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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.

here is a picture of the sensor

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    $\begingroup$ you need to provide more details on the values you are observing, the measuring systems, and where on the pump you are measuring. $\endgroup$
    – NMech
    Jun 3 at 7:22
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    $\begingroup$ How big is "huge?" 20% or 200% or what? $\endgroup$
    – alephzero
    Jun 3 at 13:41
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    $\begingroup$ some plots might help narrow things down. remember that filtering and calibration play a big part in measuring vibration. $\endgroup$
    – Abel
    Jun 3 at 13:43
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    $\begingroup$ Can you please share the specification of the hansford vibration sensor? May be a pictures might help too. $\endgroup$ Jun 9 at 13:44
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    $\begingroup$ How the calibration was done, against what? You can take the reading on another piece of equipment that has the known/verified vibration characteristics and see the result to determine whether there is a consistent descripency between the meter and the computer. $\endgroup$
    – r13
    Jun 21 at 20:11
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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

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