## Impact Hammer Double Hit – An Investigation

An Impact Hammer double hit is viewed as a common problem, and most hammer impact testing software offers a "Double hit" rejection function. Signals captured with double impacts are not…

## A Guide To Resonance

Welcome to our latest blog post, where we delve into the fascinating world of resonance and natural frequency! Over the years, we've consistently noticed that our articles exploring these topics…

## Are My Hammer Impact Results Valid? (3) Time Invariance

As mentioned in our previous two articles, when performing experimental modal testing of a structure or component using impact (or ping) testing, it is important to consider and verify the…

## Averaging Frequency Response Functions From A Structure

The following was written by Adrian Lincoln in response to a customer asking about averaging Frequency Response Functions (FRFs) Further to your reply it should be noted that there is…

## [Video] Storing FRFs, coherence & time series

James Wren (Prosig UK) explains how to store FRFs, coherence and/or time series data in modal hammer testing using Prosig's P8000 & DATS software. http://www.youtube.com/watch?v=JLumlmoRCvM

## What is the difference between Operating Deflection Shapes (ODS) and Operational Modal Analysis (OMA)?

ODS = Motion of structure vibrating naturally (for example bridge vibration) or when excited by an unknown force (for example generator vibration). Prosig’s Structural Animation software performs ODS analysis.

OMA = Modal Analysis
Prosig’s Modal Analysis software performs OMA. (more…)

Figure 5: H1(f)

## A Simple Frequency Response Function

The following article will attempt to explain the basic theory of the frequency response function (FRF). This basic theory will then be used to calculate the frequency response function between two points on a structure using an accelerometer to measure the response and a force gauge hammer to measure the excitation.

Fundamentally a FRF is a mathematical representation of the relationship between the input and the output of a system.

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