Bently Nevada 3500/45 – Position Monitor for Axial Position, Differential Expansion, and Rod Position

The Bently Nevada 3500/45 Position Monitor (often written as 3500-45) is the go-to 4‑channel module for axial position, differential expansion (DE), rod position, and case expansion measurements in a 3500 rack. From my experience, it’s the cleanest way to bring proximity probe position signals into a machinery protection system—with dual alarm setpoints, OK status checking, 4–20 mA outputs per channel, and buffered transducer outputs for diagnostics. Plants typically use it on steam/gas turbines, large compressors, and reciprocating machines where precise positional trending protects bearings and rotors.

Key Features

• 4-channel position monitoring: Measures axial position, differential expansion, rod position, or case expansion—mapped per channel.
• Proximity probe based: Accepts Bently Nevada proximity transducers via the rack I/O; certain I/O options in the field also support DC linear position sensors for case expansion.
• Dual-setpoint protection: Per-channel Alert and Danger setpoints with OK/not‑OK logic for sensor and circuit health.
• 4–20 mA and buffered outputs: One 4–20 mA per channel for DCS/PLC, plus buffered transducer outputs (front BNC and rear terminal) for diagnostics and balancing.
• Tight rack integration: Alarms and events are shared over the backplane; trips are typically driven by 3500/32 or 3500/33 relay modules.
• Configuration over TDI: Set up via the 3500-22M TDI and engineering software—fast to clone across units, which helps during outages.

Technical Specifications

Application Fields

You’ll typically see the 3500/45 wherever position measurements drive protection or startup permissives:

• Steam turbines: differential expansion and thrust position to protect against rubs and thermal growth issues
• Gas turbines & generators: axial position monitoring tied to trip/permissive logic
• Reciprocating compressors: rod position tracking for rider band condition and early wear indication
• Large pumps and fans: case expansion or axial position trending during hot restarts

Advantages & Value

• Protection-grade accuracy: Purpose‑built for proximity‑based position signals; alarm logic is deterministic and easy to audit.
• Seamless compatibility: Native to the 3500 ecosystem—pairs cleanly with 3500/32 or 3500/33 relays and the 3500‑22M TDI.
• Lower installed cost: Integrated 4–20 mA and buffered outputs reduce external signal conditioning hardware.
• Maintenance friendly: Buffered outputs make it simple to verify transducer health without disturbing the protection path.

Installation & Maintenance

• Cabinet & environment: Mount the 3500 rack in a clean, ventilated enclosure; avoid condensation and corrosive atmospheres.
• Transducer wiring: Use Bently Nevada proximitor cabling and grounding practices; keep cable runs away from high‑noise power conductors.
• Alarm strategy: Configure Alert/Danger setpoints and OK logic to match site philosophy; map trips through 3500 relay modules.
• Safety: De‑energize the rack before inserting/removing modules; observe ESD precautions to protect the backplane.
• Routine care: Periodically verify 4–20 mA spans, review event logs, clean cabinet filters, and schedule firmware/config backups via the TDI.

Quality & Certifications

• CE marking for EMC and safety (3500 family)
• UL/cUL and CSA certifications are commonly available for 3500 modules
• RoHS conformity where applicable
• Manufacturer warranty is typically 12 months; we support a 365‑day warranty on supply