Product Core Brief

• Model: 3500/50-03-GCN
• Brand: Bently Nevada (Baker Hughes)
• Series: 3500 Machinery Protection System
• Core Function: Dual-channel tachometer monitor providing precise speed, acceleration, and rotation direction measurement with integrated Keyphasor® routing.
• Product Type: Tachometer / Speed Monitor Module
• Key Specs: Dual Channel | Proximitor & Magnetic Pickup Inputs | Keyphasor® Output
• Condition: New Surplus / OEM Original

Key Technical Specifications

• Module Type: Tachometer Monitor
• Channel Count: 2 Independently Configurable Channels
• Supported Sensors: Proximitor® (Eddy Current) & Magnetic Pickups
• Measurement Parameters: Speed, Acceleration, Rotation Direction, Reverse Rotation
• Keyphasor® Feature: Generates and routes Keyphasor® signals to the backplane
• Peak Hold Function: Records max speed, max reverse speed, and reverse rotation counts
• Alarm Logic: User-programmable setpoints with Alert and Danger relays
• System Compatibility: 3500 M-Series Monitors, 3500/32 Relay Modules
• Configuration: 3500 Rack Configuration Software
• Suffix Note: “GCN” indicates regional/compliance variant

Product Introduction

Serving as the primary speed and phase reference for the 3500 Machinery Protection System, this Bently Nevada 3500/50-03-GCN accurately tracks rotor dynamics for turbines, compressors, and generators. It accepts both eddy current and magnetic pickup sensors, providing comprehensive speed monitoring and directional tracking in a single dual-channel module.

Beyond basic RPM tracking, this module acts as a system-wide phase reference by generating and distributing Keyphasor® signals across the backplane. This eliminates the need for a dedicated Keyphasor® module in smaller racks, reducing hardware costs while maintaining precise phase angle measurements for orbit plots and balancing diagnostics.

QA & Testing SOP

Speed monitors must be flawless before installation. We verify both the analog front-end and digital processing.

1. Anti-Counterfeit & Visual Audit: We inspect the Bently Nevada silkscreen, verify the GCN suffix, and check the front panel sensor connectors for bent pins or physical damage.
2. Backplane Enumeration Test: We install the module in an OEM 3500 test rack to verify it correctly enumerates and accepts configuration parameters via the 3500 Configuration Software.
3. Signal Injection Test: We inject calibrated Proximitor and magnetic pickup signals to verify the module accurately measures speed, acceleration, and direction within ±0.1% tolerance.
4. Keyphasor® Output Validation: We verify the module generates a clean Keyphasor® pulse and correctly routes it to the backplane for other monitors to consume.
5. ESD Safe Packaging: High-speed digital ICs are sensitive to electrostatic discharge. We pack these modules in anti-static shielding bags with desiccant to prevent latent damage.

Installation Pitfalls & Guide

❗ Sensor Type Mismatch: This module accepts both Proximitor and magnetic pickup sensors, but they are not interchangeable in software. Proximitor sensors require DC gap voltage verification (9.75V ± 0.2V), while magnetic pickups are AC-coupled. Misconfiguring the sensor type will result in erratic speed readings or complete signal loss.

❗ Keyphasor® Target Alignment: If using this module as the system Keyphasor® source, ensure the keyway or reflective tape on the rotor is properly aligned and the sensor gap is within specification. A weak or noisy Keyphasor® signal will corrupt phase angle measurements across the entire 3500 rack.

❗ Peak Hold Reset: The Peak Hold function records maximum speed events. After maintenance or overspeed testing, you must manually reset the Peak Hold values through the configuration software. Forgotten peak values can trigger false alarms during the next startup.

Replacement SOP:

1. Pre-Install: Document the current speed setpoints and Keyphasor® configuration; place the machine in bypass/maintenance mode.
2. Removal: Power down the 3500 rack; disconnect sensor wiring (label everything); remove mounting screws and extract the module.
3. Install: Slide the 3500/50-03-GCN into the designated slot, ensure firm backplane seating, and secure mounting screws.
4. Power-On Test: Power up the rack, download the configuration, verify sensor signals, and confirm DCS speed readings match expected values before removing bypass.

Technical FAQ

What does the “GCN” suffix mean, and is it compatible with my standard 3500/50?
The “GCN” suffix typically denotes a regional variant (often Greater China) or specific compliance marking. Functionally, it is identical to a standard 3500/50-03 and will work in any 3500 rack. However, always match the exact suffix when replacing a failed unit to avoid potential firmware or compliance discrepancies during an audit.

Can I use this module for overspeed protection?
Yes, but with caveats. The 3500/50 can trigger alarms and relay trips for overspeed conditions. However, for critical API 670 overspeed protection, Bently Nevada recommends using a dedicated 3500/53 Overspeed Detection module or redundant 3500/50 modules with 2oo2 voting. Always consult your safety integrity level (SIL) requirements.

Do I need a separate Keyphasor® module if I install this?
No. One of the key advantages of the 3500/50 is its built-in Keyphasor® generation and backplane routing. If you only need one Keyphasor® reference for your rack, this module eliminates the need for a dedicated 3500/25 Keyphasor® monitor.

What is the maximum speed this module can measure?
The 3500/50 can measure speeds up to 20 kHz (1,200,000 RPM equivalent for single-tooth targets). For typical industrial turbines and compressors running up to 15,000 RPM, this module provides more than adequate resolution and bandwidth.

Why is this sold as new surplus?
This unit was pulled from sealed OEM overstock or an unfulfilled project before installation. We test it on our OEM 3500 test racks to verify functionality, but we aren’t replacing internal components. You are getting unused factory silicon with original manufacturing tolerances at a fraction of the active OEM list price.

Need the matching 3300 XL Proximitor sensors or the 3500/53 Overspeed Detection module for your application? I can pull those up for you.