HOW TO MEASURE THE ROTATION SPEED WITH A STROBE LIGHT?
Identifying the rotation speed of your rotating equipment can be challenging. Variable frequency drives, safety guards and transmission components with speed ratio (ex: belts, gearboxes, etc.) are all elements which could make this task more difficult.
Discover the tips to make your task easier !
1. Check the information on the nameplate on your motor.
- For an asynchronous motor, if the motor is not connected to VFD, the actual rotating speed should be close to the one indicated on the nameplate. For example, for the motor with the nameplate below, the synchronous speed is 1800 RPM and the full rated-load speed is 1770 RPM. You should find the actual speed between those values.
- On the other hand, if the motor is connected to a VFD, generally speaking, 100% of the VFD should equal the synchronous speed of your motor. The nameplate can help you to limit the search range.
2. There’s always a peak at the rotation frequency of your equipment.
It might not be the highest in amplitude or the lowest in frequency but there will be a peak, and this whether for your driver or driven component.
- Look at your spectrum to help you identify the rotation speed.
- Synchronize your strobe light with the identified speed.
3. 1/2, 1/3, 1/4, …
The objective of using a strobe light is, for example, to locate an element on the rotating part, the keyway or a bolt head, and to flash one time per revolution so the rotating part seems motionless.
You will have the same impression if your strobe light is at a fraction of the speed of your equipment, although the located element will be blurrier then it would be if it would be sync with the rotation speed.
If you are in doubt, double the speed of your strobe light. If you already have the correct speed, the identified element will appear twice.
4. 2x, 3x, 4x, …
An identified element will appear motionless several times per turn when your strobe light is set at a multiple of the actual rotation speed.
5. A high speed tool !
The strobe light is a valuable tool for equipment with high rotation speed. Depending on the environment, it can be challenging to identify a slow rotation speed with a strobe light.
In vibration, the rotation speed is paramount, it is therefore important to identify it correctly. Many options are available depending on your situation. The strobe light can also be a tool of choice for inspecting couplings, belts/chains and motor fans while your equipment is in operation. You can synchronize the proper frequency and inspect different components of your equipment without shutting it down.