LVDT and Sensors Overview Quiz

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Questions and Answers

What is a major advantage of absolute encoders compared to incremental encoders?

They indicate the current position of the shaft with unique output codes. (correct)

They require less physical space to install.

They operate at higher speeds.

They are less expensive to manufacture.

What type of code can absolute encoders use for their output?

Natural binary code (correct)

Hexadecimal code

Decimal code

Octal code

Which statement about the disk of an absolute encoder is true?

It is designed to be transparent for light passage.

It contains a single track for reading position.

It only records the maximum rotation angle.

It has multiple concentric tracks corresponding to the encoder's resolution. (correct)

What problem can occur if the power is momentarily shut off in systems using incremental encoders?

Angular information may produce an error due to missed pulses. (C) Signup and view all the answers

What defines the 'bit'-resolution of an absolute encoder?

The number of tracks on the coded disk. (A) Signup and view all the answers

What happens to the EMF signals in the two secondary windings when the soft iron magnetic core armature is in the null position?

They cancel each other out. (B) Signup and view all the answers

Which of the following describes the output signal characteristics of an LVDT?

It exhibits both amplitude and polarity changes based on core displacement. (A) Signup and view all the answers

What is one of the advantages of an LVDT compared to a potentiometer?

Better resistance to environmental conditions. (C) Signup and view all the answers

What principle do inductive proximity sensors operate under?

Faraday's Law of inductance. (D) Signup and view all the answers

Which factor is NOT an advantage of using an LVDT?

Low cost. (A) Signup and view all the answers

What is a typical application of an LVDT?

As a pressure transducer. (A) Signup and view all the answers

What type of objects can inductive proximity sensors detect?

Both ferrous and non-ferrous metal objects. (B) Signup and view all the answers

Which feature is characteristic of the construction of LVDTs for their operation?

Presence of a soft iron magnetic core. (B) Signup and view all the answers

What is the typical output condition for incremental encoders?

They provide output only when the shaft is rotated. (B) Signup and view all the answers

Which type of incremental encoder is known for providing position and velocity information?

Single channel encoder (D) Signup and view all the answers

How is the direction of rotation determined in a quadrature encoder?

By which output channel, A or B, leads. (C) Signup and view all the answers

What is a primary disadvantage of using incremental encoders?

They require external counters to determine absolute position. (D) Signup and view all the answers

What outputs are typically produced by a quadrature encoder?

Two separate square waves, channel A and channel B. (C) Signup and view all the answers

What type of encoder uses two photo detectors offset by 90 degrees?

Incremental encoder (C) Signup and view all the answers

In what application are incremental encoders commonly used?

For converting mechanical motion into digital information. (B) Signup and view all the answers

Why is external counting necessary for incremental encoders?

To determine absolute position during operation. (C) Signup and view all the answers

What phenomenon does the Hall effect describe?

Voltage generation perpendicular to electric current and magnetic field (A) Signup and view all the answers

Which of the following is NOT a typical use of Hall effect sensors?

Measuring displacement (A) Signup and view all the answers

What distinguishes Eddy Current Based Position Sensors from Hall Effect Based Sensors?

Eddy current sensors can measure displacement and oscillation (C) Signup and view all the answers

Which factors influence the operation of a Hall effect sensor?

Both electric current and the magnetic field strength (A) Signup and view all the answers

In the context of eddy current sensors, what happens when a conductive target enters the alternating magnetic field?

A small current is induced in the target. (B) Signup and view all the answers

What is a key advantage of using non-contact devices like Hall effect sensors?

Protection against wear and tear (D) Signup and view all the answers

Eddy currents produced in conductive materials oppose which type of field?

The sensor's magnetic field (D) Signup and view all the answers

Which statement about Hall effect sensors is true?

They can detect the strength and direction of magnetic fields. (B) Signup and view all the answers

Which characteristic makes fiber optic position sensors effective in harsh environments?

They are immune to electromagnetic radiation. (A) Signup and view all the answers

What are the two types of fiber optic sensors?

Intrinsic and extrinsic sensors. (C) Signup and view all the answers

What measurement is a fiber optic sensor primarily used to detect?

