How LVDT Works | Construction and Working

EasyMechLearn

23 Jan 201806:08

Summary

TLDRThis lecture delves into the workings of the Linear Variable Differential Transformer (LVDT), a device renowned for its precision in measuring linear displacement. It operates on the principle of mutual inductance, with a cylindrical former at its core, surrounded by a primary coil and two secondary coils. The movable ferromagnetic core's position relative to the coils determines the output voltage, indicating displacement direction and magnitude. The video explains the three core positions and the corresponding voltage outputs, highlighting the use of a phase-sensitive detector for direction sensitivity. Advantages include a wide measurement range, no frictional losses, high input sensitivity, low hysteresis, and direct conversion to electrical signals. However, the device's sensitivity to stray magnetic fields and environmental factors like vibrations and temperature are noted as drawbacks.

Takeaways

🌟 LVDT stands for Linear Variable Differential Transformer and operates on the principle of mutual inductance.
🔍 LVDTs are popular for measuring linear displacement with commercial models offering a range from plus/minus 0.25 millimeters to plus/minus 250 millimeters.
🏗️ The construction of an LVDT includes a cylindrical former, a primary coil, and two secondary coils, with a ferromagnetic core that moves freely within.
📍 The operation of LVDT is explained through three core positions: null (center), left of null, and right of null, affecting the output voltage.
🔧 A phase-sensitive detector is used with LVDT to determine the direction of core movement, as the output voltage alone cannot indicate direction.
⚙️ When the core moves left, the EMF in secondary coil 1 is greater than in coil 2, resulting in a net negative displacement.
🔄 Conversely, when the core moves right, the EMF in secondary coil 2 exceeds that in coil 1, leading to a net positive displacement.
📊 LVDTs offer several advantages, such as a wide measurement range, no frictional losses, high input and sensitivity, low hysteresis for excellent repeatability, and direct conversion to electrical signals.
🔌 They can also function as secondary transducers, converting other types of measurements, like pressure, into electrical signals after calibration.
⚠️ Disadvantages include sensitivity to stray magnetic fields and susceptibility to vibrations and temperature changes, necessitating protective setups.

Q & A

What does LVDT stand for?
-LVDT stands for Linear Variable Differential Transformer.
What is the principle on which LVDT operates?
-LVDT operates on the principle of variation of mutual inductance.
What is the full scale displacement range of commercial LVDTs?
-Commercial LVDTs are available with a full scale displacement range of plus minus 0.25 millimeters to plus minus 250 millimeters.
What are the main components of an LVDT?
-The main components of an LVDT are a cylindrical former, a primary coil, two secondary coils, and a movable ferromagnetic core.
What type of voltage source is used to excite the primary winding of an LVDT?
-The primary winding of an LVDT is excited by a 1 to 10 volts AC voltage source.
How are the secondary coils in an LVDT connected?
-The secondary coils in an LVDT are connected in series.
What is the null position in an LVDT?
-The null position in an LVDT is when the core is at the center, resulting in equal voltage induced in both secondary coils and a net output of zero.
What is the role of a phase sensitive detector in LVDT?
-A phase sensitive detector is used to make the measurement direction sensitive by comparing the phase of the secondary output with the primary signal to judge the direction of movement.
What happens when the core of an LVDT moves to the left-hand side?
-When the core moves to the left-hand side, the EMF voltage induced in secondary coil one is greater than in secondary coil two, resulting in a net negative displacement.
What are some advantages of using an LVDT?
-Advantages of using an LVDT include a wide range for measurement of displacement, no frictional losses, high input and sensitivity, low hysteresis for excellent repeatability, direct conversion to electrical signals, and the ability to act as secondary transducers.
What are the disadvantages of using an LVDT?
-Disadvantages of using an LVDT include sensitivity to stray magnetic fields and being affected by vibrations and temperature.

Outlines

00:00

🔍 Introduction to LVDT and Its Working Principle

This paragraph introduces the Linear Variable Differential Transformer (LVDT), a device used for measuring linear displacement based on the principle of mutual inductance. It discusses the construction of an LVDT, which includes a cylindrical former, a primary coil, and two secondary coils connected in series. The paragraph also explains the working of LVDT through three core positions: null (center), left, and right of the null position. The output voltage differences between the secondary coils indicate the direction and magnitude of displacement. A phase-sensitive detector is mentioned as a necessary component to make the measurement direction-sensitive.

05:01

🛠 Advantages and Disadvantages of LVDTs

The second paragraph delves into the advantages of LVDTs, such as their wide measurement range (from 0.25 mm to 250 mm), lack of frictional losses due to the core moving inside a hollow former, high input and sensitivity (producing an output that does not require amplification), low hysteresis for excellent repeatability, and direct conversion of linear displacement into electrical signals. It also mentions that LVDTs can act as secondary transducers, such as in the case of a LibDem tube that converts pressure into linear displacement. However, the paragraph also highlights the disadvantages, including sensitivity to stray magnetic fields and the impact of vibrations and temperature on their performance.

