Bently Nevada 991-25-50-01-05 Thrust Transmitter

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991-25-50-01-05 Overview

The 991-25-50-01-05 Thrust Transmitter is intended primarily for the original equipment manufacturers (OEMs) of centrifugal air compressors or small pumps, motors, or fans who prefer to provide a simple 4 to 20 mA proportional axial displacement (thrust) signal as the input to their machinery control system.
The 991-25-50-01-05 transmitter is a 2-wire, loop-powered device that accepts input from our 3300 NSv proximity probe and its matching extension cable (available in 5 m and 7 m system length options). The 991-25-50-01-05 transmitter conditions the signal into appropriate engineering units proportional to the shaft’s axial position1, 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.

991-25-50-01-05 Parameters

Power Requirement: +12 to +35 Vdc input at the transmitter terminal
Output Signal: 4-20 mA proportional over specified full-scale range (2-wire configuration)
Full-scale Range: 25-0-25 mils (center zero for thrust position)
Loop Accuracy: Within ±1.5% over specified full-scale range (typical)
Maximum Loop Resistance: 1,000 Ω including cable at 35 Vdc
PROX OUT Scale Factor: 7.87 mV/μm (200 mV/mil) ±6.5% typical
PROX OUT Impedance: 10 kΩ output impedance calibrated for 10 MΩ load
Linear Range (Prox Out): 0.25 to 1.65 mm (10 to 65 mils)
Not OK/Signal Defeat: Output goes to <3.6 mA within 100 μs after Not OK condition
Operating Temperature (Transmitter): -35°C to +85°C (-31°F to +185°F)
Operating Temperature (Probe): -52°C to +177°C (-62°F to +351°F)

FAQ about 991-25-50-01-05

1. What is the primary application for the 991-25-50-01-05 Thrust Transmitter?

It is intended primarily for OEMs of centrifugal air compressors, small pumps, motors, or fans who need to provide a simple 4-20 mA proportional axial displacement (thrust) signal as input to their machinery control system.

2. What is the correct gap setting for the probe?

Probe adjustment and range are critical in thrust position measurements. Incorrect probe gap settings may prevent the transmitter from reaching full-scale in either the normal or counter directions. For proper adjustment, follow the instructions in the manual.

3. What happens if the proximity probe fails or has a loose connection?

The "NOT OK/Signal Defeat" circuit activates. The transmitter output will drop to less than 3.6 mA within 100 microseconds of a fault. This lets the control system distinguish between a "zero thrust" reading and a fault condition.

4. How do I connect diagnostic equipment (like an oscilloscope) to the PROX OUT?

The PROX OUT signal is not isolated from the 4-20 mA loop, and its phase is inverted. To safely connect AC-powered diagnostic equipment, you must use the 990/991 Test Adapter (122115-01) , which provides isolation and corrects the signal polarity.

5. What are the limitations of using a 991-25-50-01-05 thrust transmitter compared to a full monitoring system?

While useful for alarming on thrust position and trending, the 4-20 mA signal does not support advanced monitor functions such as Timed OK channel defeat, Danger Bypass, or Trip Multiply.

6.What does the "-05" agency approval option include?

The "-05" option provides multiple hazardous area approvals, including CSA Division 2 for North America, ATEX Zone 0 and Zone 2 for Europe, and ABS maritime approval for marine applications.