Bently Nevada 130944-01 128275-01F Proximitor Monitor Module – 3300 Series

Bently Nevada 130944-01 / 128275-01F: Two-Stage Eddy-Current Measurement Chain for API 670 Machinery Protection

The Bently Nevada 130944-01 monitor card paired with the 128275-01F Proximitor® signal conditioner forms a tightly coupled, two-component measurement chain engineered for non-contact shaft radial displacement, axial position, and eccentricity monitoring within the 3300 Series machinery protection platform. This assembly is a field-proven solution deployed across power generation turbines, centrifugal compressors, and petrochemical rotating equipment where API 670 compliance, relay determinism, and continuous diagnostic transparency are mandatory engineering requirements — not optional features.

The measurement architecture separates signal conditioning from threshold logic. The 128275-01F Proximitor® handles the analog front-end: it drives the eddy-current probe coil at a fixed oscillator frequency, demodulates the impedance-modulated return signal caused by shaft proximity variation, and outputs a calibrated DC voltage at a sensitivity of –200 mV/mil (–7.87 V/mm). This conditioned signal is then routed via shielded twisted-pair to the 130944-01 monitor card, which performs digital threshold comparison, relay actuation, 4–20 mA retransmission, and backplane data reporting — all within a single rack slot. The separation of conditioning and logic functions allows independent replacement of either component without disturbing the probe wiring or rack cabling, a significant maintenance advantage in live-plant environments where minimizing outage scope is operationally critical.

The –01F hardware revision of the Proximitor® incorporates enhanced EMI filtering on the oscillator drive circuit, specifically targeting conducted interference in the 2–20 kHz band generated by variable-frequency drives (VFDs) commonly co-located in compressor train motor control centers. Earlier –01A and –01C revisions exhibited measurable sensitivity drift under sustained VFD-coupled interference; the –01F revision resolves this through a multi-stage LC filter network at the probe cable interface, reducing susceptibility to <3% of the –01A baseline under equivalent interference conditions. Thermal stability of the sensitivity coefficient is also improved across the 0–65 °C operating range, reducing field recalibration frequency in installations subject to wide ambient temperature variation — a documented operational cost driver in outdoor compressor enclosures.

Within the 130944-01 monitor card’s signal processing path, the conditioned DC voltage from the Proximitor® is split into two parallel processing branches. The first branch applies a low-pass filter to extract the static DC component, representing average shaft centerline position — used for axial thrust position monitoring and slow-roll eccentricity measurement. The second branch applies a high-pass filter to extract the dynamic AC component, representing shaft vibration amplitude; a peak-to-peak detection circuit converts this to displacement in engineering units (mils or µm). Both branches feed independent comparator circuits that evaluate Alert and Danger thresholds stored in on-card non-volatile EEPROM. Threshold values are immune to power cycling — a critical reliability requirement for protection systems that may experience rack power interruptions during plant startup sequences.

The relay output architecture follows a de-energize-to-trip (DTT) fail-safe convention. The OK relay, Alert relay, and Danger relay coils are held energized during normal operation. Any threshold breach, internal card fault, loss of probe drive voltage, or power supply deviation de-energizes the relevant relay coil, driving the contact to the trip state without requiring an active command signal from the rack controller. This architecture ensures that a wiring fault, card failure, or power loss defaults to a protective action rather than a permissive state — a fundamental requirement for SIL 2-rated protection loops per IEC 61511.

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Technical Parameters

Hardware Logical Analysis

The 128275-01F Proximitor® operates as a self-contained analog signal conditioner. Its internal oscillator generates a fixed-frequency carrier signal — typically in the 1–2 MHz range for standard eddy-current probe systems — which is applied to the probe coil via a coaxial cable. As the conductive shaft surface approaches or recedes from the probe tip, the eddy-current losses in the shaft material modulate the probe coil’s effective impedance. The Proximitor® demodulates this impedance variation into a linear DC voltage output. The –01F revision’s oscillator circuit incorporates a temperature-compensated crystal reference, reducing frequency drift to <0.05% across the full operating temperature range — a measurable improvement over earlier revisions that used RC-based oscillators with temperature coefficients of approximately 200 ppm/°C.

The 130944-01 monitor card’s analog input stage includes a differential receiver with a common-mode rejection ratio (CMRR) of >80 dB at 50/60 Hz, providing effective rejection of ground-loop-induced noise on the Proximitor®-to-monitor cable run — a common interference mechanism in large rotating machinery installations where the probe mounting structure and the rack enclosure may be at different ground potentials due to stray currents in the machine baseplate.

The card’s dual-branch signal processing architecture — simultaneous DC position extraction and AC vibration extraction from a single probe channel — eliminates the need for separate position and vibration monitor cards for applications requiring both measurement variables. This reduces rack slot consumption by 50% compared to single-function monitor designs, a significant consideration in 3300 Series racks where slot count is fixed and expansion requires additional rack hardware.

The DTT relay coil drive circuit is powered from a dedicated internal supply rail, isolated from the measurement signal path. This isolation ensures that a fault in the analog measurement chain — such as an ADC overflow or filter coefficient error — does not prevent the relay from de-energizing. The relay coil current is continuously monitored by an internal watchdog circuit; loss of coil current below a defined threshold triggers an OK relay de-energization within one scan cycle, providing a hardware-level fault indication independent of the card’s firmware state.

System Integration Benefits

• Direct rack replacement without wiring changes: The 130944-01 is electrically and mechanically pin-compatible with the 3300 Series single-slot card guide. Replacement of a failed card requires no jumper changes, firmware updates, or field wiring modifications — reducing mean time to repair (MTTR) in live-plant environments.
• Simultaneous dual-variable measurement: A single 130944-01 card monitors both DC shaft position and AC vibration amplitude from one probe channel, halving the rack slot requirement versus single-function monitor architectures and reducing system BOM cost.
• Deterministic relay timing for API 670 compliance: The DTT relay architecture delivers a worst-case response time of <100 ms from threshold breach to contact state change, satisfying API 670 Section 5.3 relay timing requirements for Category A machinery protection.
• Native System 1 software integration: Backplane data transmission is natively compatible with Bently Nevada System 1 Evolution software, enabling real-time waveform display, alarm management, and long-term trend storage without protocol gateways or signal converters.
• Isolated 4–20 mA output for DCS integration: The isolated analog retransmission output connects directly to any DCS analog input card, providing continuous process variable data to the plant control layer independent of the protection relay state — supporting both monitoring and control functions from a single measurement source.
• Power-cycle-immune setpoint retention: Alert and Danger thresholds stored in on-card EEPROM are retained through power interruptions, eliminating the risk of protection gaps caused by setpoint reset to factory defaults following rack power cycling during plant startup.
• Redundant rack qualification: The module is qualified for 3300 Series redundant rack configurations, where dual monitor cards cross-check measurement values and arbitrate relay outputs — increasing protection system availability for API 670 Category A critical machinery.
• Hardware-level diagnostic transparency via OK relay: The dedicated OK relay provides a continuous hardware health signal. Internal faults — including probe drive voltage loss, ADC failure, or internal supply deviation — de-energize the OK relay without requiring software polling, providing an unambiguous fault indication to the plant DCS alarm system.
• EMI-hardened Proximitor® front-end: The –01F revision’s multi-stage LC filter network at the probe cable interface reduces susceptibility to VFD-coupled conducted interference, maintaining measurement accuracy in compressor train environments where VFD switching noise is a persistent signal integrity challenge.

Quality Assurance & Global Logistics

Every Bently Nevada 130944-01 / 128275-01F unit dispatched from our Xiamen, China facility undergoes a structured pre-shipment inspection protocol before release to logistics:

• Visual inspection of PCB assembly, edge connector pins, and front-panel indicators for physical damage, corrosion, or component displacement
• Board-level cleaning and conformal coating integrity verification under UV inspection
• Functional power-on verification: OK relay energization confirmed, analog output response within ±0.5% of nominal sensitivity
• Serial number and hardware revision cross-referenced against shipping documentation and part traceability records
• ESD-safe anti-static packaging with desiccant insert, foam-lined outer carton, and tamper-evident sealing for international transit

A Certificate of Conformance (CoC) is available on request for quality-critical procurement processes. Our 12-month warranty covers manufacturing defects and provides return-to-base repair or replacement at no charge within the warranty period.

International logistics from Xiamen are handled via DHL Express, FedEx International Priority, and UPS Worldwide Expedited, with typical transit times of 3–5 business days to Europe, North America, and Southeast Asia. Full export documentation — commercial invoice, packing list, and HS code declaration — is prepared for every shipment. Sea freight consolidation is available for bulk orders of 5 units or more upon request.

Contact Information

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