Bently Nevada Vibration Probe Troubleshooting


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3300 series of Bently nevada vibration probe suddenly became zero. When probe is dismantled troubleshoot carried out it response good while interfacing with metal plate. Troubleshooting of proximitor carried out, it's found okay.

Again probe is mounted on turbine casing but response is not up to mark. regular fluctuation of vibration recorded.

pls provide any details for troubleshooting.

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Have you checked the three-wire, twisted, shield cable used to connect the proximitor to the monitor? Especially the shield drain wire to make sure it is grounded at one end only (by convention, at the monitor end)?

Please write back to let us know what you discover!
Measure voltage on 3300 monitor buffered outputs. It should be about -10Vdc. If not, adjust the gap voltage. Check extention cable and connector. Use contact spray in the junction between probe cable and extension cable. Check proximitor system length. Make sure probe+ext cable match the proximitor system length.

You can also put a logger or a multimeter on the buffered outputs in the front of the 3300 module, and log min/max voltage while you are bending the cable/connector to see if there is a bad connection. Measure AC voltage at the buffered output. It should match the scale factor marked on the proximitor.

Hopefully this will help you.


Already troubleshoot carried out. Gap voltage is -10V D.C is adjusted and probe taken in line, but high fluctuation in vibration reading seen.

Any suggestion pls let me know..
Thanks for the feedback; but it's incomplete.

It can only be:

1) A bad prox (proximity) probe (which you have eliminated)

2) A bad prox cable, between the prox probe and the proximitor (including too tight of a bend radius where the cable connects to either the prox probe or the proximitor) [Did the problem begin after the prox cable was replaced?]

3) A bad proximitor (including intermittent problems with the miniature screw-on connector)

4) A bad channel on the input card to B-N monitor (you can try exchanging two inputs to the card to see if the problem follows the probe or stays on the same input) [I think newer monitors have at least two inputs per card]

5) A bad three-wire, twisted shielded cable between the proximitor and the B-N monitor (which you don't seem to have troubleshot/eliminated), <b>OR</b> the cable is not the proper cable for the application (temperature; capacitance) [Have you meggared the cable between the proximitor and the B-N monitor input card?]

6) Electrical noise on the cable between the proximitor and the B-N monitor input card (because the shield drain wire is not terminated, or is not terminated properly) [Is three-wire, twisted, shielded cable used between the proximitor and the B-N monitor input card?]

Many of us have seen heat-induced problems on these cables--if the prox extension cable (the one between the prox probe and the proximitor) is run through a hot area. The insulation can be damaged, and only experience problems when it gets hot.

Just look at the entire circuit from the prox probe to the B-N monitor. If there are IS (Intrinsically Safe) barriers in the circuit between the proximitor and the B-N monitor input card, they could be bad or intermittent.

Please write back to let us know what you find!