Download 8 Transducers2

8. Transducers (측정)
Transducer: devices that convert some physical quantity, such as temperature or light
level, to a voltage or some other electrical quantity
A preamplifier (preamp) is an electronic amplifier which precedes another amplifier to
prepare an electronic signal for further amplification or processing. The preamplifier
circuitry may or may not be housed as a separate component. In general, the function of
a preamp is to amplify a low-level signal to line-level. A list of common low-level signal
sources would include a pickup, microphone, turntable or other transducer. Equalization
and may also be applied.
In a home audio system, the term 'preamplifier' may sometimes be used to describe
equipment which merely switches between different line level sources and applies a
volume control, so that no actual amplification may be involved. In an audio system, the
second amplifier is typically a power amplifier (power amp). The preamplifier provides
voltage gain (about: 10millivolts to 1volt) but no significant current gain. The power
amplifier provides the higher current necessary to drive loudspeakers.
transducer: any device that converts energy from one form to
another, eg a loudspeaker, where electrical energy is converted
into sound waves
소리 측정
Microphones
Microphones are transducers which detect sound signals and produce an
electrical image of the sound, i.e., they produce a voltage or a current
which is proportional to the sound signal. The most common
microphones for musical use are dynamic, ribbon, or condenser
microphones. Besides the variety of basic mechanisms, microphones can
be designed with different directional patterns and different
impedances.
Dynamic Microphones
Advantages:
•Relatively cheap and rugged.
•Can be easily miniaturized.
Disadvantages:
•The uniformity of response to
Principle: sound moves the cone
and the attached coil of wire moves different frequencies does not
match that of the ribbon or
in the field of a magnet. The
generator effect produces a voltage condenser microphones.
which "images" the sound pressure
variation - characterized as a
pressure microphone.
Ribbon Microphones
Principle: the air movement
associated with the sound moves
the metallic ribbon in the magnetic
field, generating an imaging voltage
between the ends of the ribbon
which is proportional to the velocity
of the ribbon - characterized as a
"velocity" microphone.
Advantages:
•Adds "warmth" to the tone by
accenting lows when close-miked.
•Can be used to discriminate
against distant low frequency noise
in its most common gradient form.
Disadvantages:
•Accenting lows sometimes
produces "boomy" bass.
•Very susceptible to wind noise. Not
suitable for outside use unless very
well shielded.
Condenser Microphones
Advantages:
•Best overall frequency response
makes this the microphone of choice
for many recording applications.
Disadvantages:
•Expensive
•May pop and crack when close
miked
•Requires a battery or external power
supply to bias the plates.
Principle: sound pressure changes
the spacing between a thin metallic
membrane and the stationary back
plate. The plates are charged to a
total charge
where C is the capacitance and V
the voltage of the biasing battery.
A change in plate spacing will cause
a change in charge Q and force a
current through resistance R. This
current "images" the sound pressure,
making this a "pressure"
microphone.
Electret Condenser Microphone (ECM)
-electret 물질 : 자체로서 전하를 띄고 있는 물질 (예 : fluoropolymers,
polypropylene, polyethyleneterephthalate)
-capacitor의 한 전극을 electret물질로 코팅하면, 따로 전압을 거는 회로가 필
요 없음.
-electret 물질이 코팅된 전극과 다른 전극으로 구성된 capacitor의 전압을
JFET로 읽어서 증폭
-소형화가 쉽기때문에, 작은 모바일 기기에 많이 사용됨
Piezoelectric Microphones
소리에
여기에
이러한
만들어
의해서 diagphragm이 흔들리면,
고정된 piezo crystal이 휘게 되고,
휨은 piezo crystal 양단에 전압을
준다
Dynamic Loudspeaker Principle
A current-carrying wire in a magnetic field experiences a magnetic
force perpendicular to the wire.
