What is an LVDT?
It is a position sensing device that provides AC output proportional to the core displacement that passes through its windings.
The distance sensors type LVDT are inductive measuring elements. They are based on the inductive principle of variable core Transducer. This allows a linear movement of the core inside the sensor body causes a variation of induction between primary and secondary, which results in a change of output signal, proportional to that displacement.
How does an LVDT work?
The Transducer has three coils arranged end to end around a bar. The central winding is the primary winding and the external windings are the secondary windings. A ferromagnetic core of cylindrical shape, subject to the object whose position wishes to be measured, is displaced with respect to the coils along the axis of the bar.
When an alternating current flows through the primary, it causes a voltage that is induced to each secondary proportionally to the mutual inductance with the primary. The oscillator frequency causing the alternating current is in the range of 1 to 10 kHz.
As the core moves, the mutual inductance changes, causing the voltage induced in the secondary to change. The coils are connected in series but reversed, so the output voltage is the difference (that’s why it is “differential”) between the two secondary voltages. When the core is in its central position, it is equidistant from the two secondary ones, the induced voltages are the same but of opposite sign, so the output voltage is zero.
When the core is displaced in one direction, the voltage in one coil increases while in the other decreases, causing the output voltage to also increase from zero to its maximum
The LVDT provides a linear relationship between the displacement and the voltage, while the core is exposed to all the coils of the primary winding
Characteristics and advantages
- Extremely accurate
- High resolution
- Long lifespan
- Insensitive to interference
- Resistance to difficult environments (humidity, dust, etc.)
- Resistance to acceleration
- Easy installation