Bently Nevada 991-01-XX-01-05 Transmitter with PROX OUT BNC Diagnostic Output and Test Input Pin

Product Overview

The Bently Nevada 991-01-XX-01-05 is a two-wire, loop-powered thrust position transmitter that converts the raw signal from a non-contacting eddy-current proximity probe into an industry-standard 4–20 mA output proportional to the shaft’s axial position. Developed by Bently Nevada, part of Baker Hughes, it belongs to the 991 transmitter family and is built around a simple but powerful idea: give machine builders and plant operators a direct axial displacement signal they can wire straight into a PLC, DCS or SCADA analogue input card, without installing a full rack-based monitoring system.What makes the Bently Nevada 991-01-XX-01-05 distinctive is that the Proximitor signal conditioning electronics are integrated inside the transmitter housing, so no external Proximitor unit, rack or backplane is required. The device accepts one 3300 NSv proximity probe with its matching extension cable — the compact probe family specifically chosen where installation clearance around a thrust collar is minimal — and outputs a linear 4–20 mA signal across the configured full-scale thrust range, with 12 mA representing the electrical centre of that range.Decoding the ordering string helps procurement get it right. In the 991-AA-BB-CC-DD structure, the AA position designates the full-scale range variant, BB (shown here as XX) is the customer-specified system length, CC = 01 selects 35 mm DIN-rail clips, and DD = 05 designates the multi-approval package covering CSA Division 2, ATEX Zone 0, ATEX Zone 2 and ABS maritime certification. Because the Bently Nevada 991-01-XX-01-05 is a calibrated system, the transmitter, probe and extension cable must be length-matched as a set.In practice, the unit occupies a specific and valuable niche: continuous thrust position indication and alarming on smaller or non-critical rotating machines where a full API 670 protection rack is not justified, but catastrophic rotor-to-stator contact is still unacceptable.

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Description

Technical Specifications

Parameter Name	Parameter Value
Product Model	991-01-XX-01-05
Manufacturer	Bently Nevada (Baker Hughes)
Product Type	Two-wire, loop-powered thrust / axial shaft displacement transmitter
Series	991 Thrust Transmitter
Ordering Code Structure	991-AA-BB-CC-DD (A: full-scale option, B: system length, C: mounting, D: agency approval)
Transducer Input	1 non-contacting 3300 NSv proximity probe with matching extension cable
Signal Output	4 to 20 mA DC, proportional to axial displacement, 2-wire configuration
Supply Voltage	+12 to +35 V DC at the transmitter terminals
Loop Accuracy	Within ±1.5 % of full-scale range, typical
Maximum Loop Resistance	1000 Ω including cable, at 35 V DC
Current Limiting	23 mA typical
Zero and Span Adjustment	Non-interacting external potentiometers beneath the transmitter label
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 output impedance, calibrated for a 10 MΩ load
Minimum Target Size	9.5 mm (0.375 in) diameter
Not OK / Signal Defeat Response	Output falls below 3.6 mA within 100 μs of a Not OK condition
Signal Recovery Time	Restored within 0.1 s after the Not OK condition clears
Mounting Option (C = 01)	35 mm DIN-rail clips
Agency Approval (D = 05)	CSA Division 2, ATEX Zone 0, ATEX Zone 2, including ABS maritime approval
Operating Temperature (Transmitter)	−35 °C to +85 °C
Storage Temperature (Transmitter)	−51 °C to +100 °C
Probe Operating Temperature	−52 °C to +177 °C
Relative Humidity	100 % condensing, non-submerged
Enclosure Construction	Potted construction, AISI 303/304 stainless steel case
Transmitter Weight	0.43 kg (0.9 lbm)
Dimensions (H × W × D)	53.3 mm × 73.9 mm × 100.1 mm
Country of Origin	USA

Main Features and Advantages

Integrated signal conditioning, no external rack: The single most practical advantage of the Bently Nevada 991-01-XX-01-05 is that the Proximitor sensor electronics live inside the transmitter body. There is no separate conditioner enclosure to mount, no rack slot to allocate and no interconnecting cable between a probe and a distant conditioning module. For an OEM building a compressor skid or a packager fitting out a pump set, that translates into fewer components, fewer termination points and a shorter commissioning sequence, while still delivering a calibrated, engineering-unit output.Diagnostics without interrupting the loop: A non-isolated PROX OUT terminal pair and a front-panel BNC connector provide buffered dynamic vibration and gap voltage signals, so a portable analyser can be connected to verify probe gap, inspect the raw waveform and confirm mechanical condition — all while the 4–20 mA loop continues feeding the control system. A dedicated Test Input pin allows loop verification with a variable DC source, and non-interacting zero and span potentiometers support field calibration without the adjustments disturbing each other.Failsafe behaviour on transducer faults: Machinery protection is only as good as its failure mode. The Bently Nevada 991-01-XX-01-05 incorporates a Not OK / Signal Defeat circuit that drives the output below 3.6 mA within 100 microseconds if the probe fails or a connection loosens, and a Power-up Inhibit circuit that prevents false readings during supply transients. The result is that a broken measurement chain announces itself as a fault instead of silently holding a plausible value.Built for wet, corrosive and marine locations: Potted construction allows operation in 100 % condensing humidity, the operating envelope spans −35 °C to +85 °C, and the -05 approval package adds CSA Division 2, ATEX Zone 0 and Zone 2 certification plus ABS maritime approval — making the Bently Nevada 991-01-XX-01-05 suitable for offshore platforms, LNG carriers, refinery hazardous areas and compressor enclosures where unprotected electronics would not survive.Compact footprint: At 53.3 × 73.9 × 100.1 mm and 0.43 kg with factory-fitted 35 mm DIN-rail clips, large numbers of transmitters can be mounted side by side in a local junction box or marshalling panel.