센서의원리
메카트로닉스시스템의구성 ECU Model of 기계시스템 인터페이스회로 ( 시그널컨디셔닝 ) 마이컴 인터페이스회로 ( 드라이빙회로 ) 센서 액츄에이터 ( 구동기 ) 기계시스템
회로이론복습 - 전하 (electric charge): 전기적인성질을가지고있는물질, 단위 [C] - 전류 (electric current): 단위시간당흐른전하량, 단위 [A] - 전압 (electric voltage), 전위차 (electric potential difference): 단위전하당한일, 단위 [V] - 전력 (power): 단위시간당한일, 단위 [W]
회로이론복습 부하 (electric load 또는 load): 전기에너지를소비하는모든장치 전원 (electric source 또는 source): 전기에너지를공급하는장치 크기와극성이일정한직류 (direct current: DC) 크기와극성이주기적으로변하는교류 (alternating current: AC)
회로이론복습 저항 (resistance): 전기에너지의흐름을방해하는성질 - 저항에의해에너지는열로소비된다. - 저항의단위는 [Ω] 이며옴 (ohm) 으로읽는다. 옴의법칙 v ir 인덕터 (inductance): 전기에너지가자기에너지로바뀌는성질 - 인덕터 ( 코일 ) 에의해에너지는자기에너지형태로소비 ( 변환 ) 된다. - 인덕터의단위는 [H] 이며헨리 (henry) 라고읽는다. 커패시터 (capacitance): 전하가축적되는성질 - 커패시터 ( 콘덴서 ) 에의해에너지는전하의형태로축적된다. - 저항의단위는 [F] 이며패럿 (farad) 으로읽는다. v L i C di dt dv dt
회로이론복습 키르히호프의전압법칙 (KVL: Kirchhoff s Voltage Law) 하나의폐회로를형성하는모든소자에대하여소자에의한전압상승분의합은소자에의한전압강하분의합과같다. 수식표현
회로이론복습 키르히호프의전류법칙 (KCL: Kirchhoff s Current Law) 하나의노드를중심으로들어오는전류값의합은그노드에서나가는전류값의합과같다. 수식표현
회로이론복습 직렬연결또는직렬결선 (series connection): 저항을일렬로늘어놓고그대로연결하는방식
회로이론복습 직렬연결또는직렬결선 (series connection) KVL 에의해, 직렬회로를흐르는전류는회로어느곳에서나같다.
회로이론복습 병렬연결또는병렬결선 (parallel connection): 여러개의저항을머리는머리끼리, 꼬리는꼬리끼리접속하는연결방식
회로이론복습 병렬연결또는병렬결선 (parallel connection) KCL 에의해, 병렬회로의저항에걸리는전압은모두같다.
회로이론복습 병렬연결또는병렬결선 (parallel connection) 저항 R 1, R 2, R 3 가병렬연결된회로에전류 I 가흐를때, 각저항에흐르는전류는?
회로이론복습 테브닌 (Thevenin) 과노턴 (Norton) 의정리 복잡한회로를블랙박스로둔다. 단순한전압전원하나와직렬로연결된저항소자로표현 ( 테브닌등가회로 ) 단순한전류전원하나와병렬로연결된저항소자로표현 ( 노턴등가회로 ) 전원과저항값의계산이단자간전류및전압값의측정으로도이루어질수있어서실용적
회로이론복습 테브닌등가회로 블랙박스회로내부를하나의전압전원과그와직렬로연결된저항소자로표현하는것 a-b 단자를통해부하로흐르는전류를 i, 단자간의전압을 v 라고하면다음과같은관계를얻을수있다.
회로이론복습 테브닌의정리 주어진회로에서테브닌등가회로를찾아내는기법 (1) v oc 의계산 - 단자 a-b 가개방되어있다면 R th 에흐르는전류 i = 0 이고, - 단자 a-b 사이의전압 v ab 의값은 v oc 와같다. - 단자의개방회로에서전압전원을구하므로 v oc 는개방회로전압
회로이론복습 (2) R th 의계산 - 단자 a-b 에서블랙박스쪽으로들여다본저항값으로계산 - 전압전원 v oc 를 0 으로둬회로를단락 ( 즉, 독립전원의비활성화 ) 참고 비활성화는독립전압전원의경우에단락, 독립전류전원의경우에는개방
회로이론복습 다음회로에서단자 a-b 의테브닌등가회로를구하라.
