Bently Nevada 991-06-70-01-CN 991 Thrust Transmitter

Description

The Bently Nevada 991-06-70-01-CN is a 2-wire, loop-powered 991 Thrust Transmitter engineered to measure axial shaft position and thrust displacement on rotating machinery. The transmitter processes raw signals from a compatible proximity probe system and conditions them into a stable 4 to 20 mA DC output directly proportional to mechanical movement. This design allows for direct integration into PLCs, DCS architectures, or SCADA systems without requiring a dedicated machinery protection monitor rack. It provides continuous, cost-effective monitoring for critical industrial assets where axial displacement tracking is required to prevent catastrophic thrust bearing failure.

Features

• Loop-powered 2-wire architecture reduces field wiring overhead and installation costs.
• Standard 4 to 20 mA DC analog output connects directly to process control systems.
• Front-panel BNC jack provides a buffered raw voltage signal for diagnostics and portable data collectors.
• Non-contacting eddy current sensing technology ensures long-term wear-free operation.
• Compact, space-saving design suitable for direct high-density DIN rail mounting.

Applications

• Centrifugal compressor axial thrust displacement monitoring
• Steam and gas turbine rotor position tracking
• High-pressure boiler feed pump shaft alignment
• Industrial gearbox thrust bearing wear diagnostics
• Forced draft and induced draft fan shaft positioning

Ordering Information

• 991: Thrust Transmitter
• 06: 3300 XL 8 mm proximity probe compatibility with 1.0 mm linear range
• 70: 7.0 metres system length option
• 01: 35 mm DIN rail mounting option
• CN: Approvals option certified for specialized regional or country-specific standards (China/NEPSI/GB)

Technical Specifications

Connections / Interfaces

Installation Guidelines

• DIN Rail Attachment: Secure the housing firmly onto a standard 35 mm DIN rail using the integrated DIN mount clips inside a protective industrial enclosure rated IP54 or higher.
• Bulkhead Mounting Option: Alternatively, use the 4 mounting holes ($5.8 \text{ mm}$ diameter) spaced at $69.9 \text{ mm} \times 63.5 \text{ mm}$ for flat panel/bulkhead installations with the provided 6-32 x 1.326 screws.
• Shielding Protocol: Connect the input transducer cable shield to the SHLD terminal. The external control loop shield must be grounded at the control system (PLC/DCS) side only to eliminate ground loops.
• Probe Gapping: Set the physical probe gap using a digital voltmeter across the BNC jack or COM terminals to verify the sensor sits within its linear voltage range before operation.
• Separation of Wiring: Route all input sensor cables and output current loop wiring away from high-voltage AC lines or variable frequency drive cables to mitigate EMI/RFI noise.

Compliance and Certifications

• CN Approval Variant (Certified for regional hazardous area compliance, such as NEPSI / GB standards)

FAQ

What are the exact enclosure dimensions for cabinet layout planning?

The base footprint measures 100.1 mm in length by 73.9 mm in width, with a maximum profile height of 53.3 mm when the 35 mm DIN rail clip is attached.

What size are the alternative bulkhead installation holes?

The unit features 4 mounting holes with a diameter of 5.8 mm, laid out in a precise 69.9 mm by 63.5 mm rectangular center pattern.

What is the function of the BNC connector on the faceplate?

It provides an unconditioned, buffered raw voltage output for connecting diagnostic instruments and dynamic signal analyzers without disrupting the 4 to 20 mA current loop.

Does this device require a separate power supply line?

No, it operates entirely on loop power, drawing its operating voltage directly from the 4 to 20 mA signal line.

What happens if the system length option is mismatched with the probe?

Connecting a probe/extension cable combination that does not match the specified 7.0-metre calibration will result in severe measurement non-linearity and scale factor errors.

Can this transmitter be mounted in an outdoor environment?

It must be installed within a weatherproof NEMA 4X or IP65/66 rated field junction box to protect it from moisture, dust, and direct sunlight.

Is the transmitter output compatible with standard analog input cards?

Yes, the 4 to 20 mA output directly connects to standard differential or single-ended analog input cards on any PLC or DCS.

What is the meaning of the CN suffix code?

The CN suffix denotes specific regional certification compliance, commonly matching China national safety and hazardous area standards.

Can the unit be calibrated in the field for different linear ranges?

No, the linear range and scale factors are hard-wired and factory-calibrated. Range changes require a different model configuration.

How does reverse loop polarity affect the transmitter?

The device features internal diode protection against reverse polarity, meaning it will not function when wired backward but will not be damaged.