Bently Nevada 125760-01 | 3500/33 16-Channel Relay Module | Obsolete Machinery Protection Spare Parts
Bently Nevada 125760-01 | 3500/33 16-Channel Relay Module | Obsolete Machinery Protection Spare Parts - Image 2
Bently Nevada 125760-01 | 3500/33 16-Channel Relay Module | Obsolete Machinery Protection Spare Parts - Image 3
Bently Nevada 125760-01 | 3500/33 16-Channel Relay Module | Obsolete Machinery Protection Spare Parts - Image 4

Bently Nevada 125760-01 | 3500/33 16-Channel Relay Module | Obsolete Machinery Protection Spare Parts

  • Model: 125760-01
  • Brand: Bently Nevada (a Baker Hughes company)
  • Core Function: 3500/33 16-Channel Relay Module – provides up to 16 independently configurable alarm relay outputs for the 3500 Machinery Protection System, used for annunciation, interlocks, and non-safety-critical shutdown signaling
  • Lifecycle Status: Obsolete (End-of-Life declared by Bently Nevada)
  • Procurement Risk: Very High – no longer manufactured; extremely limited availability on secondary markets; units often lack functional verification, calibration records, or firmware integrity checks
  • Critical Role: Serves as a high-density output interface for plant alarms, DCS integration, and auxiliary permissives; while typically not used for final safety shutdowns, its failure can compromise operator awareness, maintenance alerts, and process coordination—indirectly increasing operational risk
Category:

Description

Key Technical Specifications (For Spare Parts Verification)

  • Product Model: 3500/33 Relay Module
  • Bently Part Number: 125760-01
  • System Family: 3500 Machinery Protection System
  • Relay Channels: 16 independent electromechanical relays (Form A contacts: SPST normally open)
  • Contact Ratings:
    • 2 A @ 30 VDC (resistive load)
    • 0.5 A @ 125 VAC
    • Maximum switching voltage: 250 VAC / 125 VDC
  • Input Source: Receives alarm status from 3500 monitor modules (e.g., 3500/42M, /44M, /25) via backplane
  • Configuration: Each relay assignable to specific alarm conditions (Alert, Danger, OK-to-Run, etc.) using Rack Configuration Software (RCS)
  • Diagnostics: LED indicators per channel (energized/de-energized); module fault detection via backplane communication
  • Redundancy: Not redundant; intended for non-critical or annunciation-only functions
  • Form Factor: Full-height module (occupies one slot in 3500 rack)
  • Certification: Designed for use in API 670 systems; not recommended for SIL-rated safety shutdowns due to lack of contact feedback or voting architecture
  • Operating Temperature: 0°C to +65°C

System Role and Operational Impact

The 125760-01 (3500/33) is primarily deployed for high-channel-count alarm annunciation and auxiliary control in large rotating machinery applications, such as:

  • Sending vibration alerts to central control rooms
  • Activating local panel lamps or horns
  • Enabling/disabling auxiliary pumps or lubrication systems
  • Providing “machine healthy” signals to sequence controllers

Unlike the 3500/20 or 3500/53, the 3500/33 uses single-pole, normally open (Form A) relays without force-guided contacts, making it unsuitable for direct safety shutdown functions per IEC 61508. However, its reliability remains important because:

  • Loss of alarm signaling delays operator response
  • Missing permissive signals can cause process inefficiencies or startup failures
  • In complex plants, multiple 3500/33 modules may feed data historians or asset management systems

A failed 3500/33 does not typically cause immediate equipment damage but degrades situational awareness and maintenance responsiveness.

Reliability Analysis and Common Failure Modes

Despite industrial-grade construction, aging 125760-01 modules are prone to:

  • Contact wear or oxidation: High channel count increases cumulative switching cycles; low-current signaling loads can lead to film buildup, causing high contact resistance or intermittent opens.
  • Coil driver circuit failure: Semiconductor components degrade over time, especially under thermal stress, leading to stuck-open relays.
  • Backplane communication errors: Corrosion or vibration-induced loosening causes configuration mismatches or “ghost” relay states.
  • Power supply droop: Under full load (all 16 relays energized), internal regulation may sag, causing marginal relays to drop out.
  • EEPROM corruption: Rare, but possible after decades of service, resulting in incorrect alarm-to-relay mapping.

Design limitations include:

  • No contact supervision or weld detection
  • Lower current rating than 3500/20 or /53 modules
  • Higher density increases thermal load in confined racks

For preventive maintenance, technicians should:

  • Periodically verify continuity on critical annunciation circuits
  • Avoid using 3500/33 for inductive loads (e.g., solenoids) without external suppression
  • Monitor RCS logs for “Module Fault” or unexpected relay state changes
  • Ensure adequate ventilation in the 3500 rack to prevent thermal derating
BENTLY 125760-01

BENTLY 125760-01

Lifecycle Status and Migration Strategy

Bently Nevada has discontinued the 125760-01 as part of its focus on integrated digital communication (e.g., 3500/94 Enhanced Gateway) and reduced reliance on discrete relay modules for non-safety functions. The 3500/33 is no longer produced, and factory support is unavailable outside rare legacy agreements.

Continued use introduces risks:

  • Inability to replace failed units with verified spares
  • Growing difficulty integrating with modern control architectures (e.g., OPC UA, Ethernet/IP)
  • Increased maintenance burden due to aging electromechanical components

Interim Mitigation Measures

  • Source replacements only from Bently-authorized refurbishers who provide full channel-by-channel functional testing
  • Maintain at least one spare per major 3500 system
  • Where possible, migrate annunciation functions to digital protocols (Modbus TCP, OPC) via a 3500/92 or /94 gateway

Long-Term Strategy

Bently Nevada recommends:

  • Replacing legacy relay-based annunciation with System 1 v22+ APM dashboards and email/SMS alerting
  • Using the 3500/94 Enhanced Gateway to stream alarm states directly to DCS or cloud platforms
  • Reserving electromechanical relays only for hardwired safety or regulatory-mandated interfaces

While not a safety-critical component, the obsolescence of the 125760-01 erodes operational visibility and increases lifecycle costs. Proactive migration to digital communication reduces hardware dependency and enhances diagnostic agility—supporting long-term reliability and modernization goals.

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