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The 991-25-XX-01-CN is an industrial-grade, two-wire, loop-powered thrust position transmitter for monitoring the axial displacement of rotating machinery. Operating with a full-scale range of 25-0-25 mils, it converts proximity probe inputs into a 4-20 mA current loop and features Chinese NEPSI hazardous area certification alongside standard 35 mm DIN rail clips. For more technical specifications regarding this device, refer to the official Bently Nevada documentation.
Non-isolated PROX OUT and COM terminals plus a coaxial connector provide a dynamic vibration and gap voltage signal output for diagnostics
Non-interacting zero and span potentiometers under the Transmitter label supports loop adjustment
Test Input pin allows quick verification of loop signal output, using a variable DC voltage source as the input
The 991 Thrust Transmitter is intended primarily for the original equipment manufacturers (OEMs) of centrifugal air compressors or small pumps, motors, or fans who prefer to provide a simple 4 to 20 mA proportional axial displacement (thrust) signal as the input to their machinery control system. The transmitter is a 2-wire, loop-powered device that accepts input from our 3300 NSv proximity probe and its matching extension cable (available in 5 m and 7 m system length options). The transmitter conditions the signal into appropriate engineering units proportional to the shaft’s axial position1, and provides it as a 4 to 20 mA industry-standard signal for input to the control system where machinery protection alarming and logic occurs.
Proper probe gap adjustment is essential for the 991-25-XX-01-CN to achieve its 25-0-25 mils full-scale span in both normal and counter directions. While providing rotor axial position measurement and thrust trending, the transmitter operates with technical limits compared to continuous monitoring systems. It handles position alarming and non-OK checking, but lacks advanced functions like Timed OK channel defeat, Danger Bypass, and Trip Multiply. Connected PLCs utilize this data solely for trending and cannot integrate into plant-wide diagnostics like System 1 or Rule Paks.
Important Notice: Other accessories, manuals, cables, calibration data, software, etc. are not included with this equipment unless listed in the above stock item description.
Bently Nevada 991-25-XX-01-CN Thrust Transmitter Manuals, Datasheets, Drivers, Link
Important Notice: Other accessories, manuals, cables, calibration data, software, etc. are not included with this equipment unless listed in the above stock item description.
Thermal Power Plants
Installed at the rotor ends of high-pressure and IP cylinders in large-capacity steam turbines to continuously monitor large-stroke axial shaft displacement, preventing rotor-to-stator crashes caused by severe thrust pad wear.
Petrochemical Refining
Deployed on high-pressure centrifugal compressors and large multi-stage rich-liquid energy recovery turbines in hydrogenation units to convert millimeter-level axial shaft displacement into 4-20mA signals directly sent to DCS for safety interlocks.
Iron, Steel and Black Metallurgy
Used on the input shafts of large blast furnace axial blowers, high-pressure dedusting fans, and large gearbox distribution boxes of hot rolling mills to monitor metal wear of large-stroke thrust bearings under heavy thrust loads.
Large-Scale Inorganic Chemical Industry
Transmits large-stroke axial position displacement to the interlock protection network of DCS systems at critical power stages of synthesis gas compressors and synthesis units under high-temperature and high-pressure gas environments.
Nuclear Power Auxiliary Systems
Used inside local cabinets of nuclear power plant conventional island cooling water circulating pumps and auxiliary steam turbine generator sets, achieving physically isolated monitoring between low-voltage control loops and large-stroke field high-voltage power sides.
When operating the 991-25-XX-01-CN, you must strictly ensure that the combined electrical length of the proximity probe and extension cable perfectly matches the transmitter's calibrated system length (defined by the middle -XX option, typically 5.0 or 9.0-meter configurations), as any mismatch will severely distort the 2.5 mm linear range.
During mechanical overhauls and probe installation, use a voltmeter to precisely adjust the initial physical gap until the buffered GAP voltage stabilizes at the voltage value corresponding to the nominal zero-point. The transmitter's metal chassis and the signal loop shield wiring must employ single-point shield grounding to suppress heavy electromagnetic crosstalk. Finally, when performing maintenance in hazardous explosion-proof areas, never open the enclosure cover or adjust terminal connections while the circuit is energized.
Alternative Names
Alternative Names
991 25 XX 01 CN991-25-XX-01-00991-25-XX-01-01991-25-XX-01-0599I-25-XX-0I-CN991-25-XX-O1-CN99I-25-XX-OI-CN991-25-XX-01-BR991-25-XX-01-BU
Technical notes
Technical notes
Bently Nevada 991-25-XX-01-CN thrust transmitter integrates the Proximitor signal conditioning circuitry, enabling standalone operation without the need for an external independent central monitoring rack. At the physical sensor layer, it must be exclusively interfaced with a Bently Nevada 3300 NSv proximity transducer probe and its matching extension cable system.
How to correctly use products like the 991-25-XX-01-CN?
Install the transmitter inside a field enclosure using a 35mm DIN rail. Connect the input terminal to a 3300 NSv proximity probe system. Connect the output terminal to a two-wire current loop to transmit the 4-20 mA signal directly to an analog input module of a PLC, DCS, or SCADA system.
Which sensor probe model is compatible with the 991-25-XX-01-CN?
The transmitter accepts input signals exclusively from the Bently Nevada 3300 NSv proximity probe
What are the environmental endurance and physical protection indicators of the 991-25-XX-01-CN?
The transmitter body features a fully potted internal electronic structure, offering a high mechanical protection level that delivers robustness against severe field environments with up to 100% condensing relative humidity.
What are the fundamental field installation and wiring requirements for the 991-25-XX-01-CN?
Secure the transmitter inside the cabinet via standard DIN rails. Use shielded twisted-pair wiring with a maximum conductor cross-section of 1.5 mm² (16 AWG) for the terminal connections. The combined electrical length of the probe and extension cable must strictly match the transmitter's factory system length option (XX meters) to ensure impedance balance.
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