MEDICAL INSTEUMENTATIO N. 동서의료공학과 정 진 웅

A kinds of resistive Sensors. 1. Strain gage 2. Potentioneter 3. FSR 4. Thermister and so on.

1. (Axial) stress M y x On the surface The (average) force per unit area is denoted as σ “stress” (cf = pressure) F is sometimes called “load”

2. Strain F F L Strain is unitless Because unit N is divided with unit N

3. & curve Brittle material (ex, glass) rapture Non linear area (ultimate stress) linear area

3. & curve ductile material (ex, Al, steel) Elastic area Plastic area rapture : Al

3. & curve ductile material (ex, Al, steel) rapture Elastic area : steel For elestic region (linear region) (σ ≤ σPL)

4. Cantilever L F neglesible E : constant A & L : almost constant

4. Cantilever F L

5. Strain gage substrate Electrical wire Flexible material From now on, this wire have a length L and surface area A Surface Area ‘A’

6. Gage factor For metal strain gage G : 0 ~ 1.6 For semi-conductor strain gage G : 100~179 (high temperature coefficient)

7. Problem 3 Q3) 4 metal strain gage that have gage factor 4 are set up in a machine. And gage 1 and 2 is increased length ΔL on the force that pull down machine, gage 3 and 4 is decreased length ΔL, and there is relationship ΔL/L = k * f (k is constant). Design by bridge circuit that out voltage proportionate force. Represent out-voltage by force. Drive voltage is dc 5v

7. Problem 3 solution R2R2 R4R4

8. Problem 4 Q4) I plan to make a force measurement system using that 2 p-type Si strain gage with gage factor 100and 2 n-type Si strain gage with gage factor-100. I attach 2 p-type Si strain gage on the cantilever and 2 n-type Si strain gage under the cantilever. (a)Design the circuit that bridge circuit with 4 strain gage and amplify the bride circuit’s output. And, find each strain gage type. Drive voltage is dc 1v. (b) When forced on the cantilever, we suggest cantilever change with same length between upper surface and under surface. Strain gage’s maximum length change rate is ±0.05%, strain gage’s non load resistor is 200 ohm. Find the benefit to change the result output from 5v through force. (c) Suggest the method to do calibration that force measurement.

8. Problem 4 solution

(c) To do calibration, Use a program ‘matlab’ with matrix transformation. Then you can do calibration

9. Problem 6 Q6) Under pressure sensor, 2 p-type Si strain gage with gage factor +100 and 2 n- type strain gage with gage factor -100 are attatched on the diaphragm. When forced with pressure on the diaphragm, same strain is made on the strain gage, then that sensitivity is 10 ⁻⁵ %/mmHg, when not forced with pressure, strain gage’s resistor is 50ohm. Suggest that relationship between pressure and strain is linear. (a)When pressure change between 0 ~ 500mmHg, find the change with p-type and n-type Si strain gage’s resistor values. (b) Design bridge circuit composed 4 strain gage and check on the figure location of each strain gage. (c) Make a bridge circuit’s drive voltage is dc 1v, and add measurement amplifier to change result output between 0 ~ 1v, then find the benefit.

9. Problem 6 solution I am so, so sorry professor Mr.Woo. I don’t know how to solve it. Without fail, I will find the method. Sorry..

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