Sensor dan Transduser Rudi Susanto
Definisi Sensor dan transduser Sensor adalah suatu peralatan yang berfungsi untuk mendeteksi gejala-gejala atau sinyal-sinyal yang berasal dari perubahan suatu energi seperti energi listrik, energi fisika, energi kimia, energi biologi, energi mekanik dan sebagainya
Contoh; Camera sebagai sensor penglihatan, telinga sebagai sensor pendengaran, kulit sebagai sensor peraba, LDR (light dependent resistance) sebagai sensor cahaya, dan lainnya. Transduser adalah sebuah alat yang bila digerakan oleh suatu energi di dalam sebuah sistem transmisi, akan menyalurkan energi tersebut dalam bentuk yang sama atau dalam bentuk yang berlainan ke sistem transmisi berikutnya”. Transmisi energi ini bisa berupa listrik, mekanik, kimia, optic (radiasi) atau thermal (panas).
Skema Input Output Tranduser
Detectable Phenomenon Stimulus Acoustic Biological & Chemical
Electric
Magnetic
Quantity Wave (amplitude, phase, polarization), Spectrum, Wave Velocity Fluid Concentrations (Gas or Liquid)
Charge, Voltage, Current, Electric Field (amplitude, phase, polarization), Conductivity, Permittivity
Magnetic Field (amplitude, phase, polarization), Flux, Permeability
Optical
Refractive Index, Reflectivity, Absorption
Thermal
Temperature, Flux, Specific Heat, Thermal Conductivity
Mechanical
Position, Velocity, Acceleration, Force, Strain, Stress, Pressure, Torque
Choosing a Sensor
Sensor Block Diagram Primary Transduction
measurand Isyarat input
• Blok diagram sensor
Secondary Transduction Isyarat output
Passive Sensor • Mengkonversi sifat-sifat/isyarat fisik atau kimia ke dalam isyarat yang lain tanpa bantuan sumber energi
Contoh
Active Sensor • Mengkonversi sifat-sifat/isyarat fisik atau kimia ke dalam isyarat yang lain dengan bantuan sumber energi • Merupakan pilihan utama untuk isyarat-isyarat yang lemah/kecil
Active Sensor Primary Transduction
measurand
Secondary Transduction Isyarat output
Isyarat input Auxiliary Energy Source
• Blok Diagram Active Sensor
Analog Output • Active sensor di industri elektronika mempunyai standar isyarat listrik baik analog (berupa tegangan atau arus) maupun digital
Digital Output • Computer Based atau Microprocessor
Sensor dan Cara Kerjanya
Positional Sensors: potentiometer Can be Linear or Rotational
Processing circuit
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Positional Sensors: LVDT Linear Variable Differential Transformer
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Positional Sensors: Inductive Proximity Switch • Detects the presence of metallic objects (noncontact) via changing inductance • Sensor has 4 main parts: field producing Oscillator via a Coil; Detection Circuit which detects change in the field; and Output Circuit generating a signal (NO or NC) Used in traffic lights (inductive loop buried under the road). Sense objects in dirty environment. Does not work for non-metallic objects. Omni-directional.
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Positional Sensors: Rotary Encoders • Incremental and absolute types • Incremental encoder needs a counter, loses absolute position between power glitches, must be re-homed • Absolute encoders common in CD/DVD drives
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Temperature Sensors • Bimetallic switch (electro-mechanical) – used in thermostats. Can be “creep” or “snap” action. Creep-action: coil or spiral that unwinds or coils with changing temperature
• Thermistors (thermally sensitive resistors); Platinum Resistance Thermometer (PRT), very high accuracy. 20
Thermocouples • Two dissimilar metals induce voltage difference (few mV per 10K) – electro-thermal or Seebeck effect
• Use op-amp to process/amplify the voltage • Absolute accuracy of 1K is difficult
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Light sensors: photoconductive cells • Light dependent resistor (LDR) cell
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Light level sensitive switch
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Photojunction devices phototransistor photodiode
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Photovoltaic Solar Cells • Can convert about 20% of light power into electricity • Voltage is low (diode drop, ~0.6V)
Solar power is 1.4kW/m^2
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Photomultiplier tubes (PMT) • Most sensitive of light sensors (can detect individual photons) • Acts as a current source
electrons
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Motion sensors/transducers • Switches, solenoids, relays, motors, etc. • Motors • DC • Brushed/brushless Stepper motor • Servo • Stepper motors • AC
Brushed motor – permanent magnets on armature, rotor acts as electromagnet Brushless motor – permanent magnet on the rotor, electromagnets on armature are
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Sound transducers microphone
speaker
• Note: voice coil can also be used to generate fast motion 29
Piezo transducers • Detect motion (high and low frequency) • Sound (lab this week), pressure, fast motion • Cheap, reliable but has a very limited range of motion
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Tugas! 1.Teori Pengantar Sensor 2.Rangkaian Elektronika Sensor 3.Prinsip Kerja 4.Algoritma Program dalam Implementasi
