Bently Nevada 128987-130-01-CN Proximity Sensor Probe – 3300 XL Series

Bently Nevada 128987-130-01-CN: Eddy Current Proximity Probe for Continuous Machinery Protection

The Bently Nevada 128987-130-01-CN is an 8 mm eddy current proximity probe with a 130-inch (3,302 mm) integral cable, engineered for non-contact displacement and vibration measurement on rotating machinery. Operating on the principle of electromagnetic induction, the probe generates a high-frequency oscillating magnetic field at its tip. When a conductive target enters this field, eddy currents are induced on the target surface, loading the oscillator circuit and producing a DC output voltage proportional to the gap distance. This physics-based measurement mechanism delivers sub-micron resolution without mechanical contact, eliminating wear-related drift over the service life of the installation.

Designed as a primary sensing element within the Bently Nevada 3300 XL and 3500 series machinery protection architecture, the 128987-130-01-CN operates as part of a three-component cable system: probe, extension cable, and driver/monitor. The total cable system length — probe plus extension — must equal the specified system length to maintain the factory-calibrated scale factor of 200 mV/mil (7.87 V/mm). Deviation from the specified total length introduces a proportional gain error that cannot be corrected at the monitor level without recalibration.

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Technical Parameters

Hardware Logical Analysis

The 128987-130-01-CN probe tip houses a precision-wound coil embedded in a thermally stable epoxy matrix. The coil forms the inductive element of a Colpitts-type oscillator circuit located in the driver module. At the probe tip, the oscillator operates at approximately 1.0 MHz, a frequency selected to balance penetration depth into the target material with sensitivity to surface-layer eddy current distribution. The 1 MHz carrier frequency limits eddy current skin depth to roughly 0.08 mm in AISI 4140 steel, ensuring that surface finish variations — rather than bulk material properties — dominate the measurement. This is a deliberate design constraint: it makes the probe sensitive to shaft surface condition and requires that target surfaces meet a minimum finish specification (typically Ra ≤ 0.8 µm) to achieve rated accuracy.

The 130-inch integral cable is a precision coaxial assembly with controlled characteristic impedance. The cable’s distributed capacitance is factored into the factory calibration; substituting a cable of different length or construction without recalibration will shift the oscillator operating point and alter the scale factor. The cable jacket is rated to the same −35°C to +177°C envelope as the probe body, allowing the assembly to traverse high-temperature zones between the probe mounting location and the junction box without thermal derating.

EMC performance is achieved through the coaxial cable shield, which provides continuous ground reference from the probe tip to the driver input. The shield is terminated at the driver end only (single-point grounding) to prevent ground loop currents from modulating the measurement signal. In installations with high common-mode electrical noise — such as variable-frequency drive environments — the single-point shield termination reduces noise coupling by 40–60 dB compared to double-ended shield grounding. The probe housing itself is electrically isolated from the machine casing via the non-conductive probe holder, preventing shaft-to-case ground currents from flowing through the measurement circuit.

The 316 stainless steel probe body provides corrosion resistance in wet or chemically aggressive environments, including steam turbine bearing pedestals exposed to condensate and lube oil mist. The M10 × 1.0 thread pitch allows fine axial adjustment of the probe gap during commissioning, with each full rotation advancing the probe 1.0 mm — equivalent to approximately 39.4 mil of gap change, or a −7.87 VDC shift in output at the nominal scale factor.

System Integration Benefits

• Direct 3300 XL / 3500 Series Compatibility: The 128987-130-01-CN is factory-calibrated to the Bently Nevada driver ecosystem. No field gain adjustment is required at commissioning; the monitor accepts the probe output directly and applies the stored scale factor for engineering-unit conversion.
• Deterministic Real-Time Response: The eddy current measurement chain has no moving parts and no mechanical resonance. The probe output tracks shaft displacement with a bandwidth exceeding 10 kHz, well above the frequency content of typical rotor vibration spectra (10 Hz – 2,000 Hz for most turbomachinery), ensuring no phase lag or amplitude attenuation within the measurement band.
• API 670 Alarm and Trip Setpoint Traceability: Because the scale factor is certified at the factory, alarm and trip setpoints entered in the monitor in engineering units (mil or µm) are directly traceable to the calibration certificate. This satisfies API 670 requirements for setpoint documentation without additional field verification.
• Diagnostic Transparency via Gap Voltage: The DC gap voltage provides a continuous, observable health indicator for the probe installation. A gap voltage outside the −10 VDC ± 2 VDC nominal range at the set gap indicates probe misalignment, target surface damage, or cable system fault — all diagnosable without removing the probe from service.
• Multi-Parameter Measurement from a Single Probe: A single 128987-130-01-CN installation simultaneously provides radial vibration (AC component), average shaft centerline position (DC component), and — when paired with a keyphasor — 1× and 2× synchronous vibration vectors. This eliminates the need for separate transducers for each parameter.
• DCS Integration via Standard Signal Conditioning: The −24 VDC / DC voltage output is compatible with standard signal conditioning modules that convert the probe output to 4–20 mA for DCS historian input. Verified compatibility with Emerson DeltaV, Honeywell Experion PKS, and ABB 800xA via appropriate I/O modules.
• Reduced Maintenance Interval: Non-contact operation eliminates the wear mechanisms that limit the service life of contact-type sensors. In continuous 24/7 service on baseload turbines, eddy current probes routinely achieve 8–10 year maintenance intervals, reducing planned outage frequency and associated labor costs.
• Redundant Monitoring Architecture Support: The probe output can be split to feed both a primary protection monitor and a condition monitoring system simultaneously, supporting 1oo2 or 2oo3 voting architectures without additional hardware. The high-impedance driver input does not load the probe circuit when multiple monitors are connected in parallel.

Quality Assurance & Global Logistics

Each 128987-130-01-CN unit supplied by siemensplc.com is sourced from authorized Bently Nevada (Baker Hughes) distribution channels or verified surplus inventory with full traceability documentation. Prior to shipment, every probe assembly undergoes bench verification of gap voltage at the nominal 50 mil gap and scale factor confirmation across the 0–90 mil linear range. Units that fall outside the ±1% scale factor tolerance are rejected and not offered for sale.

Calibration certificates referencing the specific unit serial number are available upon request and are provided in PDF format for inclusion in plant maintenance management systems (CMMS). OEM documentation — including the Bently Nevada installation drawing and system specification sheet — is supplied with each order to support as-built documentation requirements.

Packaging uses anti-static foam inserts within a rigid outer carton. The probe tip is protected by a machined plastic cap to prevent coil damage during transit. For international shipments, the carton is sealed with tamper-evident tape and includes a packing list with part number, serial number, and calibration reference.

Logistics operations are based in Xiamen, China. Standard export documentation — commercial invoice, packing list, and certificate of origin — is prepared for each shipment. DHL Express, FedEx International Priority, and UPS Worldwide Express are the primary carriers, with typical transit times of 3–5 business days to Europe, North America, and Southeast Asia. For time-critical requirements, same-day dispatch is available for orders confirmed before 14:00 CST. Freight forwarder coordination for sea freight consolidation is available for bulk orders exceeding 50 kg.

Contact Information

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