Bently Nevada 3500/40M-01-01 125680-01
Bently Nevada 3500/40M-01-01 125680-01
Bently Nevada 3500/40M-01-01 125680-01
Bently Nevada 3500/40M-01-01 125680-01
Bently Nevada 3500/40M-01-01 125680-01

Bently Nevada 3500/40M-01-01 125680-01 | Machinery Speed Monitor Module & 3500 Monitoring System

  • Model: 3500/40M-01-01 125680-01
  • Alt. P/N: 3500/40M-01-01 (base config), 125680-01 (enhanced firmware variant)
  • Series: 3500 Monitoring System (Machinery Protection)
  • Type: Machinery Speed Monitor Module (4-Channel Processor)
  • Key Feature: 4 independent channels (speed/keyphasor), 0-50,000 RPM range, dual redundant inputs, 125680-01 enhanced overspeed logic
  • Primary Use: Monitoring rotational speed, detecting overspeed/underspeed, and providing phase reference for 3500-protected machinery
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Part number: Bently Nevada 3500/40M-01-01 125680-01
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Description

Key Technical Specifications​
  • Model Number: 3500/40M-01-01 125680-01
  • Manufacturer: Bently Nevada (Baker Hughes)
  • Channels: 4 independent (configurable for speed or keyphasor input)
  • Input Type: Magnetic pickups (variable reluctance), eddy current probes (Proximitor), TTL/CMOS digital pulses
  • Speed Range: 0-50,000 RPM (0-833 Hz at 60 pulses/rev)
  • Frequency Response: 0-10 kHz (covers full spectrum of speed transients)
  • Output Signal: Digital speed data (RPM, frequency) to 3500 framework; relay contacts for alarm/trip
  • Overspeed Detection: User-programmable thresholds (e.g., 110% of rated speed), 1ms response time
  • Supply Voltage: 24V DC (±10%, from 3500 rack power supply)
  • Operating Temperature: 0°C to +65°C (rack-mounted)
  • Electrical Isolation: 500Vrms (channel-to-rack, per IEC 60664-1)
  • Dimensions: 119mm x 25mm x 102mm (WxHxD, 3500 half-height slot)
  • Weight: 0.17kg

    Bently Nevada 3500/40M-01-01 125680-01

    Bently Nevada 3500/40M-01-01 125680-01

Field Application & Problem Solved​
In the field, rotational speed is the heartbeat of turbines, compressors, and generators—but inaccurate speed monitoring leads to nuisance trips or missed overspeed faults. Older single-channel modules can’t handle redundant inputs, and basic speed monitors lack the logic to distinguish transient spikes from true overspeed. This 4-channel module solves that by acting as the “speed brain” of the 3500 system. You’ll find it on steam turbines (tracking governor response), gas compressors (detecting surge-induced speed drops), or hydro generators (monitoring runaway risk). Its core value is redundancy and precision: dual inputs per channel (e.g., two magnetic pickups on a turbine shaft) eliminate single-point failures, while 1ms overspeed detection (faster than human reaction) prevents catastrophic failure. For example, in a refinery’s FCCU turbine, it caught a 5% overspeed caused by governor valve sticking—tripping the unit in 2ms, far quicker than the old electromechanical relay. The 125680-01 firmware adds adaptive filtering to ignore VFD-induced noise, cutting false trips by 80% in paper mills.
Installation & Maintenance Pitfalls (Expert Tips)​
  • Wrong Pickup Air Gap: Magnetic pickups need 0.5-1.5mm gap (per spec); eddy current probes need 1-2mm. Set too wide, and you lose signal at low speeds; too tight, and you risk rubbing. Use a non-ferrous feeler gauge—neversteel. I’ve seen a pump trip because someone used a steel gauge, magnetizing the pickup.
  • Ignoring Redundant Input Wiring: The 4 channels support dual inputs, but rookies wire both to the same pickup. Always use separate pickups for redundancy—e.g., one on the drive end, one on the non-drive end of a turbine. Label each input clearly (“Turbine Speed A/B”).
  • Shield Grounding Errors: Coaxial cables for magnetic pickups must have shields grounded only at the 3500 rack. Grounding at both ends creates 60Hz hum, which mimics a valid speed signal at 3600 RPM. Tape exposed shields with conductive tape near VFDs.
  • Skipping Overspeed Threshold Validation: The 125680-01 firmware allows dynamic threshold adjustment, but set it too close to rated speed (e.g., 105% instead of 110%) and you’ll get nuisance trips during load changes. Test thresholds with a portable tachometer (e.g., Fluke 820) under full load.
  • Neglecting Keyphasor Alignment: When using a channel for keyphasor (phase reference), ensure the pickup aligns with the shaft keyway. Misalignment >5° skews orbit plots—use a strobe light to verify TDC (top dead center) alignment.

    Bently Nevada 3500/40M-01-01 125680-01

    Bently Nevada 3500/40M-01-01 125680-01

Technical Deep Dive & Overview​
The 3500/40M-01-01 125680-01 is a 4-channel speed monitor for Bently’s 3500 Machinery Protection System. It acts as the “speed processor”: raw pulses from shaft-mounted pickups (magnetic/eddy current) are amplified, filtered (to remove EMI), and counted by internal microcontrollers. For speed measurement, it calculates RPM by dividing pulse frequency by the number of pulses per revolution (user-configurable). For overspeed protection, it compares real-time RPM to user-defined thresholds—if exceeded, it triggers relay contacts (trip/alarm) in <1ms. The 125680-01 firmware enhances this with adaptive noise filtering (ignores VFD harmonics) and dual-redundant input voting (if one input fails, the other takes over). It pairs with 3500/25 (keyphasor) and 3500/42M (vibration) modules to provide a complete machine health picture. In short, it’s the “guardian” of rotational speed—fast enough to stop a disaster, smart enough to avoid false alarms.

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