I work in a pump station and I've noticed that when I measure the bearing vibration by a vibration meter, the measured value differs from what is shown on the computer monitor (2.5 mm/s measured directly and 0.78 shown on the monitor) which is measured by a hansford vibration sensor mounted on top of the bearing on the Y direction. I put the vibration meter magnet just next to the sensor and the meter is calibrated. so I would appreciate if anyone gave me a possible reason.
If this is still an issue, I believe the reason for this is that the computer monitor displays the peak-to-peak value and the direct measurement displays the RMS value.
2.5 mm/s (peak-peak) = ±1.25 mm/s (0-peak) RMS(1.25) = 1.25/sqrt(2) = 0.88 mm/s
That is, 2.5 mm/s peak-peak = 0.88 mm/s rms.
The difference between this 0.88 and the 0.78 is probably due to difference in instrumentation of some kind. Hard to tell without any more details of the instruments.
Likely, its one or more of the following: mounting position, mounting technique, instrument accuracy, signal noise