Key Technical Specifications
| Parameter | Detail |
|---|---|
| Part Number | 24765-01-01 |
| Description | DC-LVDT Housing Expansion Sensor Assembly |
| Manufacturer | Bently Nevada (Baker Hughes) |
| Sensor Type | LVDT — Linear Variable Differential Transformer |
| Linear Range | 25.4 mm (1.0 in) — “-01” range option |
| Output Type | DC-LVDT (conditioned analog output) |
| Compatible Monitor | Bently Nevada 3500/45 Differential Expansion / Axial Position Monitor |
| System Family | 3500 Machinery Protection System |
| Typical Application | Steam turbine casing thermal expansion monitoring |
| Installation | Mounted on turbine foundation relative to fixed reference point |
| Condition | Obsolete — new surplus, tested surplus, or refurbished |
Product Introduction
Turbine casing expansion does not forgive sloppy instrumentation. If the casing cannot slide freely during heat-up, you get binding at the sliding feet, distorted alignment, and eventually rubbing between rotating and stationary parts. The 24765-01-01 is the sensor that catches that problem early. It is a DC-LVDT casing expansion transducer from Bently Nevada, installed between the turbine foundation and a fixed reference so the 3500/45 monitor can track how much the casing has grown as it heats up.Engineers specify this sensor because it is mechanically simple and electrically stable. The LVDT core moves with the casing, the coil assembly stays fixed, and the monitor sees a clean DC voltage proportional to displacement. The 25.4 mm range covers most industrial steam turbine expansion travel. This part is not glamorous, but it is one of those sensors you only notice when it is missing from the spare cabinet.
Quality SOP & Tech Pitfalls
The Lab Report (SOP)
- Visual inspection — check the LVDT housing, core rod, mounting hardware, cable gland, and nameplate for “24765-01-01.”
- Mechanical check — verify the core moves freely without binding, scratches, or lateral play.
- Electrical test — measure coil resistance and insulation with a Fluke 115 or equivalent.
- Stroke verification — run the core through its 25.4 mm range and confirm a smooth, monotonic DC output.
- Linearity check — verify output vs. displacement shows no dead zones or sudden jumps.
- Cable and connector inspection — look for cracked insulation, moisture ingress, or corroded pins.
- Documentation — record serial number, revision, scale factor if marked, and test results.
- Anti-static and moisture-sealed packaging before shipment.
The Engineer’s Warning (Pitfalls)Do not mount this sensor rigidly without confirming the core has enough travel. If the turbine expands beyond the LVDT stroke, you will either bend the core rod or get a hard saturation alarm right when you need the reading most. I have seen a startup delayed because someone installed the expansion sensor with the core already near end-of-travel; once the unit heated up, the monitor flagged a fault and nobody could tell whether the casing was stuck or the sensor was mispositioned.Also, confirm it is wired to a 3500/45 channel configured for DC-LVDT expansion, not axial position or differential expansion without the correct scaling. Wrong scaling turns a good sensor into a bad alarm.
Installation & Configuration Guide
1. Pre-Installation ⚠️
- Follow site LOTO and turbine maintenance procedures.
- Verify the replacement is 24765-01-01 and matches the original mechanical arrangement.
- Photograph the existing mounting, core position, cable routing, and 3500/45 channel configuration.
- Confirm the 3500/45 channel is set for casing expansion and the correct LVDT scale factor.
2. Removal
- Allow the turbine casing and foundation to cool if required by site procedure.
- Support the sensor assembly before loosening mounting brackets.
- Disconnect the cable at the monitor or junction box; label both ends.
- Remove the LVDT housing and core linkage carefully to avoid bending the core rod.
3. Installation
- Set the core to the cold-position reference before final tightening. This is critical.
- Mount the housing to the fixed reference and attach the core linkage to the casing expansion point.
- Ensure the core moves axially without side load or binding.
- Verify the full travel stays within the 25.4 mm linear range.
- Reconnect the cable and confirm shielding/grounding per site practice.
4. Power-On & Testing
- Restore power to the 3500 rack.
- Verify the 3500/45 channel recognizes the sensor and shows a stable reading.
- Compare the displayed expansion value with the expected cold reference.
- During warm-up, watch for smooth, continuous expansion with no sudden jumps.
- Confirm alarm and trip setpoints are correct before returning the unit to full service.
Compatible Replacement Models
- ✅ 24765-01-01 — Direct replacement when the linear range, mounting arrangement, and cable assembly match.
- ⚠️ 24765-02-01 — Same sensor family but with a different linear range (50.8 mm / 2.0 in). It can work only if the 3500/45 channel scaling and mechanical travel are reverified.
- ⚠️ 24765-01-00 / 24765-02-00 — Earlier or alternate assembly options. May require confirmation of output type, scale factor, and mechanical compatibility.
- ❌ Non-24765 LVDT sensors — Generic LVDTs are not drop-in replacements for a 3500/45 DC-LVDT expansion channel without full recalibration, mechanical redesign, and commissioning.
Frequently Asked Questions (FAQ)
What does the 24765-01-01 actually measure?
It measures turbine casing thermal expansion — how far the casing moves relative to the foundation as it heats up. The LVDT core travels with the casing, and the 3500/45 converts that movement into a monitored value.Can I use it with any 3500 module?
No. The 24765 DC-LVDT expansion sensor is intended for use with the Bently Nevada 3500/45 monitor. Using it with the wrong module or wrong channel configuration will produce incorrect readings.What does “-01-01” mean?
The first “-01” indicates the 25.4 mm (1.0 in) linear range option. The second “-01” relates to the assembly/spring configuration. Always confirm against the OEM ordering guide or nameplate.Will a 24765-02-01 work in place of -01-01?
Only if you verify the mechanical travel and reconfigure the 3500/45 scaling. The -02 version has a 50.8 mm range, so the voltage-per-mm relationship and alarm setpoints must be checked.Can I reuse the old cable?
If the cable, connector, and shielding are intact and test cleanly, yes. But do not ignore moisture damage or intermittent opens. A bad cable will look like a bad sensor.How do I know if it is failing?
Typical signs include drifting readings, sudden jumps, end-of-travel saturation, or a channel fault on the 3500/45. Check mechanical binding first, then verify electrical output.Do you offer a warranty?
Yes — 12 months on tested units. Because this is obsolete hardware, cosmetic condition may vary, but electrical function and mechanical stroke are verified before dispatch.
