Bently 991-01-XX-01-00 2-Wire Thrust Transmitter with 3300 NSv Probe Compatibility

Product Overview

The Bently Nevada 991-01-XX-01-00 is a compact, loop-powered thrust transmitter engineered specifically for original equipment manufacturers (OEMs) of centrifugal air compressors, small pumps, motors, and fans who require a straightforward 4-20 mA proportional axial displacement signal for their machinery control systems. Unlike traditional rack-based monitoring systems that demand separate Proximitor sensors and dedicated monitor modules, the Bently Nevada 991-01-XX-01-00 integrates the Proximitor function directly into its potted housing, eliminating the need for an external signal conditioning unit. This integrated design dramatically simplifies installation, reduces wiring complexity, and lowers total system cost for OEM applications where space and budget constraints are significant considerations.

The Bently Nevada 991-01-XX-01-00 operates as a 2-wire, loop-powered device that accepts input from a single Bently Nevada 3300 NSv proximity probe and its matching extension cable. The transmitter conditions the probe’s eddy-current signal into a precise 4-20 mA output proportional to the shaft’s axial position, providing an industry-standard signal directly compatible with PLCs, DCS platforms, and machinery control systems. The Bently Nevada 991-01-XX-01-00 is available in 5.0-meter and 7.0-meter system length configurations, accommodating various machine geometries and installation layouts without requiring custom cable assemblies.

The Bently Nevada 991-01-XX-01-00 distinguishes itself through a comprehensive suite of diagnostic and fault-handling features. Non-isolated PROX OUT and COM terminals provide access to the raw dynamic vibration and gap voltage signals for troubleshooting without interrupting the measurement loop. A Test Input pin enables quick verification of loop signal output using a variable DC voltage source. Most critically for machinery protection reliability, the Bently Nevada 991-01-XX-01-00 incorporates a Not OK/Signal Defeat circuit that drives the output below 3.6 mA within 100 microseconds upon detecting a faulty probe or loose connection, preventing false high outputs that could trigger spurious alarms or mask genuine thrust events.

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Description

Technical Specifications

Parameter Name	Parameter Value
Product Model	991-01-XX-01-00
Manufacturer	Bently Nevada
Product Type	Thrust Transmitter (Loop-Powered)
Input Compatibility	One 3300 NSv Proximity Probe with extension cable
Power Supply	+12 to +35 Vdc at transmitter terminals
Output Signal	4-20 mA DC, 2-wire configuration
Accuracy	±1.5% over full-scale range (typical)
Maximum Loop Resistance	1,000 Ω including cable at 35 Vdc
Current Limiting	23 mA typical
Signal Defeat Response	Output drops below 3.6 mA within 100 µs
Operating Temperature	-35°C to +85°C (-31°F to +185°F)
System Length Options	5.0 meters / 7.0 meters
Mounting	35 mm DIN-rail clips or bulkhead screws

Main Features and Advantages

The Bently Nevada 991-01-XX-01-00 delivers substantial engineering value through its integrated design philosophy and robust fault-handling capabilities.

Integrated Proximitor eliminates external hardware: By incorporating the Proximitor sensor function directly within the transmitter housing, the Bently Nevada 991-01-XX-01-00 removes the requirement for a separate signal conditioning unit. This consolidation reduces component count, simplifies wiring, and minimizes potential failure points—particularly valuable in OEM applications where system reliability directly impacts end-user satisfaction.

Comprehensive diagnostic access: The Bently Nevada 991-01-XX-01-00 provides non-isolated PROX OUT and COM terminals that expose the raw probe signal for diagnostic purposes. Technicians can inspect dynamic vibration and gap voltage directly at the transmitter without disrupting the 4-20 mA loop, enabling efficient troubleshooting and verification of probe performance during commissioning or maintenance activities.

Robust fault protection for machinery safety: The Not OK/Signal Defeat circuit within the Bently Nevada 991-01-XX-01-00 actively prevents false alarms by driving the output below 3.6 mA when a probe fault or loose connection is detected. This response occurs within 100 microseconds and restores within 0.1 seconds after the condition clears, ensuring that control systems correctly interpret fault conditions rather than mistaking them for valid thrust measurements.

Environmental durability: The Bently Nevada 991-01-XX-01-00 features potted construction that withstands 100% condensing humidity environments, making it suitable for installation in areas where moisture ingress would compromise lesser transmitters. The stainless steel housing and polyphenylene sulfide transducer tip provide additional resistance to corrosion and mechanical wear.

Application Field

The Bently Nevada 991-01-XX-01-00 serves OEMs and end-users across diverse industries where compact, reliable axial position monitoring is required without the complexity of full rack-based protection systems.

Centrifugal air compressors represent a primary application for the Bently Nevada 991-01-XX-01-00. These machines utilize fluid-film thrust bearings that require continuous monitoring to detect excessive axial movement that could indicate bearing wear, loss of lubricating film, or rotor instability. The transmitter provides the 4-20 mA thrust signal directly to the compressor’s control system, enabling operators to trend axial position, establish alarm thresholds, and initiate protective shutdowns when necessary.

Small pumps, motors, and fans in process industries and manufacturing facilities also benefit from the Bently Nevada 991-01-XX-01-00’s capabilities. In these applications, the transmitter offers a cost-effective alternative to full monitoring systems while still providing essential axial displacement data for machinery protection and predictive maintenance. The compact form factor and DIN-rail mounting options allow the Bently Nevada 991-01-XX-01-00 to be installed within OEM control panels or junction boxes, simplifying integration into new equipment designs.

The Bently Nevada 991-01-XX-01-00 also finds application in retrofit scenarios where existing machinery lacks thrust monitoring but requires enhanced protection. Its loop-powered 2-wire configuration enables installation using existing instrument cabling, minimizing modification costs and downtime.