An LVDT (Linear Variable Differential Transformer) is a type of sensor commonly used to measure displacement or linear position. It operates on the principle of electromagnetic induction to detect changes in position and convert them into an electrical signal. The LVDT consists of a primary coil and two secondary coils wound around a cylindrical core made of a ferromagnetic material.
Here's how an LVDT measures displacement using the differential voltage induced in its transformer coil:
Basic Construction: The LVDT consists of a primary coil (also known as the primary winding) and two secondary coils (also known as the secondary windings) wound on a hollow cylindrical core. The primary coil is typically energized by an alternating current (AC) source.
Core and Core Motion: Inside the hollow core, there is a movable ferromagnetic core, often referred to as the armature. This core is free to move linearly along the axis of the LVDT.
Centered Position: When the core is in the centered position (no displacement), an equal magnetic flux passes through both secondary coils, inducing equal voltages in them. This results in zero output voltage across the secondary coils.
Displacement: When an external force or displacement is applied to the core (in either direction along the axis), the symmetry of the magnetic flux changes. This causes the magnetic flux to link more closely with one of the secondary coils and less with the other. The result is that the induced voltage in one secondary coil increases, while the induced voltage in the other secondary coil decreases.
Differential Output: The difference in voltage between the two secondary coils is called the differential voltage. This differential voltage is directly proportional to the displacement of the core from its centered position. The magnitude and direction of displacement can be determined by the amplitude and phase of the differential voltage.
Signal Conditioning: The LVDT's output is in the form of an alternating current (AC) voltage. To convert this signal into a usable form for measurement and control systems, signal conditioning is often employed. This may involve using a demodulator and filter circuitry to obtain a direct current (DC) output voltage proportional to the displacement.
Measurement: The conditioned output voltage can then be calibrated and converted into meaningful units of displacement, such as inches or millimeters, based on the specific application's requirements.
LVDTs are widely used in various industries due to their high accuracy, reliability, and robustness. They find applications in position feedback systems, automated manufacturing, robotics, aircraft and automotive systems, and many other areas where precise displacement measurement is essential.