Bently Nevada 330880-28-20-038-00-02 Proximity Transducer Assembly – 3300 XL PROXPAC

Bently Nevada 330880-28-20-038-00-02 — Factory-Calibrated PROXPAC XL Transducer System for Critical Rotating Machinery Protection

The 330880-28-20-038-00-02 is a complete, factory-matched PROXPAC XL proximity transducer assembly manufactured by Bently Nevada (Baker Hughes). It integrates a calibrated 8 mm eddy-current probe, a 5.0 m coaxial extension cable, and a dedicated proximitor driver into a single pre-configured unit. This architecture eliminates the field-calibration step that is mandatory when individual components are assembled on-site, reducing commissioning time and eliminating scale-factor mismatch errors that arise from mixing probe and proximitor lots.

Within the 3300 XL platform, this assembly is positioned as the primary sensing element for shaft radial vibration, axial position, and differential expansion measurement on critical turbomachinery — steam turbines, gas turbines, centrifugal compressors, and large pumps operating under API 670 machinery protection requirements. The PROXPAC XL designation indicates the extended-performance variant of the 3300 series, offering tighter linearity tolerance and a wider operating temperature envelope compared to the standard 3300 assembly.

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Technical Parameters

Hardware Logical Analysis

Eddy-Current Oscillator Circuit and Impedance Modulation
The probe tip houses a flat-wound coil driven by a Colpitts-type LC oscillator operating at approximately 1.0 MHz. When the conductive shaft surface enters the electromagnetic field, eddy currents are induced in the target material, extracting energy from the oscillator and reducing its tank circuit Q-factor. The proximitor’s demodulator circuit converts this amplitude and frequency shift into a DC voltage output. The 3300 XL platform uses a temperature-compensated demodulator stage that corrects for oscillator drift across the –35°C to +85°C proximitor operating range, maintaining scale factor accuracy within ±0.5% over the full thermal envelope.

Factory-Matched Calibration Chain
The PROXPAC XL assembly is calibrated as a three-component system. The probe coil inductance, extension cable capacitance, and proximitor input impedance are measured together on a calibration fixture using a target gap micrometer stage. The resulting scale factor (7.87 V/mm) is verified at five gap points across the linear range and recorded on the assembly’s calibration certificate. This matched-set approach eliminates the ±3–5% scale factor error that can accumulate when probe and proximitor from different production lots are paired in the field.

EMC Design and Shielding Architecture
The coaxial extension cable uses a double-braid shield construction with 95% optical coverage, terminated at both ends with 360° shield clamps inside the connector bodies. This configuration provides greater than 60 dB of common-mode rejection for conducted interference in the 50 Hz – 10 kHz band — the frequency range where variable-speed drive (VSD) switching noise and power-line harmonics are most problematic in turbomachinery installations. The proximitor housing incorporates a mu-metal inner shield around the demodulator PCB to attenuate radiated magnetic field interference from adjacent motor cables and bus bars.

Probe Tip Thermal Stability
The 8 mm probe tip is wound with a ceramic-coated coil former rated to 177°C continuous. The coil wire uses a high-temperature polyimide insulation system (Class H, 180°C rated) rather than the standard PTFE insulation used in lower-temperature variants. This allows direct installation in bearing housings adjacent to steam turbine exhaust stages where ambient temperatures routinely exceed 150°C, without requiring thermal standoffs or heat shields that would alter the probe-to-shaft gap geometry.