Sensor Basics: Potentiometer The resistance of a given sample will increase with the length, but decrease with greater cross-sectional area. l 접촉점의위치 저항의변화 http://en.wikipedia.org/wiki/resistivity
Sensor Basics: Potentiometer 계측방법 If R L is large compared to the other resistances (like the input to an operational amplifier), the output voltage can be approximated by the simpler equation: http://en.wikipedia.org/wiki/potentiometer
Sensor Basics: Strain Gauge Strain is the amount of deformation of a body due to an applied force. More specifically, strain (e) is defined as the fractional change in length, as shown in Figure 1. Figure 1. Definition of Strain http://zone.ni.com/devzone/cda/tut/p/id/3642 The gauge is attached to the object by a suitable adhesive, such as cyanoacrylate. As the object is deformed, the foil is deformed, causing its electrical resistance to change. This resistance change, usually measured using a Wheatstone bridge, is related to the strain by the quantity known as the gauge factor.
Sensor Basics: Strain Gauge A typical strain gauge arranges a long, thin conductive strip in a zig-zag pattern of parallel lines such that a small amount of stress in the direction of the orientation of the parallel lines results in a multiplicatively larger strain over the effective length of the conductor and hence a multiplicatively larger change in resistance than would be observed with a single straight-line conductive wire. Typical foil strain gauge. The gauge is far more sensitive to strain in the vertical direction than in the horizontal direction. http://en.wikipedia.org/wiki/strain_gage
Sensor Basics: Strain Gauge http://en.wikipedia.org/wiki/strain_gage Visualization of the working concept behind the strain gauge on a beam under exaggerated bending.
Sensor Basics: Wheatstone Bridge It is used to measure an unknown electrical resistance by balancing two legs of a bridge circuit, one leg of which includes the unknown component. http://en.wikipedia.org/wiki/wheatstone_bridge
Sensor Basics: Wheatstone Bridge In the figure, Rx is the unknown resistance to be measured; R1, R2 and R3 are resistors of known resistance and the resistance of R2 is adjustable. If the ratio of the two resistances in the known leg (R2 / R1) is equal to the ratio of the two in the unknown leg (Rx / R3), then the voltage between the two midpoints (B and D) will be zero and no current will flow through the galvanometer Vg. R2 / R1 = Rx / R3
Sensor Basics: Wheatstone Bridge If R1, R2, and R3 are known, but R2 is not adjustable, the voltage difference across or current flow through the meter can be used to calculate the value of Rx,
Sensor Basics: Piezoresistive effect The piezoresistive effect describes the changing resistivity of a semiconductor due to applied mechanical stress. In semiconductors, changes in inter-atomic spacing resulting from strain affects the bandgaps making it easier (or harder depending on the material and strain) for electrons to be raised into the conduction band. This results in a change in resistivity of the semiconductor. http://en.wikipedia.org/wiki/piezoresistive_effect
Sensor Basics: Piezoresistive effect Piezoresistivity is defined by Piezoresistivity has a much greater effect on resistance than a simple change in geometry and so a semiconductor can be used to create a much more sensitive strain gauge, though they are generally also more sensitive to environmental conditions (esp. temperature).
Sensor Basics: Capacitive Sensors Capacitive sensors use the electrical property of "capacitance" to make measurements. Capacitance is a property that exists between any two conductive surfaces within some reasonable proximity.
Sensor Basics: Capacitive Sensors Spacing variation[5] Spacing variation of parallel plates is often used for motion detection if the spacing change is less than the electrode size. The parallel plate capacitance formula shows that capacitance is inversely related to spacing. This gives a conveniently large value of capacitance at small spacing, but it does often require signal conditioning which can compensate for the parabolic capacitance-motion relationship. This is easily done by measuring impedance rather than capacitance.
