*5.3.3 Data access and signal analysis*

Because of the signal access points the students can using an oscilloscope to view the FFT plot on the screen. Most modern oscilloscopes have this feature built in. The students should clearly understand how the sampling system of the oscilloscope

#### **Figure 14.** *Machine health Hardware Station layout.*

relates to the standard parameters of an FFT. These should first be demonstrated by feeding a 1khz sine wave or square wave into the oscilloscope.


In this example we are using 15000 samples at a sampling rate of 7.5 kbps on a 1 kHz sine wave. We are using 4096 frequency bins. From this experiment students will quickly see the application of an FFT in determining frequency components in complex time domain signals (**Figure 15**).

**Figure 15.** *FFT plot of 1 kHz sinewave oscilloscope output.*

Once an understanding of the signal has been achieved, students can then do a lab experiment where they use the microcontroller to sample the incoming signal and do basic amplitude analysis on the signal. This can then be expanded to sampling on all three channels. A simple flow of sampling is demonstrated below. This sampling is done for single shot analysis, this is not a "real-time" sampling system. Realtime FFTs are typically done on FPGAs or systems with much more bandwidth capabilities (**Figure 16**).

The signal goes through an amplifier and buffer circuit to put it in the range of the ADC. The ADC is an I2C ADC, this is a better alternative to the micro-controller on board ADC because it is higher resolution. The microcontroller then samples the ADC at a known sampling rate (usually 2 kHz) and puts the samples into a buffer. This buffer can then be used for analysis.

**Figure 16.**

*Flow of sampling data from the machine Health Station.*

If the students have a method of viewing the ADC buffer in a graphic way, it can help them develop the application faster. A good solution for this is using Python to receive serial/UART data from the micro-controller and plot it on a PC.
