Medical Instrumentation II Resistive Sensor Strain gage : changes in L & Force sensing resistor : changes in A Thermistor : changes in L Potentiometer : changes in L Medical Instrumentation II FSR(Force sensing resistor) Medical Instrumentation II F A & F is proportion. R & 1/F is inverse proportion. R Thermistor R F R T RR NTC (Negative Temperature Coefficient) Design. Medical Instrumentation II (A) (B) V 0 vs F or T : Non - linear E[v] S3 R1 S2 S4 reference in = 0 ip = 0 IA VaVb Medical Instrumentation II (C) Bridge circuit (D) Linearigation RsRs RpRp Linear Range R Capacitive Sensor Medical Instrumentation II A x Most capacitor sensor are based on changes in x Inductive Sensor Self Inductance Mutual Inductance Differential Inductance Medical Instrumentation II (1) Self Inductance x F (2) Mutual Inductance - b VsVs VoVo + a - D Medical Instrumentation II (3) LVDT (Linear Variable Differential Transformer) D X = 0 b a c d e - VsVs V o (b) When core is at X = + (a) When core is at X = 0 (c) When core is at X = + V cd is Blue, V ef is Red and V o is Black V o = 0 f Problem 13. Using LVDT, A object that is a reciprocasting motion verticality direction measure location. This is y(t), changing by next page figure. 1 st coils voltage is V(t) = sin(2 x 1000t) [v]. (a) Design the LVDT output signal in 0 ~ 10ms. 2 nd coils phase isnt delay, Suppose LVDT is linear in 20mm. (b) Write verticality direction y(t) by LVDT output signal. (c) Write calibration method for output voltage represent [mm] unit Medical Instrumentation II Problem 13. LVDT Medical Instrumentation II 40mm F X=20mm X=0 X=-20mm 20mm -20mm 5ms10ms 180 Phase change t y(t) Method 1. Rectifier + LPF No Phase change! FWR LPF V(t) V o (t) V(t) t Medical Instrumentation II Method 2. Phase-sensitive demodulation Medical Instrumentation II X LPF V o (t) sin(2 x10t) V (t) IV o (t)I t g X g Matlab 3. 5~10ms 0.01ms filter . Medical Instrumentation II Piezoelectric sensor x V o (t) x(t) (1) Medical Instrumentation II (2) I H I Tf c = 1 / 2RC Medical Instrumentation II If you plan to use the piezoelectric sensor for measuring pulse the lowest frequency of pulse. Signal is assumed to be 0.1Hz. Medical Instrumentation II