Bently Nevada 330701-00-20-10-02-00 Proximity Probe – 3300 XL Series

Bently Nevada 330701-00-20-10-02-00: 8 mm Eddy-Current Proximity Probe with 5 m Integral Cable for Turbomachinery Shaft Monitoring

The Bently Nevada 330701-00-20-10-02-00 is an 8 mm diameter eddy-current proximity probe within the 3300 XL Proximity Transducer System, engineered for continuous, non-contact measurement of radial shaft displacement in critical rotating machinery. The probe operates by driving a high-frequency alternating current through a wound coil at the probe tip, generating a localized electromagnetic field. When a conductive target — typically a carbon steel or alloy steel shaft journal — enters this field, eddy currents are induced on the target surface. The resulting energy absorption loads the oscillator circuit inside the paired Proximitor® sensor, producing a DC output voltage that varies linearly with the air gap between probe face and shaft surface. The 330701-00-20-10-02-00 variant is factory-configured with a 5 m integral coaxial cable and an M10 × 1 threaded body, enabling direct installation into standard bearing housing probe bosses without adapter hardware.

Within a machinery protection architecture, this probe is positioned radially at the bearing journal — typically at the 45° X and Y orientations per API 670 — to capture the full shaft orbit. The analog DC output feeds directly into a Bently Nevada 3300 or 3500 series monitor, where the gap voltage is continuously compared against operator-defined alarm and danger setpoints. The probe’s calibrated measurement range of 0 to 2 mm (0 to 80 mil) and nominal sensitivity of 7.87 V/mm (200 mV/mil) provide sufficient resolution to detect shaft centerline shifts of less than 25 µm — a displacement magnitude that precedes bearing wipe events by a measurable margin in most turbomachinery failure sequences. Because the output is a continuous analog signal with no digital sampling delay, the monitor receives gap data with sub-millisecond latency, preserving the response speed required for machinery trip logic.

The probe body is machined from 316L stainless steel, selected for its corrosion resistance in environments exposed to turbine lube oil, seal gas condensate, and process fluid ingress. The 5 m integral cable uses a PTFE-jacketed coaxial construction, factory-terminated at both ends to maintain controlled impedance continuity from probe coil to Proximitor® input connector. This factory termination eliminates the field-spliced junction point that is a known source of impedance discontinuity and moisture ingress in retrofit installations using separate extension cables. The operating temperature range of −35 °C to +177 °C at the probe body covers the thermal envelope of the majority of steam turbine bearing housings, gas compressor seal areas, and pump bearing brackets without requiring thermal isolation standoffs.

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Technical Parameters

Hardware Logical Analysis

The probe coil of the 330701-00-20-10-02-00 is wound on a ferrite core and encapsulated in a thermally stable, low-outgassing epoxy compound. Ferrite core selection is critical: the material’s permeability must remain stable across the rated temperature range to prevent inductance drift that would shift the LC tank resonant frequency of the Proximitor® oscillator circuit. Bently Nevada specifies the coil inductance tolerance at ±0.5% across −35 °C to +177 °C, which constrains the scale factor error to within the API 670 allowable band without requiring temperature compensation circuitry in the monitor.

The 5 m integral cable is factory-matched to the probe coil as a calibrated assembly. The coaxial geometry maintains a characteristic impedance of approximately 50 Ω along the full cable length, suppressing common-mode noise pickup from variable-frequency drives, bus bars, and high-current motor windings that are common in turbomachinery installations. The PTFE jacket provides a dielectric constant of approximately 2.1, which is stable across the cable’s rated temperature range and does not contribute parasitic capacitance shifts that would detune the probe-driver resonant circuit. In contrast, field-assembled extension cable systems introduce a junction point where impedance discontinuity and moisture ingress can produce a systematic offset in the gap voltage output — a failure mode that is eliminated by the integral cable design.

The M10 × 1 thread pitch provides a mechanical resolution of 1 mm of axial probe travel per full rotation. At the probe’s nominal sensitivity of 7.87 V/mm, one full thread rotation changes the gap voltage by 7.87 V — a coarse adjustment that allows field technicians to set the initial gap to the −10 VDC center-of-range target within two to three rotations from the probe boss face. The 316L stainless steel body resists galling against the carbon steel or cast iron probe bosses used in most bearing housings, and the thread engagement length is sufficient to maintain probe axial position under the vibration acceleration levels encountered in turbomachinery bearing caps, typically up to 10 g broadband.