Sensor Basics: Capacitive Sensors Area variation[5] As these plates slide transversely, capacitance changes linearly with motion. Quite long excursions are possible with good linearity, but the gap needs to be small and well-controlled. d
Sensor Basics: Capacitive Sensors 계측방법, Signal Conditioning[5] An R-C relaxation oscillator such as the venerable 555 or its CMOS update, the 7555, converts capacitance change into a change of frequency or pulse width. The RC oscillator used with a spacing-variation capacitor will produce a frequency output which is linear with spacing, while an area-variation capacitor is linearized by measuring pulse width.
Sensor Basics: LVDT LVDT (Linear Variable Differential Transformer) A type of electrical transformer used for measuring linear displacement. An LVDT Displacement Transducer comprises 3 coils; a primary and two secondaries. http://www.rdpe.com/ex/hiw-lvdt.htm
Sensor Basics: Hall Effect For a simple metal where there is only one type of charge carrier (electrons) the Hall voltage V H is given by where I is the current across the plate length, B is the magnetic flux density, d is the depth of the plate, e is the electron charge, and n is the charge carrier density of the carrier electrons. Hall probes are often used as magnetometers, i.e. to measure magnetic fields. http://en.wikipedia.org/wiki/hall_effect
Sensor Basics: Hall Effect Physics Animation Model The Hall-Effect http://www.youtube.com/watch?v=_atdracqtpq
Sensor Basics: Hall Effect A Hall effect sensor is a transducer that varies its output voltage in response to changes in magnetic field. Hall sensors are used for proximity switching, positioning, speed detection, and current sensing applications. http://en.wikipedia.org/wiki/hall_effect_sensor
Sensor Basics: Piezoelectric Effect Piezoelectricity is the charge which accumulates in certain solid materials (notably crystals, certain ceramics, and biological matter such as bone, DNA and various proteins) in response to applied mechanical strain. A piezoelectric disk generates a voltage when deformed (change in shape is greatly exaggerated) http://en.wikipedia.org/wiki/piezoelectric_sensor
Sensor Basics: Piezoelectric Effect Even though piezoelectric sensors are electromechanical systems that react to compression, the sensing elements show almost zero deflection. Additionally, piezoelectric technology is insensitive to electromagnetic fields and radiation, enabling measurements under harsh conditions. One disadvantage of piezoelectric sensors is that they cannot be used for truly static measurements. http://en.wikipedia.org/wiki/piezoelectric_sensor
Sensor Basics: Thermoelectric Effect The thermoelectric effect is the direct conversion of temperature differences to electric voltage and vice versa. A thermoelectric device creates a voltage when there is a different temperature on each side. At atomic scale (specifically, charge carriers), an applied temperature gradient causes charged carriers in the material, whether they are electrons or electron holes, to diffuse from the hot side to the cold side, similar to a classical gas that expands when heated; hence, the thermally induced current. http://en.wikipedia.org/wiki/seebeck_effect#seebeck_effect
Sensor Basics: Thermoelectric Effect The Seebeck effect is the conversion of temperature differences directly into electricity. The effect is that a voltage, the thermoelectric EMF, is created in the presence of a temperature difference between two different metals or semiconductors. This causes a continuous current in the conductors if they form a complete loop. The voltage created is of the order of several microvolts per kelvin difference. One such combination, copper-constantan, has a Seebeck coefficient of 41 microvolts per kelvin at room temperature. S A and S B are the Seebeck coefficients (also called thermoelectric power or thermopower) of the metals A and B as a function of temperature, and T 1 and T 2 are the temperatures of the two junctions. The Seebeck effect is commonly used in a device called a thermocouple. http://en.wikipedia.org/wiki/seebeck_effect#seebeck_effect
