Bently Nevada 991-01-XX-02-05 991 Thrust Transmitter
Technical Specifications
| Category |
Key Parameter |
Official Specification Value |
| Model Configuration |
-01: Full-scale Option |
Standard displacement scale (e.g., 0.6-0-0.6 mm) converted linearly to 4-20 mA output. |
|
-XX: System Length Option |
Placeholder variable for total proximity probe system length, typically 50 (5.0 meters) or 70 (7.0 meters). |
|
-02: Mounting Option |
Bulkhead screws (flat surface plate mounting hardware configuration). |
|
-05: Agency Approval |
Multi-agency package: CSA Division 2, ATEX Zone 0, ATEX Zone 2, and ABS maritime certification. |
| Electrical |
Input Voltage |
+12 Vdc to +35 Vdc |
|
Signal Output |
2-wire, 4 to 20 mAdc (linear over specified full-scale range) |
|
Loop Accuracy |
Within ± 1.5% of specified full-scale range |
|
Maximum Loop Resistance |
1,000 Ω maximum including cable at 35 Vdc input |
|
Current Limiting |
23 mA typical |
| Sensor Compatibility |
Compatible Transducer System |
3300 NSv Proximity Probe and extension cable |
|
Dynamic Signal Output (Prox Out) |
Non-isolated BNC terminal, 10 kΩ output impedance |
|
Linear Range |
Prox Out voltage linear from 0.25 to 1.65 mm |
|
Minimum Target Size |
9.5 mm (0.375 in) diameter |
| Fault Protection |
Not OK Response Time |
Loop current drops below 3.6 mA within 100 μs |
|
Recovery Time |
Returns to loop signal within 0.1 second after fault clears |
| Environmental |
Operating Temperature |
-35 °C to +85°C (-31°F to +185°F) |
|
Storage Temperature |
-51°C to +100°C (-60°F to +212°F) |
|
Relative Humidity |
100% condensing, non-submerged (requires coaxial connector protection) |
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Application Areas
- Centrifugal Air Compressor Monitor: The 991-01-XX-02-05 is often found sitting on centrifugal compressors, basically doing thrust position measurement to keep axial movement under control. In high-speed units, even small shaft shift can turn into a bigger problem pretty fast, so this module is usually part of the protection setup rather than just monitoring.
- Steam Turbine Monitoring: In power plant environments, it gets used for steam turbine shaft thrust displacement tracking. Nothing fancy in positioning, but it keeps feeding real-time 4 to 20 mA loop-powered signal into the control system so operators can see what’s going on with the turbine thrust condition.
- Gas Turbine Protection: For gas turbines, this transmitter is more of a safeguard layer. When axial load starts building up, the unit helps detect it early through eddy current proximity sensor interface, and the system can react before mechanical damage happens inside the machine.
- Industrial Rotating Machinery: Usually you’ll see it across industrial pumps, motors, and heavy-duty fans. The setup is fairly standard—2-wire machinery protection transmitter style—with PROX OUT dynamic diagnostic output going into PLC or DCS analog input cards for continuous machinery protection monitoring.
- Hazardous Locations (ATEX Zone 0/2): In petrochemical sites or refinery zones, especially ATEX Zone 0/2 areas, the 991 series is chosen for its stable behavior in volatile conditions. It connects through bulkhead screw surface mounting and works with eddy current proximity sensor systems without much complication in the field.
- ABS Maritime Marine Application: On offshore platforms, LNG carriers, and general marine rotating assets, this transmitter is commonly used for thrust position monitoring. ABS-class marine setups usually combine it with 3300 NSv proximity probe system and 330930 extension cable pairing for stable signal transmission over distance.
- API 670 Compliant Systems: In API 670 machinery protection system architectures, it’s often treated as a standard 2-wire transmitter module. Sometimes it replaces older 990/991 Test Adapter (122115-01) configurations during retrofit work, especially when upgrading Bently Nevada transmitter spare parts inside legacy racks like Bently Nevada 3500 rack integration.
- Emergency Shutdown System (ESD): In ESD loops, the signal is routed directly into PLC/DCS analog input card monitoring. When thrust goes beyond safe range, the Not OK/Signal Defeat circuit and alarm logic help trigger shutdown actions. Basically it’s part of the fast response chain rather than passive measurement.
