applied to the embodiments alone or in various combinations.

[0104] Therefore, numerous modifications not shown in the examples are considered to be within the technical scope disclosed in the present specification, including, for example, modifications, additions, or omissions of at least one component.

[0105] Label Description

[0106] 1 Main circuit, 2 Wiring circuit breaker, 3 Electromagnetic contactor, 4 Current detector, 5 Motor, 6 Mechanical equipment, 7 Current input unit, 8 Calculation processing unit, 9 Rated information recording unit, 10 Rated information setting unit, 11 Display unit, 12 Contactor drive unit, 13 Output unit, 14 Communication unit, 100 Diagnostic device, 110 Normalized current calculation unit, 111 Load factor calculation unit, 112 FFT analysis result correction value selection unit, 113 Correction value data recording unit, 114 Current variation calculation unit, 115 FFT analysis interval determination unit, 116 FFT analysis unit, 117 Peak detection calculation unit, 118 Rotation frequency band determination unit, 119 Frequency axis conversion calculation unit, 120 Averaging calculation unit, 121 FFT analysis result correction unit, 122 Abnormality diagnosis unit, 151 Hardware, 152 Processor, 153 Storage device, 200 Monitoring device

Claims

1. A diagnostic device for an electric motor, characterized in that: include: a current input unit that inputs current value data of the motor; an FFT analysis unit that performs FFT analysis on the current value data to obtain power spectrum data; a normalized current calculation unit configured to calculate a normalized current based on the current value data; a load factor calculation unit that uses a normalized current-load factor curve obtained from setting information of the motor to determine a load factor corresponding to the normalized current calculated by the normalized current calculation unit; a correction value data recording unit that records, in a database, a correction value for adjusting an influence caused by a difference between a reference value of the power spectrum data and the load rate of the power spectrum data during diagnosis, in association with the load rate; an FFT analysis result correction value selection unit that selects the correction value based on the load factor at the time of diagnosis obtained by the load factor calculation unit and the database; An FFT analysis result correction unit, which corrects the power spectrum data during diagnosis using the correction value; as well as The abnormality diagnosis unit calculates difference values ​​of current signal strengths at power supply frequency and rotation frequency for the corrected power spectrum data and the reference value during diagnosis, and diagnoses the motor by comparing the difference values.

2. The electric motor diagnostic device according to claim 1, wherein: The reference value is the power spectrum data with the highest frequency among a plurality of power spectrum data obtained by performing FFT analysis on the current value data of the motor when it is operating normally and repeatedly accumulated over a certain period before diagnosis. The correction value is an adjustment value that makes the power spectrum data deviating from the reference value among the plurality of power spectrum data consistent with the reference value.

3. The electric motor diagnostic device according to claim 1, wherein: When the FFT analysis unit performs FFT analysis on the current value data, the method includes: a current variation calculation unit that evaluates statistical variations in the current value data; and An FFT analysis interval determination unit selects an interval in which the statistical variation is equal to or smaller than a certain value as an FFT analysis interval.

4. The electric motor diagnostic device according to claim 2, wherein: When the FFT analysis unit performs FFT analysis on the current value data, the method includes: a current variation calculation unit that evaluates statistical variations in the current value data; and An FFT analysis interval determination unit selects an interval in which the statistical variation is equal to or smaller than a certain value as an FFT analysis interval.

5. The electric motor diagnostic device according to any one of claims 1 to 4, characterized in that: include: a frequency axis conversion operation unit that converts the frequency axes of the plurality of power spectrum data so that the rotation frequency bands of the peaks caused by the rotation frequencies in the plurality of power spectrum data are aligned; as well as An averaging operation unit is used to average the plurality of power spectrum data obtained after the frequency axes are transformed respectively.

6. The electric motor diagnostic device according to any one of claims 1 to 4, characterized in that: The load factor is the ratio of the load torque during operation to the rated load torque.

7. The motor diagnostic device according to claim 5, wherein: The load factor is the ratio of the load torque during operation to the rated load torque.

8. The electric motor diagnostic device according to any one of claims 1 to 4, characterized in that: The normalized current is the ratio of the difference between the measured current and the no-load current to the difference between the rated current and the no-load current.

9. The electric motor diagnostic device according to claim 5, wherein: The normalized current is the ratio of the difference between the measured current and the no-load current to the difference between the rated current and the no-load current.

10. The motor diagnostic device according to claim 6, wherein: The normalized current is the ratio of the difference between the measured current and the no-load current to the difference between the rated current and the no-load current.

11. The electric motor diagnostic device according to claim 7, wherein: The normalized current is the ratio of the difference between the measured current and the no-load current to the difference between the rated current and the no-load current.

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