Mechatronics Engineering Lecture 5: Sensors & Transducers

Mechatronics Engineering (OFRME200) - Lecture 5

• Course level: 2
• Semester: Fall
• Instructor: Walaa Shoeib
• Faculty: Electronic Engineering, Menoufia University

Chapter 2: Sensors & Transducers

• This chapter covers sensors and transducers used in mechatronics engineering.

Linear Variable Differential Transformer (LVDT)

• An LVDT is a sensor that measures linear displacement.
• It consists of three coils (one primary, two secondaries).
• The coils are wound around a hollow, non-magnetic tube.
• A movable core is positioned inside the tube.
• Displacement of the core changes the voltage output.
• Provides linear output for the displacement.
• Null position: the amount of primary magnetic flux induced into each of the two secondary coils is exactly the same. The output voltage is zero.
• Output is an AC signal.
• Requires a demodulator to provide a DC output.

Advantages of LVDT

• Reduced frictional losses
• Low power consumption
• Direct conversion into electrical signals
• Smooth operation
• High sensitivity

Disadvantages of LVDT

• Needs extra setup (sensitive to stray magnetic fields)
• Large displacement needed for a small output
• Requires a demodulator

Capacitive Sensor

• Measures displacement, pressure, and other physical quantities.
• Passive transducer – requires external power.
• Works on the principle of variable capacitance of overlapping plates; the distance or the dielectric constant between the plates changes its capacitance.
• Used for measuring pressure and humidity in gases.
• Can also measure volume, density, and weight.

Advantages of Capacitive Transducer

• Very sensitive
• Requires low output power

Disadvantages of Capacitive Transducer

• Metallic parts need insulation
• Cables connecting transducers can cause errors

Piezoelectric Sensor

• Certain materials generate voltage when deformed by mechanical stress or force.
• Quartz crystal is a well-known piezoelectric material.
• Applications include vibration monitoring, pressure sensing, force measurement, and structural health monitoring.

Advantages of Piezoelectric Sensor

• Simple construction
• Low cost
• Wide range of pressures and temperatures

Disadvantages of Piezoelectric Sensor

• Output is low
• Primarily used only for dynamic pressure measurement.

Photoelectric Sensor (Photo Eye)

• Measures distance, absence, presence of an object.
• Uses light transmitter, infrared, photoelectric receiver (opposed, retro-reflective, proximity-sensing).
• Requires only one power source.
• Can use remote sensing with fiber optics.

Infrared (IR) Sensor

• Consists of an IR LED (emitter) and an IR photodiode(detector).
• Output voltage changes in proportion to the IR light received.
• Incidence can be direct or indirect.

Encoder Types and Technologies

• Used to measure the movement of mechanical components (rotations/translations).
• Categories of encoders:
• Linear
• Rotary
• Within each category, there are different measurement types like:
• Absolute
• Incremental
• Electromechanical technologies include magnetic, optical, inductive, capacitive, laser