The Bently Nevada 3500/50, also cataloged as the 3500/50 Tachometer Module, operates as a dedicated hardware component for rotor speed processing and overspeed protection within the 3500 Machinery Protection System. This module executes signal acquisition from proximity probes and magnetic pickups, performing frequency-to-voltage conversion to determine shaft rotative speed, rotor acceleration, and direction of rotation through real-time logic execution.

Module Configuration and Logic Mapping

• The 3500/50 provides two independent input channels for speed measurement.

• Internal Zener barriers facilitate direct connection to transducers located in hazardous zones without requiring external galvanic isolation hardware.

• Programmable alarm logic handles Zero Speed, Reverse Rotation, and Speed Band thresholds.

• Buffered transducer signals are routed through the I/O module for external diagnostic equipment connectivity.

Technical Performance Parameters

Signal Integrity and Rotor Dynamics

The 3500/50 module utilizes precision eddy-current probe scaling to ensure linear response across the input signal range. It monitors gap voltage validation against -10 VDC targets to confirm probe health and sensor-to-target distance. During signal acquisition, the module employs cross-talk suppression techniques to isolate inputs from electromagnetic interference, maintaining accurate rotor dynamics analysis. Input signals are processed through internal filtering to minimize noise, ensuring that speed measurements reflect the true mechanical state of the rotating machinery.

Package Contents

• 1 x 3500/50 Tachometer Module

• 1 x Discrete Internal Barrier I/O Module

• 1 x Installation and Configuration Manual

Mounting and Grounding Procedures

• Mount the module in any available slot of the 3500 Series rack, ensuring backplane connector engagement.

• Ensure that the I/O module is firmly secured to the rack rear chassis using the integrated thumb screws.

• Shielded cabling must be used for all transducer inputs; terminate shield drains at the designated I/O common ground lug.

• Verify that the internal barrier grounding bar is connected to a dedicated safety ground to maintain intrinsic safety compliance.

Technical Query Resolution

• Does the module support hot-swapping? Yes, the 3500/50 is designed for insertion and removal while the rack is powered without affecting adjacent modules.

• What is the purpose of the buffer outputs? The buffered outputs provide an unconditioned raw signal for use with external oscilloscopes or portable data collectors.

• Can the module be used with non-Bently Nevada transducers? While optimized for Bently Nevada sensors, it supports standard passive magnetic pickups within specified voltage ranges.

• How is the input signal filtered? The module applies programmable digital filters to eliminate high-frequency noise and jitter from the tachometer signal.

• Is external power required for the transducers? The module provides the necessary transducer excitation voltage internally for proximity probe operation.

• What happens during a power loss? The module maintains an internal fail-safe state, triggering loss-of-signal alarms to the rack interface module.

• Are the speed alarms latched? Alarms are user-configurable as latched or non-latched, depending on the specific machinery protection strategy.

• Does the firmware allow remote upgrades? Firmware updates are performed via the 3500 Configuration Software through the Rack Interface Module (RIM) connection.