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Difference between revisions of "NVGate Envelope analysis"
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===Objective:=== | ===Objective:=== | ||
Abnormal vibrations were detected on a speed reducing gear box. We | Abnormal vibrations were detected on a speed reducing gear box. We proceeded to diagnose the machine. A default in the roller bearing is suspected. An accelerometer is positioned close to the bearing and connected to the OR3X analyzer. | ||
[[Image:Envelope_01.png|framed|none]] | [[Image:Envelope_01.png|framed|none]] | ||
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OROS analyzer with NVgate Software | OROS analyzer with NVgate Software | ||
In this example we are | In this example, we are analyzing the time signal file recorded with the analyzer. Office mode of NVGate is used. | ||
===Description:=== | ===Description:=== | ||
The first step consists | The first step consists of the traditional FFT spectrum analysis of the signal in the complete frequency bandwidth (0-20 kHz). | ||
The zoom analysis is used in the second step. The third step describes the envelope analysis. | The zoom analysis is used in the second step. The third step describes the envelope analysis. | ||
Finally, we will also proceed to the analysis of the demodulated signal in the fourth step | Finally, we will also proceed to the analysis of the demodulated signal in the fourth step. | ||
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===Step 1: Traditional Spectrum Analysis=== | ===Step 1: Traditional Spectrum Analysis=== | ||
In a first step, we | In a first step, we determine the spectrum obtained from the accelerometer signal. The signal is considered on a frequency band 0-20 kHz. | ||
[[Image:Envelope_02.png|framed|none|Figure 1: Spectrum Analysis]] | [[Image:Envelope_02.png|framed|none|Figure 1: Spectrum Analysis]] | ||
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===Step 2: Zoom Analysis=== | ===Step 2: Zoom Analysis=== | ||
The traditional approach is to use a zoom analysis around 4.3 and 13.3 kHz in our case. In the NVGate software define the settings of the FFT Zoom by: | The traditional approach is to use a zoom analysis around 4.3 and 13.3 kHz in our case. In the NVGate software, define the settings of the FFT Zoom by: | ||
* | * Setting a zoom factor of 16. | ||
* | * Defining the center frequency of the zoom at 4.3 kHz in a first time. We can also use the drag and drop action to place the center frequency in the averaged spectrum window. | ||
[[Image:Envelope_03.png|framed|none|Figure 2 - Zoom Analysis Settings]] | [[Image:Envelope_03.png|framed|none|Figure 2 - Zoom Analysis Settings]] | ||
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The zoomed spectrum helps us to have a better resolution around the carrier frequency at which the signal is demodulated. For doing this kind of analysis we can use the side band markers. | The zoomed spectrum helps us to have a better resolution around the carrier frequency at which the signal is demodulated. For doing this kind of analysis we can use the side band markers. A typical signal spectrum can be seen as it usually has a central frequency line with lower amplitude side lines, as shown on the figure below: | ||
[[Image:Envelope_05.gif|framed|none|Figure 4- Envelope Analysis]] | [[Image:Envelope_05.gif|framed|none|Figure 4- Envelope Analysis]] | ||
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We | We suspect a modulation frequency of 148.4 Hz which exactly corresponds to the value of the inner bearing race defect frequency provided by the manufacturer of the ball bearing. | ||
From the shape of this spectrum we can also see there is a modulation phenomenon. This is why we are going to proceed to the envelop analysis to check the demodulated signal and its spectrum. | From the shape of this spectrum we can also see there is a modulation phenomenon. This is why we are going to proceed to the envelop analysis to check the demodulated signal and its spectrum. | ||
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Five shocks per revolution are identified in the Envelope trigger window obtained after the signal demodulation (number 4 of the Figure 6). | Five shocks per revolution are identified in the Envelope trigger window obtained after the signal demodulation (number 4 of the Figure 6). | ||
We are using the Harmonic markers in the Envelope spectrum window to detect the modulation frequency that is significant | We are using the Harmonic markers in the Envelope spectrum window to detect the modulation frequency that is significant to the defect in the gear box. In our case, we confirm that the frequency at 148.4 Hz is the modulation frequency (Figure 7). | ||
[[Image:Envelope_08.png|framed|none]] | [[Image:Envelope_08.png|framed|none]] | ||