Mechatronics Engineering Lecture 5: Sensors & Transducers

Mechatronics Engineering (OFRME200) Lecture 5

• Course: Mechatronics Engineering (OFRME200)
• Lecture: 5
• Level: 2
• Semester: Fall
• Instructor: Walaa Shoeib
• University: Menoufia University, Faculty of Electronic Engineering

Chapter 2: Sensors & Transducers

• Topic: Sensors and Transducers
• Subtitle: Chapter 2
• Note: Electronic Measurements

Linear Variable Differential Transformer (LVDT)

• Device: Linear Variable Differential Transformer (LVDT) or Linear Variable Differential Transducer (LVDT)
• Function: Measures linear displacement
• Principle: Works on the principle of variable inductance
• Components: Three coils wound sequentially around a hollow, non-magnetic tube. One primary coil and two secondary coils.
• Operation: As the core moves, the magnetic flux linking the secondary coils changes. This produces an output voltage that is proportional to the displacement. The output voltage is the difference between the voltages of the two secondary coils.
• Output: Proportional to the displacement
• Advantages: Low friction loss, low power consumption, direct conversion to electrical signals, greater sensitivity
• Disadvantages: Needs extra setup, delicate to stray magnetic fields, large displacement for little output, requires demodulator to convert AC signal to DC.
• Applications: Measuring linear displacement, force and pressure, humidity in gases

Capacitive Sensor

• Type: Capacitive displacement sensor
• Function: Used for measuring displacement, pressure and other physical quantities
• Principle: Works on the principle of variable capacitance. Capacitance between plates changes for various reasons; overlapping of the plates, distance between the plates and dielectric constant
• Advantages: Very sensitive, requires small output power
• Disadvantages: Metallic parts require insulation and cables connecting across the transducer cause error
• Applications: Measuring linear and angular displacements, force, pressure, humidity in gases, volume, density, weight, etc
• Capacitive transducer: Contains two parallel metal plates separated by a dielectric medium (air, material, gas or liquid). Changes in the distance between plates alter capacitance, which is measured.

Piezoelectric Sensor

• Principle: Certain materials generate an electric voltage when mechanically deformed; e.g. quartz crystal.
• Applications: Vibration monitoring, pressure sensing, force measurement, structural health monitoring
• Advantages: Simple construction, inexpensive materials, Wide range of pressure and temperatures.
• Disadvantages: Only for dynamic pressure measurement, low output voltage

Photoelectric Sensor (Photo Eye)

• Function: Detects distance. presence, and absence of objects
• Types:
  • Through-beam: An object in the beam path interrupts the light signal.
  • Retro-reflective: An object is reflected back in the beam to signal.
  • Proximity-sensing (diffused): Radiation must reflect off the object to reach the receiver.

Infrared (IR) Sensor

• Function: Sensing radiation
• Components: IR LED (emitter), IR photodiode (detector)
• Principle: Changes in intensity of reflected IR light are converted into output voltage changes to measure objects
• Uses: Measuring distances, detecting the presence of objects or their absence.

Encoder

• Function: Measures movement of mechanical parts/ measuring rotation/position
• Types:
  • Linear and Rotary.
• Subtypes:
  • Absolute/ Incremental
  • Magnetic, Optical, Inductive, Laser and Capacitive