Micropower thermometer

  
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The output of this circuit is a current proportional to temperature, which can be used to drive a meter for a direct readout. Alternatively, a resistor or op amp can be used to get a voltage output. The circuit is pulsed at a low duty cycle to reduce power consumption. With the component shown, the duty cycle is about 0. 2% with a one-se
Micropower thermometer - schematic

cond sample rate. This gives an average current drain of about 25 A, plus the output current. The circuit will operate with a supply of 8. 0 to 12. 0 V. A small 8. 4-V mercury battery can provide an operating life of about one year. R8 is used to trim the circuit, correct for Zener tolerance, temperature error in the sensor, and resistor tolerance. With the values shown, a 0- to 50- A output is obtained for a +50 to + 100 °F temperature change. Other ranges can be selected using the equations shown in the box on the circuit diagram. The current-source output allows long lines to be driven with no loss of accuracy. National Semiconductor Linear Applications Habdbook, 1991, p. 1229.



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