Operating rotating equipment at resonant frequencies can damage or destroy the equipment and create dangerous situations for nearby personnel. Understanding where these frequencies may exist is critical to safe and reliable operations.

In this 4:51 YouTube video, Running Bump Test for Resonance Detection, Emerson’s Drew Mackley shows how tests can be performed while the rotating equipment is operating, to identify any resonant frequencies across the machine’s operating range of frequencies.

This test, commonly called a “running bump test”, helps find any natural frequencies in the machinery. Drew describes an example where vibration data is collected with a portable vibration analyzer, in this case, the CSI 2140 Machinery Health Analyzer.

He demonstrates a running bump test with negative averaging. He selects the specific analysis test—Bump Test Equipment Running on the CSI 2140. It shows a description of the two-step process required to collect the data. The first step is to use a rubber hammer to impact the machine near the sensor in the same direction of the sensor. The online instructions direct the maintenance technician to hit the equipment once per average requested. The second step in the instructions is to collect the data without impact so that the running vibration can be automatically subtracted from the impact vibration.

These instructions built in with each particular test help guide the technician through the steps. The impacts delivered to the machine help to find the resonant/natural frequency of the machine. Drew selects the parameters of the test including 6 impacts to be performed. After he hits the motor six times, the test automatically collects the running vibration and performs the negative averaging calculations to isolate the energy from the impacts.

The CSI 2140 analyzer displays the resonant frequency at 20Hz. The machine operates at 1700 RPM which is around 30Hz, so the resonant frequency is safely below the operating speed. This test helps to eliminate resonance as a cause of any high vibration levels in the machinery.

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