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Thickness Measurements Using An LVDT

Monday, January 11, 2021

In the Aerospace and Industrial markets, a thickness measurements using an LVDT must be accurate. No industry can afford failures risking life and property. Utilizing a supplier and manufacturer of high-quality LVDTs is critical, assuring you that your LVDTs offer repeatable position sensing, and operate as designed. Sentech has over 30 years of experience in the industry, where you can be confident in their products’ quality, reliability, and outstanding service.

What is an LVDT?

A Linear Variable Differential Transformer (LVDT) is a standard electromechanical transducer commonly used in a wide range of industrial applications. They work under the principle of mutual induction and displacement by converting mechanical vibrations into variable electrical current, voltage, and electrical signals. They are designed to produce an AC voltage output proportional to the transformer’s relative displacement and the ferromagnetic core.

A LVDT consists of a coil assembly, which is typically mounted to a stationary form. The coil assembly consists of three solenoidal coils of wire wound on a hollow form. The inner coil is the primary coil whereby magnetic flux is produced and coupled to the two secondary coils, inducing an AC voltage in each coil. They convert the rectilinear motion of an object mechanically coupled to a corresponding electrical signal.

Known to be robust, the main advantage of the LVDT over other types of displacement transducers is its ability to perform under high vibration and shock levels when used in harsh environments. The LVDT moves without friction because the sliding LVDT core doesn’t touch the inside of the tube, making the LVDT a highly reliable device. The absence of sliding or rotating contacts allows it to be completely sealed against the environment. As there is no physical contact across the sensing element, LVDTs are robust because there is no ongoing wear and tear in the sensing element.

Thickness Measurement Using LVDTs

A LVDT is used to measure displacement by assigning a specific signal value for any given position of the core. The primary core position determines how tightly its signal becomes when coupled with each of the secondary coils. The two secondary coils are series-opposed, resulting in the two signals on each secondary being 180 degrees out of phase. Therefore the phase of the output signal determines its direction, amplitude, and distance.

Thickness measurement using the LVDT as a displacement sensor is a comprehensive application area. By measuring the voltage amplitude and phase, operators can determine the extent of its core motion direction and displacement.

There are distinctions between the non-destructive/destructive, non-contact/with contact, and the one-side/two-sided thickness measurements. There are no emission compliance costs because measuring techniques for thickness measurement are all emission-free.

Thickness measurements must be performed with both contacts as well as non-contact sensors. Non-contact sensor measurement techniques have an advantage due to their accuracy and measuring speeds.

You will also find there is a distinction between one-sided and two-sided thickness measurements. Two-sided thickness measurements are conducted with a minimum of a pair of sensors installed together on a single axis and measure the target synchronously. The difference between the measurement result produces the thickness of the object being measured. One-sided thickness measurements should only be performed with non-contact sensors.

A LVDT sensor can measure movements as small as a few millionths of an inch up to several inches. They are also capable of measuring positions up to ±30 inches (±0.762 meters).

LVDT Applications in Real Life

If you are wondering about LVDT applications in real life, and what measurement LVDT uses, there are several usage cases. Thickness measurements are predominantly used in process control and quality assurance. For over 60 years, the LVDT linear position sensor has evolved from its initial use as a laboratory tool. Today it is the preferred technology for reliable LVDT measurements in military, aerospace, subsea, industrial, downhole drilling, nuclear power, and process control applications.

Key Takeaways:

  • Thickness measurements are predominantly used in process control and quality assurance.
  • Thickness measurements must be performed with both contacts as well as non-contact sensors

Sentech is a global leader in designing and manufacturing position sensors, including LVDTs, RVDT’s, FASTAR sensors, HYDRASTAR sensors, signal conditioners, and solenoids. Working with us will give you peace of mind as all our signal conditioning, and sensor products are manufactured according to ISO 9001:2015, AS9100 Rev D certified processes, and ANAB accreditations. If you are looking for custom, tailored solutions for mission-critical applications, contact us today to talk to one of our renowned experts.

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