Page 12 of catalogue Linear inductive displacement sensors of Micro-Epsilon Messtechnik GmbH & Co. KG

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induSENSOR LVDT series technology and measuring principle

Inductive Displacement sensors according to the LVDT principle (Linear Variable Differential Transformer) are constructed with a primary and two secondary coils, which are arranged symmetrically to the primary winding. As a measurement object, a rod shaped magnetic core can be moved within the differential transformer. An electronic oscillator supplies the primary coil with an alternating current of constant frequency. The excitation is an alternating voltage with an amplitude of a few volts and a frequency between 1 and 10 kHz.

Depending on the core position alternating voltages are induced in the two secondary windings. If the core is located in its "zero position", the coupling of the primary to both secondary coils is equally large. Movement of the core within the magnetic field of the coil causes a higher voltage in one secondary coil and a lower voltage in - displacement 100 % the second coil. The difference between the two secondary voltages is proportional to the core displacement. Due to the differential design of the sensor, the LVDT series has an output signal which is very stable.
- signal linear measuring range 100 % + displacement

Signal LVDT
+ signal

Gauging sensor secondary coils magnetic core primary coil probe spring Slide bearings probe tip

Displacement sensor secondary coils magnetic core primary coil plunger core extension

plunger