Product Overview

The Bently Nevada 330881-28-20-050-03-02 is a PROXPAC XL Proximity Transducer Assembly used for non-contacting shaft vibration and displacement monitoring in rotating machinery. It combines a 3300 XL 8 mm proximity probe with a Proximitor Sensor inside a protective housing, forming an integrated measurement assembly for industrial machinery installations.

Unlike a conventional proximity measurement arrangement where the probe and Proximitor Sensor are installed as separate components, the PROXPAC XL places these elements together in one assembly. This eliminates the need for a separate extension cable between the probe and its associated Proximitor Sensor, while also removing the requirement for an independently mounted Proximitor housing.

The model configuration includes a 200 mm standoff adapter and 50 mm probe penetration. The probe is positioned through the machine casing or mounting structure to establish the required measurement gap between its sensing tip and the rotating shaft. This arrangement is particularly useful on compressors and turbines where the probe must be installed through a dedicated mounting opening while maintaining the correct sensing position.

For example, on a centrifugal compressor, the assembly can be installed near a radial bearing to monitor shaft vibration. As the shaft moves during operation, the proximity probe detects changes in the distance between its tip and the shaft surface. The integrated Proximitor Sensor converts these changes into an electrical signal for the machinery monitoring system.

The 330881-28-20-050-03-02 uses a 3300 XL 8 mm probe with multiple approvals, a 200 mm standoff adapter, a 50 mm probe penetration, one M20 fitting with two plugs, and a 3/4-14 NPT mounting thread. These configuration details are important when selecting a replacement assembly because they determine how the transducer fits the machine mounting arrangement.

Technical Specifications

Product Features

• Integrated PROXPAC XL Assembly: Combines the proximity probe and Proximitor Sensor in one protective housing.
• 3300 XL 8 mm Probe: Supports non-contacting shaft vibration and displacement measurement.
• Multiple Approvals Configuration: Uses the applicable approved probe and sensor arrangement.
• 200 mm Standoff Adapter: Provides the specified mounting extension for the installation.
• 50 mm Probe Penetration: Establishes the probe insertion length required by the selected configuration.
• M20 Cable Fitting: Supplied with one M20 fitting and two plugs.
• 3/4-14 NPT Mounting Thread: Matches the specified mounting-thread configuration.
• IP66 / Type 4X Housing: Provides protection for the integrated assembly in industrial environments.
• Eddy-Current Measurement: Detects shaft movement without physical contact.
• Simplified Installation: Eliminates the conventional separate Proximitor Sensor housing arrangement.
• Direct Field Wiring: Connects the monitoring system directly to the PROXPAC XL assembly.
• Industrial Machinery Monitoring: Suitable for compatible compressor, turbine, pump, and other rotating equipment installations.

Product Working Principle

The 330881-28-20-050-03-02 operates through the eddy-current measurement principle used in Bently Nevada 3300 XL 8 mm proximity systems.

The assembly contains the proximity probe and Proximitor Sensor in one housing. The probe is installed through the machine mounting arrangement, with its sensing tip positioned near the rotating shaft. The Proximitor Sensor processes the probe response and generates an electrical output corresponding to the measured distance.

The measurement sequence is:

Rotating Shaft → 3300 XL 8 mm Probe → Integrated Proximitor Sensor → Field Wiring → Machinery Monitoring System

When the probe operates near a conductive shaft, its electromagnetic field induces eddy currents in the target material. Changes in the probe-to-shaft gap affect the probe’s electrical response. The integrated Proximitor Sensor converts this response into a proportional DC voltage.

During normal operation, shaft vibration causes continuous changes in the distance between the probe and shaft surface. These changes appear as variations in the sensor output. The connected monitoring system uses the signals to calculate shaft vibration and evaluate machinery operating conditions.

The same arrangement can be used for static displacement measurement. For example, when installed near a turbine thrust bearing, the probe can monitor axial shaft movement relative to the machine casing.

The integrated construction is particularly useful where the installation requires a dedicated protective housing. Instead of mounting a separate Proximitor Sensor elsewhere in the machine area, the PROXPAC XL assembly keeps the probe and signal-conditioning components together.

Role in Bently Nevada 3300 XL Machinery Monitoring Architecture

The 330881-28-20-050-03-02 serves as an integrated proximity measurement assembly between the rotating machine and the machinery monitoring rack.

