There are three types of impact tests that we do:
1. Single channel – Bump test. This is done with a simple hammer hit (soft faced) to an object and measuring the response to determine the natural frequency of the object being impacted. To perform this test on a piece of machinery it must not be running.
2. Single Channel – Bump test, machine running. The same procedure is followed as the single channel test with the machine running, but an extra step of removing the running vibration to give us the natural frequency of the machine at rest. This test is good for when you cannot shutdown a machine but is more time consuming
3. Dual channel test with an impact hammer. This is done to a machine that is not running or a stationary object. The big advantage of this test is that it gives us a FRF number, phase data to show when and where it is occurring and coherence value to validity the readings we are getting. These are useful to calculate a correction – addition of mass or increasing stiffness to change the natural frequency of the object in question.