Bently Nevada 991-25-50-01-01 Probe Vibration Transmitter

Product Overview

When unplanned downtime from thrust-bearing failure threatens critical rotating machinery, the Bently Nevada 991-25-50-01-01 thrust transmitter delivers rapid fault detection to trigger protective action. This probe vibration transmitter accepts one non-contacting 3300 NSv proximity probe and outputs a proportional 4-20 mA signal over a 25-0-25 mils full-scale range. Designed for axial (thrust) measurement, it mounts on a standard 35 mm DIN rail and operates from a +12 to +35 Vdc supply. The Bently Nevada 991-25-50-01-01 includes a Not OK/Signal Defeat feature that forces the output below 3.6 mA within 100 microseconds of a fault, and restores normal operation within 0.1 seconds after the condition clears.

Technical Specifications

Key parameters of the Bently Nevada 991-25-50-01-01 include:

• Full-scale Option: 25-0-25 mils
• System Length: 5.0 meters (16.4 feet)
• Mounting: 35 mm DIN-rail clips
• Output Signal: 4-20 mA, two-wire
• 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)
• 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% over full-scale range (typical)
• Maximum Loop Resistance: 1,000 Ω including cable at 35 Vdc
• Current Limiting: 23 mA typical
• Not OK Signal: Output goes to less than 3.6 mA within 100 µs, restores within 0.1 seconds
• Zero and Span: Non-interacting external adjustments
• Agency Approval: CSA Division 2

Industry Applications

The Bently Nevada 991-25-50-01-01 is purpose-built for axial thrust monitoring in steam turbines, gas turbines, centrifugal compressors, and large pumps. Its 4-20 mA output integrates directly with distributed control systems (DCS) and programmable logic controllers (PLC). In high-value rotating equipment, the immediate Not OK indication provided by the 991-25-50-01-01 minimizes bearing damage and reduces unplanned repair costs.

Installation & Setup Guidance

Install the Bently Nevada 991-25-50-01-01 on a 35 mm DIN rail using the supplied clips. Connect a 3300 NSv proximity probe and matching extension cable to the transmitter’s input terminals. Apply +12 to +35 Vdc power, and verify the 4-20 mA output corresponds to the measured thrust gap. Adjust zero and span using the non-interacting external trimmers. Ensure the loop resistance does not exceed 1,000 Ω to maintain rated accuracy.

Troubleshooting & Common Issues

If the 991-25-50-01-01 output drops below 3.6 mA, a Not OK condition exists. Common causes include probe gap out of range, cable damage, or loss of power. Check the probe gap and cable continuity first. The transmitter automatically restores output within 0.1 seconds after the fault clears. For persistent errors, verify that the supply voltage stays within +12 to +35 Vdc and that loop resistance is below the 1,000 Ω maximum.

Ordering Information Table