Description
BENTLY 3701/55 289761-01 — Seismic Velocity Transducer
Product: 3701/55, Seismic Velocity Transducer
Manufacturer: Bently Nevada (a Baker Hughes business)
Part Number: 289761-01
Primary Application: An industrial seismic velocity sensor for continuous monitoring of absolute casing/bearing housing vibration (in velocity units) on rotating machinery such as turbines, compressors, pumps, fans, and motors.
1. Core Overview
The Bently Nevada 3701/55 289761-01 is a passive, self-generating velocity transducer (seismoprobe). It measures the absolutevibrational velocity of machine casing or structure where it is mounted, as opposed to measuring relative shaft displacement.
Working Principle:
It operates on electromagnetic induction. The sensor contains a permanent magnet (seismic mass) suspended by springs within a coil. When the housing vibrates, the magnet tends to remain stationary due to inertia, creating relative motion between the magnet and coil, inducing a voltage proportional to vibrational velocity.
Key Output: Produces an AC voltage signal (mV or Volts) directly proportional to vibration velocity (e.g., mm/s, in/s). No external power is required for basic operation.
2. Key Features
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Self-Powered: Generates its own signal (2-wire system).
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Rugged Design: Built for harsh industrial environments (high temperature, moisture, vibration).
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Low-Impedance Output: Robust signal suitable for long cable runs.
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Integral Cable: Permanently attached armored cable.
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Broad Frequency Range: Effective from ~4.5 Hz to 1000 Hz, suitable for monitoring rotational speeds and common fault frequencies.
3. Model Number Breakdown & Specifications
Common Technical Specifications (Typical for 3701/55):
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Sensitivity: 100 mV/in/s (±5%) @ 100 Hz (~4 mV/mm/s). Exact value is on the specific calibration sheet for 289761-01.
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Frequency Response: 4.5 Hz to 1000 Hz (±3 dB).
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Measurement Range: Up to 2.0 in/s peak (51 mm/s peak).
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Phase Response: Linear within specified range.
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Operating Temperature: Up to 125°C (257°F) for sensor body.
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Mounting: ¼-28 UNF or M6 x 1.0 threaded stud.
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Connector: Integral cable with MIL-C-5015 or BNC connector (specific type defined by suffix).
4. System Integration
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Connection: Directly connects to vibration monitor/conditioning module (e.g., Bently Nevada 3300, 3500 systems).
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Signal Path: Machine Vibration → 3701/55 Transducer → Velocity Signal → Monitor Input.
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Conditioning: Monitor may integrate velocity signal to produce displacement readings.
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Mounting: Must be securely mounted on clean, flat, unpainted surface in desired direction (vertical/horizontal/axial).
5. Typical Applications
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Casing Vibration Monitoring: Primary method for machines with rolling element bearings (motors, pumps, fans, gearboxes).
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Low-Medium Speed Machinery: Suitable for machinery with fundamental running speed above ~300 RPM.
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General Machinery Protection: Detects unbalance, misalignment, looseness via horizontal/vertical pairs on bearing housings.
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Supplemental Monitoring: Used alongside shaft-relative probes on fluid-film bearing machines.
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