## What Are dB, Noise Floor & Dynamic Range?

We are often asked what noise floor & dynamic range actually are. Most engineers are probably familiar with or have come across the decibel or dB as a unit of…

## Measure Vibration – Should we use Acceleration, Velocity or Displacement?

When using vibration data, especially in conjunction with modelling systems, the measured data is often needed as an acceleration, as a velocity and as a displacement. Sometimes different analysis groups require the measured signals in a different form. Clearly, it is impractical to measure all three at once even if we could. Physically it is nigh on impossible to put three different types of transducer in the same place.

## What Is A Hammer Test Or Hammer Impact Test?

A Hammer Impact Test is also known as a Modal Test, Impulse Test, Tap Test, Bump Test or, simply, a Hammer Test. It is a method of testing that allows…

## How Do I Upsample and Downsample My Data?

This post covers how to upsample and downsample data and the possible pitfalls of this process. Before we cover the technical details let us first explain what we mean by upsample…

## RMS From Time History And FFT Spectrum

The RMS of a time history is a measure of the signal's overall energy and is often used when extracting features from a signal for prognosis and trending of vibration…

## How do we design or modify a system to avoid resonance?

After finding the natural frequency of a system, what could be done to stop or reduce the systems resonance being excited? Basically put, how do we avoid resonance This is…

## What Is The Difference Between Single Ended & Differential Inputs?

Prosig data acquisition systems use differential inputs, but what are they and why are they so special? This subject is not always fully understood and, therefore, the focus of this…

## Converting Acceleration, Velocity & Displacement

From time to time I meet engineers who are interested in the conversions between acceleration, velocity and displacement. Often, they have measured acceleration, but are interested in displacement or vice versa. Equally, velocity is often used to find acceleration. This article outlines the nature of the conversion between these units and will suggest the preferred method for doing so. .

## What is the difference between microphone types?

We're often asked what is the difference between microphone types; free field, diffuse field and pressure. For a run-of-the-mill ½ inch microphone the short answer is nothing. However the long…

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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