Loudspeaker Details
An enormous amount of engineering work has gone into the design of today's dynamic
loudspeaker. A light voice coil is mounted so that it can move freely inside the magnetic field of
a strong permanent magnet. The speaker cone is attached to the voice coil and attached with a
flexible mounting to the outer ring of the speaker support. Because there is a definite "home" or
equilibrium position for the speaker cone and there is elasticity of the mounting structure, there
is inevitably a free cone resonant frequency like that of a mass on a spring. The frequency can
be determined by adjusting the mass and stiffness of the cone and voice coil, and it can be
damped and broadened by the nature of the construction, but that natural mechanical
frequency of vibration is always there and enhances the frequencies in the frequency range
near resonance. Part of the role of a good enclosure is to minimize the impact of this resonant
frequency.
Temperature Measurement
Thermocouples
In electrical engineering and industry, thermocouples are a widely used type of temperature sensor[1] and can also be used
as a means to convert thermal potential difference into electric potential difference.[2] They are cheap[3] and interchangeable,
have standard connectors, and can measure a wide range of temperatures. The main limitation is accuracy; System errors of
less than one degree Celsius (°C) can be difficult to achieve.[
Type K (chromel–alumel) is the most commonly used general purpose thermocouple. It is inexpensive and, owing to its
popularity, available in a wide variety of probes. They are available in the −200 °C to +1350 °C range. The type K was
specified at a time when metallurgy was less advanced than it is today and, consequently, characteristics vary considerably
between examples. Another potential problem arises in some situations since one of the constituent metals, nickel, is
magnetic. One characteristic of thermocouples made with magnetic material is that they undergo a step change when the
magnetic material reaches its Curie point. This occurs for this thermocouple at 354°C. Sensitivity is approximately 41 µV/°C.
K-type thermocouple
Thermocouple plugged to a multimeter
displaying room temperature in °C.
-서로 다른 두금속의 접합면(thermocouple)을 만들어서, 두금속간의 built-in
potential이 온도에 따라 변하는 것을 측정하여 온도측정
Thermistors
A thermistor is a type of resistor with resistance varying according to its temperature.
Thermistors are widely used as inrush current limiters, temperature sensors, self-resetting overcurrent protectors, and selfregulating heating elements. Assuming, as a first-order approximation, that the relationship between resistance and
temperature is linear, then:
ΔR = kΔT
first-order temperature coefficient of resistance
a positive temperature coefficient (PTC) thermistor, or posistor
negative temperature coefficient (NTC) thermistor.
Thermistors differ from resistance temperature detectors (RTD) in that the material used in a thermistor is generally a
ceramic or polymer, while RTDs use pure metals. The temperature response is also different; RTDs are useful over larger
temperature ranges, while thermistors typically achieve a higher precision within a limited temperature range.
Resistance thermometers, also called resistance temperature detectors (RTDs), are temperature sensors that exploit
the predictable change in electrical resistance of some materials with changing temperature. As they are almost invariably
made of platinum, they are often called platinum resistance thermometers (PRTs). They are slowly replacing the use of
thermocouples in many industrial applications below 600 °C.
-도선의 저항값이 온도에 따라 변하는 것을 측정하여 온도 측정
-도체는 온도가 올라가면 저항이 증가하고, 반도체는 감소한다.
Light Measurement
Photomultiplier
These detectors multiply the signal produced by incident light by as much
as 108, from which single photons can be resolved. The combination of
high gain, low noise, high frequency response and large area of collection
have meant that these devices still find applications in nuclear and particle
physics, astronomy, medical imaging and motion picture film scanning
(telecine). Semiconductor devices like avalanche photodiodes have
replaced photomultipliers in some applications, but photomultipliers are
still used in most cases.
typically require 1000 to 2000 volts for proper operation.
Voltage divider, damage, magnetic field
Photoconductive Cell
- CdS 등의 반도체에 빛을 쬐어주면, photocarrier가 생겨서 저항이 감소하는
현상을 이용하여 빛을 측정.
- 빛이 꺼질때 전류가 줄어드는 속도가 느려서, 가로등 등 느린 응용 분야에 사용
PN Junction Photodiode
역전압을 걸어서,
photocurrent생성 측정
PIN diode
undoped instrinsic semiconductor layer
(이영역을 길게해서, 많은 양의 광전자 생성)
PN Junction Solar Cell
전압이 없는 상태에서, photocarrier가 built-in poptential에 의해서 움직이는 전류 측정
phototransistor
-CB간에 역전압이 걸린 접합면에서, photocurrent가 흘러서
전류가 흐름
Frequency Response
Photodiodes are much faster than phototransistors (nanoseconds vs. milliseconds)
Gain
Phototransistors have a higher gain. Photodiodes require an amplifier to use.
