Bently Nevada 991-25-50-02-05 991 Thrust Transmitter

Description

The 991 Thrust Transmitter converts axial shaft displacement signals into a proportional 4 to 20 mA output for machinery control and protection systems. The unit is designed for centrifugal air compressors, pumps, motors, and fans requiring continuous thrust position monitoring through a simple loop-powered interface.

The Bently Nevada 991-25-50-02-05 is a 2-wire loop-powered transmitter compatible with the 3300 NSv proximity probe system using a 5 m extension cable configuration. The transmitter conditions the probe signal into engineering units proportional to shaft axial position and transmits the signal directly to PLC, DCS, or machinery protection systems.

The transmitter integrates the Proximitor sensor internally and does not require an external signal conditioning module. Diagnostic access is available through non-isolated PROX OUT and COM terminals together with a coaxial connector for vibration and gap voltage monitoring.

The unit supports bulkhead mounting and includes non-interacting zero and span adjustments for loop calibration. A dedicated test input pin allows verification of loop output using a variable DC voltage source.

The potted housing design supports installation in high-humidity industrial environments. The transmitter is commonly used in OEM rotating machinery packages where compact thrust monitoring is required.

Features

• 2-wire loop-powered transmitter
• 4 to 20 mA proportional thrust output
• Compatible with 3300 NSv proximity probes
• Integrated Proximitor sensor design
• Dynamic vibration and gap voltage output
• Bulkhead mounting configuration
• Non-interacting zero and span adjustments
• Power-up inhibit circuit
• NOT OK signal defeat protection
• Supports diagnostic signal access
• Potted construction for humid environments
• Suitable for compressors, pumps, motors, and fans

Applications

• Centrifugal air compressors
• Industrial pumps
• Electric motors
• Rotating machinery packages
• OEM skid systems
• Turbomachinery thrust monitoring
• Machinery protection systems
• PLC and DCS monitoring interfaces

Ordering Information

Technical Specifications

Connections/Interfaces

Installation Guidelines

Install the transmitter in a dry control enclosure or protected machinery panel area. Maintain proper shielding and grounding practices for all probe and signal cables to reduce EMI and RFI interference.

Route proximity probe cables separately from high-voltage power wiring. Avoid excessive bending or mechanical stress on coaxial cables during installation.

Verify probe gap adjustment according to the machinery shaft position requirements before commissioning. Incorrect probe positioning may prevent full-scale measurement operation.

Use isolated diagnostic equipment when accessing the PROX OUT signal. The diagnostic output is non-isolated from the 4 to 20 mA loop.

Provide sufficient ventilation around the transmitter when installed in enclosed cabinets with elevated ambient temperatures.

Compliance and Certifications

FAQ

What does the 991 transmitter measure?
It measures axial shaft displacement and converts the signal into a proportional 4 to 20 mA output.

Which probe system is compatible with this transmitter?
The unit is designed for use with the 3300 NSv proximity probe system.

Is the transmitter loop powered?
Yes. It operates as a 2-wire loop-powered device.

Can the transmitter provide vibration diagnostics?
Yes. The PROX OUT connection provides dynamic vibration and gap voltage signals.

What mounting method does this version use?
This model uses bulkhead mounting screws.

Does the transmitter require an external Proximitor module?
No. The Proximitor sensor is integrated into the transmitter.

What is the output signal type?
The standard output is 4 to 20 mAdc.

Can the transmitter connect directly to a PLC or DCS?
Yes. The output is suitable for standard industrial control system analog inputs.

What is the supported operating temperature range?
The operating range is -35 degC to +85 degC.

Is the housing suitable for humid environments?
Yes. The potted construction supports high-humidity environments.

What happens during a probe fault condition?
The NOT OK circuit drives the output below 3.6 mA during a fault condition.

Can the loop output be tested without machinery movement?
Yes. A test input pin supports loop verification using a variable DC source.

Does the transmitter support hazardous area installations?
Yes. The unit includes CSA and ATEX/IECEx approvals depending on configuration.

What industries commonly use this transmitter?
It is widely used in compressor, pump, motor, and rotating equipment monitoring systems.