Bently Nevada 3500/33-01-01 – Dual Speed/Acceleration Monitor for Critical Machinery Protection

The 3500/33-01-01 is a two-channel Speed/Acceleration monitor designed for the Bently Nevada 3500 machinery protection system. It continuously measures shaft speed and/or casing acceleration, generates alarms when limits are exceeded, and feeds key condition data to the rack—typically used on turbines, compressors, fans, and large pumps.    You might notice it’s sometimes mislabeled as a “relay module”; to be precise, the 3500/33 does not include relays—alarm relays are handled by separate modules in the 3500 rack.

From my experience, plants choose the 3500/33-01-01 when they need dependable speed and acceleration monitoring in a single module with clean integration to the rest of the 3500 system. It’s typically paired with proximity probes or magnetic pickups for speed, and industrial accelerometers for casing vibration, offering alert/danger setpoints per channel and buffered outputs for diagnostics.

• Dual independent channels (speed/acceleration) – Monitor two measurements simultaneously with separate alert and danger setpoints.

• Flexible sensor compatibility – Works with magnetic pickups or proximity probes for speed, and industrial accelerometers for acceleration (depending on I/O option set).

• Buffered transducer outputs – Quick connection for portable data collectors and troubleshooting without disturbing the process signal.

• 4–20 mA proportional outputs (when optioned) – In many cases used for PLC/DCS trending or as an easy handoff to process systems.

• Tight integration with 3500 rack logic – Alarm voting, events, and relay drive via dedicated relay modules (e.g., 3500/32M or 3500/34 for TMR strategies).

• Field-replaceable card + rear I/O – Front module swaps without disturbing field wiring on the rear I/O, which maintenance teams really appreciate during turnarounds.

• Configuration via 3500 software – Clear setup of scale factors, filtering, and setpoints; seems to be straightforward for most instrument technicians.

This model is typically deployed on:

• Steam and gas turbines – speed supervision and casing acceleration alarms during start-up and load changes.

• Centrifugal compressors – speed tracking with acceleration monitoring to catch foundation or piping-induced issues.

• Large fans and blowers – detecting resonance zones and high-speed vibration onset.

• Critical pumps – monitoring for cavitation-induced acceleration spikes and speed anomalies.

A maintenance lead at a refinery told me they upgraded to the 3500/33-01-01 to add acceleration-based alarms on a combustion air fan. In many cases, that earlier warning bought them extra minutes to avoid a forced outage.

• Reliability in harsh environments – Proven 3500 platform; seems to be the go-to in many plants for continuous protection.

• System compatibility – Drops into existing 3500 racks; data shared to DCS/PLC through the rack gateway without bolt-on converters.

• Lifecycle cost control – Reuse existing probes and wiring in most cases; simplified spares strategy across the 3500 family.

• Scalable architecture – Pair with 3500/32M or 3500/34 relay modules for trip logic; add more monitor cards as assets grow.

• Support and documentation – Clear configuration tools and widely available field knowledge reduce commissioning time.

• Cabinet standards – Install the 3500 rack in a clean, ventilated cabinet; allow front access for modules and rear access for I/O terminations.

• Wiring practices – Use shielded cables for sensor runs; ground shields at one end; route separately from high-voltage lines.

• Power and grounding – Stable DC supply to the rack and a low-impedance ground improve noise performance, especially on accelerometer inputs.

• Configuration checks – Verify scale factors, filtering, and alarm setpoints against machine operating ranges; review startup/shutdown speed profiles.

• Routine care – Periodically verify sensor bias/health, clean terminals, and back up configuration files; keep module firmware aligned with rack revision guidelines.

• Spare strategy – Keeping one 3500/33-01-01 and its matching I/O in spares is, in most cases, sufficient for multi-train sites.

• Conformity typically includes CE and UL/cUL; many configurations meet RoHS.

• Hazardous area approvals (such as ATEX/IECEx Zone 2) are common for the 3500 platform, depending on exact build options.

• Manufacturer’s standard warranty applies (commonly one year); extended service and calibration support available.

Note: 3500/33-01-01 is a dual Speed/Acceleration monitor. If you specifically need relay outputs, consider adding a 3500/32M or 3500/34 relay module in the rack.