21508-02-12-90-02 | Bently Nevada 8mm Proximity Probe

Introduction to the Bently Nevada 21508-02-12-90-02

When rotating machinery vibration threatens uptime, the 21508-02-12-90-02 from Bently Nevada delivers precise, real-time data. This proximity probe is part of the 7200 Proximity Transducer Systems, engineered for continuous monitoring in demanding industrial environments. With a calibrated range of 80 mils (2.0 mm) and a scale factor of 200 mV/mil (7.87 V/mm), it provides accurate displacement measurements that help maintenance teams detect issues early.

As a new and original factory-packed unit, the 21508-02-12-90-02 ensures reliable performance right out of the box. Its robust design withstands harsh conditions, making it a trusted choice for critical machinery protection.

Key Features and Technical Specifications

• Model: 21508-02-12-90-02 – Bently Nevada proximity probe.
• Power requirement: -17.5 Vdc to -26 Vdc at 12 mA maximum consumption.
• Calibrated range: 80 mils (2.0 mm), beginning at approximately 10 mils (0.25 mm) from the probe face.
• Scale factor: 200 mV/mil (7.87 V/mm), ±4% when calibrated as a system.
• Linearity: Within 0.8 mils (0.02 mm) of a 200 mV/mil straight line (system calibrated).
• Frequency response: 0 to 10 kHz (0 to 600,000 cpm), -5% at 10 kHz.
• Total cable length: 9 metres (351 inches), tolerance +1.0 m / -0.9 m.
• Connector option: Miniature male coaxial connector.
• Probe tip diameter: 8 mm.
• Threads: 3/8-24.
• Operating temperature: Proximitor -60°F to +212°F (-51°C to +100°C); probe and extension cable -30°F to +350°F (-34°C to +177°C).
• Relative humidity: Up to 95%, noncondensing.
• System weight: 1.3 lbs (0.59 kg).

One distinctive feature is the temperature sensitivity: typically -3% change in scale factor at +150°F (+65°C) at a 50 mils gap (1.27 mm). This means that in high-temperature environments, the probe's output remains stable, reducing the risk of false readings. For maintenance engineers, this translates to fewer unexpected alarms and more accurate trend data.

Applications and Use Cases

The 21508-02-12-90-02 is ideal for monitoring shaft vibration and axial position in turbines, compressors, pumps, and other rotating equipment. Its 8 mm tip and 9-metre cable make it suitable for installations where the probe must be mounted close to the bearing housing. For example, in a steam turbine train, this probe can continuously monitor radial vibration, helping to detect unbalance or misalignment before they cause costly damage. Additionally, its corrosion resistance to air, water, lube oil, and certain chemicals (for 8 mm probes) allows deployment in harsh process areas.

Installation and Setup

Proper installation is critical for accurate measurements. Begin by verifying the total cable length (9 metres, tolerance +1.0 m / -0.9 m) to ensure it reaches the monitor without splicing. Mount the probe using the 3/8-24 threads, ensuring the probe face is positioned at the recommended gap (approximately 10 mils from the target surface). Connect the miniature male coaxial connector to the extension cable, and then route the cable away from high-voltage sources to avoid interference. Always follow the manufacturer's installation manual for torque specifications and target material requirements.

Maintenance and Reliability

Regular inspection of the probe and cable is essential to maintain reliable operation. Check the probe face for any buildup of contaminants that could affect the gap. Verify that the cable is securely connected and free from abrasion or cuts. Because the system is designed for continuous duty, periodic verification of the scale factor (using a calibrated system) ensures long-term accuracy. By incorporating these checks into your routine, you extend the service life of the 21508-02-12-90-02 and minimize unplanned downtime.

Compatibility and Integration

The 21508-02-12-90-02 is part of the 7200 Proximity Transducer Systems from Bently Nevada. It is designed to work with Bently Nevada monitors that accept proximity probe inputs. The 200 mV/mil output is standard for many vibration monitoring systems, making integration straightforward. For specific compatibility with your existing monitor, refer to the official Bently Nevada documentation or contact Petro Auto Tech for guidance.

Troubleshooting and Common Issues

If you experience erratic readings, first check the cable connection and the probe gap. A loose connector or incorrect gap can cause signal fluctuations. Also, verify that the power supply is within the specified range (-17.5 Vdc to -26 Vdc). If the scale factor drifts beyond tolerance, recalibrate the system as per the manual. For persistent issues, consult the Bently Nevada troubleshooting guide or reach out to Petro Auto Tech for technical support.

FAQ about the 21508-02-12-90-02

Q: What is the calibrated range of the 21508-02-12-90-02?

A: The calibrated range is 80 mils (2.0 mm), beginning at approximately 10 mils (0.25 mm) from the probe face.

Q: What power supply does the 21508-02-12-90-02 require?

A: It requires -17.5 Vdc to -26 Vdc at 12 mA maximum consumption.

Q: What is the frequency response of this proximity probe?

A: The frequency response is 0 to 10 kHz (0 to 600,000 cpm), with -5% at 10 kHz.

Q: What is the total cable length of the 21508-02-12-90-02?

A: The total cable length is 9 metres (351 inches), with a tolerance of +1.0 metre / -0.9 metre.

Q: What is the operating temperature range for the probe and extension cable?

A: The probe and extension cable operate from -30°F to +350°F (-34°C to +177°C).

Product Support and Availability

The 21508-02-12-90-02 is available from Petro Auto Tech, an industrial automation parts supplier. It is in stock and ready to ship, backed by a 12-month factory warranty. For ordering or technical questions, contact Petro Auto Tech directly.