EMERSON PR9268/303-000 Vibration Transducer – Bently Nevada

EMERSON PR9268/303-000 Eddy-Current Proximity Transducer — Shaft Displacement Measurement in Machinery Protection Loops

The PR9268/303-000 is a non-contact eddy-current proximity transducer manufactured by EMERSON under the Bently Nevada product line. It is designed for continuous, real-time measurement of radial shaft displacement and axial position in rotating machinery protection systems. The transducer operates on the principle of electromagnetic induction: a high-frequency oscillating magnetic field generated at the probe tip induces eddy currents in the conductive target surface; the resulting impedance change is converted by the associated proximitor into a DC voltage proportional to the gap distance between probe tip and shaft surface.

In a typical machinery protection loop, the PR9268/303-000 occupies the field-sensing position within a three-component measurement chain: probe, extension cable, and proximitor. The probe tip diameter of 25 mm and the 5-metre integral cable assembly are matched to the PR9268 series proximitor (Bently Nevada 3300 XL or 3500 series), ensuring calibrated sensitivity of 7.87 V/mm (200 mV/mil) across the linear measurement range of 0 to 25 mm. This sensitivity figure is traceable to factory calibration and must not be assumed interchangeable with probes of different tip diameters or from alternative manufacturers without re-calibration of the full measurement chain.

The transducer body is machined from 316L stainless steel, providing resistance to corrosive process atmospheres including hydrogen sulphide, chlorine-bearing gases, and hydrocarbon condensates encountered in oil and gas and petrochemical service. The MIL-C-5015 series connector at the cable termination provides a positive-locking, environmentally sealed interface rated to IP67, preventing moisture ingress in outdoor or wash-down installations. The cable jacket is constructed from PTFE-insulated conductors within a braided stainless-steel shield, maintaining signal integrity in environments with high radiated electromagnetic interference from variable-frequency drives, large motor starters, and high-current bus bars.

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Technical Parameters

Hardware Logical Analysis

Electromagnetic Induction Measurement Principle: The PR9268/303-000 probe tip contains a wound coil driven by a radio-frequency oscillator within the proximitor at approximately 1 MHz. When the probe tip is positioned within the linear range of a conductive target (typically AISI 4140 or equivalent shaft steel), the oscillating field induces eddy currents in the target surface. These eddy currents create a counter-magnetic field that loads the oscillator circuit, reducing coil impedance. The proximitor demodulates this impedance change and outputs a calibrated DC voltage. The non-contact nature of this measurement eliminates bearing friction, mechanical hysteresis, and wear-related drift that would affect contact-type displacement sensors over time.

EMC Design and Shielding Architecture: The integral cable assembly uses a triaxial construction: the inner conductor carries the high-impedance probe signal, the intermediate shield is driven at the same potential as the inner conductor (guard drive), and the outer shield is grounded at the proximitor end only. This driven-guard topology eliminates capacitive leakage between the signal conductor and ground across the 5-metre cable run, preserving measurement accuracy in environments where cable routing passes near high-voltage conductors or switching power supplies. The braided stainless-steel outer shield provides attenuation of radiated interference exceeding 40 dB at frequencies up to 100 MHz, consistent with IEC 61000-4-3 Class A immunity requirements.

Thermal Stability and Gap Compensation: The probe coil assembly is wound on a ceramic former with a low thermal coefficient of expansion. The proximitor electronics include a temperature-compensation network that corrects for the small variation in coil inductance with temperature across the −35 °C to +120 °C operating range. This ensures that the 7.87 V/mm sensitivity figure remains within ±1% of nominal across the full thermal envelope, which is critical in steam turbine bearing housings where probe body temperatures can vary by 80 °C between cold start and full-load operation.

Target Material Dependency: The calibrated sensitivity of 7.87 V/mm applies specifically to AISI 4140 steel targets with a minimum surface conductivity and permeability matching the factory calibration standard. For non-standard target materials (e.g., titanium alloy shafts, Inconel sleeves, or stainless-steel journals), the effective sensitivity will deviate from the nominal value. In such installations, the full measurement chain must be re-calibrated using the actual target material to maintain API 670 accuracy requirements. This is a hardware-level constraint of all eddy-current proximity systems and is not specific to the PR9268 series.

