Product Introduction
The Bently Nevada 991-25-50-02-01 Thrust Transmitter is a precision Probe Vibration Transmitter engineered for axial position monitoring in critical rotating machinery. As part of the Bently Nevada 991 series, this unit converts proximity probe signals into a 4-20 mA output for seamless integration with control systems. Designed for reliability, it features a Not OK/Signal Defeat function that forces the output below 3.6 mA within 100 µs upon fault detection—a critical safety feature for preventing undetected failures.
Technical Specifications Breakdown
The Bently Nevada 991-25-50-02-01 delivers accurate axial position data under demanding conditions. Below are key parameters derived from the product datasheet:
| Parameter |
Value |
| Full-scale Option |
25-0-25 mils |
| System Length |
5.0 meters (16.4 feet) |
| Mounting |
DIN rail, Bulkhead screws |
| Output Signal |
4-20 mA (2-wire) |
| Linear Range (Prox Out) |
0.25 to 1.65 mm |
| Power Requirement |
+12 to +35 Vdc at transmitter terminal |
| Loop Accuracy |
±1.5% typical over full scale |
| Maximum Loop Resistance |
1,000 Ω at 35 Vdc |
| Current Limiting |
23 mA typical |
| Operating Temperature |
-35°C to +85°C |
| Storage Temperature |
-51°C to +100°C |
| Weight |
0.43 kg (0.9 lbm) |
| Agency Approval |
CSA Division 2 |
These specifications ensure accurate and reliable axial thrust measurement in hazardous environments.
Industry Applications
The Bently Nevada 991-25-50-02-01 is ideal for axial position monitoring in steam turbines, compressors, and large pumps. In a typical turbine application, the transmitter accepts a single non-contacting 3300 NSv proximity probe and cable, converting the gap voltage into a proportional 4-20 mA signal. The CSA Division 2 approval allows installation in areas with flammable gases or vapors. The Not OK/Signal Defeat feature provides immediate fault indication, reducing downtime in critical processes.
Installation & Setup Guidance
Mount the Bently Nevada 991-25-50-02-01 on a standard DIN rail using the provided bulkhead screws. Connect the 3300 NSv proximity probe via the 5.0-meter extension cable. Power the transmitter with +12 to +35 Vdc at the terminal—ensure polarity is correct. The 4-20 mA output connects in a 2-wire configuration to your PLC or DCS. Calibrate zero and span using the non-interacting external adjustments. For optimal performance, keep loop resistance below 1,000 Ω and avoid exposing the transmitter beyond its -35°C to +85°C operating range.
Troubleshooting & Common Issues
The primary failure mode addressed by the Bently Nevada 991-25-50-02-01 is a loss of signal due to probe damage or electrical faults. The Not OK/Signal Defeat circuit forces the output below 3.6 mA within 100 µs of detecting a fault. This rapid response prevents false readings that could lead to catastrophic turbine overspeed or thrust bearing damage. Once the fault is cleared, the output restores within 0.1 seconds. If the output remains low, check the probe gap, cable integrity, and supply voltage. The current limiter (23 mA typical) protects against short circuits. Regular inspection of probe and cable connections is recommended to maintain accuracy.