LVDT and Sensors Overview Quiz

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.

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.