Bently Nevada 991-25-70-01-01 Vibration Transmitter

Bently Nevada 991-25-70-01-01 Vibration Transmitter

The Bently Nevada 991-25-70-01-01, also cataloged as the 991 Thrust Transmitter, operates as a dedicated hardware component for converting proximity probe signals into a 4-20 mA axial displacement output within centrifugal compressor control systems.

Suffix Breakdown & Model Matrix

Hardware Specifications

Mechanical Monitoring & TSI Integration

The 991 Thrust Transmitter integrates an internal Proximitor sensor, eliminating the requirement for external signal conditioning modules. It utilizes eddy-current probe scaling compatible specifically with the 3300 NSv series to measure axial shaft position. During commissioning, gap voltage validation is conducted via the non-isolated diagnostic terminals to confirm the probe is within the target linear operating range. The transmitter ensures cross-talk suppression through fixed internal filtering, while the Not OK/Signal Defeat circuit prevents faulty transducer signals from triggering false alarms in the primary control logic.

Frequently Asked Questions

Q: Does the 991 transmitter require an external Proximitor?

A: No. The transmitter features an integrated Proximitor sensor, which conditions the signal directly from the 3300 NSv probe and extension cable, reducing total hardware footprint.

Q: How is the loop output verified during maintenance?

A: Test Input Pin. A variable DC voltage source can be applied to the Test Input pin to simulate probe proximity, allowing verification of the 4-20 mA loop response without requiring physical rotor movement.

Field Installation Guidelines

• Mounting: Utilize the provided DIN-rail clips or bulkhead screws. Given the potted construction, ensure the unit is mounted in an orientation that allows access to the zero and span potentiometers.
• Wiring: Connect the 4-20 mA loop wires to the designated terminals. Use shielded twisted-pair cabling to minimize noise, ensuring the shield is grounded at the control system end only.
• Calibration: Remove the transmitter label to access zero and span potentiometers for loop adjustment. Ensure the signal is verified against the mechanical gap measurement using a digital multimeter at the PROX OUT terminal.
• Environment: While potted for 100% condensing humidity, ensure cable entries are sealed using appropriate cable glands to maintain the environmental protection rating.