What is an LVDT?
An LVDT (Linear Variable Differential Transformer) is a sensor that turns linear position into an electrical signal. Because its core does not touch the windings, it measures without friction.
How does an LVDT work?
- The primary winding is excited with an AC signal.
- A moving ferromagnetic core couples the magnetic flux to two secondary windings.
- With the core in the middle, the two secondary voltages are close and the difference signal is at its lowest.
- As the core moves to one side, the difference grows. Its amplitude shows how far the core has moved, and its phase shows the direction.
Why does an LVDT signal need conditioning?
An LVDT does not give a directly usable position value. The primary has to be excited, the secondary signals read and demodulated, and the result converted into a value the control system can use. A signal conditioning circuit does this job.
Where is it used?
- Measuring spool position in servo valves
- Position feedback in hydraulic cylinders and actuators
- Aerospace and defence systems
- Test and measurement setups
Advantages of an LVDT
- No wear or friction, because it works without contact
- Long mechanical life
- High resolution
- Can be designed for harsh environments
Frequently asked questions
What is the difference between an LVDT and a potentiometer?
A potentiometer has a sliding contact that wears over time. In an LVDT the core does not touch the windings, so this wear does not occur.
Why does an LVDT run on AC?
An LVDT works on the transformer principle. A voltage appears in the secondary windings only when the magnetic flux from the primary is changing.
To read LVDTs
MotorTech HSV and MotorTech EHA read 2 LVDT channels on the board, and SensorTech handles sensor reading and signal conditioning.