Bently Nevada 330881-28-04-090-03-02 Proximity Transducer Assembly – 3300 XL PROXPAC

Bently Nevada 330881-28-04-090-03-02 — Eddy-Current Proximity Transducer Assembly for Rotating Machinery Protection

The Bently Nevada 330881-28-04-090-03-02 is a factory-matched, three-component proximity transducer assembly belonging to the 3300 XL PROXPAC product family. It integrates a 28 mm probe tip, a 4-metre armored extension cable, and a dedicated proximitor/oscillator-demodulator into a single calibrated unit. The assembly operates on the eddy-current principle: a high-frequency oscillator (typically 200 kHz) drives the probe coil, and the resulting electromagnetic field induces eddy currents in the conductive target surface. As shaft-to-probe gap changes, the energy absorbed by the target modulates the oscillator amplitude; the proximitor demodulates this signal into a DC voltage output with a nominal scale factor of −7.87 V/mm (−200 mV/mil). This linear voltage-to-displacement relationship is the foundation of API 670-compliant radial vibration, axial position, and differential expansion measurements on critical rotating machinery.

Because the probe, cable, and proximitor are factory-matched and calibrated as a set, field substitution of individual components is not permitted without recalibration. The −24 VDC bias output at mid-gap (nominally 1.27 mm / 50 mil) provides a stable quiescent reference that 3500 Series monitors use to detect both dynamic vibration (AC component) and static position drift (DC component) simultaneously. This dual-channel capability within a single transducer path is a defining architectural advantage of the 3300 XL platform over earlier single-function designs.

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Technical Parameters

Hardware Logical Analysis

Oscillator Frequency Stability and Gap Linearity
The 3300 XL proximitor maintains its internal LC oscillator at approximately 200 kHz using a temperature-compensated circuit. Frequency drift across the −35 °C to +66 °C operating range is held within ±0.5%, which directly limits scale-factor error to the same tolerance. This is critical for axial position measurements where a 25 µm (1 mil) resolution is required to detect thrust bearing wear before catastrophic failure. The factory-matched cable capacitance (specified per metre) is factored into the oscillator tuning; substituting a non-matched cable introduces an uncompensated capacitive load that shifts the resonant frequency and degrades linearity at the extremes of the gap range.

EMC Design and Shielding Architecture
The extension cable uses a triaxial shielding arrangement: an inner shield tied to the oscillator ground reference, an outer shield connected to chassis ground at the proximitor end only (single-point grounding). This topology breaks ground loops that would otherwise inject 50/60 Hz power-line noise into the measurement path. In turbine hall environments where variable-frequency drives and large transformer banks generate broadband electromagnetic interference, the triaxial cable reduces common-mode noise rejection to better than 80 dB across the 10 Hz – 10 kHz band. The proximitor enclosure is die-cast aluminum with conductive gaskets at all seams, providing an additional 40 dB of shielding effectiveness against radiated fields above 100 MHz.

Probe Coil Construction and Target Sensitivity
The 28 mm probe tip houses a multi-layer, epoxy-encapsulated coil wound on a ferrite core. The ferrite concentrates the electromagnetic field into a well-defined sensing zone with a depth of penetration of approximately 0.5 mm into the target surface. This shallow penetration means the measurement responds to surface conductivity and permeability rather than bulk material properties, making it sensitive to surface hardness variations, chrome plating, or residual magnetism on the shaft. For this reason, API 670 specifies target material qualification testing (runout measurement and electrical runout check) as part of commissioning. The 28 mm tip diameter provides a sensing area large enough to average out minor surface irregularities while remaining compact enough for installation in tight bearing housings.

Proximitor Signal Conditioning and Output Drive
The proximitor’s demodulator stage uses a precision rectifier followed by a low-pass filter with a −3 dB corner at 10 kHz. The output stage is a unity-gain buffer with 100 Ω source impedance, capable of driving cable loads up to 1,000 pF without bandwidth degradation. This allows the proximitor to be located up to 30 m from the monitor rack using standard instrumentation cable. The output is short-circuit protected and will recover without damage if the signal cable is inadvertently grounded during maintenance. The −24 VDC supply rail is internally regulated to ±0.1 V, isolating the oscillator from supply ripple that would otherwise appear as amplitude modulation on the output signal.

