Product Overview

The Bently Nevada 21500-00-28-10-02 is a 7200 Series 5 mm Standard-Mount Proximity Probe used for non-contacting shaft vibration and displacement measurement in rotating machinery. It operates through eddy-current sensing technology, detecting changes in the distance between the probe tip and a conductive target, typically a rotating machine shaft.

Unlike conventional contact-based sensors, the 5 mm proximity probe measures shaft movement without touching the rotating surface. Its compact sensing tip and threaded mounting case make it suitable for installations where the available mounting space or probe opening requires a smaller-diameter transducer.

The 21500-00-28-10-02 features a standard 1/4-28 UNF mounting thread, a 2.8-inch overall case length, and a nominal 1-meter total probe length. Its unarmored cable terminates in a miniature male coaxial connector for connection to the corresponding 7200 Series extension cable and Proximitor driver.

In a steam turbine installation, for example, the probe can be mounted near a journal bearing to monitor radial shaft vibration. As the shaft rotates, small changes in the distance between the probe tip and shaft surface produce corresponding changes in the measurement signal. The connected monitoring equipment uses these variations to evaluate shaft movement and identify abnormal vibration conditions.

The 21500-00-28-10-02 belongs to the Bently Nevada 7200 Proximity Transducer Systems family. It is intended to operate as part of a matched measurement chain rather than as an independent powered transmitter. The probe, extension cable, and Proximitor driver must be compatible with one another to maintain the required measurement characteristics.

For replacement applications, the complete ordering reference should be checked carefully. Probe diameter, mounting thread, case length, cable configuration, total length, and connector type all affect mechanical installation and electrical compatibility.

Technical Specifications

Product Features

• 7200 Series 5 mm Probe: Suitable for non-contacting shaft vibration and displacement measurement.
• Standard-Mount Configuration: Uses a 1/4-28 UNF threaded mounting arrangement.
• 5 mm Sensing Diameter: Provides a compact sensing interface for proximity measurement applications.
• 2.8-Inch Case Length: Matches the specified overall case-length configuration.
• 1-Meter Total Length: Includes the specified integral probe lead.
• Unarmored Cable: Uses a non-armored cable configuration for the selected installation.
• Miniature Male Coaxial Connector: Connects the probe to a compatible 7200 Series transducer arrangement.
• Fiberglass Probe Tip: Forms the sensing structure at the probe end.
• 2.0 mm Calibrated Range: Supports shaft displacement measurement within the specified system range.
• 7.87 V/mm Scale Factor: Provides the nominal sensitivity of the matched 7200 measurement system.
• Dynamic Measurement Capability: Supports vibration monitoring over the specified frequency range.
• Industrial Machinery Applications: Suitable for compatible turbine, compressor, pump, and generator monitoring installations.

Product Working Principle

The 21500-00-28-10-02 operates using the eddy-current measurement principle. It detects changes in the distance between the probe tip and a conductive target without requiring physical contact with the rotating shaft.

The probe is mounted near the monitored surface using its 1/4-28 UNF threaded case. When connected to a compatible 7200 Series Proximitor driver, it becomes part of an electromagnetic measurement circuit.

The measurement process follows this sequence:

Rotating Shaft → 7200 Series 5 mm Probe → Extension Cable → Proximitor Driver → Machinery Monitoring System

The probe generates an electromagnetic field around its sensing tip. When positioned near a conductive shaft, eddy currents develop within the target material. Changes in the distance between the probe and shaft affect the electrical characteristics of the measurement circuit.

The Proximitor driver processes the probe response and converts the distance variation into a proportional electrical output. Within the calibrated range, the output changes according to the gap between the probe tip and the target surface.

During normal machine operation, shaft vibration causes continuous changes in the probe gap. These variations appear in the output signal and allow the monitoring equipment to evaluate shaft vibration.

The same measurement arrangement can also be used for static displacement monitoring. For example, a probe installed near a turbine thrust bearing can track axial shaft movement relative to the stationary machine structure.

The 5 mm sensing configuration is particularly useful in installations where mounting space is limited or where the existing machine hardware is specifically configured for a smaller-diameter proximity probe.

Role in Bently Nevada 7200 Proximity Transducer System Architecture

The 21500-00-28-10-02 serves as the sensing component within a Bently Nevada 7200 proximity measurement system.

