Bently Nevada 991-25-70-01-05 Thrust Transmitter

Bently Nevada 991 Thrust Transmitter with DIN-Rail Mounting and Global Approvals

Product Introduction

The 991-25-70-01-05 belongs to the Bently Nevada 991 series of thrust transmitters. This device converts axial displacement signals from a 3300 NSv proximity probe into a standard 4-20 mA current loop output. Specifically, it suits OEMs of centrifugal air compressors, small pumps, motors, and fans that need a proportional thrust signal for their control systems. Moreover, the transmitter integrates the Proximitor function internally, so no external signal conditioning module is required.

Key Technical Specifications

The 991-25-70-01-05 operates as a loop-powered device requiring +12 to +35 Vdc at the transmitter terminals. Its full-scale range is 25-0-25 mils (0.6-0-0.6 mm), with a linear range of 0.25 to 1.65 mm for the Prox Out signal. Meanwhile, the 4-20 mA output accuracy stays within ±1.5% over the specified full-scale range.

The transmitter accepts input from one non-contacting 3300 NSv proximity probe and its matching extension cable. The system length option -70 denotes a 7.0-meter (23.0-foot) cable length. Furthermore, current limiting occurs at 23 mA typical, and the maximum loop resistance is 1,000 Ω including cable at 35 Vdc. Zero and span adjustments are non-interacting and accessible externally.

Additionally, the Not OK/Signal Defeat circuit drives the output below 3.6 mA within 100 µs after a fault occurs. Signal restoration happens within 0.1 seconds after the fault clears. This rapid fault response prevents false alarms caused by probe failure or loose connections.

Mechanical and Environmental Parameters

The mounting option -01 provides 35 mm DIN-rail clips, allowing quick snap-on installation inside machinery protection cabinets. Its compact housing suits dense panel layouts where space is limited. The operating temperature range spans -35°C to +85°C (-31°F to +185°F), while storage temperature extends from -51°C to +100°C (-60°F to +212°F). Weighing just 0.43 kg (0.9 lbm), the unit ships at minimal freight cost.

The agency approval option -05 is the most comprehensive in the 991 line. It includes CSA Division 2, ATEX Zone 0, ATEX Zone 2, and ABS maritime approval. Therefore, users can deploy this transmitter in petrochemical plants, offshore platforms, and marine vessels where flammable vapors or salt-laden air may be present.

Installation Guide

First, verify that the DIN-rail section is clean and free of debris before snapping the transmitter into place. Next, clip the unit onto the 35 mm rail until the locking tab engages firmly. Connect the 3300 NSv probe and extension cable to the transmitter input. Then, wire the 4-20 mA loop observing correct polarity for the 2-wire configuration.

Route the probe coaxial cable through grounded conduit to minimize electromagnetic interference. Ensure that the input voltage at the transmitter terminals never exceeds 35 Vdc to protect internal circuitry. Finally, perform a loop check using the TEST input to verify output accuracy across the full-scale range.

Packaging List

• 1 × Bently Nevada 991-25-70-01-05 Thrust Transmitter

• 1 × DIN-rail mounting clip set

• 1 × Technical documentation folder

FAQ

Q1: What distinguishes the -05 approval option from -01?
A1: The -05 option adds ATEX Zone 0, ATEX Zone 2, and ABS maritime approval on top of CSA Division 2. Choose it for offshore or European hazardous-area projects.

Q2: Can this transmitter work with probes other than the 3300 NSv?
A2: No. The 991-25-70-01-05 is calibrated specifically for Bently Nevada 3300 NSv proximity probes and matching extension cables.

Q3: What happens if the probe cable breaks during operation?
A3: The Not OK circuit drives the output below 3.6 mA within 100 µs, alerting the control system to a fault condition.

Q4: Does the DIN-rail clip option require additional hardware?
A4: No. The -01 option includes 35 mm DIN-rail clips that snap directly onto standard rail without extra brackets.