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Sensors/Transducers 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. R•I•T 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 R•I•T Major Measurement Blocks 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. R•I•T Cont. 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. R•I•T Transducers Optical transducers • Light Emitting Diodes • Photo-transistors • Optoisolators • Photo cells • Solar cells • Photo conductors R•I•T Cont. Temperature Transducers • Resistance Temperature Detector (RTD) • Thermistors • Thermocouples • Junction Transistor Temperature Sensors R•I•T 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 R•I•T Semiconductor Energy Gap 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. R•I•T Materials for LED Devices 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 R•I•T 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. Displacement Transducers • Potentiometric • Linear Variable Differential Transformer (LVDT) • Straint Gage R•I•T Your Presentation (Name) Topic – First – Second Another Topic – First – Second R•I•T