Product Introduction
When axial thrust monitoring fails, the Bently Nevada 991-25-50-01-05 Probe Vibration Transmitter provides robust protection. This industrial module is designed for continuous, reliable measurement of axial shaft position in rotating machinery. The 991-25-50-01-05 integrates seamlessly with 3300 NSv proximity probes to deliver a linear 4-20 mA output proportional to thrust. Its Not OK/Signal Defeat function ensures the output drops below 3.6 mA within 100 µs upon fault detection, preventing false readings and enabling rapid shutdown. This failure-aware design makes the 991-25-50-01-05 a critical component for turbine, compressor, and pump applications where unplanned downtime cannot be tolerated.
Technical Specifications Breakdown
| Parameter |
Value |
| Output Signal |
4-20 mAdc, 2-wire |
| Power Supply |
+12 to +35 Vdc at transmitter terminal |
| Accuracy |
Within ±1.5% over specified full scale range (typical) |
| Linear Range |
0.25–1.65 mm for Prox Out; suitable for 0.6-0-0.6 mm or 25-0-25 mils current loop |
| Maximum Loop Resistance |
1,000 Ω including cable at 35 Vdc |
| Current Limiting |
23 mA typical |
| Operating Temperature |
-35°C to +85°C (-31°F to +185°F) |
| Weight |
0.43 kg (0.9 lbm) |
The 991-25-50-01-05 offers non-interacting external zero and span adjustments, simplifying calibration. Its 4-20 mA loop accuracy is rated from the TEST signal input to voltage across a 250 Ω resistance, ensuring reliable data for control systems.
Installation & Setup Guidance
Mount the Bently Nevada 991-25-50-01-05 on a 35 mm DIN rail using the provided clips (option 01). Connect one non-contacting 3300 NSv proximity probe and its extension cable to the transmitter input. Apply +12 to +35 Vdc power at the terminal. Set full-scale option -25 (25-0-25 mils) and system length -50 (5.0 meters, 16.4 feet) per your application. Verify loop resistance does not exceed 1,000 Ω. After mounting, adjust zero and span using the external potentiometers. For ATEX Zone 0/2 or CSA Division 2 environments, confirm the agency approval option 05 covers your area classification.
Maintenance & Reliability
To maximize uptime, periodically inspect the DIN-rail mounting and cable connections. The Bently Nevada 991-25-50-01-05 features current limiting (23 mA typical) that protects the loop against overcurrent conditions. Its wide operating temperature range (-35°C to +85°C) and storage range (-51°C to +100°C) suit harsh industrial environments. The Not OK/Signal Defeat function promptly indicates sensor or wiring faults, reducing diagnostic time. Regularly check the 4-20 mA output against a known reference to confirm accuracy stays within ±1.5%. For applications requiring ABS maritime approval, the 991-25-50-01-05 includes that certification.
Troubleshooting & Common Issues
If the output remains below 3.6 mA, a Not OK condition exists—verify probe gap and cable integrity. The 991-25-50-01-05 restores normal output within 0.1 seconds after the fault clears. For erratic readings, ensure loop resistance is below 1,000 Ω and power supply is stable between +12 and +35 Vdc. If accuracy drifts, recalibrate zero and span using the non-interacting adjustments. The transmitter accepts only 3300 NSv probes; using other types may cause incorrect linearity. For persistent issues, contact PLC Source PRO for support. This module is a direct replacement for earlier thrust transmitters, offering improved fault response.