991-25-50-03-CN Bently Nevada Thrust Transmitter Overview
When axial position monitoring demands precision and reliability, the 991-25-50-03-CN from Bently Nevada delivers. This probe vibration transmitter converts proximity probe signals into a standard 4-20 mA output, making it a cornerstone for machinery protection systems. Engineered for thrust measurement, it supports a full-scale range of 25-0-25 mils, ensuring accurate axial position tracking.
With a compact DIN rail mount and a 5.0-meter system length, this transmitter integrates seamlessly into existing panels. The 991-25-50-03-CN operates on +12 to +35 Vdc input, providing flexibility across various control systems. Its 4-20 mA output simplifies interface with PLCs, DCS, and SCADA systems, reducing installation complexity.
Key Features and Technical Specifications
The 991-25-50-03-CN is designed for demanding industrial environments. Below are its core specifications:
- Product Type: Probe Vibration Transmitter
- Model: 991 Thrust Transmitter
- Full-Scale Option: 25-0-25 mils
- System Length: 5.0 meters (16.4 feet)
- Mounting: DIN rail with clips and screws
- Output Signal: 4-20 mA (two-wire)
- Power Requirement: +12 to +35 Vdc at transmitter terminal
- Linear Range: 0.25 to 1.65 mm for Prox Out; suitable for 0.6-0-0.6 mm or 25-0-25 mils loop 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)
- Accuracy: ±1.5% over full scale (typical)
- Maximum Loop Resistance: 1,000 Ω at 35 Vdc
- Current Limiting: 23 mA typical
One distinctive feature is the Not OK/Signal Defeat function. In a fault condition, the output drops to less than 3.6 mA within 100 µs, alerting operators immediately. This rapid response enhances system safety and prevents undetected failures.
Applications and Use Cases
The 991-25-50-03-CN is primarily used for axial thrust measurement in rotating machinery such as turbines, compressors, and large pumps. Its 25-0-25 mils range suits applications requiring precise axial position monitoring. For example, in a steam turbine, the transmitter continuously tracks rotor axial displacement, enabling early detection of thrust bearing wear. This proactive approach minimizes unplanned downtime and extends equipment life.
Additionally, the DIN rail mounting simplifies installation in control cabinets, while the 4-20 mA output integrates with existing automation systems. The transmitter's wide operating temperature range (-35°C to +85°C) ensures reliable performance in harsh environments.
Installation and Setup
Mounting the 991-25-50-03-CN is straightforward. The DIN rail clips and screws provide secure attachment to standard rails. Connect the non-contacting 3300 NSv proximity probe and extension cable to the transmitter input. Then, wire the 4-20 mA output to your control system, ensuring the loop resistance does not exceed 1,000 Ω at 35 Vdc. Power the transmitter with +12 to +35 Vdc at the terminal.
For optimal performance, verify that the probe gap is set within the linear range (0.25 to 1.65 mm). Use the non-interacting zero and span adjustments to calibrate the output. Always follow the manufacturer's manual for detailed wiring diagrams and safety precautions.
Maintenance and Reliability
Regular inspection of the 991-25-50-03-CN ensures long-term reliability. Check the DIN rail mounting for tightness and inspect cables for damage. Periodically verify the output signal against a known reference to confirm accuracy. The transmitter's robust design withstands temperature extremes, but avoid exposing it to excessive vibration or moisture.
Because the device uses non-contacting probes, there is minimal wear. However, ensure the probe tip remains clean and properly positioned. Following the manufacturer's maintenance schedule helps prevent unexpected failures and extends service life.
Compatibility and Integration
The 991-25-50-03-CN is compatible with Bently Nevada 3300 NSv proximity probes and extension cables. Its 4-20 mA output works with any control system accepting standard analog signals, including PLCs, DCS, and SCADA. The two-wire configuration simplifies wiring and reduces installation cost.
For new installations, verify that the system length (5.0 meters) matches your probe cable requirements. The transmitter's axial use case aligns with thrust monitoring applications, but it can also be used for other position measurements within its linear range.
Troubleshooting Common Issues
If the output signal is erratic, check the loop resistance and power supply voltage. Ensure the probe is within the linear range and not damaged. If the output drops below 3.6 mA, a Not OK condition exists—inspect the probe and wiring. Use the zero and span adjustments to recalibrate if necessary.
For persistent issues, consult the Bently Nevada documentation or contact AutoDCSTech for technical support. Always follow safety protocols when working on live systems.
Product Support and Availability
The 991-25-50-03-CN is available from AutoDCSTech. For pricing, lead time, and technical assistance, contact our team. We ensure genuine Bently Nevada products and reliable support for your automation needs.
