Tips for achieving optimal vibration measurements
To help ensure that the vibration data you collect is as accurate and useful as possible, you’ll want be sure you’re taking the measurements under the right conditions and in the right way. Below are some guidelines to follow.
1. Take measurements with the machine operating under normal conditions
For example, perform measurements when the rotor, housing and main bearings have reached their normal steady operating temperatures and with the machine running under its normal rated condition (for example, at rated voltage, flow, pressure and load). On machines with varying speeds or loads, perform measurements at all extreme rating conditions in addition to selected conditions within these limits.
2. Select the best measurement point on the machine
Avoid painted surfaces, unloaded bearing zones, housing splits and structural gaps.
3. Be consistent
When measuring vibration with a handheld sensor, it is imperative that you perform consistent readings, paying close attention to the sensor’s position on the machinery, the sensor’s angle to the machinery and the contact pressure with which the sensor is held on the machinery. Measurements should be taken at the same precise location for comparison (moving the probe only a few inches can produce drastically different vibration readings). To ensure measurements are taken at the exact same spot, mark the measurement point with permanent ink or machine a shallow conical hole with a drill point. Magnetic mounts are even better for consistency and permanently mounted sensors are the best for consistency.
4. Measure in three directions whenever possible
Ideally, vibration should be measured in the axial direction (A), the horizontal direction (H) and the vertical direction (V).
5. Get close
Measurements should be taken as close to the bearing as possible.
6. Avoid the case
If possible, avoid taking readings on the case, as the case could be vibrating due to resonance or looseness.
7. Choose flat
If possible, choose a flat surface to press the sensor tip against.
8. Use the correct angle and pressure
Always measure perpendicular to the surface (90°, ±10°), with even, consistent hand pressure (firm, but not so firm as to dampen the vibration signal).