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Medical Instrumentation

Medical Instrumentation. HW #3 2004200456 Lim Myeong Jun. Contents. Resistive sensor Capacitive sensor Inductive sensor LVDT Problem solution Piezoelectric sensor Electromagnetic spectrum Radiation thermometer. Resistive sensor. ∵ ρ : Specific resistance.

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Medical Instrumentation

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  1. Medical Instrumentation HW #3 2004200456 Lim Myeong Jun

  2. Contents • Resistive sensor • Capacitive sensor • Inductive sensor • LVDT • Problem solution • Piezoelectric sensor • Electromagnetic spectrum • Radiation thermometer

  3. Resistive sensor ∵ ρ : Specific resistance Strain gage : Changes in L & ρ Force sensing resistor : Changes in A Thermister : Changes in temperature Potentiometer : Changes in Length

  4. Force sensing resistor(FSR) F R

  5. Thermister R Ceramic NTC thermister (Negative temperature coefficient) PTC thermister (Positive temperature coefficient)

  6. Thermister A ) + Vout - Vo, Vs, F, T : Non linear B ) - +

  7. Thermister C ) Bridge circuit D ) Linearization Rs Rp R Linear range

  8. Capacitive & Inductive sensor • Capacitive sensor A Most capacitive sensor is based on changes in x. εR x • Inductive sensor Self Inductance Mutual Inductance Difference Inductance

  9. LVDT • LVDT(Linear Variable Differential Transformer) c a x=D x= δ d f x=0 x=-δ e x=-D b Primary coil

  10. LVDT Magnetic core + Vo - Line is Vs and dot is Vo at magnetic core Mutual Inductance Sensor

  11. LVDT • When core is x=0

  12. LVDT • When core is x=+δ

  13. LVDT • When core is x=- δ

  14. Problem #13 • Vertical displacement Given by Vs(t) = sin(2π*1000t) [V] (f = 1000Hz, T = 1ms) 180º Phase change

  15. Problem #13 Method 1: Rectifier + LPF Full wave rectifier x=D x=0 x=-D LPF D=20mm, 2D=40mm V(t) t

  16. Problem #13 Method 2: Phase-Sensitive demodulation x(t)·Vo²(t) V(t) Vo(t) LPF(Low Pass Filter) x(t) = sin(2π· 1000t) V(t) t

  17. Problem #14 • In phase-sensitive demodulation Vm(t) V(t) Vo(t) LPF(Low Pass Filter) x(t) = sin(2π· 1000t)

  18. Problem #14 • formula

  19. Piezoelectric sensor x q : Charge , x : Deflection Fig. piezoelectric sensor That means piezoelectric sensor has no DC response.

  20. Piezoelectric sensor 1) i=0 + IA - i(t) Vo(t) i=0 Vs(t) = R*i(t)

  21. Piezoelectric sensor 2) i(t), Current flow - IA + Vo(t) 0V Change Amplifier

  22. Piezoelectric sensor |H| If you plan to use the piezoelectric sensor, for measuring pulse, the lowest frequency of pulse, signal is assumed to be 0.1Hz k/c f fc = 1/2πRC

  23. Thanks for your attention!

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