System Integration Benefits

• Direct API 670 Compliance: The PR9268/303-000 is designed and calibrated to meet API 670 requirements for machinery protection instrumentation, enabling direct integration into safety-instrumented systems without additional field calibration when paired with the correct Bently Nevada proximitor and extension cable.
• Deterministic Real-Time Response: The eddy-current measurement chain has a frequency response flat to 10 kHz, providing deterministic, latency-free displacement data to the monitoring rack. This bandwidth is sufficient to capture sub-synchronous instability events, oil-whirl, and rub-impact transients in high-speed turbomachinery operating at up to 60,000 RPM.
• Plug-Compatible with 3500 Series Racks: The PR9268/303-000 is electrically and mechanically compatible with Bently Nevada 3500 series I/O modules, including the 3500/42M Proximitor/Seismic Monitor. No signal conditioning adapters or impedance-matching networks are required, reducing installation complexity and eliminating potential signal degradation points.
• Diagnostic Transparency via Gap Voltage Monitoring: The DC output voltage at the proximitor terminal block provides a direct, measurable indicator of probe-to-shaft gap. Maintenance personnel can verify probe installation gap (typically 1.0 mm, corresponding to −8 VDC) with a standard digital voltmeter without interrupting machine operation, enabling non-intrusive commissioning verification and periodic gap checks.
• Redundant Measurement Configurations: Two PR9268/303-000 probes mounted at 90° (X–Y configuration) on the same bearing journal provide orthogonal displacement vectors, enabling the monitoring system to compute shaft orbit plots. This dual-probe arrangement is the standard configuration for API 670 radial vibration monitoring and provides the data necessary for machinery diagnostics beyond simple amplitude alarming.
• Long Cable Runs Without Signal Degradation: The driven-guard cable construction maintains measurement accuracy over the 5-metre integral cable plus up to 9 metres of extension cable (PR9268/010-000 or PR9268/020-000), for a total system cable length of up to 14 metres. This accommodates installations where the proximitor must be located outside the hazardous area or in a remote junction box.
• Hazardous Area Suitability: The PR9268/303-000 is suitable for use in Zone 1 and Zone 2 hazardous areas when installed with an approved Zener barrier or galvanic isolator between the proximitor and the monitoring rack power supply. The intrinsically safe installation parameters are documented in the Bently Nevada system safety manual and are compatible with standard IEC 60079-11 entity concept calculations.
• Minimal Maintenance Burden: The non-contact measurement principle, sealed MIL-C-5015 connector, and 316L stainless-steel housing combine to produce a sensor with no wear components and no periodic calibration requirement under normal operating conditions. Scheduled maintenance is limited to visual inspection of the cable jacket and connector seating, reducing maintenance labour costs over the sensor service life.

Quality Assurance & Global Logistics

Every PR9268/303-000 unit supplied through siemensplc.com is sourced from verified supply channels with full traceability to EMERSON-authorised distribution. Each unit undergoes a structured incoming inspection protocol: physical examination of the probe body, cable jacket, and MIL-C-5015 connector for mechanical damage or non-conforming markings; electrical verification of coil resistance and insulation integrity; and functional output linearity check against a calibrated reference gap fixture. Units that do not meet the original EMERSON factory specification are rejected and not offered for sale.

Shipments originate from Xiamen, China, a major international logistics hub with direct access to DHL Express, FedEx International Priority, and UPS Worldwide Expedited services. In-stock units are dispatched within 1–3 business days of order confirmation. For time-critical plant shutdowns or emergency maintenance situations, same-day dispatch is available for orders confirmed before 14:00 CST. Commercial invoices, packing lists, and certificates of conformance are provided with every shipment to support customs clearance in all major import jurisdictions. HS Code 9026.80 applies to this product category for export classification purposes. Volume pricing and consolidated freight arrangements are available for orders of five or more units; contact the sales team for a proforma invoice.

Contact Information

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