The probe detects changes in the distance between its sensing tip and the rotating shaft. Its electrical response travels through the associated extension cable to the Proximitor driver, which processes the signal and supplies the measurement output to the monitoring equipment.

Rotating Shaft → 21500 Proximity Probe → Extension Cable → Proximitor Driver → Monitoring Equipment → Machinery Protection System

The probe, extension cable, and Proximitor driver should be treated as a matched transducer system. Total electrical system length, connector configuration, and driver compatibility need to be checked before replacing an individual component.

Industrial Applications

The 21500-00-28-10-02 is suitable for rotating machinery installations requiring non-contacting shaft vibration and displacement measurements through a 5 mm sensing arrangement.

Installation and Maintenance

1. Verify the Complete Model Reference: Confirm the 21500-00-28-10-02 identification before installation or replacement.
2. Check Probe Diameter: Verify that the existing measurement arrangement requires a 5 mm proximity probe rather than an 8 mm configuration.
3. Inspect Mounting Threads: Confirm that the mounting point matches the standard 1/4-28 UNF-2A threaded case.
4. Verify Case Length: Check the 2.8-inch overall case length against the available mounting depth and installation arrangement.
5. Confirm Total Probe Length: Verify that the 1-meter total length matches the required installation configuration.
6. Inspect the Connector: Examine the miniature male coaxial connector for damaged contacts, contamination, or mechanical wear.
7. Check Cable Condition: Inspect the unarmored cable for cuts, damaged insulation, crushing, or deterioration near the probe connection.
8. Verify Driver Compatibility: Confirm that the associated Proximitor driver is suitable for the 7200 Series 5 mm measurement system.
9. Check Electrical System Length: Verify the complete probe and extension cable combination against the driver requirements.
10. Adjust the Probe Gap: Position the sensing tip according to the applicable 7200 system specifications and required measurement range.
11. Verify Measurement Output: Check the electrical output at the Proximitor driver and compare the reading with the expected value for the installed probe gap.
12. Record Installation Information: Document the probe model, mounting configuration, total length, driver identification, initial gap setting, and monitoring channel assignment.

If the monitoring signal becomes unstable or produces an unexpected reading, inspect the probe tip, connector, cable condition, mounting position, and Proximitor driver before replacing the sensing element.

Compatible System Components

Recommended Related Models

Key Advantages

• 5 mm sensing configuration for compact mounting arrangements.
• Standard 1/4-28 UNF threaded mounting case.
• 1-meter total probe length.
• Miniature male coaxial connector.
• Unarmored cable configuration.
• Fiberglass sensing tip construction.
• Supports dynamic shaft vibration and static displacement monitoring.
• Compatible with the corresponding 7200 Series transducer arrangement.
• Applicable to turbine, compressor, pump, and generator installations.

Technical FAQs

1. What is the difference between the 21500 and 21504 proximity probes?

The main difference is the sensing diameter and mounting configuration. The 21500 is a 5 mm standard-mount probe with a 1/4-28 UNF mounting thread, while the 21504 is an 8 mm standard-mount probe with a 3/8-24 UNF mounting thread. They should not be treated as mechanically interchangeable without checking the existing mounting arrangement and transducer configuration.

2. Can the 21500-00-28-10-02 operate independently without a Proximitor driver?

No. The probe is a sensing component rather than a standalone powered transmitter. It requires a compatible 7200 Series Proximitor driver and the appropriate cable arrangement to generate a usable measurement output for the monitoring equipment.

3. What does the 00-28-10-02 configuration indicate?

The suffix identifies several physical and connection characteristics of the probe:

• 00: 0.0-inch unthreaded length.
• 28: 2.8-inch overall case length.
• 10: 1.0-meter total probe length.
• 02: Miniature male coaxial connector.

These configuration details should be checked when matching a replacement probe to an existing installation.

4. Can a 5 mm probe replace an existing 8 mm probe?

Not automatically. Although both belong to the 7200 Proximity Transducer Systems family, their sensing diameters and mounting threads differ. The machine mounting opening, probe position, cable arrangement, Proximitor driver, and complete measurement calibration must be evaluated before considering a change from one configuration to another.