Engineered for Continuous Axial Position Protection
The Bently Nevada 991-25-50-03-05 991 Thrust Sensor is a high-performance, loop-powered thrust transmitter developed for continuous monitoring of shaft axial displacement in critical rotating machinery. Designed for centrifugal compressors, pumps, turbines, motors, and other industrial equipment, the 991 Series converts signals from a compatible 3300 NSv proximity probe system into a precise 4–20 mA analog output for direct connection to PLC, DCS, SCADA, and machinery protection systems. Its integrated Proximitor® electronics reduce installation complexity while providing stable, long-term measurement performance.
The 991-25-50-03-05 configuration combines a 2.5 mm (25–0–25 mil) measurement range, 5-meter transducer system, DIN-clip and screw mounting, and the 05 hazardous-area approval option, making it suitable for demanding industrial applications where reliable thrust monitoring and regulatory compliance are equally important.
Technical Specifications
| Parameter | Specification |
|---|
| Manufacturer | Bently Nevada |
| Model Number | 991-25-50-03-05 |
| Product Type | 991 Thrust Sensor / Thrust Transmitter |
| Measurement Type | Shaft Axial Displacement (Thrust Position) |
| Full Scale Range | 2.5 mm (25–0–25 mil) |
| Compatible Probe | 3300 NSv Proximity Probe |
| Transducer System Length | 5.0 m (16.4 ft) |
| Output Signal | 4–20 mA linear analog output |
| Power Supply | 12–35 VDC |
| Wiring | Two-wire, loop powered |
| Mounting Method | DIN clips and mounting screws |
| Signal Conditioning | Integrated Proximitor® electronics |
| Diagnostic Output | PROX OUT and COM |
| Maximum Loop Resistance | Up to 1000 Ω at 35 VDC |
| Typical Accuracy | ±1.5% of full scale |
| Operating Temperature | -35°C to +85°C |
| Storage Temperature | -52°C to +177°C |
| Dimensions | Approx. 100 × 74 × 53 mm |
| Weight | Approx. 0.43 kg |
Typical Applications
The 991-25-50-03-05 is designed for reliable axial displacement monitoring across a broad range of industrial rotating equipment.
| Industry | Typical Equipment |
|---|
| Oil & Gas | Centrifugal compressors, pipeline pumps |
| Petrochemical | Process compressors and expanders |
| Power Generation | Steam turbines and generators |
| Chemical Processing | High-speed rotating machinery |
| Manufacturing | Industrial motors, fans and blowers |
| OEM Systems | Compressor and pump packages |
Typical applications include:
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Shaft thrust position monitoring
-
Axial displacement measurement
-
Thrust bearing protection
-
Predictive maintenance programs
-
Machinery condition monitoring
-
PLC, DCS and SCADA integration
Key Features and Benefits
Optimized for Axial Displacement Monitoring
The 991 Series is purpose-built for shaft thrust position measurement, helping maintenance teams detect excessive axial movement before it develops into costly bearing or rotor failures.
Integrated Proximitor® Electronics
Built-in signal conditioning eliminates the need for a separate Proximitor module, simplifying installation, reducing wiring requirements, and improving overall system reliability.
Flexible 5-Meter Transducer System
The 50 configuration provides a 5-meter system length, allowing convenient installation when transmitters are mounted away from the monitored machine.
DIN Clip Mounting
The 03 mounting option includes DIN clips and mounting screws, enabling quick installation inside industrial control cabinets and OEM equipment panels.
Hazardous-Area Certified Configuration
The 05 approval option supports installations in hazardous environments and includes certifications such as CSA Division 2, ATEX Zone 0, ATEX Zone 2, and ABS marine approval, depending on the product configuration.
Standard 4–20 mA Output
The industry-standard 4–20 mA output allows seamless integration with modern automation platforms, making the transmitter suitable for new installations as well as retrofit projects.
Technical FAQs
1. What is the 991-25-50-03-05 used for?
It continuously measures shaft axial displacement (thrust position) and converts the measurement into a proportional 4–20 mA signal for machinery protection systems.
2. Which proximity probe is compatible?
It is designed for use with the Bently Nevada 3300 NSv proximity probe and its matching extension cable.
3. What does the "25" option indicate?
The 25 option specifies a 2.5 mm (25–0–25 mil) full-scale axial displacement measurement range.
4. What does the "50" option represent?
It identifies a 5-meter (16.4 ft) transducer system length.
5. What does the "03" mounting option mean?
The 03 configuration includes DIN mounting clips and screws for secure installation inside control panels.
6. What does the final "05" approval option represent?
The 05 option denotes a hazardous-area approved version that includes certifications such as CSA Division 2, ATEX Zone 0, ATEX Zone 2, and ABS marine approval, depending on the supplied configuration.
7. What power supply is required?
The transmitter operates from a 12–35 VDC two-wire loop-powered supply.
8. Does the transmitter require an external Proximitor?
No. The Proximitor® electronics are integrated within the transmitter housing.
9. What diagnostic outputs are available?
The transmitter provides PROX OUT and COM terminals for dynamic signal and gap voltage diagnostics.
10. Which equipment commonly uses this model?
It is commonly installed on centrifugal compressors, steam turbines, industrial pumps, motors, and fans requiring continuous thrust position monitoring.
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