Make Things Go Smoothly Even When They Shouldn't
Inaccurate PSD Estimation Methods Give Smooth Lines but Mask Underlying Issues
It’s human nature to want life to go smoothly. No one likes family drama, problems with the neighbors or a frustrating day at the office. When it comes to vibration testing, lab technicians and managers have good days and are generally pretty happy when there are smooth lines perfectly centered within tolerance bands signaling that test requirements have been met. But the corners of their mouths edge downward when a raggedness appears on their PSD plots. It’s perfectly understandable! After all, the equipment being tested – such as satellites and airplanes – is quite expensive and an out-of-tolerance condition simply cannot be tolerated (at least very well).
Don’t Fear the Ragged Line
What lab technicians and managers might not realize is that a little raggedness, especially at the beginning of a test, is a natural part of PSD estimation. Really…it’s a good thing! Let’s say they run a vibration test at 120 degrees of freedom. Once the start button is pressed and the data begins to average, there will be estimation error causing the line to bounce in and out of tolerance. When the desired degrees of freedom are reached, the coveted smooth line should appear unless there is an actual control error. This requires a bit of time, some nail biting, and lots of patience.
Forcing a Smooth Line is Not Too Smooth
Unfortunately, lab technicians and managers don’t enjoy sitting back and waiting. They also don’t necessarily distinguish estimation errors from control errors – any raggedness is just bad news!
And so they have learned methods to get around the sources of their pain. One popular technique is to use low level data to obtain a smooth line and then simply apply a multiplier to show product behavior at a higher level. A smooth line is generated almost instantly at high level by this method but at the cost of a very inaccurate test and picture of reality. In fact, the technician or lab manager might be over or under testing the product. The bottom line is that products will behave differently when there is a change in level and using a multiplier masks what is actually going on.
iDOF – Smooth Day, Every Day
Vibration Research (VR) understands how important it is for lab technicians and managers to have “smooth days” at the office. We are also passionate about accurate methods. As the innovator in vibration control, our team of engineers developed a statistically accurate way to remove estimation error while displaying control error. Now, VR customers can have it all! Almost everyday can be smooth sailing thanks to, our patented test module, Instant Degrees of Freedom (iDOF).
If a fast and accurate smooth line is important for your vibration testing, download our technical paper to learn more about iDOF.