Bently Nevada 991-01-XX-01-00 MOD 288865-01 Thrust Transmitter with 4-20 mA Output

Product Overview

The Bently Nevada 991-01-XX-01-00 is a two-wire, loop-powered thrust position transmitter from the Bently Nevada 991 family, supplied here under factory modification 288865-01. Its purpose is refreshingly simple: take the raw signal from a 3300 NSv proximity probe watching the end of a shaft, and turn it into a clean, industry-standard 4 to 20 mA signal that any PLC, DCS or machinery protection system can understand. Instead of a separate Proximitor driver, signal conditioner and monitor rack, the Bently Nevada 991-01-XX-01-00 integrates the Proximitor sensor electronics directly into the transmitter housing, which is why it has become a favourite with OEMs building centrifugal air compressors, small pumps, motors and fans.What makes the Bently Nevada 991-01-XX-01-00 particularly practical is that it gives away nothing on diagnostics. Alongside the 4 to 20 mA loop it offers non-isolated PROX OUT and COM terminals plus a coaxial connector carrying the dynamic vibration and gap voltage signal, so a technician can still look at the raw waveform when a machine starts behaving oddly. Non-interacting zero and span potentiometers sit under the transmitter label for loop adjustment, and a Test Input pin lets you verify the whole loop with a variable DC source, without moving the shaft.Reliability features are built in deliberately, because this device often feeds protection logic. A Power-up Inhibit circuit blocks signal errors during supply transients, and a Not OK / Signal Defeat circuit drives the output below 3.6 mA within 100 microseconds if the probe or its connection fails, so a broken cable produces a recognisable fault state rather than a dangerous false reading. With potted construction rated for up to 100% condensing humidity, 35 mm DIN-rail clip mounting and a -35 °C to +85 °C operating range, the Bently Nevada 991-01-XX-01-00 is designed for cabinets and machine skids that are anything but climate-controlled.

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Description

Technical Specifications

Parameter Name	Parameter Value
Product Model	Bently Nevada 991-01-XX-01-00 (with MOD 288865-01)
Manufacturer	Bently Nevada (a Baker Hughes business)
Product Type	Thrust / Axial Position Transmitter (2-wire, loop-powered)
Ordering String	991-AA-BB-CC-DD — AA = 01 (OEM full-scale code), BB = XX (configurable system length), CC = 01 (35 mm DIN-rail clips), DD = 00 (no agency approval)
Transducer Input	One non-contacting 3300 NSv proximity probe with matching extension cable
Full-Scale Measurement	OEM code 01; 991 family covers 0.6-0-0.6 mm or 25-0-25 mils configurations
Power Requirement	+12 to +35 Vdc at the transmitter terminals
Output Signal	4 to 20 mAdc proportional to axial position, 2-wire configuration
Loop Accuracy	Within ±1.5% of full scale (typical)
Maximum Loop Resistance	1,000 Ω including cable at 35 Vdc
Current Limiting	23 mA typical
Zero and Span	Non-interacting external adjustments under the transmitter label
Fault Response (Not OK / Signal Defeat)	Output falls below 3.6 mA within 100 µs of a fault; restored within 0.1 s after the fault clears
PROX OUT Linear Range	0.25 to 1.65 mm (10 to 65 mils)
PROX OUT Scale Factor	7.87 mV/µm (200 mV/mil), ±6.5% typical including interchangeability error
PROX OUT Impedance	10 kΩ, calibrated for a 10 MΩ load, short-circuit protected
Minimum Target Size	9.5 mm diameter
PROX OUT Lead Length	3 m maximum (BNC diagnostic connection)
Transmitter Operating Temperature	-35 °C to +85 °C
Transmitter Storage Temperature	-51 °C to +100 °C
Probe Operating Temperature	Approximately -52 °C to +177 °C
Humidity	Up to 100% condensing, non-submerged (potted construction)
Electrical Classification	CSA/NRTL/C for North America, VDE for Europe, CE marked
Dimensions (H × W × D)	Approximately 100.1 mm × 73.9 mm × 53.3 mm
Weight	Approximately 0.43 kg transmitter; 0.82 kg typical total system
Country of Origin	USA

Main Features and Advantages

Proximitor integrated, cabinet simplified: The Bently Nevada 991-01-XX-01-00 removes the external Proximitor unit that a conventional eddy-current chain requires. That means fewer components to buy, fewer terminals to wire, fewer things to mis-terminate at two in the morning, and a much smaller footprint — a real advantage when the transmitter has to live inside a compressor skid panel or a crowded marshalling cabinet.Diagnostics remain fully available: Despite the integration, the Bently Nevada 991-01-XX-01-00 still exposes PROX OUT and COM terminals and a coaxial connector carrying the dynamic vibration and gap voltage signal. Maintenance teams can connect portable equipment and confirm whether an alarm reflects genuine rotor movement or a probe that has drifted out of its linear range, which is the difference between a five-minute check and an unnecessary bearing inspection.Fast, honest fault behaviour: When a probe fails or a connector works loose, the Not OK / Signal Defeat circuit of the Bently Nevada 991-01-XX-01-00 drives the loop below 3.6 mA within 100 microseconds and restores it within 0.1 seconds once the fault clears. Protection logic therefore sees an unmistakable out-of-range condition instead of a plausible but wrong thrust value, and the Power-up Inhibit circuit does the same job for supply transients at start-up.Commissioning made simple: The Test Input pin allows the whole 4 to 20 mA loop, the wiring and the receiving card to be verified with a variable DC voltage source, so loop checks can be completed before the machine ever turns. Non-interacting zero and span potentiometers let a technician trim the loop without fighting the classic problem where span adjustment shifts zero.Environmentally over-specified on purpose: Potted construction rated for 100% condensing humidity, a -35 °C to +85 °C operating range and a corrosion-resistant housing mean the Bently Nevada 991-01-XX-01-00 tolerates wash-down areas, outdoor enclosures and turbine hall heat. Combined with 35 mm DIN-rail clip mounting, installation is a snap-on operation rather than a drilling exercise.