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  • Integrated Proximitor Sensor requires no external unit
  • Non-isolated “PROX OUT " and "COM" terminals plus a coaxial connector provide a dynamic vibration and gap voltage signal output for diagnostics
  • Non-interacting zero and span potentiometers under the Transmitter label supports loop adjustment
  • Test Input pin allows quick verification of loop signal output, using a variable DC voltage source as the input
  • A Power-up Inhibit circuit eliminates signal errors due to line voltage transients
  • A Not OK/Signal Defeat circuit prevents high outputs or false alarms due to a faulty proximity probe or loose connection
  • Choice of DIN-rail clips or bulkhead mounting screws as standard options simplifies mounting
  • Potted construction for high humidity (up to 100% condensing) environments
  • Compatibility with 3300 NSv proximity probe allows transducer installation in small areas with minimal clearance, typical of centrifugal air compressors


The Bently Nevada 991 Thrust Transmitter provides a 4-20 mA signal proportional to thrust position and is designed for use on smaller, non-critical machinery. Its primary use is on centrifugal air compressors with fluid-film thrust bearings. The 991 Thrust Transmitter can measure up to 1.2 mm or 50 mils of total thrust movement.

The 991 thrust transmitter is a 2-wire, loop-powered device that accepts input from Bently Nevada's 3300 NSv proximity probes and matching extension cables (available in 5 and 7 meter system length options). The transmitter conditions the signal into appropriate engineering units proportional to the shaft's axial position, and provides it as a 4 to 20 mA industry-standard signal for input to the control system where machinery protection alarming and logic occurs.

Bently Nevada 991 Thrust Transmitter Specifications
Input Accepts 1 non-contacting 3300 NSv Proximity Probe and extension cable
Power Requires +12 to +35 Vdc input at the transmitter terminal
Signal Output 4 to 20 mAdc over specified full-scale range in 2-wire configuration
Loop Accuracy Within ±1.5% over specified full-scale range
Maximum Loop Resistance 1,000 Ω including cable at 35 Vdc
Current Limiting 23 mA typical
Zero and Span Non-interacting external adjustments
NOT OK/Signal Defeat Signal output will go to less than 3.6 mA within 100 μs after a Not OK condition occurs. Signal output is restored within 0.1 seconds after the Not OK condition is removed
Proximitor Sensor Output Compatible with ungrounded, portable test equipment. When using grounded, ac-powered test equipment, use the 122115-01 Test Adapter for signal isolation
Output Impedance Prox Out has a 10 kΩ output impedance calibrated for a 10 MΩ load
Linear Range 0.25 to 1.65 mm for Prox Out. Suitable for 0.6-0-0.6 mm or 25-0-25 mils current loop linear ranges
Prox Out Incremental Scale Factor 7.87 mV/μm (200 mV/mil) ± 6.5% typical including interchangeability errors when measured in increments of 0.25 mm over the linear range using a flat 30 mm target
Temperature Stability Incremental scale factor remains within ±10% of 7.87 mV/μm from 0 °C to +70 °C
Minimum Target Size 9.5 mm diameter
Leadwire Length Maximum for Proximitor Sensor Output (BNC connector), maximum cable distance is 3 meters
Non-Hazardous, Zone 2 or Div 2 Hazardous area locations 13 km (8 miles) maximum between transmitter and receiving device for signal output
Intrinsically Safe Hazardous area locations 68 meters (225 ft.) maximum between transmitter and receiving device for signal output
Electrical Classification General Purpose Approval by Canadian Standards Association (CSA/NRTL/C) in North America and by VDE in Europe. The 991 has the CE mark for Europe


This product can be used in the following applications: