Bently Nevada 24701-33-05-00-025-04-02 Proximity Probe Housing – 3300 XL

Bently Nevada 24701-33-05-00-025-04-02 – Mechanical Anchor of the Eddy-Current Measurement Loop in API 670-Classified Machinery Protection Systems

Within a turbomachinery protection architecture, the measurement chain that governs trip decisions begins not at the monitor rack but at the physical interface between the probe tip and the rotating shaft. The Bently Nevada 24701-33-05-00-025-04-02 is the factory-integrated housing assembly that establishes and maintains that interface. It belongs to the 3300 XL Proximity Transducer System — a platform engineered to meet the full measurement uncertainty budget defined in API 670, 5th Edition, for radial vibration, axial position, and differential expansion monitoring on critical and essential rotating equipment.

The assembly integrates an 8 mm eddy-current probe tip, a 316 stainless steel housing body machined to OEM dimensional tolerances, and a 2.5 m integral coaxial cable terminated for direct connection to a Bently Nevada Proximitor driver. The integral cable construction is a deliberate design choice: field-assembled probe-to-extension-cable connectors are the statistically dominant failure point in eddy-current loops, accounting for a disproportionate share of spurious trips and nuisance alerts in long-term plant operation. By eliminating that connector junction, the 24701-33-05-00-025-04-02 removes a variable-impedance node from the signal path and reduces the probability of moisture-induced insulation degradation at the most mechanically stressed point of the assembly.

The housing is rated for continuous service from −35 °C to +177 °C, covering the full thermal envelope encountered in steam turbine bearing pedestals, hot-gas expander casings, and boiler feed pump bearing housings. The 316 SS alloy selection provides resistance to chloride-induced pitting and H₂S stress corrosion cracking, both of which are disqualifying failure modes for 304 SS or carbon steel housings in refinery and offshore applications. IP67 ingress protection prevents condensate and oil mist from penetrating the cable-to-probe junction during the thermal cycling that characterizes turbomachinery startup and shutdown sequences.

Real-time Stock & RFQ: [email protected] | WhatsApp: +86 18359268345

Technical Parameters

Hardware Logical Analysis

The 3300 XL eddy-current system operates on a 1.0 MHz carrier oscillator housed within the Proximitor driver. The oscillator energizes a multi-turn coil wound at the probe tip; the coil generates a toroidal electromagnetic field that penetrates the conductive target surface to a skin depth determined by the target material’s resistivity and magnetic permeability. For AISI 4140 steel shafts — the most common turbomachinery shaft material — the skin depth at 1.0 MHz is approximately 8 µm, meaning the eddy-current field interacts with a thin surface layer rather than the bulk material. This characteristic makes the measurement sensitive to shaft surface finish and any conductive contamination (oil film, metallic debris) at the gap, which is why API 670 specifies shaft surface roughness limits of Ra ≤ 0.8 µm in the probe observation zone.

The housing assembly’s bore-to-probe-tip coaxiality is held to ±0.05 mm by CNC turning operations at the OEM facility. This tolerance directly governs angular alignment between the probe face and the shaft surface. At a 5° misalignment angle, the cosine projection error is approximately 0.38% of the measured gap — within API 670’s ±1% system accuracy budget. At 10°, the error reaches 1.52%, consuming the entire accuracy budget before accounting for Proximitor gain tolerance, cable impedance variation, or target material deviation. The 3/8-24 UNF thread pitch of 0.042 in/turn (1.058 mm/turn) provides the axial resolution needed to set the 1.0 mm nominal gap in increments finer than 0.1 mm per 1/12 turn, enabling precise field adjustment without specialized tooling.

The 316 SS housing body provides a continuous conductive path from the probe cable braid to the machine casing ground stud, establishing a low-impedance common-mode rejection path for electromagnetic interference. In installations adjacent to variable-frequency drives (VFDs) with switching frequencies of 2–16 kHz, or near high-current bus bars carrying 50/60 Hz fundamental and harmonic content, this ground continuity suppresses common-mode noise pickup on the coaxial signal cable. Without it, interference appears as a superimposed AC component on the Proximitor DC output, which the 3500-series monitor interprets as shaft vibration — generating false alerts at frequencies unrelated to any mechanical phenomenon. The cable strain relief molded at the housing exit point prevents flexural fatigue at the coaxial cable’s outer braid-to-connector solder joint, a failure mode that produces intermittent open-circuit events manifesting as spike transients in the time-domain waveform — indistinguishable from actual impact events in automated diagnostic algorithms.

