Product Introduction
The Bently Nevada 991-25-50-03-CN is a precision Probe Vibration Transmitter designed for continuous axial thrust monitoring in rotating machinery. This industrial automation module converts non-contact proximity probe signals into a linear 4-20 mA output, enabling real-time vibration analysis and protection. Engineered for critical applications, the 991-25-50-03-CN ensures high reliability with fast fault response and robust environmental tolerance.
Technical Specifications Breakdown
The Bently Nevada 991-25-50-03-CN delivers exceptional performance with the following key parameters:
| Parameter |
Value |
| Output Signal |
4-20 mA (2-wire) |
| Power Supply |
+12 to +35 Vdc at transmitter terminal |
| Full-Scale Option |
25-0-25 mils (thrust) |
| System Length |
5.0 meters (16.4 ft) probe extension |
| Mounting |
DIN rail with clips and screws |
| Operating Temperature |
-35 °C to +85 °C |
| Storage Temperature |
-51 °C to +100 °C |
| Weight |
0.43 kg (0.9 lbm) |
| Loop Accuracy |
±1.5% typical over full scale |
| Maximum Loop Resistance |
1,000 Ω at 35 Vdc |
| Current Limiting |
23 mA typical |
The 991-25-50-03-CN accepts one 3300 NSv proximity probe and offers non-interacting zero and span adjustments. Its linear range spans 0.25 to 1.65 mm for Prox Out, compatible with 0.6-0-0.6 mm or 25-0-25 mils current loop ranges.
Industry Applications
This Bently Nevada 991-25-50-03-CN is ideal for axial thrust monitoring in steam turbines, compressors, and large pumps. In power generation, it provides early detection of thrust bearing wear, preventing catastrophic failures. In oil and gas applications, the 991-25-50-03-CN delivers continuous vibration data to control systems, enabling predictive maintenance. The Not OK signal defeat feature (output drops below 3.6 mA within 100 μs) ensures immediate alarm during fault conditions, reducing downtime.
Installation & Setup Guidance
Mount the Bently Nevada 991-25-50-03-CN on a standard DIN rail using the included DIN clips and screws (option 03). Ensure the probe extension cable is connected securely to the transmitter. Power the unit with +12 to +35 Vdc at the terminal; observe polarity. Connect the 4-20 mA loop in a 2-wire configuration with a maximum loop resistance of 1,000 Ω. Adjust zero and span using the non-interacting potentiometers. Verify output with a loop calibrator before commissioning. The transmitter should be located within 5.0 meters (16.4 ft) of the probe tip.
Maintenance & Reliability
The Bently Nevada 991-25-50-03-CN requires minimal maintenance. Inspect the DIN rail connections and verify the 4-20 mA loop annually. Clean the transmitter enclosure with a soft cloth; avoid solvents. The wide operating temperature range (-35 °C to +85 °C) ensures reliability in harsh environments. The Not OK signal defeat function self-monitors for internal faults and restores output within 0.1 seconds after the fault clears, reducing spurious trips. This robust design supports long service life and consistent performance.
Troubleshooting Guide
Common issues with the Bently Nevada 991-25-50-03-CN include output stuck at 4 mA or no output. Check the power supply voltage (12-35 Vdc) and loop wiring for opens. If output remains at 4 mA, verify probe gap and target material. A reading below 3.6 mA indicates a Not OK condition; check probe and cable integrity. The zero and span adjustments should be set per the full-scale range (25-0-25 mils). Use a 250 Ω resistor to test loop accuracy. For persistent faults, contact PLC Source PRO for support. Note: the 991-25-50-03-CN is designed for axial applications only; do not use for radial measurements.