Precision Axial Displacement Monitoring for Reliable Rotating Equipment
The Bently Nevada 991-25-70-01-01 991 Thrust Sensor is a compact, loop-powered thrust transmitter designed to provide continuous monitoring of shaft axial displacement in critical rotating machinery. Built for OEM equipment and industrial process applications, it converts signals from a compatible 3300 NSv proximity probe system into a standard 4–20 mA output, enabling seamless integration with PLC, DCS, SCADA, and machinery protection systems. The 991 Series is widely used on compressors, pumps, motors, and fans where dependable thrust position monitoring helps improve equipment availability and reduce maintenance costs.
The 991-25-70-01-01 configuration features a 25–0–25 mil (approximately 2.5 mm) measurement range, a 7-meter transducer system length, 35 mm DIN-rail mounting, and the 01 agency approval option. With integrated Proximitor® Sensor electronics, the transmitter eliminates the need for an external signal conditioner, simplifying installation while delivering stable and accurate performance in demanding industrial environments.
Technical Specifications
| Parameter | Specification |
|---|
| Manufacturer | Bently Nevada |
| Model Number | 991-25-70-01-01 |
| Product Type | 991 Thrust Sensor / Thrust Transmitter |
| Measurement Function | Shaft axial displacement (thrust position) |
| Full Scale Range | 25–0–25 mil (≈ 2.5 mm) |
| Compatible Probe | Bently Nevada 3300 NSv Proximity Probe |
| System Length | 7.0 m (23 ft) |
| Output Signal | 4–20 mA proportional analog output |
| Power Supply | +12 to +35 VDC |
| Electrical Configuration | Two-wire loop powered |
| Mounting Method | 35 mm DIN-rail clips |
| Signal Conditioning | Integrated Proximitor® Sensor |
| Diagnostic Connections | PROX OUT and COM terminals |
| Operating Temperature | -35°C to +85°C |
| Storage Temperature | -52°C to +177°C |
| Relative Humidity | Up to 100% condensing (non-submerged) |
| Dimensions | Approx. 82 × 35 × 75 mm |
| Weight | Approx. 0.43 kg |
Typical Applications
The 991-25-70-01-01 is engineered for continuous thrust position monitoring in industrial rotating equipment where dependable machinery protection is essential.
| Industry | Typical Equipment |
|---|
| Oil & Gas | Centrifugal compressors, process pumps |
| Petrochemical | Rotating process machinery |
| Power Generation | Steam and gas turbine auxiliary systems |
| Manufacturing | Industrial motors, fans, blowers |
| Water & Wastewater | High-capacity pumping systems |
| OEM Equipment | Compressor and pump skids |
Common applications include:
-
Axial shaft displacement monitoring
-
Thrust bearing protection
-
Machinery condition monitoring
-
Predictive maintenance programs
-
PLC/DCS process feedback
-
Machine alarm and shutdown systems
Why Choose This Model?
Integrated Proximitor® Electronics
Unlike conventional monitoring systems that require separate signal conditioners, the 991 transmitter incorporates Proximitor® electronics within the enclosure. This integrated architecture reduces installation complexity, minimizes wiring, and improves long-term system reliability.
Flexible 7-Meter System Configuration
The 70 option provides a 7-meter transducer system, allowing greater flexibility when the probe installation point is located some distance from the control cabinet. This makes the transmitter well suited to packaged machinery and OEM installations.
Space-Saving DIN-Rail Installation
With its 35 mm DIN-rail mounting configuration, the transmitter installs quickly inside industrial control cabinets, reducing commissioning time while making future maintenance more convenient.
Standard 4–20 mA Process Output
The transmitter provides a highly stable 4–20 mA output proportional to shaft axial position, enabling straightforward integration into virtually any industrial automation or machinery protection platform.
Designed for Continuous Industrial Operation
Built for harsh industrial environments, the 991 Series delivers dependable performance across a wide operating temperature range, making it suitable for continuous-duty rotating equipment applications.
Simplified Maintenance and Diagnostics
Dedicated PROX OUT and COM diagnostic terminals allow maintenance personnel to access dynamic vibration and gap voltage signals for commissioning, troubleshooting, and performance verification.
Technical FAQs
1. What is the Bently Nevada 991-25-70-01-01 used for?
It continuously measures shaft axial displacement and converts the measurement into a 4–20 mA output for machinery monitoring and protection systems.
2. What does the "25" option indicate?
It specifies a 25–0–25 mil full-scale measurement range, suitable for monitoring thrust position in rotating equipment.
3. What does the "70" configuration represent?
The 70 option indicates a 7-meter (23 ft) transducer system length.
4. What does the "01" mounting option mean?
It identifies the 35 mm DIN-rail mounting configuration for installation in industrial control panels.
5. What does the final "01" approval option represent?
The final 01 identifies a specific agency approval configuration within the Bently Nevada ordering system. The applicable certification should be verified against the product nameplate or official ordering guide.
6. Which probe system is compatible?
The transmitter is designed for use with the Bently Nevada 3300 NSv proximity probe and matching extension cable system.
7. Does the transmitter require an external Proximitor module?
No. The signal conditioning electronics are integrated into the transmitter housing.
8. What power supply is required?
The unit operates from a 12–35 VDC loop-powered supply.
9. What diagnostic features are available?
It includes PROX OUT and COM terminals that provide access to dynamic signals and gap voltage for diagnostics and maintenance.
10. Which machines commonly use the 991 Series?
Typical installations include centrifugal compressors, pumps, motors, blowers, and industrial fans requiring continuous thrust position monitoring.
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