There is a reason, apart from a mechanical fault in the machine, why the vibration pattern could change. The reason is in the palm of your hand. When the sensor is attached to the machine, the vibration from inside the machine causes the sensor to vibrate, which is picked up by the electronics inside.
If the sensor is not mounted correctly, the sensor will vibrate in a way unrelated to the machine, and the vibration data will be useless. So the data collection person’s job is very important.
You don’t want to be left wondering: Did the vibration go up because I accidentally mounted the sensor in the horizontal direction instead of the vertical direction?
The sensor must directly contact the machine surface. The stronger and more stiff the connection, the more likely you will get a measurement with an acceptable frequency response. The surface must be smooth and flat, and must be free of paint chips, rust, or grit. One should not attach a sensor directly to a painted surface.
The mounting method chosen is in part dictated by the application: routine portable collection where the sensor is temporarily mounted, or continuous monitoring where the sensor is permanently mounted.
There are a number of options:
- Magnets (two-pole or flat)
- Quick connect
By far, the best option is stud mounting, where the accelerometer is directly connected to the machine surface. Short of welding the sensor to the machine, this option gives the best high frequency response.
But it is less practical with a program based around a portable data collector.
In a walk-around data collection program, we need a way to quickly connect and disconnect the sensor from the machine. While the quickest options – or what seem like the quickest connect and disconnect options – may provide us with inferior data, a screw-in sensor mount may take a bit longer but provides much better data.
Here are the common options:
- Hand-held “stinger” probes
- Magnet mount on pad or machine surface
- Quick connect
- Screw-in mounts
We discuss these options in great detail in our manuals and courses. But in short, make sure the option you choose is practical for the data collector without compromising accuracy and repeatability, and ensure the vibration analyst is trained in collecting good data.