Sensor Basics: Coriolis Effect In physics, the Coriolis effect is an apparent deflection of moving objects when they are viewed from a rotating reference frame. In a reference frame with clockwise rotation, the deflection is to the left of the motion of the object; in one with anti-clockwise rotation, the deflection is to the right. The vector formula for the magnitude and direction of the Coriolis acceleration is where (here and below) a c is the acceleration of the particle in the rotating system, v is the velocity of the particle in the rotating system, and Ω is the angular velocity vector which has magnitude equal to the rotation rate ω and is directed along the axis of rotation of the rotating reference frame, and the symbol represents the cross product operator. http://en.wikipedia.org/wiki/coriolis_effect
Sensor Basics: Coriolis Effect coriolis effect (2-11) http://www.youtube.com/watc h?v=mcps_odqoyu Foucault's pendulum - 2 http://www.youtube.com/watc h?v=wlhhwykswik
산소센서 Zirconia sensor 기전력 Titania sensor 가변저항 http://en.wikipedia.org/wiki/oxygen_sensor
산소센서 Zirconia sensor The zirconium dioxide, or zirconia, lambda sensor is based on a solid-state electrochemical fuel cell called the Nernst cell. Its two electrodes provide an output voltage corresponding to the quantity of oxygen in the exhaust relative to that in the atmosphere. http://www.vcoa.org/700-900- faq/enginesensors.html
산소센서 Titania sensor A less common type of narrow-band lambda sensor has a ceramic element made of titanium dioxide (titania). This type does not generate its own voltage, but changes its electrical resistance in response to the oxygen concentration. http://blog.naver.com/postview.nhn?blogid=autokyw&logno=70044118012
공기량센서 (Airflow Sensor) Vane meter sensor (VAF sensor) Hot wire sensor (MAF) Coldwire" sensor Kármán vortex sensor http://en.wikipedia.org/wiki/mass_flow_sensor
공기량센서 (Airflow Sensor) Vane meter sensor (VAF sensor) http://www.aa1car.com/library/vaf_sensors.htm
공기량센서 (Airflow Sensor) Hot wire sensor (MAF) The theory of operation of the hot wire mass airflow sensor is similar to that of the hot wire anemometer (which determines air velocity). This is achieved by heating a wire with an electric current that is suspended in the engine s air stream, like a toaster wire. The wire's electrical resistance increases as the wire s temperature increases, which limits electrical current flowing through the circuit. When air flows past the wire, the wire cools, decreasing its resistance, which in turn allows more current to flow through the circuit. As more current flows, the wire s temperature increases until the resistance reaches equilibrium again. The amount of current required to maintain the wire s temperature is directly proportional to the mass of air flowing past the wire. The integrated electronic circuit converts the measurement of current into a voltage signal which is sent to the ECU.
공기량센서 (Airflow Sensor) Kármán vortex sensor A Kármán vortex sensor works by setting up a laminar air stream. The air stream is disrupted by a vertical bow in the sensor. This causes a wake in the air stream and subsequently the wake will collapse repeatedly and cause Kármán vortexes. The frequency of the resulting air pressure oscillation is proportional to the air velocity. These vortexes can either be read directly as a pressure pulse against a sensor, or they can be made to collide with a mirror which will then interrupt or transmit a reflected light beam to generate the pulses in response to the vortexes. The first type can only be used in pull thru air (prior to a turbo- or supercharger), while the second type could theoretically be used push or pull thru air (before or after a forced induction application like the previously mentioned super- or turbocharger). Instead of outputting a constant voltage modified by a resistance factor, this type of MAF outputs a frequency which must then be interpreted by the ECU.
