The use of a strobe light or stroboscope is another tool in the toolbox of the analyst in the field of Reliability. This tool can be used for a variety of purposes including checking or verifying the rotational speed of a component if the shaft or coupling is accessible.
The user can inspect it without stopping or shutting down the equipment. If the model of stroboscope the user has is capable of being triggered from an external source for the flash rate the user can move the flashing strobe around the machine’s moving parts to see which one appears to stop which can indicate that this is the source for the triggering and therefore the source of vibration.
Most stroboscopes have an output that can send a signal to a vibration instrument to be used as a tachometer input to the instrument. Dynamic balancing can be performed using a stroboscope instead of a laser, optical or infrared tachometer.
A key safety consideration is that one must remember when utilizing a stroboscope that rotating structures (such as shafts or couplings) only appear to be frozen or stopped when the stroboscope flash rate is synchronized to the same frequency as the shaft’s rotational speed.
People who are not familiar with stroboscopes have reached out to touch what appears to be a stopped shaft and become seriously injured. When using a stroboscope and the machine has not been started the user can use a marker and place a horizontal mark on one side of the shaft and a vertical mark on the opposite side so when the machine is running and you adjust the internal oscillator in the stroboscope to match the rotating shaft’s frequency you will either see a vertical or a horizontal mark; if you see a plus sign then the flash frequency is either half or double the shaft frequency.
For a sample on how a strobe light is applied for Synchronous Peaks vs. Non-Synchronous Peaks, watch this video from our partner, Karl Hoffower with Failure Prevention Associates, LLC
Balancing, Vibration Analysis by Gary James CRL