Temperature Response
Photodiodes vary less with temperature
Optocoupler
Optocouplers are used in electronics-sensitive applications. For example, you
may use this in a mobile robot application to separate the microcontroller
circuitry (low voltage/power) from the motor driver circuitry (high
voltage/power).
CMOS Image Sensor (CIS) :
현재 대부분의 디지탈 카메라에 사용
TR1
TR3
TR2
-Reset에 Vdd를 걸어서 TR을 켜서 다이오드에 역전압 전하 저장
TR1
TR3
TR2
-빛이 들어오게 셔터를 열어서 photocurrent를 흘려줌으로써,
다이오드의 전하를 서서 뺀다.
TR1
TR3
TR2
-셔터를 막아서 빛을 차단하고, Row Sel을 열어서 TR을 열고,
Column Sense를 통해 전압 측정.
-이때, 다이오드에 있는 역전압크기에 따라 TR의 저항이 변해서
전달되는 저항의 값이 달라짐
Charge Coupled Device (CCD) Image Sensor
전하 전송 방식
-Photodiode에서 만들어진 전하를 모아서, charge coupled device를 통해서 전송해서 이미지
-수평-수직 전송을 병행해서 pixel별로 이미지를 읽어들임
-Photodiode 면적이 CMOS image 센서보다 넓고 전하를 모을 수 있어서,
고감도 저잡음 응용에 적합
-전하 전송을 위하여 상대적으로 고전압이 필요해서, 여러가지 다른 전압원이 필요.
자기장 측정
Giant Magentoresistance(GMR) Sensor
GMR 현상
GMR 센서의 예
GMR 센서 칩
하드
디스크
기록방식
하드디스크의 자화선
-두층의 강자성층(Ferromagnetic layer) 사이에, 자성이 없는 도체막이 있는 구조
-GMR 현상 : 외부자기장이 없으면, antiferromagnetic coupling때문에 두 강자성층은 반대방
향으로 자화된다. 이때 여기에 흐르는 전자는 스핀이 안맞아서 잘 흐리지 못하고, 저항이 커
진다. 외부자기장이 있으면, 강자성층이 같은 방향으로 자화되면서, 전자가 스핀이 맞아서 저
항이 줄어들게 된다.
-현재 하드디스크에 사용 :
Magnetic Field Sensor
Hall Sensor
Superconducting Quantum Interference Devices (SQUID)
superconductor
superconductor
insulator
-왼쪽그래프에서, 반복되는 전압 출력은 SQUID를 관통하는 자속에 비례하여 발생한다.
반복되는 정도는 하나의 자속 양자Φ0 와 같다.
전자기파 측정
라디오 신호 측정 : 광석 라디오
반파 정류
Capacitor를 통해서
고주파를 없애버리는
Low Pass Filter
이어폰
(저항)
-안테나 : dipole wire
-LC회로를 이용하여 특정 주파수 선정
-다이오드를 통해 반파정류
-RC회로를 통해 고주파 제거
LC회로
(특정 주파수 선정)
방송국
(고주파에 저주파
신호를 얹어서 방송)
라디오 신호증폭 회로
라디오 신호
측정/정류/검파
회로
Non-inverting amplifier
for AC
힘 측정
Strain & displacement
LVDT: Linear Variable Differential Transformer
A strain gauge (alternatively: strain gage) is a device
used to measure the strain of an object. Invented by
Edward E. Simmons and Arthur C. Ruge in 1938, the
most common type of strain gauge consists of an
insulating flexible backing which supports a metallic foil
pattern. The gauge is attached to the object by a
suitable adhesive, such as superglue.[1] 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.
