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Predictive maintenance & condition monitoring


Figure 11. LTspice schematic showing voltage outputs for faulty and nonfaulty vibration data.


Figure 9. Increasing the timestamp resolution to five decimal places.


then select Format > Format Cells, as shown in Figure 8.


Once the timestamp column is populated and the significant digits expanded, copy both columns of each sheet to its own Notepad or another text editor file, as shown in Figure 10. You should have three text files containing the vibration data for axes X, Y, and Z in the condition-based monitoring system. This data can now be read directly


into LTspice. Construct a schematic in LTspice, as


shown in Figure 11. In this design, there are six voltage sources corresponding to fault and no fault data for axes X, Y, and Z. This enables a Fourier analysis to be performed on the vibration data from a new motor so it can be compared with the Fourier analysis of the data from a suspected faulty motor. A big advantage of this method


Figure 12. Creating a piecewise linear voltage source from the vibration data.


Figure 10. Text file containing time and vibration data.


is that the frequency plot of a new (not faulty) motor can be overlaid on that of a suspected faulty motor, so the difference in performance can be seen. The LTspice command .options plotwinsize=0 numdgt=15 removes the default compression in LTspice and sometimes produces clearer results. The simulation will run faster if this line is omitted but may produce less accurate results. Once the schematic is complete, right-click each voltage source, select the Advanced


button, select the PWL File radio button, then enter the file name of the appropriate text file containing the vibration data, as shown in Figure 12. This creates a piecewise linear voltage source consisting of a series of voltages and their corresponding time instances. Your life will be easier if these text files are stored in the same directory as the LTspice file. The transient analysis should then be


configured to run for the duration of the original vibration test using the command .tran 1 Run the simulation. The simulation may take some time to complete depending on the data points and the length of the transient analysis.


Figure 13. Time domain results of the vibration data for a faulty and nonfaulty motor. 20 October 2020 Instrumentation Monthly


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