실험 7. 생체온도및손가락힘측정 Force sensing resistor (FSR) Thermistor 실험절차
압력센서의종류 특징기계식센서고분자센서전기식 / 반도체센서 외형 측정대상 기체 / 액체 큰하중 미세변동 측정면적 중 / 대면적 중면적 소면적 가격 중 고 고 융합도 저 고 중 활용도 저 중 중
압력측정방식의비교 Type Data Pros Cons Piezo-capacitive [1,2] Change in capacitance Excellent sensitivity, Good spatial resolution, Large dynamic range Stray capacitance, Noise susceptible, Complexity of measurement electronics Piezo-resistive [3,4] Change in resistance High spatial resolution, High scanning rate in mesh, Structured sensors Lower repeatability, Hysteresis, Higher power consumption Piezo-electric [5,6] Inductive Linear variable differential transformer (LVDT) [7,8] Strain (stress) polarization Change in magnetic coupling High frequency response, High sensitivity, High dynamic range Linear output, Uni-directional measurement, High dynamic range Poor spatial resolution, Dynamic sensing only Moving parts, Low spatial resolution, Bulky Optoelectric [9] Light intensity/spectrum change Good sensing range, Good reliability, High repeatability, High spatial resolution, Immunity from EMI Bulky in size, Non-conformable Strain gauges [10,11] Change in resistance Sensing range, Sensitivity, Low cost, Established product Calibration, Susceptible to temperature changes Susceptible to humidity, Design complexity, EMI induced errors, Nonlinearity,mainly 1D Multi-component sensors [12-14] Coupling of multiple intrinsic parameters Ability to overcome certain limitations via combination of intrinsic parameters, Discrete assembly, Higher assembly costs Fabric based EIT pressure sensor [15] Change in electrical impedance Low cost, scalable, versatile, no mechanical parts, no wiring in sensing pad, conformable, design simplicity, good sensing range, good repeatability, immunity from environmental noise Low spatial resolution
Force Sensing Resistor Resistance changes when a force or pressure is applied Consist of a conductive polymer Sensing film consists of both Pressure R Resistance electrically conducting and non-conducting particles suspended in matrix
Temperature Sensor Contact Direct contact to the measured object Mechanical temperature sensors Thermometer (Mercury-in-glass thermometer) Bimetal Electrical temperature sensors Thermistor Thermocouple Non-contact Laser, Infrared thermometer
Thermistor A type of resistor whose resistance varies significantly with temperature, more than in standard resistors NTC : Temperature PTC : Temperature Resistance Resistance
Bridge Circuit Two circuit branches (usually in parallel with each other) are "bridged" by a third branch connected between the first two branches at some intermediate point along them For laboratory measurement purpose Unknown resistance to be measured Extremely high accuracy R 2 R 1 = R x R 3 R x = R 2 R 1 R 3
실험준비물 - 저항 470W 3개, 100kW 3개 - Force sensing resistor - Thermistor - DC 전원공급기 - 파형발생기 - 오실로스코프, 멀티미터
실험단계 1 1) 다음의브릿지회로구성 2) V1 은 9V DC 를인가, Rs 위치에 Force sensing resistor 연결 3) V2 양단의전압측정 V2 양단의전압 : 4. 513V
실험단계 2 1) Rs 에다섯개의손가락을각각이용하여힘을인가 2) 변화를기록 손가락힘이셀수록압력센서의저항값이감소하여 V2 양단에걸리는전압이줄어든다는것을알수있다. 피실험자 1 피실험자 2 피실험자 3 엄지 0.858 0.757 0.965 검지 0.594 0.752 1.023 중지 0.672 0.583 0.872 약지 1.388 1.313 0.700 새끼 2.923 1.463 0.635
실험단계 3 1) V1 에 10kHz, 2Vpp 의정현파인가 2) V2 의변화를오실로스코프를이용하여측정 3) 오실로스코프의 math 기능이용 피실험자 1 (V pp ) 엄지 0.80 검지 0.72 중지 0.76 Peak to peak : 2.0V pp 약지 0.88 새끼 1.08
실험단계 4 1) V1 에 9V DC, 브릿지의저항을 100kW, Rs 에 thermistor 연결 2) V2 전압을멀티미터를이용하여측정 100kW 100kW Rs 의저항값 : 12.9kW V2 전압 : -3.422V 100kW
실험단계 5 1) Thermistor를손가락을이용하여온도상승 2) 변화를측정 피실험자 1 0초 -3.424V 2초 -3.501V 4초 -3.579V 6초 -3.644V 8초 -3.710V 10초 -3.722V 12초 -3.727V 14초 -3.730V 16초 -3.732V 18초 -3.732V 20초 -3.732V
실험단계 6 1) Thermistor 를코밑또는입주변에위치 2) 호흡을하면서온도변화측정 피실험자 1 흡기 호기 1회 -3.515V -3.440V 2회 -3.525V -3.475V 3회 -3.506V -3.470V
주의사항 1. V2의 +/-방향을정해놓고측정 V2의출력을 math기능을이용 2. Force sensing resistor을사용할하여때, 측정하기오래잡으면위해, 손의온도때문에저항이커져서전압증가channel 1과 channel 2 의 + 3. 오실로스코프를사용시 math 단자를기능원사용부위에접촉시키고, ground 지점을전원접지에연결하여측정 Channel 1 Channel 2