Bently Nevada 991-25-70-01-00 991 Thrust Transmitter

991 Thrust Transmitter 991-25-70-01-00

Product Introduction

The Bently Nevada 991-25-70-01-00 is a loop-powered thrust transmitter engineered for axial shaft position measurement in industrial machinery. This model offers a full-scale range of 25-0-25 mils and a system length of 7.0 meters (23.0 feet) . It accepts input from one non-contacting 3300 NSv proximity probe and its matching extension cable. The transmitter uses a 35 mm DIN-rail mounting option with clips, enabling quick installation in standard control cabinets. Furthermore, the -00 agency approval option means no specific certifications are required, making it ideal for non-hazardous installations where cost efficiency matters. For reliable thrust monitoring in turbines, compressors, and pumps, the 991-25-70-01-00 delivers consistent performance with simple field calibration.

Power and Electrical Specifications

This transmitter requires a +12 to +35 Vdc power supply at its terminal block, accommodating a wide range of industrial DC sources. It produces a 4 to 20 mAdc signal over the full-scale range using a standard 2-wire configuration, simplifying wiring and reducing installation costs. The loop accuracy is rated within ±1.5% (typical) when measured from the TEST signal input across a 250 Ω load resistor. Additionally, the maximum loop resistance is 1,000 Ω including cable at 35 Vdc, and the current limiting is typically 23 mA. The zero and span adjustments are non-interacting external potentiometers, allowing technicians to calibrate the output independently without affecting the other setting. This design significantly reduces setup time and improves accuracy.

Linear Range and Probe Configuration

The 991-25-70-01-00 provides a linear range from 0.25 to 1.65 mm for Prox Out signals, suitable for 0.6-0-0.6 mm or 25-0-25 mils current loop linear ranges. For optimal operation, the connected 3300 NSv probe must be gapped within this linear region to achieve the specified full-scale output. The transmitter's frequency response is optimized for axial thrust monitoring, though dynamic performance depends on the probe and target characteristics. Furthermore, the minimum target size follows the 3300 NSv probe specifications, ensuring compatibility with standard machinery shaft targets. This configuration guarantees accurate axial position feedback for machinery protection systems.

NOT OK and Environmental Ratings

A vital safety feature is the NOT OK/signal defeat function. The output drops to less than 3.6 mA within 100 µs after a NOT OK condition occurs, providing immediate fault indication to the control system. Once the condition clears, the signal restores within 0.1 seconds , significantly faster than many competing transmitters. The operating temperature ranges from -35°C to +85°C , while storage temperature spans -51°C to +100°C , ensuring reliable performance in harsh industrial environments. Since this model carries the -00 approval option, it is intended for non-hazardous locations only. Its rugged construction and straightforward design make it suitable for a wide range of industrial monitoring applications.

Installation and DIN Rail Mounting

Mounting the 991-25-70-01-00 is simple using the included 35 mm DIN-rail clips (Mounting Option 01). First, snap the transmitter firmly onto a standard 35 mm DIN rail until the clips engage securely. Next, connect the 3300 NSv probe and extension cable to the input terminals, observing correct polarity. Then, wire the power supply (+12 to +35 Vdc) to the terminal block, ensuring proper connections. For the 4-20 mA loop, keep total resistance below 1,000 Ω at 35 Vdc to maintain accuracy. Finally, adjust the zero and span potentiometers using a small non-metallic screwdriver while monitoring the output with a precision multimeter. The non-interacting adjustment feature simplifies this process considerably.

Packaging and Shipping

Each 991-25-70-01-00 unit is packaged in anti-static foam within a sturdy corrugated carton for maximum protection during transit. The package contains the transmitter assembly, DIN-rail clips, and a wiring diagram for quick reference. The net weight is 0.43 kg (0.9 lbm) , and the gross weight including packaging is 0.66 kg. All orders are dispatched via FedEx, UPS, or DHL with tracking numbers provided upon shipment. Please note that calibration certificates and warranty documents are not included with this listing.

Frequently Asked Questions (FAQ)

1. Can I use this transmitter with a 3300 XL probe instead of the NSv?
No, the 991-25-70-01-00 is specifically calibrated for use with the 3300 NSv proximity probe and its extension cable.

2. What is the difference between the -01 and -03 mounting options?
The -01 option uses 35 mm DIN-rail clips only, while the -03 option includes both DIN clips and additional mounting screws for extra security.

3. How do I verify the 4-20 mA output is correct?
Connect a multimeter in series with the loop and measure the current while adjusting the zero and span potentiometers.

4. Is the 991-25-70-01-00 approved for hazardous areas?
No, the -00 agency approval option indicates this model is not certified for hazardous locations; it is intended for non-hazardous use only.

5. What is the recommended power supply voltage for best accuracy?
A 24 Vdc supply is typically recommended, but the unit operates from +12 to +35 Vdc with accuracy maintained across this range.