21504-28-68-05-02 | Bently Nevada 80 mils Proximity Probe

Introduction to the 21504-28-68-05-02 Proximity Probe

When unplanned downtime threatens your rotating machinery, the 21504-28-68-05-02 from Bently Nevada provides the precise vibration data you need. This 8 mm proximity probe is part of the 7200 series and is 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, this probe delivers accurate displacement measurements that help you detect shaft vibration, misalignment, and bearing wear early.

Key Features and Technical Specifications

• Part Number: 21504-28-68-05-02
• Model: Probe Proximity Vibration
• Manufacturer: Bently Nevada
• Total Length: 0.5 metre (20 inches), tolerance +0.13 m / -0.05 m
• Power: -17.5 Vdc to -26 Vdc at 12 mA maximum consumption
• Calibrated Range: 80 mils (2.0 mm), begins at approximately 10 mils (0.25 mm) from probe face
• Scale Factor: 200 mV/mil (7.87 V/mm), ±4% if 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)
• Temperature Sensitivity: Typically -3% change in scale factor at +150°F (+65°C) at 50 mils gap
• Operating Temperature (Proximitor): -60°F to +212°F (-51°C to +100°C)
• Operating Temperature (Probe & 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 advantage is the wide frequency response from 0 to 10 kHz, which covers both slow-speed and high-speed machinery. This makes the probe suitable for a broad range of rotating equipment.

Applications and Use Cases

The 21504-28-68-05-02 is ideal for monitoring shaft vibration in turbines, compressors, pumps, and motors. Its corrosion-resistant construction (for 8 mm probes) withstands direct contact with air, water, lube oil, ammonium hydroxide, sulfuric acid (10%), MEK, or DMF, ensuring reliable performance in harsh process areas.

Because the probe begins measuring at approximately 10 mils from the target, it can detect subtle changes in shaft position that indicate developing faults. This early warning helps maintenance teams schedule repairs before catastrophic failure occurs.

Installation and Setup

Proper installation is critical for accurate readings. The probe features a 3/8-24 thread and a standard case configuration. When mounting, ensure the probe face is positioned correctly relative to the shaft to achieve the desired gap within the calibrated range.

For best results, calibrate the probe as a system with the associated proximitor and extension cable. This minimizes interchangeability errors and ensures the scale factor remains within ±4%.

Maintenance and Reliability

To maintain long-term accuracy, periodically inspect the probe and cable for physical damage or contamination. Although the probe resists many chemicals, routine cleaning with a soft cloth is recommended to prevent buildup that could affect measurements.

Given the wide operating temperature range of the probe and extension cable (-30°F to +350°F), the 21504-28-68-05-02 can be installed in hot environments without compromising performance. Regular verification of the output signal against a known reference helps confirm the system remains within specification.

Compatibility and Integration

The 21504-28-68-05-02 is designed for use with Bently Nevada 7200 series proximity transducer systems. It connects via a miniature male coaxial connector (option 02) and is compatible with standard Bently Nevada monitors and diagnostic equipment.

For detailed integration guidance, refer to the official Bently Nevada documentation or contact Petro Auto Tech for support.

Troubleshooting Common Issues

If you notice erratic readings, first check the gap between the probe face and the target. An incorrect gap can push the measurement outside the calibrated range, leading to inaccurate data.

Also verify that the power supply provides the required -17.5 Vdc to -26 Vdc at 12 mA maximum. Fluctuations outside this range can affect the probe's output. Finally, inspect the coaxial connector for loose connections or corrosion.

FAQ about the 21504-28-68-05-02

Q: What is the calibrated range of the 21504-28-68-05-02?

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 21504-28-68-05-02 require?

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

Q: What is the frequency response of this probe?

A: The frequency response is 0 to 10 kHz (0 to 600,000 cpm).

Q: Can the probe withstand corrosive environments?

A: Yes, the 8 mm probe is corrosion-resistant to air, water, lube oil, ammonium hydroxide, sulfuric acid (10%), MEK, and DMF.

Q: What is the total length of the 21504-28-68-05-02?

A: The total length is 0.5 metre (20 inches), with a tolerance of +0.13 m / -0.05 m.

Product Support and Availability

The Bently Nevada 21504-28-68-05-02 is available from Petro Auto Tech in new, original factory packaging. Each unit includes a 12-month factory warranty. Contact Petro Auto Tech for current availability and ordering information.