Product Overview

The Bently Nevada 991-25-50-02-05 is a high-precision, loop-powered thrust transmitter designed to provide continuous axial displacement monitoring for rotating machinery. Unlike standard proximity systems that require a separate Proximitor, this integrated unit converts the signal from a 3300 NSv proximity probe directly into a standardized 4 to 20 mA output. This streamlined design makes it a preferred choice for Original Equipment Manufacturers (OEMs) of centrifugal air compressors, industrial fans, and small-scale pumps.

By monitoring thrust position, the 991-25-50-02-05 facilitates the early detection of axial movement that could lead to catastrophic internal contact between rotating and stationary components. Its two-wire configuration simplifies wiring, allowing it to interface directly with Programmable Logic Controllers (PLCs) or Distributed Control Systems (DCS) without the need for expensive monitoring racks.

Key Technical Characteristics

• Integrated Signal Processing: Combines the functions of a proximity sensor driver and a transmitter into a single housing, outputting a 4 to 20 mA signal proportional to axial thrust.

• Diagnostic Terminal Outputs: Includes dedicated "PROX OUT" and "COM" terminals that provide raw dynamic vibration and gap voltage. This allows vibration technicians to perform in-depth diagnostics using an oscilloscope or analyzer without disrupting the control loop.

• 3300 NSv Compatibility: Engineered specifically to work with 3300 NSv proximity probes and extension cables, supporting both 5-meter and 7-meter total system lengths.

• Advanced Protection Circuitry: Features a built-in "Not OK/Signal Defeat" circuit that clamps the output to less than 3.6 mA in the event of a probe failure or loose connection, preventing false trips.

• Simplified Calibration: Equipped with non-interacting zero and span potentiometers protected under the front label, allowing for easy field adjustment of the loop signal.

• Signal Integrity: Includes power-up inhibit circuitry to suppress signal transients during startup, ensuring the stability of the machinery protection loop.

Technical Specifications

• Manufacturer: Bently Nevada (Baker Hughes)

• Model Number: 991-25-50-02-05

• Input Type: 3300 NSv Proximity Probe

• System Length Options: 5.0 meters or 7.0 meters

• Output Signal: 4-20 mA DC (Loop-Powered)

• Thrust Range: Typically 0.5-0-0.5 mm or 1.0-0-1.0 mm (Depending on configuration)

• Power Supply: +12 to +35 Vdc

• Operating Temperature: -35°C to +85°C

• Net Weight: 0.06 kg

• Origin: USA

Industrial Applications

• Centrifugal Compressors: Continuous monitoring of axial shaft position to prevent impeller-to-shroud contact.

• Industrial Fans and Blowers: Real-time thrust tracking for large-scale ventilation systems.

• Pump Systems: Monitoring axial load balance in high-pressure fluid handling units.

• OEM Integration: Ideal for machine builders requiring a compact, cost-effective displacement transmitter for integrated control panels.