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Inexpensive Linear Thermometer

2017-03-17 09:34  
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As a sensor in the design of this linear thermometer, the LM34 is used. The output is the difference between
Inexpensive Linear Thermometer

two base-emitter voltages AVeb ?°f two transistors operated at different collector-current densities. where the current densities are IC and let, k is Boltzmann`s constant, and q is the electron charge. Because all factors, including the ratio IciUci are constant, the output of the LM34 (National Semiconductor) is a linear function of in the range over - 50?° to 300?°F, which provides the output voltage of 10 mV/ ?°F with a max. nonlinearity of ?±0.35?°F. The output of the LM34 is amplified by a three-op-amp instrumentation amplifier. The fourth op amp gives the possibility to control the offset voltage of the amplifier. The gain A of the instrumentation amplifier can be set to any desired value by the choice of the resistance R2 only.



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