Bently Nevada 3500/33 | 16‑Channel Relay Module

Bently Nevada 3500/33 16‑Channel Relay Module (149986‑01) – Alarm & Trip Outputs for API‑670 Machine Protection Racks

The Bently Nevada 3500/33 is a 16‑channel relay output module used to drive alarms, interlocks, and shutdown circuits from a 3500 protection rack. It’s typically chosen when you need flexible, highly reliable relay logic that follows machine‑protection events—Alert, Danger, Not‑OK—without extra external logic hardware. From my experience, it’s a straightforward way to tie your 3500 measurements into plant ESDs, PLCs, annunciators, and trip solenoids with clean, configurable behavior.

Key Features

• 16 configurable relay outputs – Each channel typically provides an isolated dry contact to drive alarms, trips, or interlocks.
• Alarm Drive Logic (ADL) – Flexible logic lets you combine multiple conditions (e.g., AND/OR of Alert, Danger, Not‑OK) to control each relay.
• Latching and voting options – Supports latching/non‑latching behavior, with 2‑out‑of‑3 voting when used in TMR rack configurations.
• Fail‑safe behavior – Relays can be set to energize or de‑energize on alarm; many sites prefer de‑energized on fault/power loss for safety.
• Backplane integration – Communicates over the 3500 backplane; no external power needed and configuration is handled via the rack interface (TDI).
• Front module + rear I/O design – The rear I/O module handles field terminations, so swapping the front card rarely requires rewiring.
• System‑wide status visibility – Relay and channel status appear at the rack display and in software, which simplifies proof testing and audits.

Technical Specifications

Application Fields

You might notice the 3500/33 in places where relay reliability really matters. Typical deployments include:

• Gas/steam turbines and large compressors – trip interlocks, fuel shutoff, and vibration‑based danger trips
• Pumps, fans, and expanders – annunciation of Alert/Danger states and permissives for startup sequences
• Generators and big motors – integration to DCS/PLC DI points for alarms, run inhibiting, and emergency stops
• Refining, petrochemical, and pipeline stations – tie‑ins to ESD/ESDVs and plant alarm panels for API‑670 compliance

Advantages & Value

• Reliability first – Proven 3500 architecture, with options to use fail‑safe and voting logic to reduce nuisance trips.
• Compatibility – Works natively with any 3500 monitor module; typically no external interposing relays for standard DI/annunciator loads.
• Lower wiring effort – Rear I/O terminations keep cabinet wiring tidy and make module replacement fast.
• Audit‑friendly – Clear status indication and logic documentation help during Functional Safety or API‑670 proof tests.
• Lifecycle support – Spares and field know‑how are widely available, which seems to keep ownership costs predictable.

Quick customer note from a turnaround last spring: “We mapped four danger conditions into a single 2oo3‑voted trip on the 3500/33. Proof testing went smoother than expected, and we cut false trips to near zero.”

Installation & Maintenance

• Cabinet environment – Mount in a 3500 rack within a clean, ventilated control cabinet. Keep ambient within the rack’s rating and allow front/rear service access.
• Wiring practices – Use appropriately rated field wiring to the relay contacts. For inductive loads (solenoids, relays), add snubbers or flyback diodes to protect contacts and reduce EMI.
• Grounding & segregation – Separate relay wiring from low‑level sensor cables where possible; bond shields at a single point to avoid loops.
• Commissioning – Verify Alarm Drive Logic, latching behavior, and fail‑safe settings. Perform a proof test of each relay to confirm contact operation and DCS/PLC indication.
• Routine care – Periodically actuate relays during planned outages, check terminal tightness, and review event logs for nuisance alarms. Firmware alignment with the rack/TDI is recommended.
• Spare strategy – Keeping a spare front 3500/33 and its matching rear I/O (e.g., 149986‑01 variant) typically shortens MTTR.

Quality & Certifications

• CE and UL/cUL compliance for 3500 series modules (region dependent)
• RoHS conformity for electronic assemblies in most markets
• Manufactured under ISO 9001 quality systems
• Typical manufacturer warranty: 1 year; extended coverage available in many cases

If you’re matching an existing rack, share the full module options and I/O part number so we can confirm exact compatibility—relay type and terminal style can vary slightly by 149986‑xx variant.