Key Features
- Axial Thrust Monitoring: Engineered for precision shaft thrust position monitoring and axial displacement measurement in high-speed rotating machinery.
- 3300 NSv Probe Interface: Designed exclusively to interface with the Bently Nevada 3300 NSv proximity probe system and matching extension cables.
- 4-20 mA Loop Output: Features a 2-wire machinery protection transmitter design, converting mechanical displacement linearly into a standard 4 to 20 mA signal for PLC/DCS integration.
- Dynamic Diagnostic Output: Provides a non-isolated BNC terminal for PROX OUT dynamic diagnostic output, allowing real-time gap voltage and vibration analysis.
- Rapid Fault Protection: Includes an advanced integrity circuit that drops the loop current below 3.6 mA within 100 microseconds during a transducer failure.
- Ruggedized Design: Built for critical asset protection, withstanding harsh environments from -35°C to +85°C and 100% condensing humidity.
- Global Agency Approvals: The -05 option delivers a certified package for hazardous locations (ATEX Zone 0/2, CSA Div 2) and holds ABS maritime marine approval.
- Bulkhead Plate Mounting: The -02 option offers robust bulkhead screws surface mounting for secure installation near the monitored machinery.
Frequently Asked Questions
Q1: What is the primary function of the Bently Nevada 991-01-XX-02-05 transmitter?
A1: The 991-01-XX-02-05 sits in machinery protection loops mainly for axial thrust position monitoring. It’s a 2-wire loop-powered transmitter, nothing overcomplicated in structure, just taking the signal from a proximity sensor line and turning it into a linear 4 to 20 mA output for PLC/DCS analog input card monitoring. Usually found in turbine or compressor protection setups where stability matters more than anything else.
Q2: Which proximity sensor system is compatible with the 991-01-XX-02-05 thrust transmitter?
A2: It’s basically built around the Bently Nevada 3300 NSv proximity probe system, so that’s the one it expects. Extension cables from the same family go along with it. Mixing it with other sensor series isn’t really a good idea—loop accuracy and calibration can drift, and the whole measurement chain won’t behave as intended.
Q3: What does the "XX" variable represent in the part number 991-01-XX-02-05?
A3: In this case, “XX” is just a length selection code. It defines the overall system cable length. Common configurations are usually 50 for around 5 meters and 70 for about 7 meters. When ordering, this part actually needs to be specified clearly, otherwise you end up with mismatch in the transducer setup.
Q4: Can the 991-01-XX-02-05 be installed on marine vessels and offshore platforms?
A4: Yes, it’s commonly used in marine environments. The “-05” approval option covers ABS maritime marine application certification, so you’ll see it on offshore rigs, LNG carriers, and shipboard rotating machinery. It handles that kind of environment without needing special modifications beyond standard installation practice.
Q5: What hazardous area certifications are covered by the 991-01-XX-02-05 transmitter?
A5: The unit is designed for hazardous locations and comes with approvals like CSA Division 2 and ATEX Zone 0 / Zone 2. In real field use, that means it can go into refinery or chemical plant instrumentation areas where volatile gas conditions exist, as long as installation rules are followed.
Q6: How does the 991-01-XX-02-05 handle transducer system faults or loose wiring?
A6: There’s a built-in Not OK / Signal Defeat circuit that reacts pretty quickly. If wiring issues or sensor faults show up, the loop current drops below 3.6 mA in a very short time, around microseconds scale, which helps the control system avoid false trips. Once the issue clears, it comes back online automatically.
Q7: What mounting option is provided by the 991-01-XX-02-05 hardware configuration?
A7: The “-02” option refers to bulkhead screw surface mounting. It’s a straightforward setup—mount it onto a flat plate or inside a field enclosure near the compressor or turbine. Nothing complex, just practical field installation design for industrial environments.
Q8: Can we perform dynamic diagnostics while the 991-01-XX-02-05 is operating in the control loop?
A8: Yes, you can. It includes a PROX OUT diagnostic output through a non-isolated BNC terminal. Engineers usually connect a 990/991 Test Adapter (122115-01) when they need live gap voltage or vibration-related checks. The key point is that this can be done without interrupting the 4–20 mA loop, which is important in running machinery.
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