Transcript IBM Presentation - Rochester Institute of Technology

Sensors/Transducers
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Four Transducer Parameters
•Accuracy: closeness with which a measurement
approaches the true value of a measured
variable, expressed as a percent of full-scale
output
• Precision: an expression of the repeatability of
measurements determined from the number of
significant figures available.
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Cont.
• Resolution: an expression of the smallest
significant number to which a measurement
can be determined
• Error: the deviation of a measurement from
a true value of a measured variable,
expressed usually as a percent of the fullscale output
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Major Measurement Blocks
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Transducer: Converts the controlled
variable into another form suitable for the
next stage. The variable may be voltage,
temperature, current, pressure, ph level, etc.
 Signal conditioning: Adjustment of the type
and/or level of the measurement signal to
provide compatibility with the next stage.
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Cont.
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Transmitter: propagates the measurement
information from the site of measurement to
the control site where the control function is
to occur. In some cases the analog signal is
converted to digital signals in binary
format, then it is transmitted to a remote site
in serial form, e.g. RS232, RS432, or
wireless.
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Transducers
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Optical transducers
• Light Emitting Diodes
• Photo-transistors
• Optoisolators
• Photo cells
• Solar cells
• Photo conductors
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Cont.
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Temperature Transducers
• Resistance Temperature Detector (RTD)
• Thermistors
• Thermocouples
• Junction Transistor Temperature Sensors
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LED Theory
LED as an electroluminescent device:
• Low currents and voltage required to
produce useful light output
• Light emitting area is defined by
photolithographic process
• High speed at which the device could be
switched
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Semiconductor Energy Gap
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Distance between the conduction band and the
valence band
 Semiconductor PN junction
 Electrons and holes recombine through:
• Direct recombination
• Indirect recombination
The photon energy can be converted to wavelength:
λ = (1240/E) nm
E is the energy transition in electron volts.
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Materials for LED Devices
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Material Band Gap
Ge
0.66 eV
Si
1.09 eV
GaAs
1.43 eV
GaP
2.24 eV
GaAS60P40 1.91 eV
Al Sb
1.6 eV
In Sb
0.18 eV
Si C
2.2 – 3.0
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Emission Transition
1880 nm
Ind.
1140 nm
Ind.
910 nm
Direct
560 nm
Ind.
650 nm
Direct
775 nm
Ind.
6900nm Direct
563-413 nm Ind.
Cont.
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Displacement Transducers
• Potentiometric
• Linear Variable Differential Transformer
(LVDT)
• Straint Gage
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