Understanding LVDT Measurement

An LVDT, which stands for Linear Variable Differential Transformer, is a type of electrical transformer used for measuring linear displacement (position). It is a common sensor found in many industrial and scientific applications where precise measurement of linear movement is required.

The basic principle of an LVDT relies on the change in magnetic coupling between a primary coil and two secondary coils due to the movement of a core within the coils. The core is attached to the object whose displacement is being measured.

How LVDT Measures Displacement

Let's break down the working of an LVDT sensor for measuring displacement:

• The LVDT has a central primary coil and two identical secondary coils wound symmetrically on either side of the primary coil.
• An AC voltage is applied to the primary coil.
• This produces a magnetic field, which induces voltages in the two secondary coils.
• A movable core, usually made of a ferromagnetic material, slides inside the hollow center of the coils. This core is connected to the point where displacement needs to be measured.
• When the core is exactly in the center position (null position), the magnetic field lines couple equally with both secondary coils. The induced voltages in the secondary coils are equal in magnitude but 180 degrees out of phase. When these voltages are connected in series opposition, the net output voltage is zero (or close to zero).
• When the core moves away from the center position, the magnetic coupling with one secondary coil increases, while the coupling with the other decreases.
• This difference in coupling results in a difference in the induced voltages in the secondary coils. The net output voltage from the series opposition connection of the secondary coils becomes non-zero.
• The magnitude of the output voltage is proportional to the magnitude of the displacement of the core from the null position.
• The phase of the output voltage indicates the direction of the displacement (e.g., phase A for movement in one direction, phase B for movement in the opposite direction).

Therefore, the LVDT converts the physical linear movement (displacement) into an electrical voltage signal.

Analyzing the Options

Let's look at the given options and why LVDT is used for measuring one specific parameter:

Based on its operating principle and primary application, an LVDT is specifically designed for measuring linear displacement.

Revision Table: LVDT Basics

Additional Information on LVDT Applications

LVDTs are widely used due to their robustness, high accuracy, linearity, and infinite resolution within their measurement range. Some common applications of LVDTs include:

• Position feedback in control systems (e.g., servo actuators).
• Measurement of small displacements in scientific experiments.
• Sensing displacement in industrial automation and machinery.
• Measuring thickness of materials.
• Gauging and quality control applications.
• Structural monitoring.

They are often preferred over other displacement sensors like potentiometers because they are non-contacting (between the core and coils), meaning there is no friction or wear, leading to a longer lifespan and better reliability.