LVDT: Principle of Operation with 3 Coils and Moving Core

An LVDT (Linear Variable Differential Transformer) is composed of 3 colinear coils and a moving core. The middle coil, also called the primary coil, is connected to an AC generator. The 2 other coils, called secondary coils, are connected together. The induction from the primary to the secondary coils is affected by the position of the core. The core position can then be deduced from the measurement of the amplitude and the phase of the secondary coils.

In essence, an LVDT works by transforming the linear displacement of the core into a measurable electrical signal. The primary coil generates an alternating magnetic field that induces a voltage in the secondary coils. The position of the core within the magnetic field determines the amount of voltage induced in each secondary coil. By measuring the difference in voltage between the two secondary coils, we can determine the position of the core.

Here's a breakdown of the LVDT's operation:

• Primary Coil: Connected to an AC generator, it creates a changing magnetic field.
• Secondary Coils: Two coils placed symmetrically around the primary coil. They act as receivers of the magnetic field.
• Moving Core: A ferromagnetic core that slides freely within the coils. Its position determines the magnetic coupling between the coils.

How it works:

1. The primary coil creates an alternating magnetic field.
2. The moving core alters the magnetic flux linking the primary and secondary coils.
3. This change in flux induces a voltage in the secondary coils, proportional to the core's position.
4. The output voltage from the secondary coils is measured and interpreted to determine the core's displacement.

Advantages of LVDTs:

• High Accuracy: LVDTs offer excellent accuracy in displacement measurement.
• Non-Contact Measurement: They do not physically contact the object being measured, minimizing wear and tear.
• Wide Operating Range: LVDTs can handle large displacement ranges.
• Robust Construction: They are durable and resistant to environmental factors.

Applications:

LVDTs are widely used in various industries, including:

• Aerospace
• Automotive
• Machine tools
• Medical devices
• Process control

Their ability to provide accurate and reliable displacement data makes them essential for numerous applications where precise position monitoring is crucial.