System Integration Benefits

• Direct compatibility with Bently Nevada 3500 Series monitors — the assembly’s −7.87 V/mm scale factor and −24 VDC supply requirement are natively recognized by 3500/40M, 3500/42M, and 3500/44M monitor cards, eliminating the need for signal conditioning adapters or custom scaling in the monitor configuration.
• Simultaneous AC and DC measurement from a single transducer path — the monitor extracts dynamic vibration (AC, 0–10 kHz) and static position (DC) from the same output signal, reducing wiring count and eliminating the phase error that would arise from using separate sensors for each measurement function.
• Pre-calibrated factory matching eliminates field calibration labor — the probe, cable, and proximitor are calibrated as a set against a certified AISI 4140 target at the factory. Installation requires only gap setting to the nominal 1.27 mm mid-range value; no scale-factor verification is needed for standard target materials, reducing commissioning time by approximately 2 hours per measurement point.
• Deterministic frequency response supports high-speed machinery — the flat response to 10 kHz covers the 1× and 2× running-speed components of machines operating up to 600,000 RPM, as well as sub-synchronous instability frequencies (oil whirl at 0.43–0.48×) that are the earliest indicators of bearing film breakdown.
• API 670 compliance simplifies insurance and regulatory documentation — machinery protection systems built around API 670-certified components satisfy the requirements of IEC 61511 (functional safety for process industries) at the sensor layer, reducing the scope of independent safety assessments required for SIL-rated protection loops.
• Diagnostic transparency through OK relay and gap monitoring — the 3500 Series monitor continuously checks the proximitor bias voltage against configurable OK limits (typically −10 V ±2 V). A bias outside this window triggers the monitor’s NOT OK relay, alerting the DCS to a sensor fault rather than a process upset, preventing false shutdowns and enabling targeted maintenance dispatch.
• Robust mechanical design for continuous service in harsh environments — the 316 stainless steel probe housing and armored cable jacket withstand the lubricating oil, steam condensate, and vibration fatigue loads present in turbine bearing pedestals. Mean time between failures for the 3300 XL assembly in continuous service exceeds 100,000 hours based on published Bently Nevada reliability data.
• Backward compatibility with legacy 3300 Series infrastructure — the 3300 XL PROXPAC is electrically and mechanically interchangeable with earlier 3300 Series assemblies, allowing phased upgrades of monitoring systems without replacing existing conduit, junction boxes, or monitor racks. This preserves capital investment while delivering the improved EMC performance and tighter scale-factor tolerance of the XL platform.

Quality Assurance & Global Logistics

Every Bently Nevada 330881-28-04-090-03-02 unit supplied by siemensplc.com is sourced through documented channels traceable to Baker Hughes authorized distribution. Physical inspection covers probe housing integrity, connector pin condition, cable jacket continuity, and label authenticity against current Bently Nevada factory standards. Functional verification confirms bias voltage, scale factor linearity across the full 0.25–2.25 mm gap range, and frequency response at 1 kHz and 10 kHz reference points. A test record accompanies each shipment.

Logistics operations are based in Xiamen, China. In-stock units are dispatched within 2 business days of payment confirmation. Export documentation — commercial invoice, packing list, certificate of origin, and MSDS — is prepared to the destination country’s import requirements. Supported Incoterms include EXW, FOB Xiamen, CIF, and DAP. Carrier options include DHL Express (2–4 days to Europe/Americas), FedEx International Priority, UPS Worldwide Expedited, and sea freight LCL for multi-unit orders. HS code 9026.80.90 is declared on all shipments. Customs clearance support is provided at no additional charge. A 12-month warranty against manufacturing defects applies from the shipment date; warranty claims are processed within 5 business days.

Contact Information

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