SHOCK & VIBRATION MEASUREMENT

CHAPTERS

1) What frequency range do you care about?
2) What amplitude range is of interest?
3) Who needs the data and why?
4) Where is the test environment?
5) When is the test date?
6) When will the vibration analysis need to be completed?

1) What frequency range do you care about?
2) What amplitude range is of interest?
3) Who needs the data and why?
4) Where is the test environment?
5) When is the test date?
6) When will the vibration analysis need to be completed?

Before we can get into sensor selection we need to answer some key questions:

1) What frequency range do you care about?

The frequency range will drive hardware; I’ve seen far too many engineers have the wrong sensor and even the wrong DAQ (data acquisition) system for their application that can lead to erroneous results.

2) What amplitude range is of interest?

Obviously you’ll need to select a sensor with a measurement range that includes the amplitudes you or your customer care about; but it also heavily influences your DAQ selection. Very small vibrations/accelerations like those in seismic applications will require not only a very low noise and high sensitivity accelerometer; you’ll also need a DAQ system with very low noise and ultra-high resolution. On the higher amplitude end, it’s important to bear in mind what type of acceleration levels the DAQ hardware will see. When measuring a wider range, resolution will also be important.

3) Who needs the data and why?

You’ll need to lean towards higher quality systems if your customer has a particular test standard they need to have the system qualified to. The United States military has a testing standard, MIL-STD-810 (vibration is section 514.6 and shock is 516.6) for example; you won’t be able to qualify your system to meet such a standard with low quality equipment. On the other hand, if you just need a rough handle of the shock and vibration levels in your environment to get started in the design process or if you’re trying to satisfy a curiosity, lower quality systems may be adequate. There are other applications, such as health monitoring, that aren’t necessarily looking for absolute vibration values. Rather, relative vibration levels and how it changes with time is important.

4) Where is the test environment?

Will this be in the lab or in the field? If testing will be limited only to the lab then more complicated test equipment can be used. Conversely though, if the testing is done in the field, ease-of-use will be a driver of your hardware selection. The type of environment will also heavily influence sensor selection such as temperature range, humidity, electromagnetic noise; and even corrosive or radioactive conditions.

5) When is the test date?

All too often engineers realize they need testing once a problem has already presented itself. Lead time of equipment now becomes incredibly important especially because they can have 6 to 8 week lead times. Often times the engineer won’t have that time available to wait.

6) When will the vibration analysis need to be completed?

This may drive your software selection. If you have a limited time to perform the analysis you may want to go the route of simpler and cheaper software packages to give you that quicker overview of the data. On the other hand if you have a development effort that has a heavy emphasis on analysis and the time available to support that analysis effort then a more complex software package may be warranted. Along that same vein, it may be worthwhile to use a programming language like MATLAB or Python to develop your own analysis scripts specific to your analysis needs.