Live FFT Mode and Single FFT Mode

Vibration ( acceleration ) amplitude can be analyzed in the frequency domain (or spectrum) to gain a deeper understanding of the vibration profile. Most vibration analysis will typically be done in the frequency domain. A discrete Fourier transform (DFT) computes the spectrum, but nowadays this has become synonymous with the fast Fourier transform (FFT), which is just an efficient algorithm for the DFT. FFT analysis and advanced filtering can be done in the FFT analysis page of the BroadVibra software. It turns out that some applications need to review the time domain waveform and frequency domain waveform in real-time. Therefore, Broadsens recently added live FFT function, that can show the wireless vibration sensor's FFT result in almost real-time.

To use the live FFT function, please choose "Live FFT" data acquisition (DAQ) mode. Multiple wireless vibration sensors can take data at the same time. In the right figure, there are four wireless vibration sensors taking data in live FFT mode. In live FFT mode, when there are multiple sensors, then all sensors are synchronized to take data at the same time. That is, if a wireless vibration sensor connects to the wireless gateway first, then the sensor will wait for the other sensors to connect to the gateway. When all sensors in the same group are connected to the wireless gateway, then they start taking data at the same time. When all sensors finish taking data, the gateway will perform FFT analysis for all sensors in the same group, display both the time domain waveform and frequency domain result. Then the gateway issues another command to the sensors to take data again. Since all sensors are connected to the gateway already, they will take data immediately without waiting.

 

Live FFT analysis of vibration signal

If there is only one sensor in the group, then the sensors starts taking data immediately when it connects to the gateway.

In single FFT mode, all wireless vibration sensors in the same group are synchronized to take data once, and the FFT analysis result is shown in the bottom chart (Figure 22). If there is single sensor in a group, then the sensor takes data immediately after it connects to the gateway. Temperature is still measured and saved in the database, but will not show in the bottom chart.

Sampling rate, DAQ points and acceleration range can be adjusted at single FFT mode. If MQTT FFT switch is enabled, then the FFT result is transmitted via the MQTT broker to a remote server. The FFT result is in JSON format.
Single FFT mode is to help user quickly look at the FFT result and checks out the machine condition. User can still go to “FFT analysis” page and perform the FFT analysis, and export the FFT result and time-domain data into CSV file. There is no filter added in the single FFT mode. To apply a filter to the data, then it needs to be done at the “FFT analysis” page.

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