Electronic Thermometer Circuit

  
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This is an electronic thermometer using an inexpensive silicon transistor as the temperature sensor. This circuit is based on LM112 op amp. This is the figure of the circuit; This circuit can provide better than 1 §C accuracy over a 100 §C range. The emitter-base turn-on voltage of silicon transistors is linear with temperature. If the operating c
Electronic Thermometer Circuit - schematic

urrent of the sensing transistor is made proportional to absolute temperature the non-linearly of emitter-base voltage can be minimized. Over a b55 §C to 125 §C temperature range the non-linearly is less than 2 mV or the equivalent of 1 §C temperature change. An LM113 diode regulates the input voltage to 1. 2V. The 1. 2V is applied through R2 to set the operating current of the temperature-sensing transistor. Resistor R4 biases the output of the amplifier for zero output at 0 §C. Feedback resistor R5 is then used to calibrate the output scale factor to 100 mV/ §C. Once the output is zeroed, adjusting the scale factor does not change the zero.



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