Bently Nevada 330705-02-18-90-02-00 Proximity Probe – 3300 XL Series

Bently Nevada 330705-02-18-90-02-00: 11 mm Reverse Mount Eddy Current Probe in the 3300 XL Machinery Protection Chain

Within a continuous-process plant, the proximity probe is the first transducer in a machinery protection chain — it converts shaft displacement into a voltage signal that every downstream monitor, trip relay, and historian depends on. The Bently Nevada 330705-02-18-90-02-00 occupies that position in the 3300 XL measurement system. It is an 11 mm tip-diameter, reverse-mount eddy current probe engineered for radial vibration and shaft position measurement on rotating machinery governed by API 670 requirements. Its reverse-mount geometry — connector at the sensing end rather than the cable end — solves a specific mechanical constraint: bearing housings where the probe must be inserted from the non-drive side, a configuration common in single-stage overhung centrifugal pumps, certain steam turbine bearing pedestals, and compact gearbox assemblies where axial access to the standard probe port is obstructed by adjacent piping or structural steel.

The 3300 XL platform to which this probe belongs operates on a three-component measurement chain: probe, extension cable, and proximitor (driver/signal conditioner). The 330705-02-18-90-02-00 is the sensing element of that chain. Its 11 mm coil geometry defines the linear measurement range — nominally 0.25 mm to 2.26 mm gap (10 mil to 89 mil) against a standard AISI 4140 steel target — and its output sensitivity of −7.87 V/mm (−200 mV/mil) is the calibration constant that the 3300 XL proximitor uses to convert raw oscillator frequency shift into a calibrated DC voltage proportional to gap distance. This voltage is then read by the 3500 Series monitor rack, which applies alarm and trip setpoints per the machinery protection philosophy document.

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Technical Parameters

Hardware Logical Analysis

The eddy current probe operates on Faraday’s law of electromagnetic induction. The probe coil, driven by the 3300 XL proximitor oscillator at approximately 1.0 MHz, generates a high-frequency alternating magnetic field that penetrates the conductive target surface. As the target approaches the probe tip, eddy currents induced in the target surface increase in magnitude, loading the oscillator circuit and reducing its oscillation amplitude. The proximitor’s demodulation circuit converts this amplitude change into a DC voltage output linearly proportional to the probe-to-target gap. The 11 mm coil diameter of the 330705-02-18-90-02-00 is a deliberate design choice: it provides a field penetration depth sufficient to resolve shaft surface irregularities at frequencies up to 10 kHz — adequate for machinery running at speeds up to 600,000 CPM (10,000 Hz) — while maintaining a compact enough footprint to fit within the bearing housing bore constraints typical of API 610 pump designs.

The reverse-mount mechanical architecture inverts the standard probe body orientation. In a conventional probe, the integral cable exits from the back of the probe body, and the sensing tip faces the target. In the 330705-02-18-90-02-00, the coaxial connector exits from the sensing-tip end, and the probe body is threaded into the housing from the opposite direction. This allows the probe to be installed through a radial port that opens toward the non-drive end of the machine, with the cable routed away from the bearing housing without crossing the shaft centerline plane — a routing constraint that is critical in hazardous area installations where cable routing paths are fixed by conduit infrastructure.

EMC performance is achieved through the coaxial cable construction: the integral cable uses a double-shielded coaxial geometry with a characteristic impedance matched to the 3300 XL proximitor input. This minimizes signal reflection and common-mode noise pickup in environments with high electromagnetic interference from variable-frequency drives, large motor starters, and bus-bar switching transients — all common in the same electrical rooms that house machinery protection panels. The probe body itself is constructed from 316 stainless steel, providing corrosion resistance in wet gas, sour service, and high-humidity environments without introducing ferromagnetic material that would distort the probe’s magnetic field geometry.

System Integration Benefits

• Direct 3300 XL Chain Compatibility: The 330705-02-18-90-02-00 is factory-calibrated as part of the 3300 XL system. When paired with the correct 3300 XL extension cable and proximitor, the combined measurement chain meets the ±1% full-scale accuracy specification without field recalibration — reducing commissioning time on new installations.
• 3500 Series Monitor Integration: The −7.87 V/mm output scale factor is natively recognized by Bently Nevada 3500/40M, 3500/42M, and 3500/45 monitor modules. Alarm and trip setpoints entered in engineering units (µm or mil) are automatically converted by the monitor firmware — no manual scale factor entry required.
• Deterministic Frequency Response: The 1.0 MHz oscillator frequency provides a flat frequency response from DC to 10 kHz, ensuring that both static shaft position (DC gap) and dynamic vibration components (AC gap variation) are captured with equal fidelity. This is essential for machinery protection systems that must simultaneously monitor 1× running speed vibration and slow-roll shaft bow.
• Hazardous Area Deployment: The probe is compatible with Bently Nevada Zener barriers and galvanic isolators approved for use in Zone 1 / Division 1 hazardous areas. The reverse-mount cable routing simplifies conduit sealing at the bearing housing penetration point, a requirement under IEC 60079-14 for Ex d installations.
• Diagnostic Transparency via Gap Voltage Monitoring: The DC gap voltage output provides a continuous, real-time diagnostic channel. A shift in DC gap voltage at constant speed indicates shaft centerline migration — an early indicator of bearing wear, thermal growth, or misalignment — before vibration amplitude alarms are reached. This extends the diagnostic window available to maintenance engineers.
• Reduced Mechanical Interference: Non-contact eddy current measurement eliminates the mechanical loading effect that contact-type displacement sensors impose on the shaft. At shaft speeds above 3,000 RPM, even a 1 g contact force from a mechanical probe introduces measurable synchronous vibration — the 330705-02-18-90-02-00 imposes zero mechanical load on the rotating element.
• Long-Term Calibration Stability: The probe coil is encapsulated in a thermally stable epoxy compound within the stainless steel body. Thermal cycling between −35 °C and +177 °C produces less than 0.5% sensitivity drift over the probe’s service life, maintaining measurement accuracy without periodic recalibration in most API 670 applications.
• Interchangeability Within the 3300 XL Ecosystem: The 330705-02-18-90-02-00 is a direct replacement for any failed 3300 XL 11 mm reverse-mount probe in an existing installation. No re-engineering of the signal conditioning chain, monitor configuration, or alarm setpoints is required — the replacement probe assumes the same calibration constants as the original, minimizing the time from probe failure to system restoration.

Quality Assurance & Global Logistics

Every unit of the Bently Nevada 330705-02-18-90-02-00 supplied by siemensplc.com is sourced through verified supply channels with full part traceability. Prior to dispatch, each probe undergoes a structured inspection protocol: visual examination of the probe tip surface for mechanical damage, connector pin inspection for corrosion or deformation, cable jacket inspection for abrasion or kinking, and label verification against the manufacturer’s part number format. Where test equipment is available, the probe oscillator loading characteristic is verified against the 3300 XL specification to confirm the coil is electrically intact.

Shipments originate from our warehouse in Xiamen, China — a major international logistics hub with direct air freight connections to Singapore, Dubai, Frankfurt, Los Angeles, and Houston. Standard export documentation includes a commercial invoice, packing list, and certificate of conformance. For customers requiring additional documentation — material test reports, country-of-origin certificates, or MSDS — these are prepared upon request prior to shipment. Typical air freight transit times are 3–7 business days to most destinations in Southeast Asia, the Middle East, and Europe; 5–10 business days to North and South America. DHL, FedEx, and UPS express services are available for time-critical requirements. All shipments are insured against transit loss and damage. A 12-month warranty covers manufacturing defects from the date of shipment.

Contact Information

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