The gauge factor GF is defined as:
where RG is the resistance of the undeformed
gauge, ΔR is the change in resistance caused by
strain, and ε is strain.
strain = deformation
압축형 압전 가속도계
• 그림 (a) : 평판 또는 원판 모양의 압전소자를 베이스와 추(錘) 사이에 고정시킨 구
조
• 그림 (b) : 압전현상의 종효과를 이용한다.
• 구조가 간단하고 기계적 강도도 커서 큰 가속도 및 충격 계측에 적합하다.
• 그러나 분극방향과 출력방향이 일치하므로 순간적인 온도변화에 의한 출력(이것
을 초전기(焦電氣) 출력이라고 하며, 1[Hz] 이하의 성분을 가진다.)이 발생하기 때
문에 낮은 진동수, 미소레벨의 진동 계측에는 부적합하다.
(a) 구조
(b) 분극방향과 출력방향
전단형 압전 가속도계
• 그림(a) : 평판 또는 원통 모양의 압전소자를 사용하여 한쪽의 전극 면에는 무거운
추를, 다른 전극은 베이스에 고정시켜 압전소자에 전단이 발생하도록 한다.
• 그림(b) : 압전소자의 분극방향과 출력방향이 직교하기 때문에 온도변화에 의한 출
력이 작아진다.
• 압전계수(d15)가 압축형(d33)보다 약 1.5배 크기 때문에 감도를 크게 할 수 있다.
• 전단형 가속도계는 일반 기계 진동은 물론 구조물, 지반, 지진 등의 낮은 진동수 계
측, 잡음이 작기 때문에 미소 레벨 계측에 적합하다.
정전용량형 가속도 센서
• 정전용량의 변화를 이용해 가속도를 검출하는 기술은 가속도계에서 가장 널리
사 용 되 는 원 리 이 며 , 다 양 한 형 태 의 정 전 용 량 형 가 속 도 계 (capacitive
accelerometer)가 시판되고 있다.
• 와셔 모양(washer-shape)의 질량 m이 탄성체(스프링 상수 k)에 매달려 있고, 이
것은 두 개의 원형판 사이에 놓이게 된다.
• 상하 두 원형판에는 있는 두 고정전극과 질량은 평행판 커패시터 C를 형성한다.
• 그림 (a) : 가속도가 0일 때는 질량 m은 움직이지 않고, 질량-상하부 고정전극
사이의 간격 d는 모두 같다. 따라서 정전용량도 동일하며
(a) 가속도 인가 전
(b) 가속도 인가 후
정전용량형 마이크로 가속도 센서
• 미소한 실리콘 질량과 상하부 전극 사이에는 커패시터가 형성되어 있다.
• 실리콘을 미세가공하여 마이크로 크기의 질량을 만든다. 또 유리와 실리콘을 접합한 후, 유리에 상부
전극과 하부 전극을 만든다.
• 정전용량형 MEMS 가속도 센서는 2[g]이하부터 수 100[g]의 가속도를 1[kHz]까지 측정할 수 있고,
5000[g] 이상의 충격에도 견딜 수 있다.
• 또한 초소형, 저가격이고, 또 하나의 칩에 신호처리회로를 집적화시킨 원 칩(one chip)이거나, 센서 칩
과 신호처리 칩을 하나의 패키지로 하여 고기능화한 것이 대부분이다.
• 현재 자동차의 에어 백 등 광범위하게 사용되고 있다.
ΔC를 전압으로 변환
경사각 센싱
a : sensitivity
1g
1g
• Angle =0
• Output = 0
Earth’s surface
• Angle = θ
• Output = a 1g sin θ
터치 센서 :
Projected Capacitive Touch Screen
-유리판 밑에 전극을 깔아서, 한개 전극의 self capacitance
또는 전극간의 mutual capacitance를측정
진공상태 측정
Vacuum gauges
Many techniques have been developed for the measurement of pressure and vacuum. Instruments used
to measure pressure are called pressure gauges or vacuum gauges.
A manometer could also be referring to a pressure measuring instrument, usually limited to measuring
pressures near to atmospheric. The term manometer is often used to refer specifically to liquid column
hydrostatic instruments.
