Precision Axial Position Monitoring for High-Reliability Machinery Systems
The Bently Nevada 991-25-70-01-IN 991 Thrust Sensor is a compact and reliable axial position transmitter designed for continuous monitoring of shaft thrust displacement in rotating machinery. Developed for OEM equipment manufacturers and industrial operators, the 991 Series provides a direct 4–20 mA proportional output representing shaft axial movement, allowing easy integration with PLC, DCS, SCADA, and machinery control systems.
The 991-25-70-01-IN configuration combines a 25–0–25 mil (approximately 2.5 mm) measurement range, 7-meter transducer system length, 35 mm DIN-rail mounting, and an IN approval option for specific regional installation requirements. With integrated Proximitor® Sensor technology, this transmitter delivers simplified installation, accurate thrust monitoring, and dependable performance for compressors, pumps, motors, fans, and other critical rotating assets.
Technical Specifications
| Parameter | Specification |
|---|
| Manufacturer | Bently Nevada |
| Model Number | 991-25-70-01-IN |
| Product Type | 991 Thrust Sensor / Thrust Transmitter |
| Measurement Function | Shaft Axial Displacement Monitoring |
| Full Scale Range | 25–0–25 mil (≈ 2.5 mm) |
| Compatible Probe System | Bently Nevada 3300 NSv Proximity Probe |
| Transducer 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 Type | 35 mm DIN-rail clips |
| Signal Conditioning | Integrated Proximitor® Sensor |
| Diagnostic Output | PROX OUT and COM terminals |
| Linear Current Loop Range | 25–0–25 mil |
| Operating Temperature | -35°C to +85°C |
| Storage Temperature | -52°C to +100°C |
| Loop Resistance | Up to 1000 Ω at 35 VDC |
| Transmitter Weight | Approx. 0.43 kg |
| Dimensions | Approx. 82 × 35 × 75 mm |
Industrial Applications
The 991-25-70-01-IN is designed for machinery applications where accurate axial position feedback is essential for equipment protection and operational reliability.
| Industry | Typical Equipment |
|---|
| Oil & Gas | Centrifugal compressors, process pumps |
| Petrochemical | Rotating process machinery |
| Power Generation | Turbines and auxiliary equipment |
| Manufacturing | Motors, fans, blowers |
| Water & Utilities | Large industrial pumps |
| OEM Machinery | Compressor packages and skid systems |
Common applications include:
-
Shaft thrust displacement measurement
-
Thrust bearing monitoring
-
Machinery protection systems
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Condition-based maintenance
-
Process control feedback
-
Equipment health monitoring
Product Advantages
High-Accuracy Thrust Measurement
The 991 Series is specifically designed to convert proximity probe measurements into a stable engineering signal proportional to shaft axial position. This enables operators to identify abnormal thrust movement before mechanical damage occurs.
Integrated Proximitor® Electronics
Unlike traditional systems requiring separate signal conditioners, the 991 transmitter incorporates Proximitor® electronics inside the transmitter housing. This reduces panel space requirements, simplifies wiring, and improves system reliability.
Extended 7-Meter System Capability
The 70 configuration provides a 7-meter transducer system length, offering installation flexibility when the machine monitoring point and control cabinet are separated by greater distances.
DIN-Rail Installation Convenience
The 01 mounting option provides 35 mm DIN-rail clips, allowing fast installation inside industrial control cabinets and OEM electrical panels. This design improves maintenance accessibility and reduces commissioning time.
Standard Industrial 4–20 mA Output
The transmitter provides a widely accepted 4–20 mA signal, allowing straightforward connection to modern automation platforms without additional conversion hardware.
Designed for OEM and Retrofit Applications
The compact transmitter format makes it suitable for both new machine designs and replacement upgrades where reliable axial position monitoring is required.
Technical FAQs
1. What is the Bently Nevada 991-25-70-01-IN used for?
It is used for continuous monitoring of shaft axial displacement (thrust position) in rotating machinery and provides a proportional 4–20 mA output for control systems.
2. What does the “25” option represent?
The 25 designation indicates a 25–0–25 mil full-scale measurement range, equivalent to approximately 2.5 mm axial displacement.
3. What does the “70” code indicate?
The 70 option identifies the 7-meter (23 ft) transducer system length.
4. What does the “01” mounting option mean?
The 01 option specifies 35 mm DIN-rail clip mounting for installation in control panels and automation cabinets.
5. What does the final “IN” approval code indicate?
The IN option represents a specific approval/configuration designation used for regional installation requirements. Approval details should be verified according to project specifications.
6. Which proximity probe works with this transmitter?
The 991 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 Proximitor® Sensor electronics are integrated into the transmitter, eliminating the need for a separate external unit.
8. What output signal does the unit provide?
The transmitter provides a 4–20 mA proportional current output representing measured axial shaft position.
9. What power supply is required?
The device requires +12 to +35 VDC input power at the transmitter terminals.
10. What machines commonly use the 991 Series?
The 991 Series is commonly installed on centrifugal compressors, pumps, motors, fans, and other rotating equipment requiring continuous thrust monitoring.
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