LVDT: Advantages and Disadvantages

This article explores the pros and cons of using Linear Variable Differential Transformers (LVDTs). We’ll delve into their benefits and drawbacks to help you understand their suitability for various applications.

Introduction to Inductive Transducers

Inductive transducers are devices that measure displacement by detecting changes in inductance. These changes arise from three primary factors:

• Changes in the self-inductance of a coil.
• Changes in mutual inductance between coils.
• The generation of eddy currents.

There are two main types of inductive transducers:

• LVDT (Linear Variable Differential Transformer): Used for measuring linear displacement.
• RVDT (Rotary Variable Differential Transformer): Used for measuring angular displacement.

LVDT Construction

Let’s take a look at how an LVDT is built. As shown in Figure 1, the LVDT has a primary winding that is energized by an alternating current source. This generates a magnetic field, which then induces alternating voltages in the secondary windings via transformer action.

Figure 1: LVDT Construction

Advantages of LVDT

Here are some of the key benefits of using LVDTs:

• Wide Measurement Range: LVDTs can accurately measure displacements ranging from 1.25 mm all the way up to 250 mm.
• Frictionless Operation: They operate without physical contact, eliminating losses due to friction and increasing lifespan.
• Environmental Resistance: LVDTs are generally unaffected by external environmental conditions, making them suitable for use in a variety of environments.
• High Sensitivity: They offer high sensitivity, typically around 40 V/mm, allowing for precise measurements of even small displacements.
• Low Hysteresis: LVDTs exhibit low hysteresis, resulting in more accurate and repeatable measurements.
• Low Power Consumption: They are energy-efficient, typically consuming less than 1 Watt of power.

Disadvantages of LVDT

Despite their many advantages, LVDTs also have some drawbacks:

• Sensitivity to Stray Magnetic Fields: LVDTs are susceptible to interference from external magnetic fields, which can affect measurement accuracy. This requires that they are shielded from such fields.
• Temperature and Vibration Sensitivity: Temperature changes and vibrations can affect LVDT performance, leading to measurement errors.
• Need for Demodulation Circuit: To obtain a DC output signal suitable for many applications, a demodulator circuit is required.
• Limited Dynamic Response: The dynamic response of an LVDT can be limited by the mass of its core (mechanically) and the frequency of the applied voltage (electrically).
• Larger Displacements Required for Appreciable Output: LVDTs often require relatively larger displacements to produce a usable differential output signal.

By understanding both the advantages and disadvantages of LVDTs, you can make an informed decision on whether they are the right choice for your specific measurement needs.