What is an LVDT?
An LVDT (Linear Variable Differential Transformer) is a transformer device which produces an electrical output proportional to the displacement of a free moving core.
This type of transducer consists of a primary coil power-supplied by an AC signal and two secondary coils.
When the core moves inside the coils, it induces voltage V1 and V2 in each secondary coil, proportional to its displacement. The two secondary coils are connected in series and in opposite polarity, so that the output signal is the difference between these voltages.
In this configuration, the output voltage is null when the core is at the center. When it moves from the center, the differential voltage increases. This output voltage is then rectified in order to get a DC signal proportional to the displacement core.
Why choose an LVDT?
- Contactless measurement
There is no physical contact between the core and the coil assembly. This allows both vibration measurements and tests of delicate materials.
- Unlimited life-time
The no contact feature between the core and the coil assembly allows an infinite life time as well as an exceptional reliability.
These criteria allow fatigue testing use and severe environmental conditions such as space and military applications (servo controls).
- Infinite resolution
Being an inductive frictionless transducer, an LVDT has an infinite resolution only limited by the associated electronics.
- Excellent repeatability (<10-5 of FS) and insensitivity to transverse movement
- Severe environment compatibility
Due to its principle of operation and design (hermetically sealed coils inside a stainless steel body, independant free moving core assembly), this type of transducer can withstand very hard environments such as pressure up to 600 bar, temperature up to 235°C, radiation up to 2.5 x 108 rads, corrosive and explosive atmospheres ect…
- Input/ output insulation
As a transformer, the LVDT’s excitation and measurement electrical windings are completely insulated.