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Chapter 2 Basic sensors and principles

Chapter 2 Basic sensors and principles. What is a sensor?. Image: Grimnes, Høgetveit. Biomedical Engineering Education & Advanced Bioengineering Learning: Interdisciplinary Concepts. .

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Chapter 2 Basic sensors and principles

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  1. Fysisk institutt - Rikshospitalet Chapter 2 Basic sensors and principles

  2. What is a sensor? Image: Grimnes, Høgetveit.Biomedical Engineering Education & Advanced Bioengineering Learning: Interdisciplinary Concepts. ”A sensor is a mediator able to convert one or more measurands or physical variables into an equivalent signal variable of another type of quantity within a frame of a given unity” Pallàs-Areny, Webster, Sensors 2001

  3. More definitions.... Image: Grimnes-Høgetveit.Biomedical Engineering Education & Advanced Bioengineering Learning: Interdisciplinary Concepts. • Sensor system: ”comprises the total signal path from the measurand to the observer and includes all sensing, conditioning and real-time processing elements in the path” • Electrode: ” An electrode is an electrochemical cell converting charge carriers from ions to electrons or vice versa. An electrode is only a half-sensor in the way that two electrodes are necessary in order to apply a current or read a potential difference in living tissue” • Probe: A ”probe is a broader concept than a sensor. A probe is often comprising multiparameter sensors (e.g. temperature) and may be held by the operator and be equipped with switches and level adjustment facilities. Example: Ultrasound probe” Source: Grimnes-Høgetveit.Biomedical Engineering Education & Advanced Bioengineering Learning: Interdisciplinary Concepts.

  4. Fysisk institutt - Rikshospitalet Transducer - sensor (føler) - probe Position

  5. Strain gages • - Strain gages: ”are primarily displacement sensors based on variations in the electrical resistance of conductors or semiconductors as a function of mechanical stress” Image: Grimnes, Høgetveit.Biomedical Engineering Education & Advanced Bioengineering Learning: Interdisciplinary Concepts. Image: www.conservationphysics.org

  6. Fysisk institutt - Rikshospitalet Pressure-transducer Strain gauge: R= L/A

  7. Pressure-transducer Strain gauge: R= L/A FYS4250 Fysisk institutt - Rikshospitalet

  8. Pressure transducerand Wheatstone bridge Image: Grimnes-Høgetveit.Biomedical Engineering Education & Advanced Bioengineering Learning: Interdisciplinary Concepts.

  9. Fysisk institutt - Rikshospitalet Force measurements

  10. Fysisk institutt - Rikshospitalet Force pressure Semiconductor transducer Piezoresistive

  11. Fysisk institutt - Rikshospitalet Plethysmograph = volummåler

  12. Fysisk institutt - Rikshospitalet Inductive displacement sensors L = n2Gμ

  13. Fysisk institutt - Rikshospitalet Linear VariableDifferential Trafo (LVDT) sign problem

  14. Fysisk institutt - Rikshospitalet Position detection, capacitive sensor

  15. Fysisk institutt - Rikshospitalet Piezoelectric transducer C=εA/x

  16. Fysisk institutt - Rikshospitalet Step response

  17. Fysisk institutt - Rikshospitalet 2.ordersystem

  18. Fysisk institutt - Rikshospitalet Temperature measurements, termocouple

  19. Thermocouple • Junction between metal A and B (hot junction), and an isothermal block with an ice bath temperature in connection to a voltmeter • A change in temperature will result in a voltage change readable on the voltmeter Image: Grimnes-Høgetveit.Biomedical Engineering Education & Advanced Bioengineering Learning: Interdisciplinary Concepts.

  20. Fysisk institutt - Rikshospitalet Temperature measurement, termistor

  21. Fysisk institutt - Rikshospitalet Radiation thermometry Black body radiation Wiens law: λm=2898/T [μm] Stefan-Boltzmann: Wt=εσT4[W/cm2]

  22. Fysisk institutt - Rikshospitalet Radiation thermometer

  23. Infrared ear thermometer Image: Harsanyi, 2000, p 102

  24. Fysisk institutt - Rikshospitalet Fiberoptical thermometer, non-metallic

  25. Fysisk institutt - Rikshospitalet Optical instrument

  26. Fysisk institutt - Rikshospitalet Radiation sources

  27. Fysisk institutt - Rikshospitalet Light emitting diode (LED)

  28. Fysisk institutt - Rikshospitalet Fiberoptics Snells lov: n2 sinθ2 = n1 sinθ1

  29. Fysisk institutt - Rikshospitalet Photomultipliers

  30. Fysisk institutt - Rikshospitalet Diode as a light detector

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