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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 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 Strain gage : Changes in L & ρ Force sensing resistor : Changes in A Thermister : Changes in temperature Potentiometer : Changes in Length
Thermister R Ceramic NTC thermister (Negative temperature coefficient) PTC thermister (Positive temperature coefficient)
Thermister A ) + Vout - Vo, Vs, F, T : Non linear B ) - +
Thermister C ) Bridge circuit D ) Linearization Rs Rp R Linear range
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
LVDT • LVDT(Linear Variable Differential Transformer) c a x=D x= δ d f x=0 x=-δ e x=-D b Primary coil
LVDT Magnetic core + Vo - Line is Vs and dot is Vo at magnetic core Mutual Inductance Sensor
LVDT • When core is x=0
LVDT • When core is x=+δ
LVDT • When core is x=- δ
Problem #13 • Vertical displacement Given by Vs(t) = sin(2π*1000t) [V] (f = 1000Hz, T = 1ms) 180º Phase change
Problem #13 Method 1: Rectifier + LPF Full wave rectifier x=D x=0 x=-D LPF D=20mm, 2D=40mm V(t) t
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
Problem #14 • In phase-sensitive demodulation Vm(t) V(t) Vo(t) LPF(Low Pass Filter) x(t) = sin(2π· 1000t)
Problem #14 • formula
Piezoelectric sensor x q : Charge , x : Deflection Fig. piezoelectric sensor That means piezoelectric sensor has no DC response.
Piezoelectric sensor 1) i=0 + IA - i(t) Vo(t) i=0 Vs(t) = R*i(t)
Piezoelectric sensor 2) i(t), Current flow - IA + Vo(t) 0V Change Amplifier
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