Its probe detects shaft movement, while the internal Proximitor Sensor converts the measurement into an electrical output. The resulting signal is transmitted through field wiring to a compatible monitoring input.

Rotating Shaft → 3300 XL 8 mm Probe → PROXPAC XL Integrated Assembly → Monitoring Module → Machinery Protection System

The actual monitoring arrangement depends on the selected monitoring module, channel configuration, field wiring, and machinery measurement requirements.

Industrial Applications

The PROXPAC XL assembly is suitable for rotating machinery installations where the proximity probe and signal-conditioning electronics need to be accommodated in a common protective housing.

Installation and Maintenance

1. Verify the Complete Model Reference: Confirm the 330881-28-20-050-03-02 identification before installation or replacement.
2. Check the Probe Configuration: Verify that the assembly contains the specified 3300 XL 8 mm proximity probe with multiple approvals.
3. Confirm Standoff Length: Check the 200 mm standoff adapter against the machine mounting arrangement and available installation space.
4. Verify Probe Penetration: Confirm that the 50 mm probe penetration matches the required mounting depth and sensing position.
5. Inspect Mounting Threads: Check the 3/4-14 NPT mounting connection for damage, contamination, or thread mismatch.
6. Check Cable Fittings: Verify the supplied M20 fitting and two plugs against the intended cable entry arrangement.
7. Inspect the Housing: Examine the PPS enclosure for cracks, deformation, damaged sealing surfaces, or signs of environmental deterioration.
8. Check Electrical Connections: Inspect the internal connections and field wiring for loose conductors, damaged insulation, or incorrect termination.
9. Verify Power Supply: Confirm that the Proximitor Sensor receives the required negative DC supply voltage within its specified operating range.
10. Adjust the Probe Gap: Position the sensing tip according to the applicable 3300 XL 8 mm system requirements. The recommended gap is approximately 1.27 mm (50 mils).
11. Verify Monitoring Channel Configuration: Check the connected monitoring module, transducer type, channel assignment, and engineering units.
12. Record Commissioning Results: Document the complete assembly reference, mounting dimensions, probe gap, electrical readings, and monitoring channel identification.

If the measured shaft vibration is abnormal after installation, check the probe gap, mounting position, cable termination, power supply, and monitoring channel configuration before replacing the complete assembly.

Compatible System Components

Recommended Related Models

Key Advantages

• Integrates the proximity probe and Proximitor Sensor in one assembly.
• Eliminates the separate probe-to-Proximitor extension cable.
• Reduces the need for a separately mounted Proximitor Sensor housing.
• Uses the established 3300 XL 8 mm eddy-current measurement technology.
• Supports shaft vibration and displacement monitoring.
• Includes a specified 200 mm standoff adapter and 50 mm probe penetration.
• IP66 / Type 4X protective housing.
• Multiple approvals probe configuration.
• Suitable for industrial compressor and turbine installations.

Technical FAQs

1. What is the main difference between PROXPAC XL and a conventional 3300 XL proximity transducer arrangement?

The main difference is the integrated construction. PROXPAC XL combines the proximity probe and Proximitor Sensor within one housing. A conventional arrangement normally uses a separately installed probe and Proximitor Sensor connected through an extension cable. The integrated arrangement can simplify mounting and reduce the number of separately installed components.

2. What do the 200 mm standoff adapter and 50 mm probe penetration mean?

The 200 mm value identifies the selected standoff adapter length, while the 50 mm value specifies the probe penetration configuration. These dimensions affect how the assembly is positioned through the machine mounting structure. Both should be checked against the actual casing geometry before installation.

3. Can the 330881-28-20-050-03-02 monitor shaft vibration continuously?

Yes. When installed with the correct probe gap and connected to a compatible machinery monitoring input, the assembly can provide continuous proximity measurement signals. The monitoring system uses these signals to evaluate shaft vibration and displacement during machine operation.

4. What should be checked when replacing this PROXPAC XL assembly?

The complete ordering reference should be matched, particularly the probe approval configuration, standoff adapter length, probe penetration, fitting arrangement, and mounting thread. The replacement should also be checked for electrical compatibility, power requirements, and monitoring channel configuration. Matching these details helps prevent mechanical installation problems and measurement errors after replacement.