Intelligent Axial Displacement Monitoring for Critical Rotating Equipment
The Bently Nevada 991-25-70-03-05 991 Thrust Sensor is a compact, two-wire, loop-powered thrust transmitter designed to provide continuous shaft axial displacement (thrust position) monitoring for critical rotating machinery. Engineered for OEM equipment and industrial process applications, the 991 Series accepts input from a compatible 3300 NSv proximity probe system and converts the measured shaft position into a precise 4–20 mA output for seamless integration with PLC, DCS, SCADA, and machinery protection systems. Integrated Proximitor® electronics eliminate the need for an external signal conditioner, simplifying installation while maintaining excellent measurement stability and long-term reliability.
Configured with a 2.5 mm (±25 mil) measurement range, 7-meter transducer system, DIN clip and screw mounting, and the 05 hazardous-area approval option, the 991-25-70-03-05 is an ideal solution for compressors, turbines, pumps, motors, and other rotating assets operating in demanding industrial environments.
Technical Specifications
| Parameter | Specification |
|---|
| Manufacturer | Bently Nevada |
| Model Number | 991-25-70-03-05 |
| Product Type | 991 Thrust Sensor / Thrust Transmitter |
| Measurement Type | Shaft Axial Displacement (Thrust Position) |
| Full Scale Range | ±25 mil (approximately 2.5 mm) |
| Compatible Probe | 3300 NSv Proximity Probe |
| Transducer System Length | 7.0 m (23 ft) |
| Output Signal | 4–20 mA proportional output |
| Power Supply | 12–35 VDC |
| Loop Configuration | Two-wire, loop powered |
| Mounting Method | DIN clips with mounting screws |
| Signal Conditioning | Integrated Proximitor® electronics |
| Diagnostic Outputs | PROX OUT and COM |
| Maximum Loop Resistance | Up to 1000 Ω at 35 VDC |
| Accuracy | ±1.5% of full scale |
| Operating Temperature | -35°C to +85°C |
| Humidity | Up to 100% condensing (non-submerged) |
| Dimensions | Approx. 100 × 74 × 53 mm |
| Weight | Approx. 0.43 kg |
Typical Applications
The 991-25-70-03-05 is designed for continuous axial position monitoring across a wide range of rotating machinery.
| Industry | Typical Equipment |
|---|
| Oil & Gas | Centrifugal compressors, process pumps |
| Petrochemical | Compressors and expanders |
| Power Generation | Steam turbines and generators |
| Chemical Processing | High-speed rotating equipment |
| Manufacturing | Motors, fans and blowers |
| OEM Machinery | Compressor and pump packages |
Typical applications include:
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Shaft thrust position monitoring
-
Axial displacement measurement
-
Thrust bearing protection
-
Machinery condition monitoring
-
Predictive maintenance
-
PLC, DCS and SCADA integration
Performance Highlights
Wide Axial Displacement Measurement
The 25 range option supports ±25 mil (approximately 2.5 mm) shaft movement, making it suitable for machinery requiring extended thrust travel monitoring.
Integrated Proximitor® Electronics
The transmitter incorporates built-in signal conditioning, eliminating the need for a separate Proximitor module while reducing wiring complexity and installation costs.
7-Meter Transducer System
The 70 configuration includes a 7-meter transducer system, providing additional installation flexibility where the monitoring cabinet is located farther from the machine.
DIN Clip and Screw Mounting
The 03 mounting option combines DIN clips with mounting screws, allowing secure installation inside industrial control panels and OEM equipment enclosures.
Hazardous-Area Approval Configuration
The 05 option supports hazardous-area applications and may include certifications such as CSA Class I Division 2, ATEX Zone 0/2, IECEx, and ABS marine approval, depending on the supplied configuration and destination market.
Reliable 4–20 mA Process Output
A standard 4–20 mA analog output enables easy integration with industrial automation systems while supporting continuous machinery protection and predictive maintenance strategies.
Technical FAQs
1. What is the 991-25-70-03-05 used for?
It continuously measures shaft axial displacement (thrust position) and converts it into a 4–20 mA signal for machinery monitoring and protection.
2. Which probe is compatible with this transmitter?
It is designed for use with the Bently Nevada 3300 NSv proximity probe and the corresponding extension cable.
3. What does the "25" option indicate?
It specifies a ±25 mil (approximately 2.5 mm) full-scale thrust measurement range.
4. What does the "70" option represent?
It identifies a 7-meter (23 ft) transducer system length.
5. What does the "03" mounting option mean?
It indicates DIN clip mounting with mounting screws for secure installation inside industrial control panels.
6. What does the final "05" option represent?
It denotes the hazardous-area approved configuration, with certifications varying according to the ordered version and region.
7. What output signal does the transmitter provide?
It delivers a linear 4–20 mA output proportional to shaft axial position.
8. Does this model require an external Proximitor module?
No. The transmitter incorporates integrated Proximitor® electronics, eliminating the need for an external signal conditioner.
9. What operating voltage is required?
The transmitter operates from a 12–35 VDC two-wire loop-powered supply.
10. Which machines commonly use this model?
It is commonly installed on centrifugal compressors, turbines, industrial pumps, electric motors, blowers, and other rotating equipment requiring continuous thrust position monitoring.
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