System Integration Benefits

• Zero-adapter installation: The 24701-33-05-00-025-04-02 threads directly into standard 3/8-24 UNF bearing housing bosses machined per Bently Nevada installation drawing 141536-01, eliminating adapter sleeves that introduce additional mechanical compliance and potential loosening under vibration.
• Calibrated output traceability: The factory-set 1.0 mm nominal gap and documented −7.87 V/mm sensitivity allow the 3500-series monitor’s engineering unit scaling to be configured from the datasheet without a site-specific calibration sweep, reducing commissioning time on multi-probe installations.
• Setpoint tightening capability: Elimination of housing-induced mechanical noise floor allows alert and danger setpoints to be positioned closer to the machinery’s normal vibration baseline — typically 25–50 µm closer than installations using field-assembled housings — improving early-warning detection of developing bearing defects.
• Maintenance gap repeatability: The documented thread pitch and jam-nut torque specification (per Bently Nevada procedure 141536-01) allow technicians to restore the original air gap after probe replacement without re-running a full calibration sweep, reducing planned maintenance duration.
• Connector-elimination reliability: Removing the probe-to-extension-cable field connector eliminates the highest-failure-rate component in the eddy-current loop, reducing the probability of connector oxidation, mechanical loosening under vibration, and moisture-induced insulation resistance degradation below the 100 MΩ threshold required for accurate measurement.
• IP67 moisture exclusion: Prevents condensate ingress at the cable-to-probe junction during thermal cycling in steam turbine bearing pedestals, where temperature differentials of 80–120 °C between startup and steady-state operation drive moisture migration into unprotected cable terminations.
• EMC ground continuity: 316 SS body provides a defined low-impedance ground path that suppresses VFD switching noise and power-frequency interference on the signal cable, maintaining the Proximitor output noise floor below the 25 mV RMS limit specified in API 670 for accurate vibration measurement.
• API 670 documentation compliance: OEM part number, material certification, and dimensional conformance documentation satisfy PSSR (Pre-Startup Safety Review) and insurance underwriter requirements for critical machinery classifications, streamlining regulatory sign-off on new installations and post-maintenance return-to-service.
• Broad platform compatibility: Electrically and mechanically compatible with the full 3300 XL 8 mm probe family and all 3500-series monitor input cards, protecting the investment in existing monitor infrastructure when replacing worn or damaged probe assemblies.

Quality Assurance & Global Logistics

Each 24701-33-05-00-025-04-02 unit shipped from our Xiamen, China operations center is sourced through Bently Nevada (Baker Hughes) authorized distribution channels and verified OEM surplus inventories with documented chain of custody. Pre-shipment inspection covers the following checkpoints:

• Thread gauge verification (3/8-24 UNF-2A GO/NO-GO) and probe tip standoff measurement against OEM drawing tolerances
• Coaxial cable insulation resistance test: ≥ 100 MΩ at 500 VDC between center conductor and outer braid
• Cable continuity check: center conductor resistance ≤ specified limit for 2.5 m cable length
• Visual inspection of housing bore surface finish, thread condition, cable jacket integrity, and connector pin condition
• Humidity indicator card confirmation: blue (≤ 30% RH) prior to moisture-barrier bag sealing
• Anti-static, moisture-barrier packaging with silica gel desiccant and foam-lined outer carton
• Certificate of Conformance (CoC) and itemized packing list included with every shipment

Outbound logistics from Xiamen are executed via DHL Express, FedEx International Priority, and UCP air freight. Typical transit times: 3–5 business days to Western Europe, 4–6 days to North America, 2–3 days to Southeast Asia and Japan. Export documentation — commercial invoice, packing list, HS 9031.80 classification, and origin declaration — is prepared in full compliance with Chinese customs regulations and destination-country import requirements. In-stock units ordered before 14:00 CST are eligible for same-day dispatch.

Contact Information

Email: [email protected]
WhatsApp: +86 18359268345
Web: siemensplc.com
Location: Xiamen, China
© 2026 siemensplc.com. All rights reserved.