LVDTs (Linear Variable Differential Transformers) are precision sensors used to measure linear displacement. While all LVDTs operate using the same basic electromagnetic principle, the mechanical configuration of the moving core varies depending on the application.
Two common types are Spring-Loaded LVDTs and Free Core LVDTs. Here’s how they differ:
Free Core LVDTs
A Free Core LVDT features a separate, unrestrained magnetic core that moves freely within the sensor body. It does not include a built-in spring or shaft assembly—movement of the core must be externally driven.
Key Features:
- Core is loose and moves independently within the bore
- Requires external guidance or mechanical coupling to the target
- A core extension rod is often used to link the free core to the object being measured, especially when the LVDT is mounted in a fixed location
- Offers a compact and flexible design
- Common in automation, hydraulics, and embedded sensor applications
Best For:
- Applications with space constraints or embedded sensor systems
- Setups where the target or host mechanism drives the core motion
- Environments where a core extension rod can transmit motion from a remote or moving part
Spring-Loaded LVDTs
A Spring-Loaded LVDT includes an internal spring mechanism that automatically returns the core to a rest or home position. These typically include a plunger-style shaft and bearing system to ensure straight-line motion and consistent contact.
Key Features:
- Built-in spring provides return force
- Integrated shaft with mechanical stops
- Designed for surface contact or gaging applications
- Typically larger due to mechanical components
Best For:
- Dimensional gaging and surface measurement
- Bench-top or quality control setups
- Non-permanent installations requiring simple setup and repeatable motion
Which One Should You Use?
| Application Needs | Recommended Type |
|---|---|
| Space-constrained or embedded systems | Free Core LVDT |
| Core needs to follow a moving part remotely | Free Core LVDT with Extension Rod |
| Automated test and measurement (e.g. gaging) | Spring-loaded LVDT |
| Return-to-zero motion required | Spring-loaded LVDT |
| When the object being measured cannot be mechanically connected to the sensor | Spring-loaded LVDT |