Bently Nevada 991-25-70-01-01 Thrust Transmitter 25-0-25 mils

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

Product Introduction

The Bently Nevada 991-25-70-01-01 is a specialized member of the 991 series, designed specifically for axial (thrust) position measurement. Unlike standard vibration transmitters, this model provides a bi-polar output spanning 25-0-25 mils, indicating both forward and reverse shaft movement from a neutral position. It works with a single 3300 NSv proximity probe to generate a 4-20 mA loop signal. Furthermore, this unit includes a 7.0-meter system length and features 35 mm DIN-rail clips for rapid installation in control cabinets. With CSA Division 2 approval, it offers reliable performance in hazardous locations.

Key Technical Specifications

The 991-25-70-01-01 delivers precise axial position measurements essential for thrust bearing monitoring. Its primary function is to accept input from one non-contacting 3300 NSv proximity probe and its extension cable, then convert this data into a two-wire, 4-20 mA output.

• Input: Accepts 1 non-contacting 3300 NSv Proximity Probe and extension cable.

• Power Supply: Requires +12 to +35 Vdc input at the transmitter terminal.

• Output Signal: 4 to 20 mAdc over the specified full-scale range (25-0-25 mils).

• 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.

• Loop Accuracy: Within ±1.5% over the full-scale range (typical), measured from TEST signal to a 250 Ω load.

• Maximum Loop Resistance: 1,000 Ω including cable at 35 Vdc.

• Current Limiting: 23 mA typical.

• Zero and Span: Non-interacting external adjustments for independent calibration.

Mechanical and Environmental Specifications

This transmitter is built to withstand extreme conditions, making it suitable for demanding turbomachinery environments.

• Mounting Option: 01 – 35 mm DIN-rail clips for panel installation.

• Transmitter Weight: 0.43 kg (0.9 lbm).

• Operating Temperature: -35°C to +85°C (-31°F to +185°F).

• Storage Temperature: -51°C to +100°C (-60°F to +212°F).

• Transducer Tip Material: Polyphenylene sulfide (PPS).

• Transducer Case Material: AISI 303 or 304 Stainless Steel (SST).

• Probe Cable: 75Ω coaxial, fluoroethylene propylene (FEP) insulated.

• Cable Armor: Flexible AISI 302 SST with optional FEP outer jacket.

• Tensile Strength: 222 N (50 lbf) probe case to probe lead, maximum.

Installation and Wiring Guidance

Correct installation ensures accurate thrust position measurement and long-term reliability. Begin by mounting the Bently Nevada 991-25-70-01-01 onto a standard 35 mm DIN rail using the included clips. Next, connect the 3300 NSv probe and extension cable to the transmitter input. Then, set the probe gap within the linear range of 0.25 to 1.65 mm from the target surface to achieve the 25-0-25 mils bi-polar output.

For the output wiring, configure a 2-wire current loop with a DC power supply between +12 and +35 Vdc. Ensure the total loop resistance does not exceed 1,000 Ω at 35 Vdc. The 991-25-70-01-01 provides non-interacting zero and span adjustments, allowing you to set the 4 mA and 20 mA points independently—this is particularly useful for bi-polar ranges where the midpoint (12 mA) represents the neutral shaft position.

Not OK and Signal Defeat Function

This transmitter incorporates a fast-acting diagnostic circuit. If a fault condition occurs—such as a probe cable break or power interruption—the output current falls below 3.6 mA within 100 µs. Consequently, your control system can detect this failure almost instantly. Once the fault is resolved, the signal automatically restores within 0.1 seconds, which is significantly faster than standard vibration transmitters. This rapid recovery minimizes process disruption and aids in quick troubleshooting.

Packaging List

• 1 x Bently Nevada 991-25-70-01-01 Thrust Transmitter

• 35 mm DIN-rail mounting clips (pre-installed)

• Installation and wiring instruction sheet

Please note: The 3300 NSv proximity probe, extension cable, and external power supply are not included and must be ordered separately.

Shipping Information

All orders are shipped via FedEx, UPS, or DHL for fast, reliable delivery. Contact our sales team for current stock availability and shipping quotes.

Frequently Asked Questions (FAQ)

1. What is the difference between the 991 and 990 series transmitters?
The 991 series is specifically designed for axial (thrust) position monitoring with bi-polar ranges like 25-0-25 mils. In contrast, the 990 series measures radial vibration with unipolar ranges such as 0-10 mils. The 991-25-70-01-01 is optimized for thrust bearing applications.

2. What does the 25-0-25 mils range mean?
This bi-polar range indicates the shaft can move 25 mils forward and 25 mils backward from a neutral center position. The 4-20 mA output maps linearly across this range, with 12 mA typically representing the neutral or "zero" thrust position.

3. Is the 991-25-70-01-01 approved for hazardous areas?
Yes. This model carries Agency Approval Option 01, which is CSA Division 2 certification. It is suitable for installation in Class I, Division 2 hazardous locations. Always verify site-specific requirements before installation.

4. Can I mount this transmitter on a panel instead of a DIN rail?
The 991-25-70-01-01 comes with Mounting Option 01, which includes 35 mm DIN-rail clips. For panel mounting, you would need a different mounting option or an adapter bracket. Contact us for alternative mounting solutions.

5. How quickly does the output recover after a fault condition?
The "Not OK" signal defeat function restores normal output within 0.1 seconds after the fault is removed. This rapid recovery is a key feature of the 991 series, minimizing downtime and ensuring continuous monitoring.