The probe’s EMC performance benefits from the coaxial cable’s outer shield, which is grounded at the Proximitor® sensor end only (single-point grounding). This topology prevents ground loop currents from flowing through the shield conductor, which would appear as a low-frequency noise component superimposed on the gap voltage signal. In installations near large transformers or switchgear, this single-point shield grounding scheme maintains signal integrity without requiring additional shielded conduit or ferrite chokes on the cable run.

System Integration Benefits

• Direct 3300 XL chain compatibility: Integrates without modification into existing 3300 XL transducer chains using 330130 series extension cables and 330180 Proximitor® sensors, preserving calibration traceability across the full measurement chain and eliminating recalibration after probe replacement.
• API 670 fifth-edition compliance: Satisfies the machinery protection standard mandated for critical rotating equipment in oil & gas, power generation, and petrochemical facilities, meeting insurance and regulatory audit requirements without supplementary certification work.
• Sub-millisecond output latency: The analog DC output carries no digital processing delay, delivering gap information to the monitor with response times below 1 ms — a requirement for machinery trip logic where delayed response directly increases the probability of mechanical damage during a bearing failure event.
• Elimination of contact-wear degradation: Non-contact measurement removes the mechanical wear mechanism that limits the service life of contact-type displacement sensors, maintaining calibration accuracy across multi-year maintenance intervals without scheduled replacement of the sensing element.
• Continuous gap voltage diagnostics: The DC output voltage serves as a real-time diagnostic channel for probe-to-shaft gap integrity. A gap voltage outside the −10 VDC ± 2 V nominal window indicates probe misalignment, shaft eccentricity, or probe coil failure — conditions distinguishable by their voltage signature without removing the probe from service.
• Thermal installation flexibility: The −35 °C to +177 °C probe body rating allows direct mounting in bearing housings across the full range of steam turbine, gas turbine, and centrifugal compressor operating temperatures without thermal standoffs or cooling provisions, reducing installation complexity and eliminating potential leak paths at standoff interfaces.
• Factory-terminated cable integrity: The integral 5 m cable removes the field-spliced junction point that is a documented source of impedance mismatch, moisture ingress, and measurement drift in retrofit installations, reducing maintenance call-outs attributable to transducer chain wiring faults.
• High-resolution early fault detection: At 7.87 V/mm sensitivity, the probe resolves shaft displacement changes below 0.1 mm within the monitor’s A/D conversion range, enabling alarm setpoints to be placed at 50–75% of the danger threshold and providing adequate warning time for controlled shutdown before bearing damage progresses to a catastrophic failure mode.
• Shaft orbit reconstruction: When deployed in orthogonal X-Y pairs per API 670, the two probe outputs allow the monitor to reconstruct the full shaft orbit ellipse in real time, providing diagnostic information on rotor unbalance, misalignment, and rub conditions that cannot be extracted from a single radial measurement channel.
• Broad target material compatibility: While calibrated for AISI 4140 alloy steel, the probe can be recalibrated for alternative target materials — including 17-4 PH stainless steel and Inconel 718 — using the Bently Nevada calibration procedure, extending applicability to high-alloy rotor shafts in aerospace-derivative gas turbines.

Quality Assurance & Global Logistics

Each Bently Nevada 330701-00-20-10-02-00 unit dispatched from our Xiamen, China facility is sourced through authorized Baker Hughes distribution channels with full lot traceability. Pre-shipment inspection covers four verification points: coil impedance measurement at 25 °C against OEM reference values, cable continuity and insulation resistance confirmation at 500 VDC, thread profile gauging to M10 × 1 tolerance, and visual inspection of the probe tip encapsulant for voids or surface damage. Units are individually packaged in anti-static foam inserts within sealed cartons, with original OEM labeling, lot number, and date code intact. Traceability documentation is archived and available upon request for quality audit purposes.

In-stock orders received before 15:00 CST are dispatched same business day from Xiamen. International express delivery via DHL Express, FedEx International Priority, or UPS Worldwide Express achieves 3–5 business day transit to major industrial hubs in Southeast Asia, the Middle East, Europe, and North America. Complete export documentation is provided with every shipment: commercial invoice, packing list, certificate of origin, and HS code 9031.80 tariff classification. A 12-month warranty against manufacturing defects is included from the date of shipment, with replacement unit or credit note issued upon confirmation of the defect condition through our technical review process.

Contact Information

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