Mindmap

Keywords

💡LVDT

LVDT stands for Linear Variable Differential Transformer. It is a type of electrical transformer used for measuring linear displacement. The video's theme revolves around explaining how LVDT works, its construction, and its advantages and disadvantages. The script describes LVDT as a popular device for linear displacement measurement with a wide range of applications.

💡Mutual Inductance

Mutual inductance is the principle on which the LVDT operates. It refers to the electromagnetic induction between two coils when a varying current in one coil induces a voltage in the other coil. In the context of the video, mutual inductance is what allows the LVDT to measure linear displacement by varying the voltage induced in its secondary coils based on the position of the ferromagnetic core.

💡Cylindrical Former

The cylindrical former is a key component of the LVDT's construction. It is a hollow cylindrical structure that houses the primary and secondary coils, as well as the ferromagnetic core. The script mentions that the primary coil is at the center of the former and is surrounded by the secondary coils, which are positioned on either side.

💡Primary Coil

The primary coil is a central winding in the LVDT that is excited by an AC voltage source. It plays a crucial role in the operation of the LVDT by generating a magnetic field that interacts with the ferromagnetic core. The script specifies that the primary coil is located at the center of the cylindrical former and is connected to a 1 to 10 volts AC voltage source.

💡Secondary Coils

Secondary coils are two additional windings in the LVDT that are positioned on either side of the primary coil. They are connected in series and have an equal number of turns. The script explains that the voltage induced in these coils varies depending on the position of the ferromagnetic core, which in turn affects the net output voltage and indicates the direction of displacement.

💡Ferromagnetic Core

The ferromagnetic core is a movable component within the LVDT that freely moves through the cylindrical former. It is made from a material that can be magnetized and interacts with the magnetic field generated by the primary coil. The video script describes how the position of the core affects the voltage induced in the secondary coils, which is essential for measuring linear displacement.

💡Null Position

The null position refers to the central position of the ferromagnetic core within the LVDT when it is not displaced. In this position, the voltage induced in both secondary coils is equal, resulting in a net output of zero. The script uses the null position as a reference point to explain the operation of the LVDT in different scenarios.

💡Phase Sensitive Detector

A phase sensitive detector is a useful circuit mentioned in the script that can determine the direction of the core's movement within the LVDT. It works by comparing the phase of the secondary output with the primary signal. This is important because from the output voltage alone, it is not possible to predict the direction of core movement.

💡Displacement Range

The displacement range of an LVDT refers to the extent of linear movement that the device can measure. The script states that commercial LVDTs are available with a full scale displacement range from plus or minus 0.25 millimeters to plus or minus 250 millimeters, highlighting the versatility of LVDTs for various applications.

💡Advantages and Disadvantages

The script outlines several advantages and disadvantages of using LVDTs. Advantages include a wide measurement range, no frictional losses, high input and sensitivity, low hysteresis, direct conversion to electrical signals, and the ability to act as secondary transducers. Disadvantages include sensitivity to stray magnetic fields and being affected by vibrations and temperature. These points are crucial for understanding the practical considerations of using LVDTs in real-world applications.

Highlights

LVDT stands for Linear Variable Differential Transformer and operates on the principle of mutual inductance variation.

It is a popular device for measuring linear displacement with commercial models offering a range from plus/minus 0.25 mm to plus/minus 250 mm.

The construction of an LVDT includes a cylindrical former, a primary coil, and two secondary coils with equal turns connected in series.

A ferromagnetic core within the LVDT is movable and can freely slide through the former.

LVDT operation is explained through three core positions: null (center), left of null, and right of null.

At the null position, the induced voltage in both secondary coils is equal, resulting in a net output of zero.

A phase-sensitive detector is used with LVDT to determine the direction of core movement due to equal induced voltages at the null position.

When the core moves left, the induced EMF in secondary coil 1 is greater than in secondary coil 2, resulting in negative displacement.

Conversely, when the core moves right, the induced EMF in secondary coil 2 exceeds that of coil 1, indicating positive displacement.

LVDTs have a wide measurement range, capable of measuring displacements from 0.25 mm to 250 mm.

They have no frictional losses as the core moves inside a hollow former, ensuring accurate displacement measurement.

LVDTs exhibit high input and sensitivity, producing an output that does not require amplification.

Low hysteresis in LVDTs ensures excellent repeatability under all conditions.

LVDTs provide direct conversion of linear displacement to electrical voltage signals.

They can also function as secondary transducers, converting other types of measurements into electrical signals.

LVDTs are sensitive to stray magnetic fields and require protection setups to prevent interference.

They are also affected by vibrations and temperature, which can impact their performance.

The lecture concludes with a teaser for the next video on the calibration of LVDT.