Common Probe Installation Errors

Common Probe Installation Errors

1. Measurements for probe installation were not sufficient to allow for a proper fit. Probe or mounting must be redesigned.

2. External holes in the case were drilled at an angle that put the probe face too far to one side of the shaft center line resulting in uncalibrated, abnormally low peak to peak readings. Probe or mounting must be redesigned or rebuilt.

3. The probe was mounted over chrome plating, coupling hubs, or shrunk-on collars, resulting in erratic readings.

4. When an axial position probe is mounted at the opposite end of the rotor from the thrust bearing, very high thrust position changes occur that are unrelated to thrust bearing condition.

5. When probes are mounted in a bracket or housing and do not extend through the hole, a false “OK” indication results. This is a dangerous condition because all indications are that the probe is observing the shaft when it is not.

6. Insufficiently rigid probe mounting brackets, resulting in resonance within the frequency of interest and of large amplitude, Vibration readings are meaningless for protection service. Actual shaft vibration may be actually higher or lower than indicated.

7. Conduit attached to small probe body, putting excessive strain on the body. This results in eventual lead failure or broken probe.

8. Probe gapped at 25 mils (0.6 mm) because “there are 50 mils (1.3 mm) of linear range”. The linear range does not start a zero; it actually starts at 20 – 30 mils (0.5 to 0.8 mm) and them is linear for another 50 mils, for 3000 Series probes.

9. Insufficient mechanical protection of probe lead and extension cable, resulting in damage from normal work around the machine.

10. Poor oil seals in probe cable conduit, filling Proximitor housing with lube oil.

11. Screwing in probe with probe lead, resulting in a broken lead. The probe is constantly connected to extension cable so that gap can be set using voltage output as a guide, causing twist load on cable and breaking wires. Connector should be periodically disconnected and the twist load removed.

Note: Never mate connectors without first checking for contamination; clean with a mild solvent and compressed air.

12. Improper length of probe extension cables for particular probe lead length and Proximitor® type. This always results in uncalibrated readings, either too high or too low.

13. May probe cables coming from a common conduit with no identification, resulting in probe/Proximitor® cross-wiring.

14. Leads on internal probes not tied down, resulting in broken leads due to aerodynamic forces.

EXPLAIN RTD CONSTRUCTION AND TYPES OF RTD

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