Temperature, strain, and pressure. (D) Signup and view all the answers

In intrinsic fiber optic sensors, what aspect of the fiber modulates the measurand?

The intensity, polarization, and phase of light. (C) Signup and view all the answers

Which field of application is NOT typically associated with fiber optic position sensors?

Consumer electronics for sound detection. (D) Signup and view all the answers

What is a primary advantage of using fiber optic position sensors in multiplexing signals?

They can operate with more than one signal simultaneously. (D) Signup and view all the answers

How is temperature defined in physical terms?

The amount of heat energy in a system. (C) Signup and view all the answers

What kind of physical parameters can fiber optic sensors measure?

Temperature, strain, pressure, and more. (B) Signup and view all the answers

Study Notes

LVDT (Linear Variable Differential Transformer)

A small AC reference voltage (called the "excitation signal") is applied to the primary winding.
The excitation signal induces an EMF signal into the two adjacent secondary windings.
The output voltage is zero when the core is in the center (null position) because the induced EMFs in the secondary windings cancel each other out.
Output signal amplitude is a linear function of the core's displacement.
Output signal polarity indicates the direction of movement.
Advantages over potentiometers: excellent voltage output to displacement, high accuracy, resolution, sensitivity, frictionless operation, and sealed for use in hostile environments.

Inductive Proximity Sensor

Detects ferrous and non-ferrous metal objects.
Operates based on Faraday's Law of inductance.
Consists of an oscillator, a coil, and a sensing circuit.
Does not detect non-metallic objects.

Hall Effect Based Magnetic Position Sensors

Determines object position by detecting magnetic fields generated from various sources (Earth, electric currents, magnets, brain waves).
Functions based on the Hall Effect: a voltage is generated perpendicular to both current and magnetic field when a current-carrying conductor is placed in a magnetic field.

Eddy Current Based Position Sensors

Non-contact devices that measure position, displacement, oscillation, and vibration of conductive targets.
Require high precision and can operate in harsh environments.
Function based on magnetic induction:
- An alternating current passed through a coil generates an alternating magnetic field.
- When a target comes into contact with this field, eddy currents are induced in the target.
- Eddy currents create a field opposing the sensor's field, resulting in an output signal.

Incremental Encoders

Convert mechanical motion into digital information.
Available in two types:
- Single channel encoder: Provides position and velocity information.
- Quadrature or Sine wave encoder: Produces two separate sine and cosine output signals.
Direction of rotation is determined by which channel produces an output first, either channel A or channel B.
Main disadvantage: Requires external counters to determine absolute angle, making them susceptible to errors if power is interrupted or pulses are missed.

Absolute Encoders

Output is an absolute measure of position, indicating the current position of the shaft.
Provide a unique output code for every position.
Coded disk consists of multiple tracks of light and dark segments, each with its own photo detector to read a unique coded position value.
Number of tracks corresponds to the encoder's resolution.

Fiber Optic Position Sensors

Use optical fibers as the sensing device.
Sense temperature, strain, pressure, displacement, velocity, and acceleration.
Based on retro reflectance of light inside an optical fiber due to the movement of the proximal mirror surface.
Immune to electromagnetic radiation, magnetic fields, lightning, and harsh environmental conditions.
Two types:
- Intrinsic sensors: The measurand modulates the transmission properties of the optical fiber (intensity, polarization, phase).
- Extrinsic sensors: Modulation occurs outside the fiber, using the fiber as a conduit for light.
Advantages: Immune to electromagnetic radiation, electrically insulating, wide temperature range, and ability to multiplex signals.

Temperature Sensors

Temperature is the most widely sensed parameter due to its impact on materials and processes at the molecular level.
Defined as the degree of hotness or coldness relative to a specific scale, or the amount of heat energy in a system or object.

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Description

Test your knowledge on LVDT, inductive proximity sensors, and Hall effect magnetic position sensors. This quiz covers the principles, advantages, and operational mechanisms of these essential electromechanical devices. Enhance your understanding of how these sensors function in various applications.