Introduction to the 991-06-70-02-01
When axial thrust monitoring is critical, the 991-06-70-02-01 from Bently Nevada provides a reliable solution. This probe vibration transmitter is designed for continuous measurement of axial shaft position and thrust bearing wear. It converts proximity probe signals into a standard 4-20 mA current loop, making it easy to integrate with existing control systems.
The 991-06-70-02-01 is part of the 991 series, specifically configured as a thrust transmitter with a full-scale range of 0.6-0-0.6 mm. This makes it suitable for applications requiring precise monitoring of axial displacement in rotating machinery.
Key Features and Technical Specifications
The 991-06-70-02-01 offers several features that enhance its performance and reliability:
- Accepts one non-contacting 3300 NSv proximity probe and extension cable, simplifying installation.
- Provides a 4-20 mA output signal over the specified full-scale range in a 2-wire configuration.
- Operates with a power input of +12 to +35 Vdc at the transmitter terminal, offering flexibility in power supply.
- Features a linear range of 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.
- Includes non-interacting external zero and span adjustments for easy calibration.
- Has a Not OK/Signal Defeat function that drops output below 3.6 mA within 100 µs of a fault, ensuring safety.
For a quick overview, here are the core specifications:
| Parameter | Value |
|---|---|
| Full-scale option | 0.6-0-0.6 mm |
| System length | 7.0 meters (23.0 feet) |
| Mounting | DIN rail, bulkhead screws |
| Output signal | 4-20 mA |
| Power requirement | +12 to +35 Vdc |
| Operating temperature | -35°C to +85°C |
| Storage temperature | -51°C to +100°C |
| Weight | 0.43 kg (0.9 lbm) |
| Agency approval | CSA Division 2 |
Applications and Use Cases
The 991-06-70-02-01 is primarily used for axial thrust monitoring in turbomachinery, compressors, and large pumps. Its 4-20 mA output allows direct connection to PLCs, DCS, or SCADA systems, providing real-time data for predictive maintenance.
In a typical installation, the transmitter is mounted on a DIN rail in a control cabinet, while the proximity probe is installed near the thrust bearing. This setup enables continuous monitoring of shaft position, helping to prevent catastrophic failures due to excessive thrust.
For example, in a steam turbine, the 991-06-70-02-01 can detect abnormal axial movement early, allowing operators to take corrective action before bearing damage occurs.
Installation and Setup
Installation of the 991-06-70-02-01 is straightforward. The transmitter mounts on a standard DIN rail, and the bulkhead screw option provides secure mounting in panel applications. Ensure the power supply is within the +12 to +35 Vdc range and that the loop resistance does not exceed 1,000 ohms at 35 Vdc.
Connect the proximity probe and extension cable to the transmitter input. The 2-wire loop configuration simplifies wiring, as the same pair carries both power and signal. After wiring, adjust zero and span using the external potentiometers to match the required full-scale range.
Always follow the manufacturer's manual for detailed wiring diagrams and safety precautions.
Maintenance and Reliability
Routine maintenance of the 991-06-70-02-01 involves periodic inspection of the transmitter and probe connections. Check for loose wiring, corrosion, or physical damage. The transmitter's operating temperature range of -35°C to +85°C makes it suitable for harsh industrial environments.
Because the device is safety-related, only perform inspections as outlined in the manufacturer's safety manual. Avoid opening the enclosure or attempting internal repairs unless authorized. Regular verification of the output signal against a known reference can help ensure accuracy.
Comparison with Similar Transmitters
Compared to other vibration transmitters, the 991-06-70-02-01 stands out due to its specific thrust measurement capability and CSA Division 2 approval. While general-purpose vibration transmitters may offer broader frequency ranges, this model is optimized for axial displacement, providing higher accuracy in that niche.
For instance, a standard 4-20 mA vibration transmitter might measure overall vibration, but the 991-06-70-02-01 focuses on thrust, making it ideal for applications where axial position is critical.
Troubleshooting and Common Issues
If the output signal goes below 3.6 mA, it indicates a Not OK condition. This could be due to a faulty probe, broken cable, or power supply issue. Check the probe gap and wiring continuity first. The signal should recover within 0.1 seconds after the fault is cleared.
Another common issue is loop resistance exceeding the maximum limit, which can cause inaccurate readings. Ensure the total loop resistance, including cable, is below 1,000 ohms at 35 Vdc. If problems persist, consult the official Bently Nevada documentation or contact AutoDCSTech for support.
Product Support and Availability
The 991-06-70-02-01 is available through AutoDCSTech, an industrial automation parts supplier. Please verify current lifecycle status and availability before ordering. For technical support, contact AutoDCSTech or refer to the official Bently Nevada documentation.
