Bently Nevada 3721 Vibration Monitoring Module Unit

Module Feature

3721 is a rack-mounted monitoring module of Bently Nevada 3700 series machinery protection system.

It receives signals from eddy current proximity probes, measures shaft radial vibration, axial position and gap voltage. It provides configurable alarm and danger relay outputs, and communicates data to host monitoring system. It conforms to API670 machinery protection standard. Widely stocked as spare for turbine, compressor and pump protection cabinet.

Working principle

The module supplies power to the eddy current probe and processes the high-frequency eddy signal.

It converts probe gap variation into vibration or position value. When the measured value exceeds preset threshold, the module triggers alarm or trip relay output, meanwhile uploads real-time data and fault events via backplane bus.

Onboard components

Probe signal conditioning circuit, A/D conversion chip, threshold logic circuit, relay output, backplane bus interface and printed circuit board assembly.

LED indicators

Front LEDs indicate power, OK, alarm and danger status.

Hardware self‑diagnosis

Built-in circuit monitors probe cable health, power supply and internal logic. Threshold and channel configuration are set via supporting software.

Programming software

Bently Nevada System 1, used for channel setup, alarm threshold configuration and historical data review.

Electrical & Process Parameters

Model: 3721 Brand: Bently Nevada Device type: Eddy current vibration and position monitor module Function: Shaft vibration and axial position measurement, alarm and trip output for rotating machinery

Mechanical & Structure

Mounting: Rack slot mounting inside 3700 series chassis Protection class: IP20 Housing: Printed circuit board with front panel

Environmental

Operating temperature: 0℃ ~ +60℃ Storage temperature: -40℃ ~ +85℃ Ambient humidity: 5~95% non‑condensing

Certification: CE Status: Original Bently Nevada monitoring spare

Installation

Cut off rack power before replacement.

Insert module into chassis slot, connect probe extension cable, configure alarm setpoints in System 1 software, verify probe gap and alarm action after commissioning.

Interface

Probe input terminal, backplane rack bus connector, alarm relay output terminal.

Diagnostic

Probe fault: Cable open/short circuit, tip damaged. Alarm false trigger: Gap voltage offset out of range. No communication: Backplane bus loose or module address error.

Product Brief

3721 module, Bently Nevada 3700 series rack vibration monitoring module spare for turbine and compressor shaft vibration and position protection replacement.