Bently Nevada 24765-02-00 Case Expansion Transducer Assembly

Description

For the continuous tracking of thermal casing growth on large utility steam turbines, the Bently Nevada 24765-02-00 transducer assembly utilizes a direct-current linear variable differential transformer (DC-LVDT) to deliver precise absolute displacement feedback. This heavy-duty system converts physical axial movement into an analog DC voltage, allowing supervisory machinery protection systems to track structural expansion and prevent casing deformation or mechanical binding. By using a DC-powered design, the assembly simplifies the instrument loop by eliminating the need for external AC excitation and demodulator modules, transmitting a scaled signal directly to the control room or monitor rack.

Key Features

• 50.8 mm (2.00 in) Linear Range: Optimized for mid-to-large-scale casing displacement tracking on industrial rotating machinery.
• Without Spring Return (Option 00): Requires a rigid mechanical coupling directly to the sliding turbine foot or casing, ensuring the sensor rod follows bi-directional movement without relying on mechanical spring tension.
• Direct-Current Operation: Integrated internal electronics accept DC power and output a clean, low-impedance DC voltage proportional to displacement.
• Rugged Protective Housing: Constructed to withstand high humidity, oil mist, and thermal cycling common in power generation turbine decks.

Applications

• Steam turbine thermal casing expansion monitoring.
• Gas turbine structural growth tracking.
• Boiler and feed pump foundation displacement measurements.
• Heavy industrial structural expansion and mechanical alignment tracking.

Technical Specifications

Empirical Engineering Insights

Alternative Models & Compatibility

The Bently Nevada 24765-02-00 is directly compatible with the 3500/45 Position Monitor or older 3300-series position monitors configured for DC-LVDT inputs. When replacing an older AC-LVDT case expansion assembly, be aware that you must bypass or remove any external AC demodulator units, as the 24765 handles excitation and conditioning internally. Ensure the monitoring system channel card is configured for DC voltage input with the correct scale factor (10.25 V/in) to avoid erroneous calibration curves.

Application Pitfalls & Engineering Notes

Because this specific assembly utilizes the Option 00 (no spring return), the sensor core rod does not automatically retract. The rod must be mechanically pinned, bolted, or tethered via a yoke assembly to the turbine casing. If this physical connection is lost or slips during thermal cycling, the transducer will remain in its last physical position, causing the monitoring system to report a static "flatline" signal. Additionally, any side loads or angular misalignment during casing movement will cause internal friction, wearing out the PTFE support bushings and creating measurement stiction.

Commissioning & Wiring Tips

When installing the transducer in cold machinery conditions, adjust the mechanical coupling so that the LVDT core sits near the negative end of its physical stroke. This maximizes the usable positive measurement range as the steam turbine heats up and expands. Ensure the field wiring shield is grounded only at the 3500 monitor rack terminal block; leaving both ends of the shield grounded can create ground loops due to potential differences between the turbine foundation and the control room instrument ground.

Installation Guidelines