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 current 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.
[Circuit source: National Semiconductor Notes]
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 current 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.
[Circuit source: National Semiconductor Notes]
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