Product Overview
The Bently Nevada 991-25-70-03-01 Probe Vibration Transmitter is a critical component for axial thrust monitoring in rotating machinery. This high-reliability transmitter converts eddy-current probe signals into a 4-20 mA output proportional to shaft displacement. Built for demanding environments, the 991-25-70-03-01 ensures fail-safe operation with its Not OK/Signal Defeat feature that drops output below 3.6 mA within 100 µs upon detection of a fault condition. Designed for B2B customers seeking precision and uptime, this module delivers consistent performance across variable temperatures from -35°C to +85°C.
Technical Specifications
| Parameter |
Value |
| Mounting |
DIN rail (DIN clips and screws) |
| Output Signal |
4-20 mA (2-wire) |
| Use |
Axial thrust measurement |
| Power Supply |
+12 to +35 Vdc at transmitter terminals |
| Linear Range (Prox Out) |
0.25 to 1.65 mm; current loop 0.6-0-0.6 mm/25-0-25 mils |
| Accuracy |
±1.5% typical over full scale (TEST signal to 250 Ω load) |
| 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) |
| Storage Temperature |
-51°C to +100°C (-60°F to +212°F) |
| Weight |
0.43 kg (0.9 lbm) |
Industry Applications
This Bently Nevada 991-25-70-03-01 transmitter excels in axial thrust monitoring for steam turbines, centrifugal compressors, pumps, and large electric motors. In gas turbine installations, the 4-20 mA signal directly interfaces with DCS or PLC systems to trigger protective actions. Operators rely on its ±1.5% accuracy and rapid Not OK response to prevent catastrophic thrust bearing failures. The 25-0-25 mils full-scale option suits standard journal bearing clearances.
Installation & Setup
Mount the Bently Nevada 991-25-70-03-01 on a DIN rail using the provided clips and screws. Connect one 3300 NSv proximity probe and extension cable to the input. Wire the 2-wire 4-20 mA loop to your controller, observing polarity and ensuring total loop resistance does not exceed 1,000 Ω. Power the transmitter with +12 to +35 Vdc at the terminals. Non-interacting external zero and span adjustments allow fine calibration without interaction between controls. Before commissioning, verify the linear range matches your thrust requirement (25-0-25 mils or 0.6-0-0.6 mm).
Troubleshooting & Common Issues
The Bently Nevada 991-25-70-03-01 incorporates a Not OK/Signal Defeat function that forces the output below 3.6 mA within 100 µs when a probe or internal fault is detected. This immediate current reduction triggers alarms, preventing undetected failures. If the output remains above 3.6 mA during a fault, inspect the probe and cable for damage. For offset or span drift, use the external adjustments while monitoring the loop current across a 250 Ω resistor. The transmitter automatically restores normal operation within 0.1 seconds after the fault clears. Ensure power supply voltage stays within +12 to +35 Vdc to avoid loop resistance limitations.
Selection Guide
When ordering a Bently Nevada 991-25-70-03-01, confirm the full-scale option (-25 for 25-0-25 mils), system length option (-70 for 7.0 meters), mounting option (03 for DIN clips and screws), and agency approval (-01 for CSA Division 2). This transmitter accepts one 3300 NSv proximity probe; ensure you have the matching extension cable. For technical inquiries or to place orders, visit PLC Source PRO (ubest101.myshopify.com) for genuine inventory and competitive pricing.