Electronic Thermometer Circuit

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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