Product Overview

The Bently Nevada 991-25-70-01-00 is a self-contained axial thrust transmitter designed to provide continuous monitoring of rotor position in rotating machinery. By integrating the functionality of a Proximitor sensor directly into a 4 to 20 mA loop transmitter, this device eliminates the need for external signal conditioners or monitor racks. It is specifically engineered to interface with the 3300 NSv proximity probe system, allowing for precise measurement of axial movement in space-constrained environments. The transmitter converts the eddy current probe signal into a linear current output, enabling direct integration into PLC or DCS systems for critical machinery protection and thrust position trending.

Hardware Parameters and Key Specifications

This 991 series transmitter is built for high-reliability data acquisition and features a ruggedized, potted enclosure suitable for extreme industrial conditions.

• Model Number 991-25-70-01-00

• Measurement Type Axial Thrust (Position)

• Output Signal 4 to 20 mA DC proportional to shaft position

• Diagnostic Interface Coaxial BNC connector and "PROX OUT" terminals for gap voltage/dynamic signals

• Full-Scale Range 1.2 mm (50 mils) total range / ±25 mils (Option -70)

• System Length 7.0 meters (Option -25)

• Mounting Configuration 35 mm DIN-rail clips (Option -01)

• Hazardous Area Approvals Multiple international certifications including ATEX/IECEx/CSA (Option -00)

• Environmental Protection Potted construction; resistant to 100% condensing humidity

• Calibration Controls Hidden non-interacting zero and span potentiometers for loop tuning

Industrial Applications and Operational Benefits

The 991-25-70-01-00 is a staple in Turbine Supervisory Instrumentation (TSI), particularly for assets like centrifugal air compressors where axial clearance is minimal and installation space is restricted. By monitoring the rotor's thrust position, it provides an early warning of thrust bearing wear or impending failure, which could otherwise lead to catastrophic metal-to-metal contact between the rotor and stator.

Its integrated "Not OK" and Signal Defeat logic ensures that faulty probes or wiring issues do not trigger false machinery trips. The inclusion of a test input pin allows field technicians to verify loop integrity using a variable DC source without dismantling the probe assembly. This makes the 991 transmitter an ideal choice for OEMs and end-users who require a compact, durable, and easily maintainable solution for monitoring rotor axial movement in high-speed industrial applications.