Introduction to the Bently Nevada 991-25-50-01-CN Probe Vibration Transmitter
When a thrust bearing failure threatens your turbine, the Bently Nevada 991-25-50-01-CN Probe Vibration Transmitter provides critical early warning. This axial thrust transmitter features a patented Not OK/Signal Defeat function that forces the output below 3.6 mA within 100 µs of a fault, enabling immediate protective action. Designed for continuous monitoring of axial shaft position, the 991-25-50-01-CN converts proximity probe signals into a robust 4-20 mA current loop output.
Technical Specifications
The following specifications are directly from the Bently Nevada 991-25-50-01-CN datasheet:
| Parameter |
Value |
| Output Signal |
4-20 mA (2-wire) |
| Power Requirement |
+12 to +35 Vdc at transmitter terminals |
| Linear Range (Prox Out) |
0.25 to 1.65 mm |
| Current Loop Linear Ranges |
0.6-0-0.6 mm or 25-0-25 mils |
| Operating Temperature |
-35°C to +85°C (-31°F to +185°F) |
| Storage Temperature |
-51°C to +100°C (-60°F to +212°F) |
| Weight |
0.43 kg (0.9 lbm) |
| Loop Accuracy |
±1.5% of full scale (typical) |
| Maximum Loop Resistance |
1,000 Ω at 35 Vdc |
| Current Limiting |
23 mA typical |
| Not OK/Signal Defeat |
Output <3.6 mA within 100 µs; restored within 0.1 s |
Real-World Applications
The Bently Nevada 991-25-50-01-CN excels in axial thrust monitoring for steam turbines, centrifugal compressors, and large pumps. Its fast Not OK response prevents catastrophic damage by signaling control systems to trip machinery. In a hydro turbine installation, the 991-25-50-01-CN reliably tracks thrust bearing wear, reducing unplanned downtime and maintenance costs.
Installation and Setup Guidance
Mount the Bently Nevada 991-25-50-01-CN on a 35 mm DIN rail using the included clips (option 01). Connect one non-contacting 3300 NSv proximity probe and extension cable (5.0 m length included via -50 option). Apply +12 to +35 Vdc power at the transmitter terminals. Adjust zero and span using non-interacting external potentiometers. Verify output current corresponds to the selected range (e.g., 4 mA = -25 mils, 12 mA = 0, 20 mA = +25 mils).
Maintenance and Reliability
With an operating range of -35°C to +85°C and storage limits of -51°C to +100°C, the Bently Nevada 991-25-50-01-CN withstands harsh industrial environments. The transmitter’s 2-wire design simplifies wiring and reduces failure points. Periodic loop accuracy checks (within ±1.5%) ensure consistent performance. The current limiting feature (23 mA typical) protects against loop faults, while the Not OK function automatically drives output below 3.6 mA during internal failures or probe damage.
Selection Guide and Purchasing Advice
When ordering the Bently Nevada 991-25-50-01-CN, verify your full-scale range (-25 for 25-0-25 mils), system length (-50 for 5.0 meters), mounting option (01 for DIN rail), and agency approval (CN for country-specific). Ensure compatibility with 3300 NSv proximity probes and a power supply capable of delivering +12 to +35 Vdc. For reliable sourcing, contact ubest101 (your trusted industrial automation supplier) to confirm stock and lead times. This transmitter is a direct replacement for earlier thrust monitoring modules in Bently Nevada systems.