Understanding Transducers: Types, Applications, and Functionality
Transducers: Converting Magnitude into Measurable Output
Transducers transform physical magnitudes into another output for easier processing. They are essential in sensors for capturing information within a system for feedback. Transducers and sensors are fundamentally the same, differing only in their placement.
Position, Proximity, and Displacement Transducers
These transducers measure position, proximity, and displacement using various methods:
- Resistive: Based on electrical resistance variation, commonly using potentiometers.
- Inductive: Measure distance between magnetic materials or variations in this distance.
- Capacitive: Detect changes in geometric parameters or dielectric properties, used for proximity, displacement, roughness, or pressure measurements.
- End of Stroke Switches: Determine object position or moving parts by changing switch contacts at movement limits, useful in level detection and lift mechanisms.
- Ultrasound: Utilize vibrations beyond human hearing for level control, altitude detection, and submerged object detection.
- Radar: Employ electromagnetic waves to detect object presence and distance.
Speed Transducers
Speed transducers measure angular speed, typically using tachometers:
- Mechanical: Simple revolution counters or centrifugal tachometers based on the Watt regulator principle.
- Electrical: Convert shaft speed into electrical signals:
- Eddy current or drag cup tachometers (automobiles, aircraft).
- Induction tachometers (varying magnetic flux).
- Alternating current tachometers (rotating magnet induces current).
- Direct current tachometers (permanent magnet stator, uniform air gap rotor).
- Frequency or frequency counter tachometers (electromagnetic or optical).
Temperature Transducers
Temperature transducers measure heat:
- Resistance Temperature Detectors (RTD): Utilize wire resistance variation with temperature (platinum, nickel, copper), often in a Wheatstone bridge circuit.
- Thermistors: Semiconductor variable resistors with temperature (NTC or PTC).
- Thermocouples: Based on the Seebeck effect, using two different metallic conductors to generate voltage due to temperature difference (Chromel, Alumel).
- Radiation Pyrometers: Based on the Stefan-Boltzmann law, measuring radiated energy proportional to temperature.
- Total radiation pyrometers: Converge radiation onto a sensitive element.
- Optical pyrometers: Use visible radiation in a narrow frequency band, comparing it to a known temperature.