Is your accelerometer giving you good vibes?

Over the past few months, several customers have sent machine databases to Warren and me to evaluate and to make recommendations. Beyond finding machinery problems using the good quality data that you analysts collect and the software utilities that help you diagnose problems, we sometimes discover other issues that may affect your analysis capabilities. We supply good quality PCB piezo-electric accelerometers with the Windrock portable and online systems but, as the saying goes, “nothing good lasts forever.” So, here is a little information that may help you determine when your accelerometer is beginning to go bad. The # 1 plot below is representative of an accelerometer going bad. There is a phenomenon called “twinning” that the piezo-electric experts say is the cause of the pattern. The # 2 plot below is representative of an accelerometer that is working properly.

The symptoms of an accelerometer going bad are:

The sensitivity and milli-volt/g output of the accelerometer will go down. Therefore, the vertical scaling “fixed data scale” in your machine setup will have to be lowered to obtain the same vertical amplitude compared to your previous data with a good accelerometer.
The enveloped pattern itself will appear to have sharp or choppy characteristics that will return to the baseline and include flat response areas across the pattern. Similar to an old pressure transducer losing its preload, the accelerometer loses its low end energy response.

If you are experiencing these characteristics in your High Frequency Vibration patterns, you may consider scheduling the replacement of your accelerometer before you are left hanging with no “Vibes” at all.