A vacuum gauge is used to measure the pressure in a vacuum
Bourdon Gauge (부르돈 게이지)
Pressure-vacuum gauge face and dial
Overview of pressure-vacuum
gauge mechanical parts (back
view)
-In 1849 the Bourdon tube pressure gauge was patented in France by Eugene Bourdon.
-The pressure sensing element is a closed coiled tube connected to the chamber or pipe in which pressure
is to be sensed. As the gauge pressure increases the tube will tend to uncoil, while a reduced
gauge pressure will cause the tube to coil more tightly. This motion is transferred through a linkage to a
gear train connected to an indicating needle. The needle is presented in front of a card face inscribed with
the pressure indications associated with particular needle deflections.
Gauge heads are specified by their maximum measured pressure (25,000 Torr down to 1 x 10-1 Torr), with each
head having a dynamic range of approximately 104 below that. Accuracies of 0.25% gauge reading are common,
with 0.08% available from high-accuracy products.
Diaphragm Manometers
Like the capacitance manometer, these gauges use the deflection of a thin metal (or silicon) diaphragm separating a
known pressure from an unknown pressure. However, in this type of gauge, the deflection is sensed by a strain gauge
attached to the diaphragm. While this limits the minimum measurable pressure to 1 Torr, it does provide a stable,
repeatable, device reading pressures up to 1,200 Torr.
Pirani Gauge
A Pirani gauge consists of a metal wire open to the pressure being measured. The wire is heated by a current flowing through it
and cooled by the gas surrounding it. If the gas pressure is reduced, the cooling effect will decrease, hence the
equilibrium temperature of the wire will increase. The resistance of the wire is a function of its temperature: by measuring
the voltage across the wire and the current flowing through it, the resistance (and so the gas pressure) can be determined. This
type of gauge was invented by Marcello Pirani.
Thermocouple gauges and thermistor gauges work in a similar manner, except a thermocouple or thermistor is used to
measure the temperature of the wire.
Useful range: Although the dynamic range for any single gauge matches the T/C, Pirani's cover a pressure range from
about 10 Torr to 1 x 10-5 Torr.
Thermocouple gauges: 1 torr ~ 1utorr
The pressure range between 10 Torr and 10-3 Torr is indicated by measuring the voltage of a thermocouple
spot-welded to a heated filament exposed to system gas. The filament, fed from a constant current supply,
reaches a temperature determined by the amount of energy extracted by the gas. At higher pressures, more
molecules hit the filament and extract more energy than at low temperatures. The filament temperatures
induce thermocouple voltage changes. These gauges are used extensively in foreline monitoring and to
provide the signal to automatically switch the main chamber from backing and high-vacuum pumps at the
crossover pressure.
Ion Gauge
Bayard/Alpert ionization gauge
Ionization gauges are the most sensitive gauges for very low pressures (high vacuums, AKA "hard" vacuums). They sense
pressure indirectly by measuring the electrical ions produced when the gas is bombarded with electrons. Fewer ions will be
produced by lower density gases. The calibration of an ion gauge is unstable and dependent on the nature of the gases
being measured, which is not always known. Thermionic emission generate electrons, which collide with gas atoms and
generate positive ions. The ions are attracted to a suitably biased electrode known as the collector. The current in the collector
is proportional to the rate of ionization, which is a function of the pressure in the system. Hence, measuring the collector
current gives the gas pressure. There are several sub-types of ionization gauge.
Useful range: 10-10 - 10-3 torr (roughly 10-8 - 10-1 Pa)
저진공 펌프
Rotary Vane Pumps
Diaphragm Pumps
The eccentrically mounted rotor
compresses the gas and sweeps
it toward the discharge port.
When gas pressure exceeds
atmospheric, the exhaust valve
opens and gas is expelled. Oil is
used as a lubricant, coolant, and
gas sealant for the vanes. Single
stage rough rotary vane pumps
have ultimate pressures around
10-2 Torr range while two stage
rough vane pumps reach 10-3
Torr. Pumping speeds vary from
1–650 cfm, depending on
whether the pump is a coarse
vane or rough vane pump.