System Integration Benefits

• Zero-Calibration Installation: The factory-matched scale factor eliminates the need for a gap-voltage calibration procedure during installation. Technicians set the physical gap to the nominal 1.0 mm (–10.0 VDC output) and verify with a multimeter — no calibration fixture or software required on-site.
• Direct 3500 Monitor Rack Compatibility: The –2 VDC to –18 VDC output and 200 mV/mil scale factor are natively accepted by all Bently Nevada 3500 series monitor cards (3500/40M, 3500/42M, 3500/45, 3500/46M) without input conditioning or scaling adjustments.
• API 670 Compliance Out of the Box: The assembly meets API 670 5th Edition requirements for proximity transducer systems used in machinery protection, including linearity, frequency response, and temperature performance specifications. No additional documentation or field verification is required for API 670 compliance audits.
• Deterministic Signal Latency: The DC-coupled output path from probe to proximitor output introduces less than 50 µs of signal latency across the full 10 kHz bandwidth. This ensures that the 3500 monitor rack receives shaft position data with sufficient time resolution to trigger relay outputs within the 1 ms response time required by API 670 for overspeed and high-vibration trips.
• Diagnostic Transparency via Gap Voltage: The DC component of the output voltage directly encodes the mean probe-to-shaft gap. Operators can monitor gap voltage trend over time to detect bearing wear (decreasing gap), shaft bow (oscillating gap at 1× running speed), and probe fouling (erratic gap voltage) without additional instrumentation — the output itself is the diagnostic signal.
• Wide Supply Voltage Tolerance: The –20 VDC to –26 VDC operating range accommodates voltage drop across long cable runs (up to 300 m with appropriate cable gauge) and power supply regulation variations in distributed control system (DCS) marshalling cabinets, without affecting scale factor accuracy.
• Non-Contacting Operation Eliminates Maintenance Intervals: Unlike contact-type displacement sensors (LVDTs, potentiometers), the eddy-current probe has no moving parts and no wear mechanism. Mean time between failures (MTBF) for the probe assembly exceeds 100,000 hours in clean industrial environments, reducing planned maintenance outage requirements.
• Drop-In OEM Replacement: The 330880-28-20-038-00-02 is dimensionally and electrically identical to the original OEM-installed assembly in 3300 XL-equipped machinery. Replacement requires only physical probe removal, cable disconnection at the proximitor terminal block, and reinstallation — no software reconfiguration of the monitor rack is needed.
• Hazardous Area Suitability: FM and CSA certifications (where applicable to the specific variant) permit installation in Class I, Division 2 (Groups A, B, C, D) hazardous locations, covering the majority of petrochemical and LNG plant environments where turbomachinery is deployed.
• Traceability for Critical Plant Documentation: Each PROXPAC XL assembly carries a unique serial number traceable to its calibration record. This supports plant asset management systems (SAP PM, Maximo) and satisfies functional safety documentation requirements under IEC 61511 for SIL-rated protection loops.

Quality Assurance & Global Logistics

Every 330880-28-20-038-00-02 unit dispatched from our Xiamen facility undergoes a structured pre-shipment inspection protocol. Physical inspection covers connector pin condition, cable jacket integrity, proximitor housing seal, and label legibility. Electrical verification includes supply current measurement at –24 VDC, output voltage check at a known gap reference, and cable continuity/insulation resistance test. Units that do not pass all inspection criteria are quarantined and not dispatched.

Original Bently Nevada / Baker Hughes part markings, serial numbers, and calibration labels are preserved intact. Traceability documentation — including calibration certificates and certificates of conformance — is available upon request and is provided as standard for orders destined for nuclear, offshore, or SIL-rated applications.

Packaging uses anti-static foam-lined cartons with desiccant packs and humidity indicator cards. For international shipments, units are double-boxed with shock-absorbing inner packaging rated to ISTA 2A transit testing standards. Express courier services (DHL Express, FedEx International Priority, UPS Worldwide Express) are used for standard orders, with typical transit times of 3–5 business days to Europe, North America, Southeast Asia, and the Middle East. Sea freight consolidation is available for bulk orders of 10 units or more.

All export documentation — commercial invoice, packing list, certificate of origin, and HS code declaration (9031.80.9090) — is prepared in compliance with Chinese customs export regulations and the import requirements of the destination country. Customers in countries requiring CITES, dual-use, or end-user certificate documentation should advise at the time of order placement.

Contact Information

Email: [email protected]
WhatsApp: +86 18359268345
Web: siemensplc.com
Location: Xiamen, China
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