Product Overview
The Bently Nevada 991-25-50-03-01 Probe Vibration Transmitter is a compact, DIN-rail mounted device designed for continuous axial thrust monitoring in rotating machinery. This industrial automation module converts non-contacting proximity probe signals into a standard 4-20 mA current loop output, providing real-time data for predictive maintenance and machinery protection systems.
Part of the reliable 991 series, the 991-25-50-03-01 offers a full-scale range of 25-0-25 mils and includes a 5.0-meter system length cable. Its robust construction ensures dependable operation in harsh industrial environments, with operating temperatures from -35°C to +85°C.
Technical Specifications
The Bently Nevada 991-25-50-03-01 delivers critical performance parameters for accurate vibration monitoring:
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Output Signal: 4-20 mA (2-wire configuration)
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Loop Accuracy: ±1.5% over full scale (typical)
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Maximum Loop Resistance: 1,000 Ω at 35 Vdc
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Current Limiting: 23 mA typical
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Power Supply: +12 to +35 Vdc input at transmitter terminal
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Linear Range: 0.25 to 1.65 mm for Prox Out; suitable for 0.6-0-0.6 mm or 25-0-25 mils current loop linear ranges
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Operating Temperature: -35°C to +85°C (-31°F to +185°F)
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Storage Temperature: -51°C to +100°C (-60°F to +212°F)
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Weight: 0.43 kg (0.9 lbm)
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Mounting: DIN rail with DIN clips and screws (option 03)
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Agency Approval: CSA Division 2 (option 01)
Industry Applications
The 991-25-50-03-01 is specifically designed for axial thrust monitoring in large rotating equipment such as steam turbines, compressors, and pumps. Its ability to output a consistent 4-20 mA signal makes it an ideal component for integration with PLCs, DCS, and vibration monitoring systems.
In a typical petrochemical plant application, the transmitter mounts on a DIN rail near the machinery, accepting input from a single 3300 NSv proximity probe. The Not OK/Signal Defeat feature ensures that if a fault occurs, the output drops below 3.6 mA within 100 µs, triggering alarms and preventing false readings.
Installation & Setup Guidance
Mount the Bently Nevada 991-25-50-03-01 on a standard DIN rail using the included DIN clips and screws. Ensure the power supply provides +12 to +35 Vdc at the transmitter terminals. Connect the 3300 NSv proximity probe and extension cable to the input. The 4-20 mA output connects in a 2-wire loop, with maximum loop resistance of 1,000 Ω at 35 Vdc.
Non-interacting external adjustments allow easy zero and span calibration. Always verify the linear range matches the probe gap and mechanical setup before commissioning.
Maintenance & Reliability
Routine inspection of the 991-25-50-03-01 should focus on verifying the integrity of the DIN rail mounting, cable connections, and probe condition. The transmitter’s operating range covers -35°C to +85°C, so ensure the ambient temperature stays within limits. The Not OK/Signal Defeat feature enhances system reliability by automatically signaling faults, reducing unplanned downtime.
No internal adjustments or periodic recalibration is needed under normal operation. However, testing the loop accuracy periodically (using the TEST signal input) ensures continued performance within the ±1.5% specification.
Troubleshooting & Common Issues
If the 4-20 mA output remains below 3.6 mA, the transmitter is likely in a Not OK state. Check the proximity probe connection, power supply voltage, and loop resistance. The Current Limiting function (23 mA typical) prevents damage during short circuits. If output drifts, verify the zero and span adjustments have not been disturbed. The transmitter recovers from a Not OK condition within 0.1 seconds after the fault is cleared.
Selection Guide & Purchasing Advice
When ordering the Bently Nevada 991-25-50-03-01, confirm the full-scale option (-25 for 25-0-25 mils), system length (-50 for 5.0 meters), and agency approval (01 for CSA Division 2). This unit is available from ubest101, a reliable supplier of industrial automation spares. Ensure your system uses a compatible 3300 NSv proximity probe and extension cable.