In general, diaphragm pumps have low pumping speeds (<10 cfm)
and produce a poor ultimate vacuum (1 Torr to 10 Torr). However,
they do exhaust into the atmosphere and their low costs make
them attractive roughing pumps.
Pressure Units
Mechanical roughing pumps, diffusion or ion pumps
pascal
(Pa)
technical
atmosphere
(at)
bar
(bar)
2
−5
1.0197×10
−5
atmosphere
(atm)
torr
(mmHg)
−6
7.5006×10
9.8692×10
−3
pound-force
per
square inch
(psi)
145.04×10
1 Pa
≡ 1 N/m
10
1 bar
100 000
≡ 10 dyn/cm
1.0197
1 at
98 066.5
0.980665
1
atm
101 325
1.01325
1
torr
133.322
1.3332×10
−3
1.3595×10
−3
1.3158×10
−3
≡ 1 mmHg
19.337×10
1 psi
6 894.76
68.948×10
−3
70.307×10
−3
68.046×10
−3
51.715
≡ 1 lbf/in
6
2
0.98692
750.06
14.504
≡ 1 kgf/cm
0.96784
735.56
14.223
1.0332
≡ 1 atm
760
14.696
2
−6
−3
2
물질의 특성 측정
4 Probe Measurement
E
-저항선의 저항을 측정할때, 프로브와의 접촉면에서의 접촉저항이 문제가 될 수 있다.
예를들어, 위의 1-4간의 전류 I1-4를 측정하였을 경우, Ammeter의 저항이 거의 0이
라고해도, 1, 4번 probe와 저항선간에는 그값을 알 수 없는 접촉저항이 있어서, 1-4
간의 저항값은 알 수가 없다.
-4 probe 방법의 경우, 1-4간의 전류 I1-4 와 2-3간의 전압 V2-3를 측정한다.
-이때, 2-3간에 흐르는 전류는 1-4간의 전류와 같을 수밖에 없다.
-또한, 2와 3번 probe를 통해서는 전류가 들어가지 않으므로, 접촉저항에 의한 전압
측정 오차는 없다.
-따라서, 2-3간의 저항 R은, R2-3 = V2-3 / I1-4
혈당 센서(현재 바이오 센서 시장의 ~80%)
-글루코스 산화효소가 글루코스(포도
당)를 산화시키면서 생기는 전자를
전극으로 받아들여, 전류를 측정하
여, 글루코스 레벨 측정
-당뇨병환자의 경우 주기적은 혈당레
벨의 측정이 필요
반도체식 가스센서
센서의 저항값의 증감여부에 따라 조절이
가능한 회로
히터가 필요한
가스센서용
기본회로
-일산화탄소 경보기는 SnO2필름을 반도체 채널로 사용.
-이경우, 깨끗한 공기에서는 산소가 붙어서 필름내의 전하를 잡아서, 저항이 크
다가, 일산화탄소가 와서 산소를 빼앗아가면 전기전도도가 증가한다.
고에너지 입자 측정
고에너지 입자 측정 방법
Geiger counter
Scintillator
Solid-state detectors
surface-barrier detectors
Cerenkov detectors
Ionization chambers
shower chamber
scintillation chamber
drift chambers
Geiger Counters
It is used to detect radiation usually gamma and beta radiation, but certain models can also detect
alpha radiation. The sensor is a Geiger-Müller tube, an inert gas-filled tube (usually helium,
neon or argon with halogens added) that briefly conducts electricity when a particle or
photon of radiation temporarily makes the gas conductive. The tube amplifies this conduction by
a cascade effect and outputs a current pulse, which is then often displayed by a needle or lamp and/or
audible clicks.
A Geiger-Müller tube (or GM tube) is the sensing element of a Geiger counter instrument that can
detect a single particle of ionizing radiation, and typically produce an audible click for each. It was
named for Hans Geiger who invented the device in 1908, and Walther Müller who collaborated with
Geiger in developing it further in 1928.[The current version of the "Geiger counter" is called the
halogen counter. It was invented in 1947 by Sidney H. Liebson (Phys. Rev. 72, 602–608 (1947)).
Geiger-Müller tube