광학식이산화탄소농도센서 NDIR 방식이산화탄소가스센서 [1] 이산화탄소가 4.26um 대역의파장을흡수하는성질이용 http://v2010.raesystems.com/~raedocs/app_tech_notes/tech_notes/tn- 169_NDIR_CO2_Theory.pdf
광학식이산화탄소농도센서 NDIR 방식이산화탄소가스센서 [1] NDIR (Non-Dispersive Infrared)
MEMS (Micro Electro Mechanical System) 소형경량화 기계식 : 25mm MEMS: 소자 2~3mm, package 8~9mm [3]
MEMS: Capacitive Sensor Parallel Plate Capacitor http://www.eecs.berkeley.edu/~boser/pdf/
MEMS: Capacitive Sensor Transverse Comb Parallel multiplates can to increase the sensor capacitance in a small volume. http://www.capsense.com/capsense-wp.pdf
MEMS: Capacitive Sensor Transverse Comb http://www.eecs.berkeley.edu/~boser/pdf/
MEMS: Capacitive Sensor Transverse Comb http://www.eecs.berkeley.edu/~boser/pdf/
MEMS Signal Conditioning 통합 ADXL 50 Layout http://www.eecs.berkeley.edu/~boser/pdf/
MEMS http://www.eecs.berkeley.edu/~boser/pdf/overview.pdf
MEMS [3] 압력센서 실리콘다이어프램 (diaphragm) 형압력센서는외부압력에의한다이어프램의휨정도계측
MEMS [3] 압력센서 1) 정전용량형 (capacitive) 2) 압저항형 (piezo-resistive) 장점온도계수낮고, 전력손실이적음선형성우수, 신호처리용이 단점소자면적이넓고, 복잡한신호처리부필요감도낮으며, 온도의존성높음
MEMS [3] 가속도센서
MEMS [3] 가속도센서
MEMS [3] 각속도센서 (Yaw-rate Sensor) 코리올리효과 (Coriolis effect) 이용
MEMS The ADXRS gyros take advantage of this effect by using a resonating mass analogous to the person moving out and in on a rotating platform. The mass is micromachined from polysilicon and is tethered to a polysilicon frame so that it can resonate only along one direction. Figure 3 shows that when the resonating mass moves toward the outer edge of the rotation, it is accelerated to the right and exerts on the frame a reaction force to the left. When it moves toward the center of the rotation, it exerts a force to the right, as indicated by the orange arrows. http://www.analog.com/library/analogdialogue/archives/37-03/gyro.html
MEMS To measure the Coriolis acceleration, the frame containing the resonating mass is tethered to the substrate by springs at 90 relative to the resonating motion, as shown in Figure 4. This figure also shows the Coriolis sense fingers that are used to capacitively sense displacement of the frame in response to the force exerted by the mass, as described further on. Figure 4. Schematic of the gyro s mechanical structure. http://www.analog.com/library/analogdialogue/archives/37-03/gyro.html
MEMS Figure 5. The frame and resonating mass are displaced laterally in response to the Coriolis effect. The displacement is determined from the change in capacitance between the Coriolis sense fingers on the frame and those attached to the substrate. http://www.analog.com/library/analogdialogue/archives/37-03/gyro.html
MEMS Figure 6. Photograph of mechanical sensor. The ADXRS gyros include two structures to enable differential Figure 7. Photograph of ADXRS gyro die, sensing in order to reject highlighting the integration of the environmental shock and vibration. mechanical rate sensor and the signal conditioning electronics. http://www.analog.com/library/analogdialogue/archives/37-03/gyro.html
센서네트워크기술 [4] 센서네트워크 특정지역에소형의노드를설치하여주변정보또는특정목적의정보를획득하고베이스스테이션에서이정보를수집하여이를활용하기위한서비스네트워크 상호간의정보전달보다는자동화된원격정보의수집을목적으로하는점에서기존네트워크와구별 USN (Ubiquitous Sensor Network): 여러개의센서네트워크필드 (field) 가게이트웨이 (gateway) 를통해외부네트워크와연결되어있는구조
참고자료 1. 조남규, 자동차의전자화추세및소요센서전망, Auto Journal 2008.06, pp. 36-42. 2. 김시동, 김병우, 자동차환경센서기술동향, Auto Journal 2008.06, pp. 22-28. 3. 권재홍, 조우성, 김정훈, 김영훈, 주병권, MEMS 기술을적용한자동차응용센서기술및동향, 주간기술동향통권 1284 호 2007.2.21, pp. 21-36. 4. 심영일, 새롭게발전하는자동차센서네트워크기술, Machinery Industry, 2008.3, pp. 66-73, 온라인자료 http://www.koami.or.kr/webzin/2k803/8.pdf. 5. L. K. Baxter, Capacitive Sensors, 온라인자료 http://www.capsense.com/capsensewp.pdf 6. 임시형, Automotive Sensors and Measurements, 섀시전기전자제어, 2010 년자동차전문기술교육자료, 엔지비, 2010 년.