PURPOSE:

The frequency response function, also known as the transfer function is defined simply as:

Response magnitude
Input Magnitude

and can be the ratios of two accelerations, two displacements, two velocities, or two forces and in the absence of resonance, results in a value of 1. In the presence of resonance, this value, which is commonly referred to as Q, is some value greater than 1 and when a value of 10 is achieved it is accepted that the DUT is in resonance. Values less than 1 can also be achieved and indicate a node or the attenuation of the input signal, i.e. Damped response.

In this application, the frequency response function is calculated as H1 meaning that an FFT is performed on the time domain response of both the input and response accelerometers before the value of Q is calculated.