Vibration Analysis Using an X6-2 USB Accelerometer

Introduction

The sensitivity and sample rate capabilities of the X6-1 and X6-2 are appropriate for low frequency vibration analysis. In this example, the X6-2 is used to illustrate the vibration difference between two residential sized central air conditioning units.

Test Setup

The X6-2 was configured to record data at 320Hz using the high gain mode. The X6-2 was mounted to each test subject with removable mounting strips made by 3M. First, data was collected at the air handler (the vibration source). Then, data was also taken at the walls of several nearby rooms to determine how far the vibration propagated throughout the building.

Two air conditioning units were selected to exemplify good and bad vibration. “The Beast” is an old, worn out system circa 1980. Those boards and cardboard boxes shown in the first picture are there to hold the Beast in place. Otherwise, it would vibrate loose from its mounts and walk down the hallway terrorizing all in its path. “The Beauty” is a new system installed at the office, courteous of hurricane Katrina. This system is significantly quieter as the data will show.

Analysis involved a Fast Fourier Transform of the z-axis data to provide the vibration frequency spectrum. A 30-second segment of data was re-sampled from 320Hz to 256Hz. The 30-second segment was then separated into blocks of 1024 samples, each block overlapping the next by 50%. FFTs of each block were run and the results summed together. The results of the individual vibration tests were plotted together for comparison..

The Beast
Figure 1: The X6-2 monitoring The Beast

The Beauty
Figure 2: The X6-2 sitting on top The Beauty

X6-2 stuck to wall
Figure 3: The X6-2 stuck to a wall

Data Analysis

The vibration sprectrum from The Beast. Notice the spikes at 17hz and 120hz.

low freq vibrations

A closer look at the lower frequencies emanating from The Beast. Notice the 17Hz signal propagating throughout the house, shaking the walls.

beastly vibrations

Here is the vibration sprectrum from The Beauty, or lack there of. This air handler barely vibrates and is almost completely silent. Very little vibration propagated into the adjoining wall.

beautiful vibrations

This final plot illustrates the stark difference between the two air conditioning units.

beauty and the beast

Conclusion

If you can feel the vibration with a touch of the hand, then both the X6-1 and X6-2 are capable of capturing that movement. Monitoring the two air conditioners illustrates the potential uses of the X6-2 USB accelerometer in the field of vibration analysis. Here, the data collected by the X6-2 provided undeniable proof that it's high time to put The Beast to rest and buy a new AC system.

Addendum

The plot below shows the vibration frequency spectrum from a desktop PC. The X6-2 was mounted with superglue to the side of the mid-sized tower case. This particular PC is probably a little noisier than most due to the graphics card and cooling fans. As stated above, the case barely vibrates to the touch but it is still registered by the X6-2.

desktop PC vibration