Bently Nevada 21504 Modules - 21504-16-32-10-02

Technical Dossier

Product Details And Specifications

Bently Nevada 21504 Series Technical Notes

The Bently Nevada 21504 series is a line of standard-mount eddy-current proximity probes engineered for continuous, non-contact vibration and position measurement in rotating machinery. Deployed across petrochemical refineries, nuclear power stations, LNG terminals, and heavy industrial compressor trains, the 21504 series forms a core sensing layer within Bently Nevada's 3300 and 7200 Series monitoring systems. Its 8 mm probe tip diameter and standardized mounting thread (M10 x 1) make it the default field-replacement probe across thousands of installed turbomachinery protection systems globally. The series operates on the eddy-current principle, requiring a matched extension cable and proximitor (driver) to complete the measurement loop — a three-component architecture that has remained consistent across multiple product generations.

The Evolution of 21504 Architecture

The series is calibrated for use with Bently Nevada's standard target material (AISI 4140 steel), with a nominal sensitivity of 7.87 V/mm (200 mV/mil) and a linear range of 0.25 mm to 2.25 mm (10 to 90 mil). This sensitivity specification is shared across the 3300 XL 8 mm probe family, ensuring backward compatibility with existing proximitor/driver modules such as the 3300 XL 01-01-10-01-00 and 3300 RAM 02-01-10-01-00.

21504 Full Catalog & Functionalities (SKU List)

The following SKUs represent the documented variant matrix of the Bently Nevada 21504 standard-mount proximity probe series, differentiated by cable length, connector type, and temperature rating:

21504-16-32-10-02: 8 mm probe, 5 m armored extension cable, standard temperature, M10 thread, standard mount.
21504-16-32-10-00: 8 mm probe, 5 m cable, standard temperature, M10 thread, no connector armor.
21504-16-32-05-02: 8 mm probe, 5 m cable, high-temperature rating, M10 thread, armored.
21504-16-32-05-00: 8 mm probe, 5 m cable, high-temperature rating, M10 thread, bare termination.
21504-16-32-15-02: 8 mm probe, 5 m cable, extended temperature range, armored connector.
21504-16-32-20-02: 8 mm probe, 5 m cable, low-temperature variant, armored, M10 mount.
21504-16-08-10-02: 8 mm probe, 2 m integral cable, standard temperature, M10 thread, armored.
21504-16-08-10-00: 8 mm probe, 2 m cable, standard temperature, bare termination.
21504-16-08-05-02: 8 mm probe, 2 m cable, high-temperature, armored connector.
21504-16-50-10-02: 8 mm probe, 15 m extension cable, standard temperature, armored.
21504-16-50-10-00: 8 mm probe, 15 m cable, standard temperature, bare termination.
21504-16-50-05-02: 8 mm probe, 15 m cable, high-temperature, armored.
21504-16-75-10-02: 8 mm probe, 22 m extension cable, standard temperature, armored.
21504-16-75-05-02: 8 mm probe, 22 m cable, high-temperature, armored connector.
21504-16-100-10-02: 8 mm probe, 30 m extension cable, standard temperature, armored, long-run installation.
21504-16-100-05-02: 8 mm probe, 30 m cable, high-temperature, armored, for high-ambient installations.

Sourcing Hard-to-Find & Obsolete 21504 Parts

For operators running 3300 Series or 7200 Series monitoring racks that are specified for 21504 probes, substitution with a 330104-series probe requires re-calibration of the proximitor gap voltage and verification of the driver module's input impedance range — a process that is not always feasible during a planned outage window. DriveKNMS supplies tested 21504 assemblies as a direct drop-in replacement, eliminating re-engineering risk and reducing mean time to repair (MTTR).

Quality Control for the 21504 Range

Each 21504 probe assembly processed by DriveKNMS undergoes a structured verification protocol prior to dispatch. Electrical continuity is verified across the full cable length using a calibrated LCR meter to confirm inductance values within the Bently Nevada-specified range (typically 95–115 µH for the probe coil). Gap voltage linearity is tested against a reference target block (AISI 4140, surface finish Ra ≤ 0.8 µm) using a calibrated proximitor driver, confirming output linearity within ±1% across the 0.25–2.25 mm measurement range.