Sensor Engineering (EIEN 346)
Handout #1
N a n o Bi o Ph o t o n i c s La b
D e pt . o f El e c t r o n i c s a n d In f o r mat i o n En g i n e e r i n g
Ko r e a Un i v e r s i t y
Sungkyu Seo
Ph.D. / Professor
Nano Bio Photonics Laboratory (NBPL)
Dept. of Electronics and Information Engineering
Korea University (Sejong Campus)
E-mail: sseo@korea.ac.kr, Tel: 044-860-1427, Homepage: http://nbpl.korea.ac.kr
Sensors?
https://www.youtube.com/watch?v=cAKnTSJb-SE (Top 10 Sensors + Projects)
Chapter 1. Data Acquisition
1.1 Sensors, Signals, and Systems
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Sensor is defined as a “device that receives and respond to a signal or stimulus.”
e.g.> device = human eye, pistol trigger, etc.
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To act appropriately, the operator must obtain information about the level of fluid in the tank.
Information is generated by the sensor which combines (1) the sight tube on the tank (manmade) and (2) the operator’s eye (natural)
Sensor’s performance must be assessed only as part of a data acquisition system
Chapter 1. Data Acquisition
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Stimulus (measurand)
: quantity, property, or condition received and converted into electrical signal
e.g.> Light intensity, wavelength, sound, force, acceleration, distance, rate of motion, and
chemical or biological compositions
Output signal
: In form of voltage, current, or charge amplitude, polarity, frequency, phase, or digital code
Sensor
: A device that receives a stimulus and responds with an electrical signal.
Detector
: Synonymous to sensor, however, detector is more often used to stress qualitative rather than
quantitative nature of measurement.
e.g.> Passive infrared detector (PIR) can indicate the existence of human movement, but
generally can not measure direction, speed, or acceleration.
Transducer
: Transducer is a converter of any one type of energy or property into another type of energy or
property, whereas sensor converts it into electrical signal.
e.g.> Loudspeaker (electrical signal variable magnetic field acoustic wave)
Actuator
: Opposite to a sensor (electrical signal non-electrical energy)
e.g.> Electric motor (electric energy mechanical action), pneumatic actuator (electric signal
air pressure into force)
Chapter 1. Data Acquisition
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Hybrid or complex sensor
: Many sensors incorporate at least one direct-type sensor and possibly a number of transducers.
e.g.> chemical sensor : exothermal chemical reaction heat electrical output (thermopile)
Direct sensor
: converts a stimulus into an electrical signal or modifies an externally supplied electrical signal
e.g.> photoeffect (emission of electron from atom excited by photon impingement)
Seebeck effect (emission of electron from temperature difference between two metals)
Hybrid sensor
: needs one or more transducers before a direct sensor can be employed to generate electric output
Chapter 1. Data Acquisition
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Objects : car, space ship, animal or human, liquid, or gas.
Sensor 2, 3, & 4 : positioned directly on or inside of the object
Sensor 1 : non-contact sensor
Sensor 5 : monitors the internal conditions of the data acquisition system
Sensor 1 & 3 : need interface devices (signal conditioners)
Sensor 1, 2, 3, & 5 : passive / Sensor 4 : active (needs an excitation circuit)
Chapter 1. Data Acquisition
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Multiplexer (MUX)
: connects the sensors to an analog-to-digital converter (A/D or ADC)
Computer
: controls a multiplexer & ADC and sends control signals to an actuator
Chapter 1. Data Acquisition
1.2 Sensor Classification
(1) Passive or Active
: A passive sensor does not need any additional energy source. It generates an electric signal in
response to an external stimulus. The examples are a thermocouple, a photodiode, and a
piezoelectric sensor. Many passive sensors are direct sensors as we defined them earlier.
The active sensors require external power for their operation, which is called an excitation
signal. The active sensors sometimes are called parametric because their own properties change
in response to an external stimulus and these properties can be subsequently converted into
electric signals. The example of an active sensor is a resistive strain gauge in which electrical
resistance relates to strain in the material. To measure the resistance of a sensor, electric current
must be applied to it from an external power source.
(2) Absolute or Relative
: An absolute sensor detects a stimulus in reference to an absolute physical scale that is
independent on the measurement conditions, whereas a relative sensor produces a signal that
relates to some special case. An example of an absolute sensor is a thermistor—a temperaturesensitive resistor. Its electrical resistance directly relates to the absolute temperature scale of
Kelvin. Another very popular temperature sensor—a thermocouple—is a relative sensor. It
produces an electric voltage that is function of a temperature gradient across the thermocouple
wires. Thus, a thermocouple output signal cannot be related to any particular temperature
without referencing to a selected baseline.
Chapter 1. Data Acquisition
Chapter 1. Data Acquisition
Chapter 1. Data Acquisition
Chapter 1. Data Acquisition
1.3 Units of Measurements
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